Abstract
We present the calculations of associated production of Z bosons and heavy (charm or beauty) quarks at the LHC energies in the framework of k T -factorization QCD approach. Our consideration is mainly based on the O α α s 2 off-shell gluon-gluon fusion subprocess g*g*→ZQ Q where produced Z boson subsequently decays into a lepton pair. Several subleading contributions from the O α α s 2 and O α α s 3 subprocesses are taken into account. Contributions from the double parton scattering mechanism are estimated. The transverse momentum dependent (or unintegrated) gluon densities in a proton are determined using the Catani-Ciafaloni-Fiorani-Marchesini evolution equation. We achieve reasonably good agreement of our predictions and latest experimental data taken by the CMS and ATLAS Collaborations, discuss the theoretical uncertainties of our calculations and demonstrate the importance of subleading quark contributions in description of the LHC data in the whole kinematical region.
Highlights
Very recently, the CMS Collaboration has presented√the measurements of Z boson production in association with charm [1] qu√arks at the LHC energy s = 8 TeV
The certain advantages are connected with the fact that, even with the LO partonic amplitudes, one can include a large piece of higher-order corrections taking them into account in the form of CCFM-evolved transverse momentum dependent (TMD) gluon densities
It gives better agreement with Tevatron data on the associated production of prompt photons and charm or beauty quarks compared to the NLO pQCD predictions [15], that is an additional motivation of our present study
Summary
Measurements of angular correlations of B-hadrons at s = 7 TeV were presented [2] and the ATLAS Collaboration has reported the experimental data on the√total and differential cross sections of Z boson production in association with beauty quark jets at s = 7 TeV [3]. Subprocess (4) is suppressed by the additional degree of strong coupling QCD constant, we include it into the consideration because it can give sizeble contribution to the production cross section due to large gluon flux at the LHC energies, especially at low η − φ distances between the produced heavy quarks.
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