Hard production of a Z boson plus heavy flavor jets at LHC and the intrinsic charm content of a proton

Abstract

The cross section of associated production of a Z boson with heavy flavor jets in pp collisions is calculated using the SHERPA Monte Carlo generator and the analytical combined QCD approach based on k T factorization at small x and conventional collinear QCD at large x. A satisfactory description of the ATLAS and CMS data on the p T spectra of Z bosons and c jets in the whole rapidity, y, region is shown. Searching for the intrinsic charm (IC) contribution in these processes, which could be visible at large y > 1.5, we study observables very sensitive to nonzero IC contributions and less affected by theoretical QCD scale uncertainties. One of such observables is the so-called double ratio, the ratio of the differential cross section of Z þ c production in the central region of jyj < 1.5 and in the forward region 1.5 < jyj < 2.5, divided by the same ratio for Z þ b production. These observables could be more promising for the search of IC at LHC as compared to the observables considered earlier.

Constraints on the intrinsic charm content of the proton from recent ATLAS data

“…The ratio falls to unity slowly with increasing E γ T , in the presence of intrinsic charm. Furthermore, measurements of Z /W + c/b production in pp collision at 13 TeV could also give additional significant information on the intrinsic charm contribution [28][29][30][31]. Our study shows that the most important source of theoretical uncertainty on w cc , from the theory point of view, is the dependence on the renormalization and factorization scales.…”

“…Recently, the estimation of w cc = 0.34 ± 0.14% was obtained in the NNPDF3.1 analysis [26] based on the global PDF fitting procedure over a wide range of LHC measurements. In our previous publications [27][28][29][30][31], we showed that the IC signal can be visible in the production of prompt photons and vector bosons Z /W in pp collisions, accompanied by heavy-flavor c/bjets at large transverse momenta and the forward rapidity region (|y| > 1.5), kinematics within the acceptance of the ATLAS and CMS experiments at the LHC. Based on our previous results [27][28][29][30][31], in the present paper we investigate the possibility to constrain the intrinsic charm probability using first ATLAS data [32] on measurements of differential cross sections of isolated prompt photons produced in association with a c-jet in pp collision at √ s = 8 TeV.…”

“…here w 0 = 0 % (central value in CTEQ66), w 1 = 1.0 % (BHPS1 in CTEQ66c) and w 2 = 3.5 % (BHPS2 in CTEQ66c), according to [10,31,38]. One can see from Figs.…”

“…The upper limit of the IC contribution obtained within the combined QCD approach is about w u. l. = 2.91 %. As it was shown in [31], the combined QCD approach does not include parton showers and hadronization, a contribution which is sizable at E γ T > 100 GeV, where the IC signal could be visible. Therefore, the results obtained from Sherpa (NLO) approach, which include these effects, are more realistic.…”

Associated non-prompt $$J/\psi + \mu $$ J / ψ + μ and $$J/\psi + J/\psi $$

“…This effect is coming from the final state parton showers only, that could be easily understood since in our calculations the initial state parton emissions are already determined from the TMD gluon density and, therefore, do not influence the k T of the gluons. However, parton showers could be very important at some kinematical regions (see, for example, [46,47]).…”