Speaker
Prof.
Antoni Szczurek
(the Institute of Nuclear Physics PAS)
Description
Some time ago two of us predicted that at large energies relevant for the LHC the production of double charm should be dominated by the double-parton scattering (DPS) mechanism [1]. Those studies of double $c \bar c$ production was extended next to the $k_t$-factorization approach which includes effectively higher-order QCD effects [2,3]. A relatively good description of the LHCb experimental data [4] was achieved for both the total yield and the dimeson correlation observables. The single-parton scattering (SPS) $g g \to c \bar c c \bar c$ contribution was discussed carefully in both collinear [3] and $k_t$-factorization [5] approaches. Their contribution to the $c \bar c c \bar c$ cross section was found to be rather small and was not able to describe details of the LHCb data.
Here we discuss production of $D^0 D^0$ (and ${\bar D}^0 {\bar D}^0$) pairs within an alternative approach where $g \to D$ fragmentation is included [6]. We consider double-parton scattering (DPS) mechanisms of double $c \bar c$ production and subsequent $cc \to D^{0}D^{0}$ hadronization as well as double $g$ and mixed $g c\bar c $ production with $gg \to D^{0}D^{0}$ and $gc \to D^{0}D^{0}$ hadronization calculated with the help of the scale dependent hadronization functions of Kniehl et al. Single-parton scattering (SPS) mechanism of digluon production is also taken into account. We compare our results with several correlation observables in azimuthal angle $\varphi_{D^{0}D^{0}}$ between $D^{0}$ mesons or in dimeson invariant mass $M_{D^{0}D^{0}}$. The inclusion of new mechanisms with $g \to D^{0}$ fragmentation leads to larger cross sections, than when including only DPS mechanism with standard scale independent $cc \to D^{0}D^{0}$ fragmentation functions. Some consequences of the presence of the new mechanisms are discussed. In particular a larger $\sigma_{eff}$ is needed to describe the LHCb data. There is a signature that $\sigma_{eff}$ may depend on transverse momentum of $c$ quarks and/or $\bar c$ antiquarks.
[1] M. Luszczak, R. Maciula and A. Szczurek, Production of two $c \bar c$ pairs in double-parton scattering,
Phys. Rev. D 85, 094034 (2012).
[2] R. Maciula and A. Szczurek, Production of $c \bar c c \bar c$ in double-parton scattering within $k_{t}$-factorization approach - meson-meson correlations, Phys. Rev. D 87, 074039 (2013).
[3] A. van Hameren, R. Maciula and A. Szczurek, Single-parton scattering versus double-parton scattering in the production of two $c \bar c$ pairs and charmed meson correlations at the LHC, Phys. Rev. D 89, 094019 (2014).
[4] R. Aaij et al. [LHCb Collaboration], Observation of double charm production involving open charm in pp collisions at $\sqrt{s}$ = 7 TeV, J. High Energy Phys. 06, 141 (2012); [J. High Energy Phys. 03, 108 (2014)].
[5] A. van Hameren, R. Maciula and A. Szczurek, Production of two charm quark-antiquark pairs in single-parton scattering within the $k_t$-factorization approach, Phys. Lett. B 748, 167 (2015).
[6] R. Maciula and V. A. Saleev, A. V. Shipilova and A. Szczurek, arXiv:1601.06981 [hep-ph].
Primary authors
Prof.
Antoni Szczurek
(the Institute of Nuclear Physics PAS)
Dr
Rafal Maciula
(the Institute of Nuclear Physics PAS)
Dr
Shipilova Alexandra
(Samara State Aerospace University)
Prof.
Vladimir Saleev
(Samara State Aerospace University)
