Resummation, Evolution, Factorization 2022

31 Oct 2022, 08:00 → 4 Nov 2022, 18:30 Europe/Berlin

REF 2022 is the 9th edition in the series of workshops on Resummation, Evolution, Factorization. The workshop focuses on transverse momentum dependent (TMD) parton densities and their connection with Monte Carlo event generators, as well as on the experimental measurements aimed at extracting information on TMD densities at the LHC, HERA and future colliders. The interplay between the necessary factorization theorems, resummation of large logarithms and the corresponding evolution equations are crucial towards higher precision calculations, necessary not only for the understanding of the data recorded by facilities like the LHC but especially for future experiments like the EIC.

The workshop takes place online only.

 

The abstract submission is closed now. If you have any questions, inquiries, please contact the organizing committee.

 

Organizing Committee:

Natasa Raicevic (U Montenegro)

Jelena Mijuskovic (U Montenegro)

Itana Bubanja (U Montenegro)

Hannes Jung (DESY)

Laurent Favart (Brussel)

Piet Mulders (Amsterdam)

 

Advisory Board:

Elke Aschenauer, Alessandro Baccetta,Armando Bermudez Martinez, Daniel Boer, Igor Cherednikov, Markus Diehl, Miguel G. Echevarria, Einan Gardi, Laurent Favart, Francesco Hautmann, Hannes Jung, Krzysztof Kutak, Piet Mulders, Gunar Schnell, Ignazio Scimemi, Andrea Signori, Pierre Van Mechelen

 

Previous meetings:

15-19 November 2021, Hamburg Online

7-11 December 2020, Edinburgh Online

25-29 November 2019, Pavia (Italy)

19-23 November 2018, Krakow (Poland)

13-16 November 2017, Madrid (Spain)

7-10 November 2016, Antwerp (Belgium)

2-5 November 2015, Hamburg (Germany)

8-11 December 2014, Antwerp (Belgium)

23-24 June 2014, Antwerp (Belgium)

Supported by:

 

 

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REF2022_POSTER_fin.pdf

Monday 31 October

1 Intro

Intro.pdf

Natasa.mp4

Parton shower systematics and TMDs

Convener: Hannes Jung (DESY)

2 Collider Events on a Quantum Computer

In recent years, quantum computing has seen staggering progress, from few-qubit devices to 100+ qubit devices on the cloud that can easily be programmed in a straightforward Python-like API. Since quantum computing can naturally incorporate quantum phenomena, it is a potential game changer for the simulation of particle physics, increasing their physics capabilities and efficiency.

QCD parton showers are crucial statistical components of event generators. We discuss recent advances in simulating the parton showering process, and thus generating collider events, on current quantum devices. Due to the statistical nature of the parton shower process, we find that gate noise (due to measurement errors and decoherence) is -- although visible -- not a primary concern at this stage, and that the description of LEP data is encouraging.

Speaker: Simon Williams (Imperial College)

Simon.mp4

SimonWilliams_REF2022.pdf

3 Multi-jet events at the LHC with TMD merging

An accurate description of events with multiple QCD jets is very important because of their high production rates at the LHC. These type of events provide crucial tests to the QCD sector of the standard model as well as a common background to new physics searches. This presentation contains new results on the merging of pure jet events with the recently developed TMD multi-jet merging method, with which we match matrix elements to TMD parton densities and TMD parton shower.

Speaker: Mees van Kampen (Student)

Mees.mp4

PureJets-TMD-merging_AMvK.pdf

4 PB method and TMD multi-jet merging at NLO

A new NLO multi-jet merging method is presented that allows to combine Parton-Branching transverse momentum dependent (PB-TMD) parton distributions with vector+jets calculations at NLO. Double counting in exclusive calculations is avoided by removing resolvable contributions, with respect to the merging scale, from the corresponding multiplicity at NLO. The merging performance is assessed using differential jet rate observables and its systematic error is estimated by varying the merging scale. We compare the new results with the PB-TMD merging calculations at LO and with the experimental LHC data corresponding to Drell Yan + jets."

Speaker: Armando Bermudez Martinez (CMS (CMS Fachgruppe QCD))

Armando.mp4

REF2022_Armando.pdf

5 Multivariable evolution in parton showers with initial state partons

One can use more than one scale variable to define the family of surfaces in the space of parton splitting parameters that define the evolution of a parton shower. In parton shower with initial state parton we need a more sophisticated analysis because the evolution of parton distribution functions must be coordinated with the parton shower evolution. We make the needed connections more precise than in our earlier work, even for the case of just one scale variable. Then we develop an example with three scale variables, which leads to advantages compared to the usual shower formulation with only one scale variable. We provide results for Drell-Yan muon pair production.

Speaker: Zoltan Nagy (T (Phenomenology))

REF2022, Oct. 31, 2022.pdf

Zoltan.mp4

15:20 Coffee Break

Parton shower systematics and TMDs

Convener: Natasa Raicevic

6 A new approach to color-coherent parton evolution

In this talk I will review the basics of color-coherent parton evolution and the emergence of angular ordering. I will then introduce an alternative way to reproduce the soft-gluon radiation pattern at single-emission level in a parton shower. After a brief discussion of analytic NLL resummation for event shapes in electron-positron collisions, I will present a new type of parton-shower kinematics mapping which satisfies the requirements needed to perform NLL resummation numerically. I will conclude with a brief discussion of future directions in the development of the novel algorithms.

Speaker: Stefan Hoeche (Fermi National Accelerator Laboratory)

REF2022_Hoeche.pdf

Stefan.mp4

PDF uncertainties, PDF theory: PDF uncertainties

Convener: Natasa Raicevic

7 MSHT20 - Inclusion of Theoretical Uncertainties and Higher Order Effects into PDFs

I will discuss our recent paper within the MSHT PDF collaboration on the inclusion of theoretical uncertainties and higher order (N3LO) terms into the MSHT PDFs, producing the MSHT20aN3LO (approximate N3LO) set. This represents the first global analysis of parton distribution functions (PDFs) at approximate N3LO as well as the first inclusion of theoretical uncertainties from missing higher orders beyond NNLO. I will review the formalism, higher orders and theoretical uncertainties included, and their effects on both the fit quality and PDFs before examining indicative N3LO predictions.

Speaker: Thomas Cridge

TCridge_MSHT20aN3LO_talk_REF22.pdf

Thomas.mp4

8 Comments on global parton analyses

We consider a few effects which are usually ignored in PDF studies.

1. The double counting of the low $k_T included in the NLO splitting and coefficient functions, and that hidden in the
   PDF input at $Q=Q_0$. Formally this is a power $Q^2/\mu^2$ correction but
   it is non-negligible at moderate scales $\mu$.
2. The $\epsilon/\epsilon$ contribution generated by the infrared (IR) divergence after the
   dimensional regularization. Since the IR divergence is cut off by confinement (or the quark mass)
   these terms must be deleted.
3. The role of the smooth transition through the heavy quark threshold and the
   need to work in the Physical scheme where at the NLO (and higher orders) there is no
   admixture of the quarks to gluon PDF (and gluons to quark PDF) which occur in the MS-bar scheme.

All these points are not uncertainties, but are real effects which certainly must be accounted for
in global parton analysis.

Speaker: Ryskin Mikhail

hid5.pdf

Misha.mp4

9 Triple-collinear one-loop splitting functions in QCD

I shall present the results for one-loop triple-collinear splitting operators for all five possible sub-processes. The expressions are exact in dimensionally-regulated massless QCD up to a single integral, which we expand to second order in the dimensional-regularisation parameter. Our results are both sufficient and indispensable for the construction of subtraction and integrated-subtraction terms for triple-collinear singularities of one-loop double-real-emission cross-section contributions as part of a next-to-next-to-next-to leading order subtraction scheme.

Speaker: Sebastian Sapeta (IFJ PAN, Kraków)

sapeta-ref22.pdf

Sebastian.mp4

17:10 Coffee Break

PDF uncertainties, PDF theory: PDF uncertainties

Convener: Laurent Favart (Université Libre de Bruxelles)

10 Alien operators and the four-loop DGLAP evolution

The scale evolution of the parton distribution functions is controlled by the anomalous dimensions of twist-two operators, which correspond to the Mellin moments of the DGLAP splitting functions. The four-loop anomalous dimensions are important for precision physics at the LHC and at the future EIC. Computing the anomalous dimensions of the flavour singlet operators is highly challenging, due to their mixing with unphysical operators, known as aliens. Indeed, the set of all contributing alien operators was unknown beyond two-loop order.
In this talk I discuss the construction of all the required aliens to compute anomalous dimensions of gluonic operators through four loops. With this approach, I calculate a set of anomalous dimensions up to four loops, finding agreement with the literature and opening the way to the calculation of the full DGLAP evolution through four loops.

Speaker: Giulio Falcioni (Nikhef)

falcioniREF22.pdf

Giulio.mp4

11 Theoretical uncertainties on the evolution of alpha_s, PDFs, and TMDs

The QCD strong coupling (alpha_s) and the parton distribution functions, both collinear (PDFs) and transverse-momentum dependent (TMDs), are fundamental ingredients for phenomenology at high-energy facilities such as the Large Hadron Collider (LHC).
It is therefore of crucial importance to estimate any theoretical uncertainties associated to them.

Both alpha_s and PDFs/TMDs obey their own renormalisation-group equations (RGEs) whose solution determines their scale evolution.
Although the kernels that govern these RGEs have been computed to very high perturbative precision, they are not exactly known.

In this contribution, we present a procedure that allows us to assess the uncertainty on the evolution of these quantities due to our imperfect knowledge of their respective evolution kernels.
Inspired by transverse-momentum and threshold resummation, we introduce additional scales, that we dubbed resummation scales, that can be varied to estimate the uncertainty on their evolution at any scale.

As a test case, we consider inclusive deep-inelastic-scattering structure functions in a region relevant for the extraction of PDFs.
We study the effect of varying these resummation scales and compare it to the usual renormalisation and factorisation scale variations.

We also present a preliminary study of the theoretical uncertainties associated to the trasverse-momentum spectrum of Drell-Yan production and the LHC focusing on the low trasverse-momentum region.

Speaker: Valerio Bertone (NIKHEF)

bertone_REF2022_31_10_2022.pdf

Valerio.mp4

12 Theoretical and sampling uncertainties in global PDF fits.

We review recent developments on the estimation of uncertainties in unpolarized nucleon PDFs by the CT group. In particular, we will discuss how global PDF analyses can be affected by the so-called “big-data paradox” and why, as a consequence, sampling uncertainties should be considered. From that point, we will also discuss theoretical non-perturbative aspects of determinations of strange, charm and light sea PDFs at large momentum fractions.

Speaker: Aurore Courtoy (Instituto de Física, UNAM)

Aurore.mp4

hopscotch_REF_22.pdf

13 PDF uncertainties in TMD extractions

A recent study of the Artemide group has analyzed the impact of PDF uncertainties in the extractions of TMD from data. This result shows that beyond the usual chi^2 analysis, a control of PDF replica distributions must be achieved in order to remove differences among different PDF sets in TMD analysis. When this is achieved, errors coming from several PDF sets are finally found compatible among each other. PDF uncertainty in TMD extraction is still the most relevant one in the overall error balance (comparable to theoretical errors).

Speaker: Ignazio Scimemi

Ignazio.mp4

REF-2022-Scimemi-pdf.pdf

Tuesday 1 November

TMD in experiment: DIS

Convener: Natasa Raicevic

14 The Electron - Ion Collider - Status and Where we are going

Understanding the properties of nuclear matter and its emergence through the underlying partonic structure and dynamics of quarks and gluons requires a new experimental facility in hadronic physics known as the Electron-Ion Collider (EIC). The EIC will address some of the most profound questions concerning the emergence of nuclear properties by precisely imaging gluons and quarks inside protons and nuclei such as their distributions in space and momentum, their role in building the nucleon spin and the properties of gluons in nuclei at high energies. In January 2020 the EIC received CD-0 and Brookhaven National Laboratory was selected as site, and June 2021 CD-1. This presentation will highlight the experimental equipment and its integration into the accelerator and give the status of the EIC project, as well what are the next major steps.

Speaker: Elke-Caroline Aschenauer (BNL)

eca.EIC.pdf

eca.EIC.REF.pptx

Elke.mp4

15 TMD Studies at the Upcoming Electron-Ion Collider

The Electron-Ion Collider (EIC) will investigate the structure of nucleons and nuclei at an unprecedented level. This will be accomplished by performing precise measurements of deep-inelastic scattering and other processes over the complete relevant kinematic range, including the transition region from perturbative to non-perturbative QCD. High luminosity and highly polarized beams will allow probes of the spatial and spin structure of nucleons and nuclei, leading to high-precision determinations of TMDs and other quantum correlation functions. These investigations will require the development and validation of novel simulation and analysis tools. In my presentation, I will introduce the affinity tool to guide the analysis and interpretation of TMD observables and a new event-level approach for the extraction of TMDs. I will also review the status of MC event generators for the EIC.

Speaker: Diefenthaler Markus

Diefenthaler-REF2022.pdf

Markus.mp4

16 Entangelement entropy in high energy collisions of electrons and protons

We investigate the proposal by Kharzeev and Levin of a maximally entangled proton wave function in Deep Inelastic Scattering of electrons and proton in the region of low Bjorken x. Using their proposed relation between parton number and entanglement entropy, we determine the latter using both conventional parton distribution functions and parton distribution functions obtained from an unintegrated gluon distribution subject to next-to-leading order Balitsky-Fadin-Kuraev-Lipatov (BFKL) evolution as well as from a dipole cross-section, subject to running coupling Balitsky-Kovchegov (rcBK) evolution. We compare our results to hadronic entropy obtained from final state hadron multiplicity.

Speaker: Martin Hentschinski (Universidad de las Americas Puebla)

entropyDIS_REF2022.pdf

MartinHentschinski.mp4

17 A Better Angle on Hadron Transverse Momentum Distributions at the EIC

We propose a novel observable $q_*$, sensitive to transverse momentum dependent distributions (TMDs) in the SIDIS process $e N \to e h X$, with $q_*/E_N$ defined purely by lab-frame angles. We prove factorization for $\mathrm{d} \sigma_h / \mathrm{d}q_*$ for $q_*\ll Q$ with standard TMD functions, enabling $q_*$ to substitute for the hadron transverse momentum $P_{hT}$. A double-angle reconstruction method is given which is exact to all orders in QCD for $q_*\ll Q$, allowing for angular reconstruction of $Q,x,y$. Resummation and convergence of perturbative QCD predictions for q* will also be discussed. By replacing measurements of $\mathrm{d}\sigma/\mathrm{d} P_{hT}\mathrm{d} \phi_h$ by $\mathrm{d}\sigma/\mathrm{d} q_*$, the prospects for precisely mapping the 3D structure of hadronization and confinement with TMDs are bright. We show that $q_{*}$ enables an order-of-magnitude improvement in the expected experimental resolution at the EIC.

Speaker: Zhiquan Sun (Massachusetts Institute of Technology)

qstarREF_ZS.pdf

Zhiquan.mp4

18 Next to Leading Order corrections to dihadron production in DIS

We calculate the Next to Leading Order corrections to dihadron production in DIS at small x using the Color Glass Condensate frame work. We show that all UV and soft divergences cancel against each other. The remaining rapidity divergences lead to JIMWLK evolution of the Leading Order cross section while the collinear divergences lead to DGLAP evolution of parton-hadron fragmentation functions. We then consider the back-to-back limit of our result and relate it to the target TMD distributions. We show that one can use our results to obtain the NLO corrections to single inclusive hadron production as well as the structure functions in DIS at small x.

Work done with F. Bergabo, based on arXiv:2207:03606

Speaker: Jamal Jalilian-Marian (Baruch College, CUNY)

Jalilian-Marian-REF-2022.pdf

Jamal.mp4

15:50 Coffee Break

Parrlel Session A: TMD in experiment

Convener: Itana Bubanja

19 Measurement of mass dependence of the transverse momentum of Drell Yan lepton pairs in proton-proton collisions at 13TeV

The double differential cross sections of the Drell-Yan lepton pair ($l^+l^-$, dielectron or dimuon) production, as functions the invariant mass $m_{ll}$, transverse momentum $pT$, and $\phi^*$, are measured. The $\phi^*$ observable is highly correlated with $pT$ and is used to probe the low-$pT$ region in a complementary way. Dilepton masses up to 1 TeV are investigated. Additionally, a measurement is performed requiring at least one jet in the final state. To benefit from partial cancellation of the systematic uncertainty, the ratios of the differential cross sections in $pT$ and $\varphi^*$ for different $m_{ll}$ ranges over the ones in the \PZ mass peak interval are presented. The collected data correspond to an integrated luminosity of $36.3 fb^{-1}$ of proton--proton collisions recorded with the CMS detector at the LHC at a center-of-mass energy of 13 TeV in 2016. Measurements are compared to state-of-the-art predictions based on perturbative quantum chromodynamics, including soft-gluon resummation.

Speakers: Jelena Mijuskovic (University of Montenegro), CMS Collaboration

Jelena.mp4

REF22_JMijuskovic.pdf

20 Azimuthal correlation measurements from Z+jets and dijets

A set of azimuthal correlation measurements from Z+jets and dijets in CMS will be presented.

Speaker: Meena Meena

Meena_azimuthal_correlation_REF_2022.pdf

Meena.mp4

21 Measurement of the 1-jettiness event shape observable in deep-inelastic electron-proton scattering at HERA

A first measurement of the 1-jettiness event shape observable in neutral-current deep-inelastic electron-proton scattering is presented. The 1-jettiness observable $\tau_{1b}$ is defined such that it is equivalent to the thrust observable defined in the Breit frame. The data were taken in the years 2003 to 2007 with the H1 detector at the HERA ep collider at a center-of-mass energy of 319 GeV and correspond to an integrated luminosity of 351.6 pb$^{−1}$. The triple-differential cross sections are presented as a function of the 1-jettiness $\tau_{1b}$, the event virtuality $Q^2$ and the inelasticity $y$ in the kinematic region $Q^{2}>150$ GeV$^2$. The data have sensitivity to the parton distribution functions of the proton, the strong coupling constant and to resummation and hadronisation effects. The data are compared to selected predictions.

H1prelim-21-032

Speaker: Johannes Hessler (ATLAS (LHC Experiment ATLAS))

Johannes.mp4

REF22_jettiness.pdf

22 First measurement of groomed events shapes in ep DIS using archived H1 data

Event shapes provide incisive probes of QCD, both its perturbative and non-perturbative aspects. Grooming techniques have been developed to separate perturbative from non-perturbative components of jets in a theoretically well-controlled way, and have been applied extensively to jet measurements in hadronic collisions. In this talk the first application of grooming techniques to event shape measurements at HERA is presented, utilizing archived electron-proton Deep Inelastic Scattering data from the H1 experiment. The analysis is based on the novel Centauro jet clustering algorithm, which is designed specifically for the event topologies of ep DIS collisions. Cross-section measurements of groomed event 1-jettiness and groomed invariant jet mass are shown. The measurements are compared to Monte Carlo models, and to a theoretical calculation based on Soft Collinear Effective Theory.

H1prelim-22-033

Speaker: Henry Thornton Klest (Stony Brook University)

Henry.mp4

REF22 Klest - H1GES Final.pdf

REF22 Klest - H1GES Final.pptx

Parralell Session B: TMD theory

Convener: Piet Mulders (Nikhef and VU University)

23 Double-Real-Virtual and Double-Virtual-Real Corrections to the Three-Loop Thrust Soft Function

We compute the ${\cal O}(\alpha_s^3)$ double-real-virtual (RRV) and double-virtual-real (VVR) soft contributions to the thrust/zero-jettiness event shape. The result clears up one of the most stubborn obstacles toward the complete ${\cal O}(\alpha_s^3)$ thrust soft function. The results presented here serve the key input to realize the next-to-next-to-next-to-leading logarithmic prime (N${}^3$LL') and even the next-to-next-to-next-to-next-to-leading logarithmic (N${}^4$LL) resummation of the thrust event shape. The obtained results also constitute the important ingredients of the $N$-jettiness-subtraction scheme at next-to-next-to-next-to-leading order (N${}^3$LO).

Speaker: Wen Chen (Zhejiang University, China)

REF2022_Chen_Wen.mp4

REF2022_ChenWen.pdf

24 Multiparton Scattering Amplitudes: The formalism of Fused-Webs

The correlators of Wilson-line operators in non-abelian gauge theories are known to exponentiate, and their logarithms can be organised in terms of the collections of Feynman diagrams called Cwebs. The colour factors that appear in the logarithm correspond to completely connected diagrams and are determined by the web mixing matrices. In this talk we present several new concepts that we recently introduced: (a) Normal ordering of the diagrams of a Cweb, (b) Fused-Webs (c) Basis and Family of Cwebs. We use these ideas together with a Uniqueness theorem to arrive at an understanding of the diagonal blocks, and several null matrices that appear in the mixing matrices. We demonstrate using our formalism that, once the basis Cwebs present upto order ${\alpha}_s^n$ are determined, the number of exponentiated colour factors for several classes of Cwebs starting at order ${\alpha}_s^{n+1}$ ​ can be predicted. We further provide complete results for the mixing matrices, to all orders in perturbation theory, for two special classes of Cwebs using our framework.

Speaker: Dr Anurag Tripathi (IIT Hyderabad)

Anurag.mp4

Anurag-REF-2022.pdf

25 Transverse Momentum Distributions at Subleading Power and Quark-Gluon-Quark Correlators

Beyond leading power there are interesting new phenomena that can be investigated in the realm of transverse momentum dependent (TMD) distribution functions, probed with processes like semi-inclusive DIS and Drell-Yan. In this talk I discuss the subleading power TMD factorization for these processes, including their dependence on novel distribution functions known as quark-gluon-quark ($qgq$) correlators, which probe new aspects of TMD hadron structure. I discuss all-order definitions for renormalized $qgq$ correlators, which both cancel novel and standard rapidity divergences, and only depend on one hadronic state. I also discuss matching calculations and renormalization group evolution for these distributions.

Speaker: Anjie Gao (Massachusetts Institute of Technology)

Anjie.mp4

AnjieREF.pdf

26 Evolution of TMD distributions of twist-three

In this talk, I present the analysis of transverse momentum dependent (TMD) distributions of twist-three made in ref[2204.03856], focusing on their evolution equations. The starting point of discussion are the correlators with the definite TMD-twist. By considering suitable combinations of these correlators, I introduce physical TMD distribution of twist-three that can be used for practical applications. I establish relations with generic TMD distribution of twist-three, and demonstrate that their evolution equations are autonomous in the large-Nc limit.

Speaker: Alexey Vladimirov (Regensburg University)

Alexei.mp4

talk.pdf

17:40 Coffee Break

Parrallel Session A: TMD in experiment: DIS (p1)

Convener: Jelena Mijuskovic (University of Montenegro)

27 Prospects for strong coupling measurement at hadron colliders using soft-drop jet mass

We compute the soft-drop jet-mass distribution from pp collisions to NNLL accuracy while including nonperturbative corrections through a field-theory based formalism. Using these calculations, we assess the theoretical uncertainties on an $\alpha_s$ precision measurement due to higher-order perturbative effects, nonperturbative corrections, and PDF uncertainty. We identify which soft-drop parameters are well-suited for measuring $\alpha_s$, and find that higher-logarithmic resummation has a qualitatively important effect on the shape of the jet mass distribution. We find that gluon jets are more sensitive to $\alpha_s$ than quark jets, and show that experimentally distinguishing quark and gluon jets is not required for this $\alpha_s$ measurement. We conclude that measuring $\alpha_s$ to the 10% level is feasible but getting down to the 1% level to be competitive with other state-of-the-art measurements will be challenging.

Speaker: Aditya Pathak (University of Manchester)

Aditya.mp4

Pathak_REF22.pdf

28 Multi-differential Jet Substructure Measurement in High $Q^{2}$ Deep-Inelastic Scattering with the H1 Detector

A study of different jet observables in high $Q^{2}$ Deep-Inelastic Scattering events close to the Born kinematics is presented. Differential and multi-differential cross-sections are presented as a function of the jet’s charged constituent multiplicity, momentum dispersion, jet charge, as well as three values of jet angularities. Results are split into multiple $Q^{2}$ intervals, probing the evolution of jet observables with energy scale. These measurements probe the description of parton showers and provide insight into non-perturbative QCD. Unfolded results are derived without binning using the machine learning-based method Omnifold. All observables are unfolded simultaneously by using reconstructed particles inside jets as inputs to a graph neural network.  Results are compared with a variety of predictions.

H1prelim-22-034

Speaker: Vinicius Mikuni (Lawrence Berkeley National Lab. (US))

H1_REF.pdf

Vinicius.mp4

29 Machine learning-assisted measurement of multi-differential lepton-jet correlations in deep-inelastic scattering with the H1 detector

The lepton-jet momentum imbalance in deep inelastic scattering events offers a useful set of observables for unifying collinear and transverse-momentum-dependent frameworks for describing high energy Quantum Chromodynamics interactions. A recent first measurement was made [1] of this imbalance in the laboratory frame using positron-proton collision data recordedf with the H1 experiment at HERA in the years 2006-2007. Using a new machine learning method, the measurement was performed simultaneously and unbinned in eight dimensions. The first results were presented as a set of four one-dimensional projections onto key observables. This work extends over those results by making use of the multi-differential nature of the unfolded result. In particular, distributions of lepton-jet correlation observables are studied as a function of the kinematic properties of the scattering process, i.e. as a function of the momentum transfer $Q^2>150$ GeV$^2$ and the inelasticity $0.2< y< 0.7$.

H1prelim-22-031
[1] PRL 128 (2022), 132002 [arxiv:2108.12376]

Speakers: Miguel Arratia (University of California, Riverside), Collaboration H1 (DESY)

Miguel.mp4

REF 22 H1 leptonjet differential.pdf

30 Discussion

Parralell Session B: TMD theory

Convener: Hannes Jung (DESY)

31 Azimuthal angular decorrelations for quark and gluon jets with energy loss due to scattering and coherent medium induced radiation

The hot and dense medium of a quark gluon plasma (QGP) that can be recreated by ultrarelativistic
heavy ion collisions, can be examined only by indirect means, e.g. via highly energetic strongly interacting particles.
Studying the mechanisms of energy loss of partonic jets, i.e. collimated and highly energetic sprays of strongly interacting
particles provides an excellent means to access the QGP.

Main mechanisms of jet-energy loss can be considered as scatterings of the jet particles off medium particles
as well as emissions induced by scatterings off medium particles. These coherent medium induced radiations can be formed while
multiple scatterings off medium particles occur, giving rise to interference effects, first described
in QCD by Baier, Dokshitzer, Mueller, Peigne, Schiff and Zakharov (BDMPS-Z).

For the present work a Monte-Carlo algorithm for jet-evolution in the medium via both scatterings and coherent medium induced radiations
was implemented. This algorithm was used together with initial jet particles originating in hard nuclear collisions
obtained via the KaTie Monte-Carlo algorithm in order to study dijet observables in heavy ion collisions.
In particular, dijet azimuthal decorrelations were studied. As compared to the results for proton-proton collisions the
dijet azimuthal decorrelations for jets in the medium are both suppressed and broadened. In addition to previous results for gluon jets
alone the same broadening and suppression behavior is also found for results that consider gluon jets as well.
The results are also compared to the dijet azimuthal decorrelations resulting from jets, where momentum components transverse to the jet axis were
selected from a Gaussian distribution.
It was found that in particular the broadening behavior is a result of a Non-Gaussian broadening of momentum components transverse to the jet-axes.

Speaker: Martin Rohrmoser (Cracow University of Technology)

Martin.mp4

ref2022.pdf

32 the Nucleon Energy Energy Correlator

Understanding the nucleon structure is one primary goal of the EIC. We propose the novel nucleon-energy-energy-correlator (N-EEC) that encodes the partonic angular distribution within a nucleon, and provides an entirely new way to image the intrinsic 3-D structures including the spin. We establish the factorization formula for it, remarkably simple and clean, involving no fragmentation-functions nor jet clustering. The predicted N-EEC displays novel features including the angular version of the Bjorken-scaling and a striking confining transition, and is expected to open up many directions such as new probes to the hot/cold medium effect and deepen our understanding of the non-perturbative QCD.

Speaker: Xiaohui Liu

eec-resummation.pdf

Xiaohui.mp4

33 Latest results on the factorization of single-inclusive $e^+e^−$ annihilation

The thrust distribution associated with single-inclusive $e^+e^−$ annihilation (SIAthr), sensitive to the transverse momentum of the detected hadron with respect to the thrust axis, represents one of the most challenging and promising case where to extend the TMD factorization beyond the standard processes. At present days, its factorization properties have been studied through two different approaches, based on SCET framework and CSS formalism respectively.
The two approaches show some tension in the results associated with the kinematic region in the bulk of the phase space, while they agree at its boundaries.
Clarifying the origin of such differences is one of the main aims of this talk. In particular, I will point out how the discrepancies are due to non-perturbative effects, so that the perturbative QCD alone leads blindly to a unique answer. The factorization theorem is then presented at NNLL in thrust and transverse momentum, properly addressing the correlation among these (measured) variables and the rapidity divergences regulator.

Speaker: Andrea Simonelli (INFN, TORINO)

Andrea.mp4

REF2022_Simonelli.pdf

34 Factorization of qTMD @ next-to-leading power

The theory and phenomenology of transverse-momentum dependent parton distributions (TMDs) have seen increasing activity in the past years. Factorization theorems for both leading-power (LP) and next-to-leading power (NLP) scenario has been discussed in the context of experimental processes such as Drell-Yan (DY) or SIDIS.
However, experimental determination of all TMD distributions is an extremely challenging problem. Therefore, lattice simulations of QCD can help bringing complementary information and guiding the phenomelogical parametrizations. On the lattice, since one cannot access directly the TMD correlator, one resorts to study an equal-time ‘quasi’-TMD correlator. However, the relation between the quasi-TMDs and the TMDs in non-trivial. In fact, the quasi-TMD correlator can be interpreted as the counterpart of the hadronic tensor in DY or SIDIS.
In this talk, I will present our results for the quasi-TMD correlator both at LP and NLP at one-loop accuracy. I will show how the quasi-TMD correlator can be factorized into the actual TMD distribution and an unknown function.

Speaker: SIMONE RODINI

rodini.pdf

Simone.mp4

Wednesday 2 November

TMD determination

Convener: Hannes Jung (DESY)

35 New TMD gluon density in the proton from the LHC data.

We propose a new transverse momentum dependent (TMD) gluon distribution in the proton. Using the latest LHC data on the soft hadron production at small transverse momenta, we determine the parameters of the initial TMD gluon density, derived within the soft QCD model at the low scale $\mu_0 \sim 1 - 2$~GeV. Then, we apply the Catani-Ciafaloni-Fiorani-Marchesini (CCFM) evolution equation to extend the obtained TMD gluon density to the whole kinematical region. Using this TMD obtained at both low and large $Q^2$ data on hard processes of $b$-jet production, Higgs boson production and the structure functions $F_{2c}, F_{2b}$ can be described quite satisfactorily.

Speaker: Maxim Malyshev (SINP MSU)

Maksim.mp4

malyshev_REF2022.pdf

36 Towards mini-global parton-branchingTMD fits

In the parton branching (PB) approach, Collinear and TMD parton densities have been determined by fits to inclusive deep inelastic scattering (DIS) HERA data. This method allows one to simultaneously take into account soft-gluon emission and the transverse momentum recoils in the parton branchings along the QCD cascade. The latter leads to a natural determination of the TMD PDFs in a proton. A crucial development will be to include data from other measurements in a wider kinematic range in order to constrain the TMD PDFs and gain sensitivity to intrinsic transverse momentum contributions. We present preliminary results at NLO for PB TMD fits using the same HERAI+II inclusive DIS, plus HERA jet data and LHC W/Z data. The results are compared to the HERAPDF2.0 predictions and a prospect of including other LHC data sets is discussed.

Speaker: Sara Taheri Monfared (DESY)

Sara.mp4

SaraTaheri-REF-2022.pdf

37 Global extraction of unpolarized quark TMDs at N3LL

In this talk we present the most recent extraction of unpolarized transverse-momentum-dependent (TMD) parton distribution functions (PDFs) and TMD fragmentation functions (FFs) from global data sets of Semi-Inclusive Deep-Inelastic Scattering (SIDIS), Drell-Yan and Z boson production. The fit is performed at the N3LL logarithmic accuracy in the resummation of qT-logarithms and features flexible non-perturbative functions, which allow to reach a very good agreement with the experimental data. In particular, we address the tension between the low-energy SIDIS data and the theory predictions, and explore the impact of the precise LHC data on the fit results.

Speaker: Giuseppe Bozzi (University and INFN, Cagliari)

guiseppe.mp4

MAP22.pdf

TMD in experiment: DIS

38 Sudakov logarithms in dijet photoproduction at low x

The differential cross section for the inclusive production of a pair of jets in the scattering of a real photon with a highly energetic proton or nucleus is calculated at next-to-leading order accuracy in the Colour Glass Condensate effective theory. Using this approach, multiple scatterings and nonlinear low-$x$ evolution are taken into account, both important in the saturation regime where the gluon density becomes very large.
When the dijet pair is approximately back-to-back in the transverse plane, large Sudakov logarithms call for an additional resummation which is usually performed in the context of transverse momentum dependent (TMD) factorisation. We show how to extract these logarithms at double logarithmic accuracy and in the large-$N_{c}$ limit, and highlight the many intricacies encountered when trying to perform low-$x$ and TMD resummation consistently.

Speaker: Pieter Taels (FWO - University of Antwerp)

Pieter.mp4

REF 2022 PT.pdf

15:20 Coffee Break

Parallel Session A: TMD theory (p3)

Convener: Piet Mulders (Nikhef and VU University)

39 NLO DGLAP splitting kernels for color non-singlet DPDs

The two partons inside a double parton distributions (DPDs) are correlated in many of their degrees of freedom. In color space, the DPD can be projected onto color singlet and color non-singlet components, where the latter describe color correlations. Color singlet DGLAP evolution of collinear DPDs (DPDFs) uses the exact same splitting kernels as the ones for ordinary parton distribution functions (PDFs) known from single parton scattering. For color non-singlet representations, however, all splitting graphs contain additional projectors on the respective representation. For this reason, their form was unknown beyond LO until now.

In this talk, I will present for the first time the full splitting kernels for unpolarized, longitudinal and quark transversity DPDFs at NLO. They were obtained using two different and independent methods. The first one is based on graph-by-graph results for PDF splitting kernels, the second one utilizes the matching formula for transverse momentum dependent matrix elements. As a by-product, the NLO anomalous dimension for the DPDF Collins-Soper kernel was also obtained for the first time.

Speaker: Florian Fabry (DESY)

Fabry_REF2022.pdf

Florian.mp4

Parallel Session B: TMD theory: quarkonium

Convener: Laurent Favart (Université Libre de Bruxelles)

40 Pseudoscalar quarkonium hadroproduction in TMD factorization

We present the discovery potential of pseudoscalar quarkonium production in hadronic collisions to access gluon TMD PDFs. In particular, we explore the phenomenology of the unpolarized and linearly polarized gluon TMD PDF in unpolarized collisions for different kinematic settings, and the potential of a fixed-target experiment at the LHC to access T-odd distributions such as the gluon Sivers TMD PDF.

Speaker: Francesco Giovanni Celiberto (ECT*/FBK Trento & INFN-TIFPA)

Francesco.mp4

talk_REF_2022_Celiberto_gluon_TMDs_etaQ.pdf

41 Single and double J/psi production in ICEM via the Parton Reggeization Approach

We study the prompt single and double $J/\psi$ hadroproduction in the Improved Color
Evaporation Model using the Parton Reggeization Approach. We make calculations in a single manner to described the experimental data for prompt $J/\psi$ transverse momentum spectra from the energy of $\sqrt{s}=19$ GeV up to modern energy of the LHC, $\sqrt{s}=13$ TeV. The numerical calculations are doing using parton-level MC generator for $k_T-$depended initial-state partons, KaTie. We use the modified KMR-type unintegrated parton distribution functions of Reggeized gluons and quarks with exact normalization based on Kimber-Martin-Ryskin-Watt model. We suggest improvement of the ICEM for the pair-production of $J/\psi$. In case of double $J/\psi$ production we investigate the relative contributions of the single-parton scattering and double-parton scattering mechanisms.

Speaker: Vladimir Saleev (None)

ref_2022_saleev_1.pdf

Vladimir.mp4

42 Resolving negative NLO cross sections problem in quarkonium production via matching with High-Eenrgy Factorization

We continue the investigation of the problem of negative NLO cross sections of heavy quarkonium production at high collision energies, started in [1]. The problem arises due to unphysical behaviour of the high partonic energy asymptotics of NLO partonic coefficient function in collinear factorisation, which can be cured via matching of the NLO calculation with Leading-Logarithmic resummation of partonic center-of-mass energy logarithms. The latter resummation is done using the formalism of High Energy Factorisation by Catani, Ciafaloni and Hautmann. The new results to be reported in the talk include the treatment of the porblem for the case of $J/\psi$ photoproduction (see also Ref. [2] for the alternative treatment of the problem via scale-fixing approach) and $\eta_c$ rapidity distributions.

[1] J.P. Lansberg, M. Nefedov and M.A. Ozcelik, Matching next-to-leading-order and high-energy-resummed calculations of heavy-quarkonium-hadroproduction cross sections JHEP 05, 083 (2022) doi:10.1007/JHEP05(2022)083 [arXiv:2112.06789 [hep-ph]].

[2] A.Colpani Serri, Y.Feng, C.Flore, J.P. Lansberg, M.A. Ozcelik, H.S. Shao and Y. Yedelkina, Revisiting NLO QCD corrections to total inclusive J/$\psi$ and $\Upsilon$ photoproduction cross sections in lepton-proton collisions, [arXiv:2112.05060 [hep-ph]].

Speaker: Maxim Nefedov (NCBJ, Warsaw)

MaximNefedov.mp4

Nefedov_quarkonia_REF-22.pdf

Parallel Session A: TMD in experiment: hadron hadron

Convener: Piet Mulders (Nikhef and VU University)

43 Searching for intrinsic charm with LHCb

The existence of non-perturbatively generated charm quarks in the proton is an open question almost as old as QCD itself. This so-called intrinsic charm has remained controversial since it was first proposed over 40 years ago. In this talk, I will discuss a LHCb study of Z-boson production in association with charm quarks that provides direct evidence for intrinsic charm. I will also discuss this measurement's impact on a recent global analysis of the charm content of the proton.

Speaker: Thomas Boettcher

boettcher_REF2022_2Nov2022_v1.pdf

Thomas.mp4

44 Effective transverse momentum in multiple jet production at hadron colliders

We consider the class of inclusive hadron collider processes in which several energetic jets are produced, possibly accompanied by colourless particles (such as Higgs boson(s), vector boson(s) with their leptonic decays, and so forth).
We propose a new variable that smoothly captures the
𝑁+1 to 𝑁-jet transition. This variable, that we dub $k_𝑇^{\text{ness}}$, represents an effective transverse momentum controlling the singularities of the 𝑁+1-jet cross section when the additional jet is unresolved.
The $k_𝑇^{\text{ness}}$ variable offers novel opportunities to perform higher-order calculations in Quantum Chromodynamics (QCD) by using non-local subtraction schemes.
We study the singular behavior of the 𝑁+1-jet cross section as $k_𝑇^{\text{ness}}\to 0$ and, as a phenomenological application, we use the ensuing results to evaluate next-to-leading order corrections to 𝐻+jet and 𝑍+2 jet production at the LHC.
We show that $k_𝑇^{\text{ness}}$ performs extremely well as a resolution variable and appears to be very stable with respect to hadronization and multiple-parton interactions.

Speaker: Jürg Haag (UZH)

Juerg.mp4

REF2022.pdf

Parallel Session A: TMD in experiment: DIS

Convener: Piet Mulders (Nikhef and VU University)

45 The photon energy spectrum in B➞Xₛγ at N³LL'

The smallest element of the CKM matrix, $|V_{ub}|$, can be extracted from measurements of semileptonic B meson decay $B\to X_ul\bar{\nu}$. However, the experimental signal of this process is obscured by large backgrounds, which are absent only at the edge of the phasespace. Resummation of perturbative series is essential in this kinematic region. Furthermore, this region is sensitive to Fermi motion of the b-quark inside the B-meson. Factorization theorems derived in Soft-Collinear Effective Theory are used to separate dynamics at different energy scales. The factorization also isolates nonperturbative effects in a so-called shape function. The shape function cannot be calculated perturbatively, but it can be measured in $B\to X_s\gamma$ decay.

I will present our preliminary predictions of $B\to X_s\gamma$ spectrum at ${\rm N^3LL'{+}N^3LO}$. We parameterize the few unknown 3-loop perturbative ingredients, - a hard function coefficient and nonsingular contributions - using nuisance parameters. The variation of these nuisance parameters provides a robust estimate of the uncertainty that arises from our ignorance of these 3-loop terms.

In order to arrive at stable predictions it is essential to use a short-distance scheme for the b-quark mass. It is well-known that the pole mass scheme suffers from a renormalon problem, which leads to very poor convergence. We demonstrate that predictions in 1S mass scheme, which has been used for this process in the past, start to break down at ${\rm N^3LO}$ due to a mismatch between the 1S scale and the soft scale of this process. I will show that the MSR mass scheme yields much more stable results.

Speaker: Ivan Novikov (DESY)

Ivan.mp4

slides.pdf

Parallel Session B: TMD theory: small x

Convener: Laurent Favart (Université Libre de Bruxelles)

46 Relation of TMD gluon density to dipole cross section and the saturation effect in DIS

The new starting TMD gluon density, obtained within the soft QCD model for pp inelastic collisions at low scales μ0, is connected directly with the dipole cross section of the deep inelastic ep scattering. The saturation of this cross section at large distances between quark and antiquark in the qq ̄ dipole or small values of μ0 is analyzed. The sensitivity of the saturation effect to different kind of initial TMD gluon densities is shown.

Speaker: Gennady Lykasov

Gennady.mp4

LYKASOV_REF_Nov2.2022.pdf

17:10 Coffee Break

Parallel Session A: TMD in experiment: DIS: Parallel Session 1

Convener: Itana Bubanja

47 Measurement and QCD analysis of inclusive jet production in deep inelastic scattering at HERA

A new measurement of inclusive jet cross sections in neutral current deep inelastic scattering using the ZEUS detector at the HERA collider is obtained. The data were taken at HERA 2 at a center of mass energy of 318 GeV and correspond to an integrated luminosity of 347 pb-1. Massless jets, reconstructed using the kT-algorithm in the Breit reference frame, are measured as a function of the squared momentum transfer Q2 and the transverse momentum of the jets in the Breit frame p(T,Breit). The measured jet cross sections are compared to previous measurements as well as NNLO QCD theory predictions. The measurement is used in a QCD analysis at NNLO accuracy to perform a simultaneous determination of parton distribution functions of the proton and the strong coupling constant, resulting in a value of alpha_s(M2Z) = 0.1138 +- 0.0014 (exp/fit) +0.0004 −0.0008 (model/param.) +0.0008 −0.0007 (scale). A significantly improved accuracy is observed compared to similar measurements of the strong coupling constant.

Speaker: Florian Lorkowski (CMS (CMS Fachgruppe QCD))

FlorianL.mp4

InclusiveJets.pdf

48 Impact of jet-production data on the next-to-next-to-leading-order determination of HERAPDF2.0 parton distributions

On behalf of the H1 and ZEUS Collaborations.
Eur. Phys. J. C82 (2022) 243

The HERAPDF2.0 ensemble of parton distribution functions (PDFs) was introduced in 2015. The final stage is presented, a next-to-next-to-leading-order (NNLO) analysis of the HERA data on inclusive deep inelastic ep scattering together with jet data as published by the H1 and ZEUS collaborations. A perturbative QCD fit, simultaneously of alpha_s(M2Z) and the PDFs, was performed with the result alpha_s(M2Z) = 0.1156 +- 0.0011 (exp) +0.0001 −0.0002 (model+parameterisation) +- 0.0029 (scale). The PDF sets of HERAPDF2.0Jets NNLO were determined with separate fits using two fixed values of alpha_s(M2Z), alpha_s(M2Z) = 0.1155 and 0.118, since the latter value was already chosen for the published HERAPDF2.0 NNLO analysis based on HERA inclusive DIS data only. The different sets of PDFs are presented, evaluated and compared. The consistency of the PDFs determined with and without the jet data demonstrates the consistency of HERA inclusive and jet-production cross-section data. The inclusion of the jet data reduced the uncertainty on the gluon PDF. Predictions based on the PDFs of HERAPDF2.0Jets NNLO give an excellent description of the jet-production data used as input.

Speaker: Katarzyna Wichmann (DESY)

Katarzyna.mp4

kwichmann-nnloJets-ref22.pdf

49 Analysis of world polarized DIS data with small-$x$, Large $N_c \& N_f $ helicity evolution

In order to solve the proton spin problem, the small-$x$ asymptotics of the helicity parton distribution functions (hPDFs) need to be understood. New theory has been developed for the small-$x$ evolution of these hPDFs, able to extrapolate the small-$x$ behaviour of the quark and gluon hPDFs. At large $N_c \& N_f$, these evolution equations close and are amenable to numerical computation. In this talk we will present the phenomenological analysis of this theory by describing the world data on the $g_1$ structure function within the JAM global analysis framework. Beyond this, we investigate the qualitative behaviour of the quark and gluon hPDFs and the challenges involved with measuring them.

Speaker: Daniel Adamiak (Ohio State University)

Daniel.mp4

REF Daniel Adamiak Presentation.pdf

50 Production of J/psi in electron-proton collision in kT factorization.

We calculate the differential cross section for the production of J/psi in electron-proton collision within the formalism of QCD kT factorization. We present distributions in transverse momentum and rapidity for COMPASS, JLab, HERMES and EIC centre of mass energies. Our results are compared with the experimental data for production J/psi at electron-proton scattering experiments. We predict the total and differential cross section for the future Electron-Ion Collider (EIC) experiment. Our study is based on the off-shell photon-gluon fusion subprocess, where non-zero transverse momentum of the gluon is considered. We use the improved colour evaporation model (ICEM) for the heavy quarkonium production. We use different unintegrated parton distribution function (uPDFs) driven by the Ciafaloni–Catani–Fiorani–Marchesini (CCFM) evolution equation at low . This is the clean process to clearly understand and to have constraint on gluon uPDFs. This study also highlights the production models of heavy quarkonium and their validity at different production processes.

Speaker: Vaibhav Rawoot

REF_2022_Vaibhav_Rawoot.pdf

Vaibhav.mp4

Parallel Session B: TMD theory: small x

Convener: Hannes Jung (DESY)

51 Inclusive hadron production in forward pA collisions

With the tremendous accomplishments of RHIC and the LHC experiments and the advent of the future Electron-Ion Collider on the horizon, the quest for compelling evidence of the color glass condensate (CGC) has become one of the most aspiring goals in the high energy Quantum Chromodynamics research. Pursuing this question requires developing the precision test of the CGC formalism. By systematically implementing the threshold resummation, we significantly improve the stability of the next-to-leading-order calculation in CGC for forward rapidity hadron productions in $pp$ and $pA$ collisions, especially in the high $p_T$ region, and obtain reliable descriptions of all existing data measured at RHIC and the LHC across all $p_T$ regions. Consequently, this technique can pave the way for the precision studies of the CGC next-to-leading-order predictions by confronting them with a large amount of precise data.

Reference

[1] Y. Shi, L. Wang, S.Y. Wei, B.W. Xiao, Phys. Rev. Lett. 128, 202302 (2022). Lengthy supplemental material: arXiv:2112.06975

Speaker: Shu-yi Wei (Shandong University)

Shu-Yi.mp4

threshold_resummation.pdf

52 Power counting to saturation

Our current understanding of the physics of saturation comes from the Color Glass Condensate that treats the nucleus as a classical source of small x gluons. On the other hand, the physics at large x is understood in terms of a factorization theorem of the PDF and a hard function.
To put the small x regime on the same footing, I ll present a rigorous factorization theorem for small x physics showing a manifest separation of the universal physics of the Nuclear medium from the probe at leading power in x. I ll show that the onset of saturation can be understood as a breakdown in expansion in an emergent power counting parameter and allows us to define the saturation scale in terms of a matrix element of a gauge invariant operator in the Nuclear state. Likewise, a power counting argument leads to a new radiation mode in our factorized formula, which greatly clarifies the role played by the medium size in deciding linear/non-linear evolution of the cross section in $\ln x$.

Speaker: varun vaidya

REF2022_Varun.pdf

Varun.mp4

53 Transverse momentum broadening from NLL BFKL to all orders in pQCD

We study, to all orders in perturbative QCD, the universal behavior of the saturation momentum $Q_s(L)$ controlling the transverse momentum distribution of a fast parton propagating through a
dense QCD medium with large size $L$. Due to the double logarithmic nature of the quantum evolution of the saturation momentum, its large $L$ asymptotics is obtained by slightly departing from the double logarithmic limit of either next-to-leading log (NLL) BFKL or leading order DGLAP evolution
equations. At fixed coupling, or in conformal N = 4 SYM theory, we derive the large $L$ expansion of $Q_s(L)$ up to order $\alpha_s^{3/2} $. In QCD with massless quarks, where conformal symmetry is broken by the running of the strong coupling constant, the one-loop QCD $\beta$-function fully accounts for the universal terms in the $Q_s(L)$ expansion. Therefore, the universal coefficients of this series are known exactly to all orders in $\alpha_s$.

Speaker: Yacine Mehtar-Tani (BNL)

REF22.pdf

Yacine.mp4

54 Infrared renormalon effects in color dipole TMD PDF at small-x.

Perturbation series in quantum field theory are usually divergent even after term by term renormalization. There are resummation procedures to regularize divergence series, for factorially divergent series Borel summation is mostly used. In the small momenta regions, within the window of momentum scale ΛQCD and saturation scale Qs where the running coupling becomes large, infrared renormalons is believed to be the source of the divergence in the perturbation series and gives estimates to the uncertainty due to non-perturbative effects. In this work [Nucl. Phys. B 953 (2020), 114961], we estimated uncertainties from the infrared renormalons in the (color dipole) gluon distribution. We have shown that non-linear saturation effects at small-x shift the first IR pole at the Borel plane towards zero from 2/β2 to 1/β2 where β2 is beta function of QCD. This leads to enhanced non-perturbative uncertainty for the (color dipole) gluon distribution.

Speaker: Nahid Vasim

Nahid.mp4

REF2022_Nahid.pdf

Intelectual excursion

Convener: Hannes Jung (DESY)

55 The evolution of the particle concept

Observation of particles has been an evolving notion in science. It has been based on our ever increasing understanding of fundamental physics. We will sketch the historical development from the observation of a spatially localizable classical particle to the discovery of the Higgs boson. We will then argue that we are at the verge of yet another evolutionary step in the notion of observation, and investigate the role of the particle concept in this respect.

Speaker: Robert Harlander

REF_Desy.pdf

Robert.mp4

Thursday 3 November

TMD theory

Convener: Hannes Jung (DESY)

56 The Fractal TMDs and the proton structure functions at low x

In this paper, we study the Parton Distribution Functions (PDFs) at low x and at NLO approximation in perturbative QCD.
To this end, a simple parametrization for the unintegrated Parton Distribution Functions based on the "Fractal" approach is considered. These functions have self-similar behavior at low x and $k_t^2$ for sea quarks and have self-similar behavior at low $ x$ for gluon distribution. By integration from these TMDs, the initial input densities are obtained and the free parameters of this model are calculated by global analysis of experimental data released by HERA experiment on electron-proton ($e^-p$) and positron-proton ($e^+p$) for natural current (NC) interactions in DIS processes for the range of $1.5 < Q^2 < 650$ ($GeV^2$) and $x<0.01$.
The uncertainty estimations in the present analysis are carried out using the standard ``Hessian'' method. Considering the overall value of $\chi^2/{\rm dof}$ and theory-to-data comparisons, the results indicate nice agreements between the experimental datasets and other phenomenological predictions at low $\textit{x}$.

Speaker: Dr Fatemeh Taghavi-Shahri (Ferdowsi University of Mashhad)

Fatimah.mp4

taghavishahri-final.mp4

Taghavishahri.pdf

57 Studying saturation effects in dijet correlations at forward LHC calorimeters

We study dijet production withing the small-x improved TMD factorization formalism, which allows to take into account the Sudakov resummation as well as the power corrections that are necessary to access the dijet decorrelation region. We study both the full b-space Sudakov resummation as well as the simplified momentum space approach, which is more suitable for Monte Carlo simulations. We compute observables for the updated ATLAS kinematics as well as for the future FoCal kinematics and discuss modifications due to final state shower and hadronization.

Speaker: Piotr Kotko (AGH UST)

Kotko_REF2022.pdf

Piotr.mp4

58 Small $q_{T}$ region in the Parton Branching approach

The low transverse momentum, $q_{T}$, region of the Drell-Yan (DY) pair is dominated by non-perturbative physics. More precisely, the region where $q_{T}<

Speaker: Mikel Mendizabal (DESY)

Mikel.mp4

REF2022_Mikel.pdf

59 Threshold Improved Transverse momentum dependent distribution functions

We introduce a new type of transverse momentum dependent (TMD) distribution function at the threshold limit in the Drell-Yan process as well as semi-inclusive deep-inelastic scattering and double-inclusive leptonic annihilation. We apply Soft-Collinear Effective Theory (SCET) and renormalization group methods to obtain QCD evolution equations for both threshold-TMD Parton distribution functions and fragmentation functions. In the end, we present the numerical predictions for different experiments (including LHC, RHIC, COMPASS, Belle etc).

Speaker: Dr Kajal Samanta (Fudan University)

Kajal.mp4

REF2022_kajal.pdf

15:20 Coffee Break

Parallel Session A: TMD in experiment: DIS

Convener: Natasa Raicevic

60 Experimental Studies of Evolution Properties of Structure Functions in Polarized SIDIS

The quark-gluon dynamics manifests itself in a set of non-perturbative functions describing all possible spin-spin and spin-orbit correlations. Single and Dihadron semi-inclusive and hard exclusive production, both in current and target fragmentation regions, provide a variety of spin and azimuthal angle dependent observables, sensitive to the dynamics of quark-gluon interactions. Studies of spin-dependent structure functions, and underlying transverse momentum distributions of partons are currently driving the upgrades of several existing facilities, and the design and construction of new facilities worldwide.
In this talk, we present some ongoing and possible future studies of Q^2-dependences of structure functions in SIDIS, required for validation of existing theoretical description of SIDIS.

Speaker: Harut Avagyan

2022-REF2022.pdf

Harut.mp4

61 Back-to-back inclusive dijets in DIS at small x: Sudakov suppression and gluon saturation at NLO

Back-to-back dijet cross-sections in deeply inelastic scattering (DIS) at small x are suppressed by many-body multiple scattering and screening effects arising from gluon saturation at high parton densities. They are similarly sensitive in these kinematics to large Sudakov logarithms from soft gluon radiation. Uncovering novel physics in this DIS channel therefore requires understanding the interplay of the two phenomena. In this work, we compute the small x inclusive dijet DIS cross-section in back-to-back kinematics at next-to-leading order (NLO) in the Color Glass Condensate effective field theory (CGC EFT). Our result includes, for the first time, all real and virtual NLO contributions to the impact factor. These include all Sudakov double and single logarithm contributions, as well as all other finite O(αs) terms that contribute at this order. We demonstrate explicitly that resummations of small x and Sudakov logarithms can be performed simultaneously in the CGC EFT. This requires that the JIMWLK kernel for small x evolution of the Weizs¨acker-Williams (WW) gluon distribution satisfies a kinematic constraint imposed by lifetime ordering of successive gluon emissions; the corresponding modifications to the kernel, corresponding to resummations of large double transverse logarithms, are precisely of the type required to stabilize JIMWLK evolution beyond leading logarithmic accuracy. We compute the azimuthal harmonics of the NLO back-to-back distributions and show their sensitivity to both the unpolarized and linearly polarized WW gluon distributions. Finally, we discuss how TMD factorization is broken by an emergent saturation scale at small x.

References:

[1] Dijet impact factor in DIS at next-to-leading order in the Color Glass Condensate. JHEP 11 (2021) 222. arXiv:2108.06347

[2] Back-to-back inclusive dijets in DIS at small x: Sudakov suppression and gluon saturation at NLO. arXiv:2208.13872

Speaker: Farid Salazar (UCLA/UCB/LBL)

Farid.mp4

Saturation_Sudakov_REF-final.pdf

Parallel Session B: TMD theory: DY and DIS

Convener: Piet Mulders (Nikhef and VU University)

62 Fiducial Drell-Yan production at the LHC improved by transverse-momentum resummation at N4LL+N3LO

Drell-Yan production is one of the precision cornerstones of the LHC, serving as calibration for measurements such as the W-boson mass. Its extreme precision at the level of 1% challenges theory predictions at the highest level. We present the first independent calculation of Drell-Yan production at order $\alpha_s^3$ in transverse-momentum ($q_T$) resummation improved perturbation theory. Our calculation reaches the state-of-the-art through inclusion of the recently published four loop rapidity anomalous dimension and three loop massive axial-vector contributions. We compare to the most recent data from CMS with fiducial and differential cross-section predictions and find excellent agreement at the percent level.

Based on 2207.07056.

Speaker: Tobias Neumann (Brookhaven National Laboratory)

Neumann_Tobias_REF2022.pdf

Tobias.mp4

63 Modified TMD Factorization and Sub-leading Power Corrections

Factorization theorems are known to be extremely powerful tools in high-energy particle physics. Processes like SIDIS, Drell-Yan vector-boson production, Higgs-boson production through gluon fusion and $e^+e^-$ to jets and/or hadrons are just some examples of processes that have been thoroughly investigated by applying rigorous factorization formulae. Furthermore, if in these processes the transverse momentum $\textbf{q}_T$ of the vector boson or final-state hadrons is measured, in the limit of small $\textbf{q}_T$, leading-power transverse-momentum-dependent (TMD) factorization is an established tool to obtain further insight into the internal structure of hadrons (like spin and helicity distributions, sea quark contributions) and/or jets involved. However, in order to properly exploit increasingly precise experimental data, it is important to investigate sub-leading contributions. In this talk, we present a novel method to compute next-to-leading-power and next-to-next-leading-power contributions to TMD cross sections. In the specific example of a Drell-Yan process, we show how our analytic results allow us to achieve next-to-next-to-leading logarithmic (NNLL) resummation, recover both the leading-power TMD factorization and collinear factorization expressions up to next-to-next-to-leading order in the small $\textbf{q}_T$ limit and provide a description of the cross section valid also at intermediate $\textbf{q}_T$. The implications for the phenomenological extraction of TMDPDFs are also discussed.

Speaker: Sergio Leal Gómez (Universität Wien)

REF_2022_Montenegro_v1.1.pdf

Sergio.mp4

64 Threshold factorization of the quark-gluon channel in the DY process at NLP

Over the years, Soft Collinear Effective Theory (SCET) has been successfully applied to many important observables in collider physics improving the accuracy of fixed-order predictions via the leading power (LP) resummation of large logarithmic contributions which appear in certain regions of phase space. Recently, much interest has gathered in subleading power corrections amongst the theoretical community. In this talk, I will discuss the framework for the threshold resummation of the quark-gluon channel of the Drell-Yan process at next-to-leading power (NLP) using SCET. I will prove the general factorisation formula and describe new objects that emerge beyond LP. That is, the NLP collinear functions and generalized soft functions. I will also show the calculation of the soft functions at the two-loop order, and show that the bare factorization theorem holds up to NNLO.

Speaker: Sebastian Jaskiewicz (Technische Universität München)

REF22_sjaskiewicz_final.pdf

Sebastian.mp4

Parallel Session A: TMD in experiment: hadron hadron

Convener: Natasa Raicevic

65 Drell Yan production at low $k_T$ at LHC with PB TMDs

This work presents the study of the low $k_T$ behaviour of the PB TMD parton distributions by investigating the production of Drell Yan pairs at different invariant masses obtained at LHC at the centre of mass energies of 8 and 13 TeV. The study will be performed by applying NLO calculations for Drell Yan production using MADGRAPH5_AMC@NLO. By applying the PB method, it will be shown that the intrinsic parton $k_T$ distribution does not affect Drell Yan and Z production at the LHC.

Speaker: Itana Bubanja

Drell Yan production at low kT at LHC with PB TMDs-12.pdf

Itana.mp4

66 Isolated photon-hadron production in high energy pp and pA collisions at RHIC and LHC.

This talk is based on "Benić, Garcia-Montero, Perkov: Phys. Rev. D 105, 114052 (2022)". In it we compute the isolated photon production in association with a charged hadron at mid rapidity in pp and pA collisions. Our approach is grounded in the Color Glass Condensate (CGC) framework of high energy QCD with the addition of the Sudakov resummation of soft gluon emissions. The observables of interest (angular distributions and out-of-plane transverse momentum distributions) are computed in the leading order qg→qγ channel and compared with the recent data from RHIC and LHC. We find that, while the CGC computation alone results in too narrow distributions, with the help of the Sudakov effect, we can get a satisfactory description of the data. With this as a benchmark, we provide predictions for the magnitude of the nuclear effect brought by the phenomena of gluon saturation in the CGC.

Speaker: Anton Perkov (University of Zagreb, Faculty of Science, Department of Physics)

Anton.mp4

Perkov_REF2022.pdf

Parallel Session B: TMD theory: small x

Convener: Piet Mulders (Nikhef and VU University)

67 Two-scale evolution from rapidity-ordered BFKL cascade

The two-scale evolution of Collins-Soper-Sterman-type for the unintegrated PDF in the regime qT << mu is derived from the BFKL evolution in physical rapidity with longitudinal momentum conservation constraint in coordinate space form. Comparisons of analytic results with Monte-Carlo implementation of the evolution are also done. This work is a continuation of the calculation done in Phys. Rev. D 104, 054039 (2021).

Speaker: Maxim Nefedov (NCBJ, Warsaw)

Maxim.mp4

Nefedov_two-scales.pdf

17:10 Coffee Break

Parallel Session A: TMD theory

Convener: Jelena Mijuskovic (University of Montenegro)

68 On the normalization of unintegrated parton densities

I will present the KMRW formalism and discuss some of its issues, including the Sudakov factor larger than one and the mismatch between the integral and differential definitions. These issues have been discussed recently, but a fully satisfying solution was still missing.

I argue and show with an explicit example that changing the normalization condition from $\int^{\mu^2} dk^2 F(x,k^2;\mu^2)$ to $\int^{\infty} dk^2 F(x,k^2;\mu^2)$ solves all the issues at once.

Speaker: Benjamin Guiot (Universidad Tecnica Federico Santa Maria)

Benjamin.mp4

REF-2022.pdf

69 Transverse Momentum Resummation to Fourth Logarithmic Order

In this talk I will discuss the recent progress in the determination of the ingredients necessary for the resummation of TMD distributions to N4LL.
In particular, I will briefly review the calculation of the three loop beam functions and fragmentation functions and then discuss the determination of the 4 loop rapidity anomalous dimension.
I will conclude by presenting some phenomenological results implementing these ingredients to reach N4LL resummmation accuracy.

Speaker: Dr Gherardo Vita (SLAC)

Gherardo.mp4

Vita - REF 2022.pdf

70 Transverse momentum dependent splitting functions in a parton branching algorithm

The outcome of high energy colliders experiments depends on predictions obtained from Monte Carlo (MC) generators, the base of which are the parton branching methods.

We construct a new parton branching algorithm which for the first time incorporates the off-shell, transverse-momentum dependent (TMD) splitting functions, defined from the high-energy limit of partonic decay amplitudes and fulfills momentum sum rule.

Based on these TMD spliting functions we construct a new TMD Sudakov form factor.

We present the first MC implementation of the algorithm for the evolution of the TMD and integrated parton distribution functions (PDFs). We use this implementation to evaluate small x corrections to the distributions.

Presented study is a first step towards a full TMD MC generator covering the small-x phase space.

Speaker: Aleksandra Lelek (University of Antwerp)

Ola.mp4

REF.pdf

71 Quark mass effects in double parton distributions

Double parton scattering (DPS) provides access to information about nucleon structure not accessible in single parton scattering: spatial, spin, and colour correlations between the partons inside the nucleon. For short distances between the two probed partons the double parton distributions (DPDs) containing this information can be calculated in perturbation theory. In this talk I will discuss how a consistent treatment of quark mass effects can be achieved in the evaluation of these short distance $1 \to 2$ splitting DPDs. In addition I will also illustrate how - even without a full calculation from Feynman diagrams - the massive splitting can be approximated at next-to-leading order in the strong coupling.

Speaker: Peter Josef Ploessl (T (Phenomenology))

2022_11_03_REF_Ploessl.pdf

Peter.mp4

Parallel Session B: TMD theory: small x

Convener: Laurent Favart (Université Libre de Bruxelles)

72 T-odd Leading-Twist Quark TMDs at Small $x$

We study the small-$x$ asymptotics of the flavor non-singlet T-odd leading-twist quark transverse momentum dependent parton distributions (TMDs), the Sivers and Boer-Mulders functions. While the leading eikonal small-$x$ asymptotics of the quark Sivers function is given by the spin-dependent odderon, we are interested in revisiting the sub-eikonal correction considered by us earlier. We first simplify the expressions for both TMDs at small Bjorken $x$ and then construct small-$x$ evolution equations for the resulting operators in the large-$N_c$ limit, with $N_c$ the number of quark colors. For both TMDs, the evolution equations resum all powers of the double-logarithmic parameter $\alpha_s \, \ln^2 (1/x)$, where $\alpha_s$ is the strong coupling constant, which is assumed to be small. Solving these evolution equations numerically (for the Sivers function) and analytically (for the Boer-Mulders function) we arrive at the following leading small-$x$ asymptotics of these TMDs at large $N_c$:
\begin{align}
f_{1 \: T}^{\perp \: NS} (x \ll 1 ,k_T^2) & = C_O (x, k_T^2) \, \frac{1}{x} + C_1 (x, k_T^2) \, \left( \frac{1}{x} \right)^{3.4 \, \sqrt{\frac{\alpha_s \, N_c}{4 \pi}}} , \notag \
h_1^{\perp \, \textrm{NS}} (x \ll 1, k_T^2) & = C (x, k_T^2) \left( \frac{1}{x} \right)^{-1}. \notag
\end{align}
The functions $C_O (x, k_T^2)$, $C_1 (x, k_T^2)$, and $C (x, k_T^2)$ can be readily obtained in our formalism: they are mildly $x$-dependent and do not strongly affect the power-of-$x$ asymptotics shown above. The function $C_O$, along with the $1/x$ factor, arises from the odderon exchange. For the sub-eikonal contribution to the quark Sivers function (the term with $C_1$), our result shown above supersedes the one obtained in our previous work due to the new contributions identified recently.

Speaker: M. Gabriel Santiago (SURA Center for Nuclear Femtography)

Gabriel.mp4

REF_2022_Santiago.pdf

REF_2022_Santiago.pptx

73 Quark and Gluon Helicity Evolution at Small x

Resolution of the proton spin puzzle, which is inability of the constituent quark model to explain discrepancy between the spin-$1/2$ of the proton and the amount of spin carried by its quarks and gluons, as measured in experiment, is an outstanding problem in modern hadronic physics. One possibility is that "missing” spin of the proton may be found at small values of Bjorken-x. As a result, in recent years the small-x asymptotics of helicity distributions for quarks and gluons have been the subject of intense studies. In this talk we will discuss the small-x evolution of the gluon and flavour-singlet quark helicity distributions calculated in the shock-wave formalism. For the first time we will show that the evolution contains mixing not only between the gluon field-strength $F_{12}$ and quark axial current $\bar{\psi}\gamma^+\gamma_5\psi$ operators, but also a sub-eikonal operator $D^i - \overleftarrow{D}^i$ which is related to the Jaffe-Manohar polarized gluon distribution. To do this, we will employ the powerful background field method which allows to unambiguously determine the form of the operators and their mixing in the helicity evolution. By solving the evolution equations in the limit of large $N_c$ we find that the small-x asymptotics of the quark and gluon helicity distributions is in complete agreement with the earlier work by Bartels, Ermolaev and Ryskin.

Speaker: Andrey Tarasov (The Ohio State University)

Andrey.mp4

REF2022.pdf

74 Revised Small-x Helicity Evolution: Numerical Results

Recently, a revised small-$x$ evolution equation for quarks and gluons inside the proton has been constructed to the double-logarithmic order, resumming powers of $\alpha_s\ln^2(1/x)$, with $\alpha_s$ the strong coupling constant. The equation takes into account the observation that the evolution of the sub-eikonal operator, $\overleftarrow{D}^i D^i$, mixes with other helicity-dependent operators from the previous works, which are the gluon field strength, $F^{12}$, and the quark axial current, ${\bar \psi} \gamma^+ \gamma^5 \psi$. Based on the new evolution, a closed system of evolution equations can be constructed in the limits of large $N_c$ or large $N_c\& N_f$. (Here, $N_c$ and $N_f$ are the number of quark colors and flavors, respectively.) We numerically solve the equations in these limits and obtain the following small-$x$ asymptotics for the $g_1$ structure function at $N_f \leq 5$:

$$g_1(x,Q^2) \sim \left(\frac{1}{x}\right)^{\alpha_h\sqrt{\alpha_sN_c/2\pi}},$$ with the intercept, $\alpha_h$, decreasing with $N_f$. In particular, at the large-$N_c$ limit, we have $\alpha_h = 3.66$, which agrees with the earlier work by Bartels, Ermolaev and Ryskin. Once the sixth quark flavor is turned on, i.e. $N_f = 6$, an oscillatory pattern in $\ln\frac{1}{x}$ emerges. However, the oscillation period spans many units of rapidity, making it difficult to observe in an experiment.

Speaker: Yossathorn Tawabutr (University of Jyväskylä)

REF22_Tawabutr.pdf

Yossathorn.mp4

75 NLO computation of diffractive di hadron production in the shockwave framework.

The cross-sections of diffractive double hadron photo- or electroproduction with large pT, on a nucleon or a nucleus, are calculated to NLO accuracy. A hybrid formalism mixing collinear factorization and high energy kt factorization, more precisely the shockwave formalism, is used to derive the results. The cancellation of divergences is explicitly shown, and the finite parts of the NLO differential cross section are found. We work in arbitrary kinematics such that both photoproduction and leptoproduction are considered, making the results usable in order to detect saturation at both the future EIC
or already at LHC, using UPC.

Speaker: emilie Li

Emilie.mp4

REF_2022_Emilie_Li.pdf

Advisory Board meeting

Friday 4 November

Parton shower systematics and TMDs

Convener: Itana Bubanja

76 New Developments for QCD Parton Showers

I will give an overview of recent developments of NLL accurate QCD parton showers for final and initial state radiation, and recent developments within the amplitude level evolution framework.

Speaker: Simon Plätzer (Universität Graz)

Simon.mp4

TMD theory

Convener: Itana Bubanja

77 NLO for hybrid kT-factorization

The hybrid kT-factorization formula, for which one initial-state parton
momentum is space-like and carries non-vanishing transverse components while
the other is on-shell, is promoted to NLO for arbitrary processes. We identify
all soft and collinear divergencies in the partonic cross section, and
recognize that the non-cancelling ones can be attributed to PDF evolution,
evolution kernel, and target impact factors. Coincidentally, we recover known
expressions for inclusive NLO impact factor corrections both for quarks and
gluons.

Speaker: Andreas van Hameren (IFJ PAN)

Andreas.mp4

vanHameren.pdf

78 Rapidity-only TMD factorization at the NLO

A production of a particle with a small transverse momentum in hadron-hadron collisions is described
by CSS-based TMD factorization at moderate Bjorken $x_B\sim 1$ and by $k_T$-factorization at small $x_B$.
A uniform description valid for all $x_B$ is provided by rapidity-only TMD factorization developed in a series
of recent papers. In this talk I present the results for the rapidity-only TMD factorization at the NLO level.

Speaker: Ian Balitsky (JLab/ODU)

Ian.mp4

ref_2022.pdf

TMD factorization

Convener: Jelena Mijuskovic (University of Montenegro)

79 Transverse momentum measurements with jets

Traditionally, transverse momentum measurements in pp collisions focus on Drell-Yan. I will show that there is a natural generalization to jets, by using a recoil-free jet axis. I will start by discussing recent results for the azimuthal angle in V+jet production, but also on-going work that goes beyond that.

Speaker: Wouter Waalewijn (University of Amsterdam / Nikhef)

azim_dec.pdf

Wouter.mp4

80 Multijet and Zj azimuthal correlations - factorization breaking

In this talk recent studies on Zj and dijet azimuthal correlations in the TMD parton branching method at NLO will be presented. The region where the azimuthal angle $\Delta\phi_{jj(Zj)} \approx \pi$ is sensitive to soft-gluon resummation and TMD effects. In this back-to-back region, factorization-breaking effects may arise for such colored final states. Therefore we propose a measurement of both Zj and jj correlations for high-pT in the same kinematic region in order to find hints of possible factorization-breaking effects by comparing the measurement to predictions in which factorization holds.

Speaker: Luis Ignacio Estevez Banos (CMS (CMS Fachgruppe QCD))

LuisIgancio.mp4

LuisIgnacio_REF_2022.pdf

81 Closing

Speaker: Hannes Jung (DESY)

Closing.pdf

Hannes.mp4