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 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 production data on both the flavor differentiation and nuclear corrections. This complementary data set provides new insights on both the LHC W^pm /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 data is accommodated in the fit. Extending the nCTEQ15 analysis to include LHC W^pm /Z data represents an important step as we advance toward the next generation of nPDFs.
Highlights
The recent results from the LHC for inclusive W/Z boson production in pp collisions prefer a large strange to light-sea ratio [29,30,31]
We observe the strange component can be as much as 20–30% of the total. These plots were produced with FEWZ [2,3] modified for the p Pb beams using the nCTEQ15 nuclear PDF (nPDF) [1]
Since the nCTEQ15 nPDFs are based on a proton where the strange parton distribution function (PDF) is given by s + s = κ(u + d), we expect these plots to represent a conservative estimate of the strange contribution to the W/Z channels
Summary
The nCTEQ project extends the proton PDF global fitting effort by fully including the nuclear dimension. Previous to the nCTEQ effort, nuclear data was “corrected” to isoscalar data and added to the proton PDF fit without any uncertainties [48]. The nCTEQ project extends the proton PDF global fitting effort by fully including the nuclear dimension.. Previous to the nCTEQ effort, nuclear data was “corrected” to isoscalar data and added to the proton PDF fit without any uncertainties [48]. The nCTEQ framework allows full communication between the nuclear data and the proton data; this enables us to investigate if observed tensions between data sets could potentially be attributed to the nuclear corrections. The details of the nCTEQ15 nPDFs are presented in Ref. The 16 free parameters used for the nCTEQ15 set model the x-dependence of the {g, uv, dv, d + u} PDF combinations, and we do not vary the d/uparameters; see Ref. We add three strange PDF parameters: {c0s+,1s, c1s+,1s, c2s+,1s}; these parameters describe, correspondingly, the overall normalization, the low-x exponent and the large x exponent of the strange distribution
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