### Conveners

#### WG5 Small-x and Diffraction

- Alessia Bruni (INFN Bologna)
- Leszek Motyka (Jagiellonian University)
- Rainer Schicker (Phys. Inst., Heidelberg)

#### WG5 Small-x and Diffraction

- Rainer Schicker (Phys. Inst., Heidelberg)
- Leszek Motyka (Jagiellonian University)
- Alessia Bruni (INFN Bologna)

#### WG5 Small-x and Diffraction

- Leszek Motyka (Jagiellonian University)
- Alessia Bruni (INFN Bologna)
- Rainer Schicker (Phys. Inst., Heidelberg)

#### WG5 Small-x and Diffraction

- Alessia Bruni (INFN Bologna)
- Rainer Schicker (Phys. Inst., Heidelberg)
- Leszek Motyka (Jagiellonian University)

#### WG5 Small-x and Diffraction

- Alessia Bruni (INFN Bologna)
- Leszek Motyka (Jagiellonian University)
- Rainer Schicker (Phys. Inst., Heidelberg)

#### WG5 Small-x and Diffraction

- Alessia Bruni (INFN Bologna)
- Leszek Motyka (Jagiellonian University)
- Rainer Schicker (Phys. Inst., Heidelberg)

#### WG5 Small-x and Diffraction

- Rainer Schicker (Phys. Inst., Heidelberg)
- Alessia Bruni (INFN Bologna)
- Leszek Motyka (Jagiellonian University)

#### WG5 Small-x and Diffraction

- Rainer Schicker (Phys. Inst., Heidelberg)
- Alessia Bruni (INFN Bologna)
- Leszek Motyka (Jagiellonian University)

Allen Caldwell
(Max Planck Institute)

4/12/16, 9:00 AM

Small-x, Diffraction and Vector Mesons

Assuming the form $\sigma^{\gamma P} \propto l^{\lambda_{\rm eff}}$ at fixed $Q^2$ for the behavior of the virtual-photon proton scattering cross section, where $l$ is the coherence length of the photon fluctuations, it is seen that the extrapolated values of $\sigma^{\gamma P}$ for different $Q^2$ cross for $l\approx 10^8$~fm. It is argued that this behavior is not physical, and that the...

Prof.
John Dainton
(Cockcroft)

4/12/16, 9:20 AM

Small-x, Diffraction and Vector Mesons

Measurements of the lepto-production of vector mesons have always been pivotal in the development of a theory of hadron dynamics, challenging and elucidating the paradigm of the moment and thereby guiding our understanding of it to its present status in terms of QCD. Always with an experimentalist's appreciation of the momentous theoretical achievements of more recent years with QCD in mind,...

Dr
Heikki Mäntysaari
(Brookhaven National Laboratory)

4/12/16, 9:40 AM

Small-x, Diffraction and Vector Mesons

The Color Glass Condensate framework has been successfully applied to many high-energy scattering processes, and it has also been seen as a powerful tool to describe initial state of heavy ion collisions. An important next step for the CGC phenomenology is to perform these calculations at next-to-leading order accuracy, which would allow a qualitative test of the saturation picture. A...

Renaud Boussarie
(CNRS, Univ. Paris-Sud, 91405 Orsay, France)

4/12/16, 10:00 AM

Small-x, Diffraction and Vector Mesons

We present the computation for the impact factor for the production of
dijets in diffractive DIS at Next-to-Leading Order using Balitsky's
shockwave formalism.

Dr
Heikki Mäntysaari
(Brookhaven National Laboratory)

4/12/16, 11:00 AM

Small-x, Diffraction and Vector Mesons

Exclusive vector meson production can be used to directly probe the gluon density of a hadron. Measuring the cross section differentially in the momentum transfer t makes it possible to determine the transverse density profile (via coherent diffraction) and density fluctuations (incoherent diffraction) of the target hadron. This knowledge on the geometric fluctuations of the proton is...

Ms
Nataliia Kovalchuk
(UNI/EXP CMS)

4/12/16, 11:20 AM

Small-x, Diffraction and Vector Mesons

The exclusive deep inelastic electroproduction of psi(2S) and J/\psi(1S)
at an ep centre-of-mass energy of 317 GeV has been studied with the ZEUS
detector at HERA in the kinematic range 2 < Q2 < 80 GeV2, 30 < W < 210 GeV
and |t| < 1 GeV2, where Q2 is the photon virtuality, W is the photon--proton
centre-of-mass energy and t is the squared four-momentum transfer at the
proton vertex. The...

Prof.
Mohammad Ahmady
(Mount Allison University)

4/12/16, 11:40 AM

Small-x, Diffraction and Vector Mesons

We use the holographic light front wavefunction for the $\phi$ meson obtained from AdS/QCD, in conjunction with the Color Glass Condensate dipole cross-section whose parameters are fitted to the most recent precise combined HERA data on inclusive Deep Inelastic Scattering, to compute the rate for diffractive $\phi$ electro-production. Our predictions are in good agreement with the available...

Dr
Sergey Levonian
(DESY)

4/12/16, 12:00 PM

Small-x, Diffraction and Vector Mesons

A first measurement is presented of exclusive photoproduction of ρ0 mesons associated with leading neutrons at HERA.
The data were taken with the H1 detector in the years 2006 and 2007 at a centre-of-mass energy of √=319 GeV and correspond to an integrated luminosity of 1.16 pb-1.
The ρ0 mesons with transverse momenta p_T<1 GeV are reconstructed from their decays to charged...

Prof.
Victor Paulo Goncalves
(Lund University)

4/12/16, 12:20 PM

Small-x, Diffraction and Vector Mesons

The color dipole formalism is extended to the study of exclusive processes associated with a leading neutron in ep collisions at high energies. We discuss the leading neutron production in $e + p \rightarrow e + n + X$ collisions at high energies and estimate the related observables, which were measured at HERA and may be analysed in future electron-proton ($ep$) colliders. We show that the...

Mr
Francesco Giovanni Celiberto
(Università della Calabria and INFN-Cosenza (Italy))

4/12/16, 2:30 PM

Small-x, Diffraction and Vector Mesons

In this talk a study of the production of Mueller-Navelet jets at 13 TeV LHC will be presented, including the BFKL resummation effects and investigating three different variants of the BLM scale optimization method. It will be shown how the cross section and the azimuthal observables are affected by the exclusion of the events where, for a given rapidity interval between the two jets, one of...

Mr
Francesco Giovanni Celiberto
(U. Calabria & INFN-CS (Italy); IFT UAM/CSIC Madrid)

4/12/16, 2:50 PM

Small-x, Diffraction and Vector Mesons

In this talk a study of differential cross sections for the production of four jets in multi-Regge kinematics will be presented, the main focus lying on azimuthal angle dependences. The theoretical setup consists in the jet production from a single BFKL ladder with a convolution of three BFKL Green functions, where two forward/backward jets are always tagged in the final state. Furthermore,...

Dr
Grigorios Chachamis
(IFT UAM-CSIC)

4/12/16, 3:10 PM

Small-x, Diffraction and Vector Mesons

First, we define new observables sensitive to BFKL dynamics in the context of multijet production at the Large Hadron Collider. We propose the study of the inclusive production of three jets well separated in rapidity from each other, with two of them being very forward. We show that the tagging of a third jet in the central region of rapidity allows for a very strong test of the BFKL...

Dr
Grigorios Chachamis
(IFT UAM-CSIC)

4/12/16, 3:30 PM

Small-x, Diffraction and Vector Mesons

We will present a study of high-energy jet production in the multi-Regge limit making use of the Monte Carlo code BFKLex which includes collinear improvements in the form of double-log contributions. Making use of the anti-kt jet algorithm in the FastJet implementation, we will present results for the average transverse momentum and azimuthal angle of the produced jets when two tagged...

Ruchi Chudasama
(Bhabha Atomic Research Centre in Mumbai, India)

4/12/16, 4:30 PM

Small-x, Diffraction and Vector Mesons

Exclusive W+ W- pair production in photon-photon collisions during the pp runs at 7 and 8TeV are observed and used to put constraints on the Anomalous Quartic Gauge Couplings. During the proton lead collisions in photon-induced vector meson production is observed via the decay of Ypsilon into two muons. The slope of the squared pT distribution is measured to determine the size of the production region.

Prof.
Ronan McNulty
(University College Dublin)

4/12/16, 4:50 PM

Small-x, Diffraction and Vector Mesons

The cross-section for central exclusive production of J/psi and Psi(2S) mesons at 13 TeV is measured using the LHCb detector. Proton dissociative backgrounds are significant reduced compared to previous measurements through the use of forward shower counters, recently installed for Run 2. Cross-section ratios to previous measurements at 7 TeV allow more precise tests of theoretical...

Mohsen Khakzad
(Institute for Studies in Theoretical Physics & Mathematics (IPM) in Tehran, Iran)

4/12/16, 5:10 PM

Small-x, Diffraction and Vector Mesons

We report a measurement of exclusive pion pair production in proton-proton collisions, dominated by $p + p \rightarrow p^{(*)} + \pi^{+} \pi^{-} + p^{(*)}$, where the $\pi^{+} \pi^{-}$ pair is produced at central rapidities $y$ and the incident protons stay intact or dissociate without being detected. The measurement is performed with the CMS detector at the LHC, using an integrated luminosity...

Dr
Piotr Lebiedowicz
(Institute of Nuclear Physics, Polish Academy of Sciences)

4/12/16, 5:30 PM

Small-x, Diffraction and Vector Mesons

We discuss exclusive central diffractive dipion production in the reactions $pp \to pp \pi^{+} \pi^{-}$ and $p\bar{p} \to p\bar{p} \pi^{+} \pi^{-}$ at high energies. The calculation is based on a tensor pomeron model and the amplitudes for the processes are formulated in an effective field-theoretic approach [1]. We include the purely diffractive dipion continuum, and the scalar and tensor...

Dr
Rainer Schicker
(Phys. Inst., Heidelberg)

4/12/16, 5:50 PM

Small-x, Diffraction and Vector Mesons

A Regge pole model for Pomeron-Pomeron total cross section in the resonance region $\sqrt{M^2}\le$ 5 GeV is presented. The cross section is saturated by direct-channel contributions from the Pomeron as well as from two different $f$ trajectories, accompanied by the isolated f$_0(500)$ resonance dominating the $\sqrt{M^{2}}\leq 1$ GeV region. A slowly varying background is taken into account....

Dr
Mariola Klusek-Gawenda
(Institute of Nuclear Physics, Polish Academy of Sciences)

4/13/16, 9:00 AM

Small-x, Diffraction and Vector Mesons

We will discuss diphoton semi(exclusive) production
in ultraperipheral $PbPb$ collisions at energy of $\sqrt{s_{NN}}=$ 5.5 TeV (LHC).
The calculation is based on equivalent photon approximation in
the impact parameter space.
The cross sections for elementary $\gamma \gamma \to \gamma \gamma$
subprocess are calculated including two different mechanisms:
\begin{itemize}
\item box...

Dr
Bertrand Ducloue
(University of Jyvaskyla)

4/13/16, 9:20 AM

Small-x, Diffraction and Vector Mesons

Forward $J/\psi$ production and suppression in high energy proton-nucleus collisions can be an important probe of gluon saturation. We study this process in the Color Glass Condensate framework and show that using the Glauber approach to extrapolate the dipole cross section of a proton to a nucleus leads to results closer to experimental data than previous calculations in this framework. We...

Jaroslav Adam
(FNSPE CTU in Prague)

4/13/16, 9:40 AM

Small-x, Diffraction and Vector Mesons

The strong electromagnetic fields generated by ultra-relativistic heavy ions offer the possibility to study
gamma-gamma, gamma-nucleus and gamma-proton processes at the LHC in ultra-peripheral Pb-Pb and p-Pb collisions (UPC).
As exclusive photoproduction of vector mesons is sensitive to the gluon distribution of the interacting target it
allows one to study saturation and shadowing...

Dr
Spencer Klein
(Lawrence Berkeley National Laboratory)

4/13/16, 10:00 AM

Small-x, Diffraction and Vector Mesons

In 2010 and 2011, the STAR Collaboration collected a large sample of triggers for ultra-peripheral collisions.In this talk, I will present several new results involving photonuclear interactions in ultra-peripheral relativistic heavy ion collisions (UPCs). I will present an analysis of 384,000 photoproduced pion pairs, coming from rho, omega and direct pion pair production.The omega component...

Dr
William Schmidke
(BNL)

4/13/16, 2:30 PM

Small-x, Diffraction and Vector Mesons

In 2010, the STAR Collaboration collected a large sample of triggers
for ultra-peripheral AuAu collisions. In this talk, I will present
measurements from this sample of J/Psi production in association with
neutrons from photonuclear breakup. Preliminary results for the cross
section as a function rapidity and pT will be presented and compared
to models; the large component at low pT...

Daniel Tapia Takaki
(The University of Kansas in Lawrence, KS, United States)

4/13/16, 2:50 PM

Small-x, Diffraction and Vector Mesons

The coherent J/psi photoproduction cross section is measured in ultra-peripheral PbPb collisions at 2.76 TeV at the CMS experiment at the LHC. The J/psi mesons are reconstructed via their decay into muon pairs. In this talk, the measurement of the coherent J/psi photoproduction cross section as well as the neutron dependence break-up mode ratios for this process will be presented. These...

Ms
Katie Graham
(University of Birmingham)

4/13/16, 3:10 PM

Small-x, Diffraction and Vector Mesons

Ultra-Peripheral Pb-Pb collisions, in which the two nuclei pass close to each other but at an impact parameter greater than the sum of their radii, provide information about the initial state of nuclei. In particular, J/psi production in such collisions proceeds by photon-gluon interactions, and gives access to nuclear PDFs. The ALICE collaboration has published measurements of UPC J/Psi...

Alex Beaudoin E Van Spilbeeck
(Universiteit Antwerpen in Wilrijk, Belgium)

4/14/16, 9:00 AM

Small-x, Diffraction and Vector Mesons

The distribution of electromagnetic and hadronic energy in the very forward phase-space is measured with the CASTOR calorimeters located at a pseudorapidity of -5.2 to -6.6 in the very forward region of CMS. The energy distributions are very powerful benchmarks to study the performance of MPI in hadronic interactions models at 13TeV collision energy. Furthermore, also the jet-spectra for very...

Igor Katkov
(DESY)

4/14/16, 9:20 AM

Small-x, Diffraction and Vector Mesons

The forward (HF) and very-forward (CASTOR) calorimeters of CMS are used to measure the density of energy per unit of pseudorapiditdy up to eta of 6.6 at 13TeV. The measurements are compared to model predictions. Furthermore, the corresponding data of transverse energy are compared to CMS measurements at lower center-of-mass energies, where all data are shifted by the beam rapidity. The result...

Prof.
Antoni Szczurek
(Institute of Nuclear Physics PAN, Krakow and Rzeszow University, Rzeszow)
,
Wolfgang Schafer
(Institute of Nuclear Physics PAN, Krakow)

4/14/16, 9:40 AM

Small-x, Diffraction and Vector Mesons

We discuss Drell-Yan production of dileptons at high energies
in forward rapidity region in a hybrid high-energy approach
which uses unintegrated gluon distributions in one proton and collinear
quark/antiquark distributions in the second proton.
Corresponding momentum-space formula for the differential cross sections
in high-energy approximation has been derived and will be...

Dr
Bertrand Ducloue
(University of Jyvaskyla)

4/14/16, 10:00 AM

Small-x, Diffraction and Vector Mesons

We discuss single inclusive hadron production from a high energy quark scattering off a strong target color field in the Color Glass Condensate formalism. Recent calculations of this process at the next-to-leading order accuracy have led to negative cross sections at large transverse momenta. We identify the origin of this problem in an oversubtraction of the rapidity divergence into the...

330.
Measurements of total elastic, inelastic and diffractive cross sections with the ATLAS detector

Maciej Marek Trzebinski
(Polish Academy of Sciences)

4/14/16, 11:00 AM

Small-x, Diffraction and Vector Mesons

The total pp cross section is a fundamental property of the strong
interaction which can not be calculated in perturbative QCD but only described
based on phenomenological models. The ATLAS collaboration has explored the
total proton-proton cross section, using measurements of the total inelastic
proton-proton cross sections and of the diffractive part of the inelastic
cross section in...

Dr
Marta Ruspa
(Univ Piemonte Orientale)

4/14/16, 11:20 AM

Small-x, Diffraction and Vector Mesons

The measurement of the soft diffractive cross sections in single- and double-diffractive final states is presented at 7TeV. Furthermore, also the jet-gap-get production is discussed.

Dr
Hans Van Haevermaet
(DESY/University of Antwerp)

4/14/16, 11:40 AM

Small-x, Diffraction and Vector Mesons

The inelastic hadronic cross section is measured at 13TeV with the CMS experiment. Different detectors are used to study the dependence on the proton momentum loss, xi. The result is given in different visible acceptance regions as well as extrapolated to the full acceptance.

Wolfgang Lukas
(University of Innsbruck)

4/14/16, 12:00 PM

Small-x, Diffraction and Vector Mesons

Inclusive charged-particle measurements at hadron colliders probe the low-energy non-perturbative region of QCD.
The ATLAS collaboration has measured the charged-particle multiplicity and its dependence on transverse momentum and pseudorapidity in special data sets with low LHC beam currents, recorded at center-of-mass energies of 8TeV and 13TeV. The new precise measurements at 8 TeV cover a...

Mr
Juan Manuel Grados Luyando
(DESY)

4/14/16, 12:20 PM

Small-x, Diffraction and Vector Mesons

Pseudorapidity and transverse momentum distributions of charged-particles produced in pp collisions at 13 TeV will be presented for different event categories: an inclusive, inelastic enhanced, SD enhanced and NSD enhanced event samples. The measurements are compared to MC predictions tuned to describe the Underlying Event properties at 7 TeV.

Sercan Sen
(Istanbul Technical University in Istanbul, Turkey)

4/14/16, 12:40 PM

Small-x, Diffraction and Vector Mesons

The successful combined data taking of the CMS and TOTEM experiments allows to characterize hadronic final states of an extremely wide pseudo-rapidity range. The measurement of the charged particles distributions over |eta<6.6| is a very important example that puts strong constraints on interaction models.