Uncertainty of parton distribution functions due to physical observables in a global analysis

Abstract

The recent measurement of the differential γ + c-jet cross section, performed at the Tevatron collider in Run II by the D0 collaboration, is studied in a next-to-leading order (NLO) global QCD analysis to assess its impact on the proton parton distribution functions (PDFs). We show that these data lead to a significant change in the gluon and charm quark distributions. We demonstrate also that there is an inconsistency between the new high precision HERA I+II combined data and Tevatron measurement. Moreover, in this study we investigate the impact of older EMC measurements of charm structure function F 2 c on the PDFs and compare the results with those from the analysis of Tevatron data. We show that both of them have the same impact on the PDFs, and thus can be recognized as the same evidence for the inefficiency of perturbative QCD in dealing with charm production in some kinematic regions.

Probing nuclear modifications of parton distribution functions through the isolated prompt photon production at energies available at the CERN Large Hadron Collider

“…In this approach, for determining the nuclear modifications one needs to fix the free-proton PDFs form an analysis already performed on the nucleon experimental data [1][2][3][4][5][6][7][8][9][10][11]. However, there is another approach in which the nPDFs are parametrised directly as a function of…”

“…In this work, we are going to perform a comprehensive study of the isolated prompt photon production in p-Pb collisions at backward rapidities to find the best kinematic regions in which the experimental measurements have most sensitivity to the nuclear modifications of parton densities.Most emphasis will be placed on the antishadowing nuclear modification. To this aim, we calculate and compare various quantities at different values of center-of-mass energy covered by the LHC and also different rapidity regions to realize which one is most useful.Besides the parton distribution functions (PDFs), whether unpolarized [1][2][3][4][5][6][7][8][9][10][11] or polarized [12][13][14][15][16][17][18], and fragmentation functions (FFs) [19][20][21][22][23], the nuclear modifications of PDFs [24][25][26][27][28][29][30][31] are also important ingredients of high energy physics calculations, in particular, for processes involving nuclei in the initial state. In fact, without having nuclear PDFs (nPDFs) which describe the structure of the colliding nuclei, the theoretical calculation of the cross sections in any nuclear collision will not be possible.…”

Study of the s−s¯ asymmetry in the proton

“…The accurate determination of PDFs in the nucleon has always been an important subject in high energy physics. Since the PDFs are the nonperturbative objects, they have to be constrained in a global analysis to experimental data [3,4,5,6,7,8,9,10,11,12,13]. In this vein, the determination of the gluon distribution both in the nucleon [93] and nuclei [94], and also the sea quark distributions and possible asymmetries between them is of particular importance.…”

“…It is well known now that the factorisation theorem of Quantum Chromodynamics (QCD) [1,2] can provide a powerful tool for calculating cross sections of high energy processes, by dividing them to perturbative and nonperturbative parts. In this respect, the nonperturbative objects such as the parton distribution functions (PDFs) [3,4,5,6,7,8,9,10,11,12,13], polarized PDFs [14,15,16,17,18,19,20], nuclear PDFs [21,22,23,24,25], and fragmentation functions (FFs) [26,27,28,29] play an essential role for testing QCD, describing the experimental data, and searching New Physics. Among them, the PDFs have always been of particular importance.…”

Predictions for the Isolated Prompt Photon Production at the LHC ats= 13 TeV

“…photons not originating from hadron decays. The study of such photons provides a probe of perturbative Quantum Chromodynamics (pQCD) and measurement of their production cross sections, because of the sensitivity of the process to the gluon content of the nucleon, can provide useful information about the gluon parton distribution function (PDF) [44][45][46][47][48]. The associated production of prompt photons and heavy quarks, where the heavy quarks are either charm or bottom, can also provide a powerful tool for searching the intrinsic heavy quark components of the nucleon [49][50][51].…”