Phenomenological implications of the intrinsic charm in the Z boson production at the LHC

Abstract

In this paper we study the Z , Z + jet, Z + c, and Z + c+ jet production in pp collisions at the LHC considering different models for the intrinsic charm content of the proton. We analyze the impact of the intrinsic charm in the rapidity and transverse momentum distributions for these different processes. Our results indicated that differently from the other processes, the Z +c cross section is strongly affected by the presence of the intrinsic charm. Moreover, we propose the analysis of the ratiosand we demonstrate that these observables can be used as a probe of the intrinsic charm.A complete knowledge of the partonic structure of the hadrons is fundamental to make predictions for the Standard Model and to beyond Standard Model processes at hadron colliders. Since the early days of the parton model and of the first deep inelastic scattering (DIS) experiments, determining the precise form of the quark and gluon distributions of the nucleon has been a major goal of high energy hadron physics. Over the last 40 years huge progress has been achieved. In particular, data from HERA have dramatically improved our knowledge as regards the small-x behavior of the parton distributions functions (PDFs) [1]. Another important improvement has occurred to our knowledge for the heavy quark contribution to the proton structure [2]. In the last years several groups have proposed different schemes to determine these distributions considering that the heavy quark component in PDFs can be perturbatively generated by gluon splitting (see e.g. [3]). This component is usually denoted the extrinsic heavy quark component. Moreover, the possibility of an intrinsic component has been studied in detail and included in the recent versions of the PDF parametrizations [4][5][6][7]. The hypothesis of intrinsic heavy quarks (IHQ) is a a e-mails: barros@ufpel.edu.br;victor.goncalves@thep.lu.se natural consequence of the quantum fluctuations inherent to Quantum Chromodynamics (QCD) and amounts to assuming the existence of a QQ (Q = c, b, t) as a non-perturbative component in the hadron wave function. A comprehensive review of the main characteristics of the IHQ models can be found in [8][9][10]. In the model proposed by Brodsky, Hoyer, Peterson and Sakay (BHPS) [11], the creation of the Q Q pair was studied in detail (for a discussion of other models for the IHQ see Refs. [12][13][14][15]). It was assumed that the nucleon light cone wave function has higher Fock states, the first one being |qqq Q Q>. The probability of finding the nucleon in this configuration was given by the inverse of the squared invariant mass of the system. Because of the heavy quark mass, this probability as a function of the quark fractional momentum, P(x), is very hard, as compared to the one obtained through the DGLAP evolution. Although this model predicts the x dependence of the intrinsic components, its normalization should be constrained by fitting the experimental data and still is an open question. In particular, two recent global analysis of the PDFs [5,...

CT14 intrinsic charm parton distribution functions from CTEQ-TEA global analysis

“…Our conclusion at the moment is that the LHC inclusive W and Z production cross sections may provide helpful correlated constraints on m c and x IC in the future. We may also consider more exclusive scattering processes [120][121][122][123][124][125][126][127]129] to look for evidence of the IC in the LHC environment.…”

Intrinsic charm content of the nucleon and charmness-nucleon sigma term

“…Calculations come from the radiatively generated charm PDF (CTEQ66), the sea-like PDF (CTEQ66c4) and the BHPS PDF (CTEQ66c2) also for P cc N = 3.5% and found that the IC manifestation could be measured with both the ATLAS and CMS detectors. [18] studied, within various models, the impact of the IC on the rapidity and transverse momentum distribution in the Z-boson production in proton-proton collisions at the LHC, and showed that the Z + c cross section is significantly sensitive to the presence of the IC.…”

“…More recently Dulat and collaborators [12] analyzed the parton distribution function (PDF) of the proton based on the NNLO approximation of perturbative QCD and included the combined H1 and ZEUS data [13], reaching the conclusion that the PDF uncertainties are just as large as the IC effects. In summary, the nucleon's IC remains elusive, however several studies predict measurable effects of such possible components in the ongoing and/ or forthcoming experiments at the LHC [12,[14][15][16][17][18][19][20] and RHIC [15,21,22].…”

Parton distribution functions and constraints on the intrinsic charm content of the proton using the Brodsky-Hoyer-Peterson-Saka approach

“…In Refs. [51][52][53] the results of c-jet production accompanied by vector bosons Z, W ± is stud-ied by using the intrinsic charm quark component. The impact of IC contributions for the prediction of γ + cjet production in pp collisions at the LHC is reported in Ref.…”