Towards the global fit of the TMD gluon density in the proton from the LHC data

Abstract

We propose a new analytical expression for the Transverse Momentum Dependent (TMD, or unintegrated) gluon density in the proton. Essential phenomenological parameters are extracted from the LHC data on inclusive hadron production in $pp$ collisions at low transverse momenta, $p_T\sim 1$~GeV. The latter are described in the framework of modified soft quark-gluon string model, where gluonic state and non-zero transverse momentum of partons inside the proton are taken into account. To determine the parameters important at moderate and large $x$ we used measurements of inclusive $b$-jet and Higgs boson production at the LHC as well as latest HERA data on proton structure functions $F_2^c(x,Q^2)$ and $F_2^b(x,Q^2)$ and reduced cross sections ${\sigma }_{\mathrm{red}}^c(x,Q^2)$ and ${\sigma }_{\mathrm{red}}^b(x,Q^2)$. The Catani-Ciafaloni-Fiorani-Marchesini evolution equation is applied to extend the initial gluon distribution into the whole kinematical region. We have achieved simultaneous description of all considered processes with ${\chi }^2/d.o.f.=2.2$, thus moving forward to the global fit of TMD gluon density from collider data. The obtained TMD gluon distribution in a proton is available for public usage and implemented into the TMDlib package and Monte-Carlo event generator PEGASUS.

Comments: 26 pages, 11 figures