Prompt photon production in the kt-factorization approach at modern colliders

Abstract

We present the results of the numerical calculations of prompt photon and Drell-Yan lepton pair production at Tevatron and LHC in the framework of the k T -factorization approach. Our predictions are compared with the D0, CDF, CMS and ATLAS experimental data. The XXth International Workshop High Energy Physics and Quantum Field Theory September 24 -October 1, 2011Sochi, Russia * Speaker.c Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.http://pos.sissa.it/ PoS(QFTHEP2011)028Prompt photon and Drell-Yan lepton pair production in the k T -factorization approach M. A. Malyshev Our study is motivated by recent measurements of the inclusive prompt photon and Drell-Yan lepton pair production performed by the CMS and ATLAS collaborations at LHC [1 -3], taken at √ s = 7 TeV. Previously the k T -factorization approach was used for the prompt photon production at Tevatron [4 -6]. A good description of the results of the D0 and CDF collaborations was achieved. Also in [7] the process of the prompt photon production with associated heavy (c, b) quarks was investigated and a reasonable agreement of the experimental data with the theoretical results was obtained. Here we expand the analysis to the LHC energies.According to the k T -factorization theorem, to calculate the cross section of the prompt photon or Drell-Yan lepton pair production one should convolute the off-shell partonic cross sections with the relevant unintegrated quark and/or gluon distributions in a proton:) is the relevant partonic cross section. The initial off-shell partons have fractions x 1 and x 2 of initial protons longitudinal momenta and non-zero transverse momenta k 1T and k 2T .Concerning the unintegrated parton distributions we use two different sets. First is the KMR set [8,9]. The KMR approach represents an approximate treatment of the parton evolution mainly based on the DGLAP equation and incorpotating the BFKL effects at the last step of the parton ladder only, in the form of the properly defined Sudakov formfactors T q (k 2 T , µ 2 ) and T q (k 2 T , µ 2 ), including logarithmic loops. In this approach both gluons and quarks densities can be obtained.For prompt photon production we also use another set of unintegrated parton distributions, obtained as a numerical solution of the CCFM evolution equation [10], namely the CCFM A0 set. However, as a result of the solution we have only gluon distribution. In order to calculate the quarks distribution, we follow the scheme, proposed in [5,6]. The unintegrated quark distribution are presented aswhere f (v) q is the unintegrated valence quarks distribution and fq -the contributions of the sea quarks arising from the last and earlier steps of the parton evolution respectively. f (v) q (x, k 2 T , µ 2 ) was calculated in [11]. The contribution from the sea quarks coming from the last evolution step, f, can be taken into account with the gluon fusion subprocess, g * g * → γqq [6]. The contribution of the sea quarks coming fro...