Impact of LHC vector boson production in heavy ion collisions on strange PDFs

Abstract

The extraction of the strange quark parton distribution function (PDF) poses a long-standing puzzle. Measurements from neutrino-nucleus deep inelastic scattering (DIS) experiments suggest the strange quark is suppressed compared to the light sea quarks, while recent studies of $$W^\pm /Z$$ W ± / Z boson production at the LHC imply a larger strange component at small x values. As the parton flavor determination in the proton depends on nuclear corrections, e.g. from heavy-target DIS, LHC heavy ion measurements can provide a distinct perspective to help clarify this situation. In this investigation we extend the nCTEQ15 nPDFs to study the impact of the LHC proton-lead $$W^\pm /Z$$ W ± / Z production data on both the flavor differentiation and nuclear corrections. This complementary data set provides new insights on both the LHC $$W^\pm /Z$$ W ± / Z proton analyses and the neutrino-nucleus DIS data. We identify these new nPDFs as nCTEQ15WZ. Our calculations are performed using a new implementation of the nCTEQ code (nCTEQ++) based on C++ which enables us to easily interface to external programs such as HOPPET, APPLgrid and MCFM. Our results indicate that, as suggested by the proton data, the small x nuclear strange sea appears larger than previously expected, even when the normalization of the $$W^{\pm }/Z$$ W ± / Z data is accommodated in the fit. Extending the nCTEQ15 analysis to include LHC $$W^\pm /Z$$ W ± / Z data represents an important step as we advance toward the next generation of nPDFs.

Study of Drell-Yan dimuon production in proton-lead collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ = 8.16 TeV

“…They are shown in figure 9. In both mass regions, the R FB is by construction equal to unity in the absence of nuclear effect (CT14), but decreasing with |y CM | with CT14+EPPS16 and CT14+nCTEQ15WZ [19]. Similar conclusions are drawn as from the rapidity dependence of the cross section, but the construction of these ratios allows for the partial cancellation of theoretical and experimental uncertainties, accounting for the correlations described in the previous section.…”

“…A first-principle description of such (nonperturbative) nuclear effects remains an open challenge, but they can be modelled using nuclear PDFs (nPDFs) determined with data in the same collinear factorisation approach as for free protons. Global fits of nPDFs [12][13][14][15][16][17][18][19] predict a suppression for small longitudinal momentum fraction x, x 10 −2 (i.e. shadowing [20] region), and an enhancement for intermediate x, 10 −2 x 10 −1 (i.e.…”

“…The error bars on the data points represent the quadratic sum of the statistical and systematic uncertainties. The theory predictions from the powheg NLO generator are also shown, using CT14[51] (blue), CT14+EPPS16[14] (red), or CT14+nCTEQ15WZ[19] (green) PDF sets. The boxes show the 68% confidence level (n)PDF uncertainty in these predictions.…”

Impact of scale, nuclear PDF and temperature variations on the interpretation of medium-modified jet production data from the LHC

“…A disentangling of the two effects became only possible when measurements from different centralities were compared. A reduction of the nuclear PDF uncertainty would require input from more data, in particular from pA collisions at the LHC [35][36][37][38][39] or eA collisions at the future EIC [72][73][74]. Nevertheless, in most cases we observed quantitatively good agreement of the central nCTEQ15 and EPPS16 predictions with the data within the experimental uncertainties.…”

“…In figure 1 we show for later reference a comparison of the nuclear PDF modifications at Q 2 = 10 GeV 2 for up/down valence and sea (including strange) quarks as well as gluons as parametrised in nCTEQ15 (red curves with hatching) [31] and EPPS16 (black central curve with shaded uncertainty bands) [32]. Note that nPDFs are continuously being updated to include in particular more LHC [35][36][37][38][39] and JLab data [40] and NNLO corrections [41,42].…”