Reinterpretation of proton strangeness between ATLAS and CMS measurements

Alim Ruzi,Bo-Qiang Ma

doi:10.1103/physrevd.104.076004

Abstract

We reexamine the shapes of the strange quark parton distribution functions (PDFs) of the proton by means of quantum chromodynamics (QCD) analysis of {\hera} deep inelastic scattering cross section measurement at DESY, and inclusive gauge boson production and $W$ boson production associated with a charm quark from LHC at CERN. We find that there is an overall agreement on the strange quark distributions obtained from CMS $W$ + charm and ATLAS $W/Z$ data at the parton momentum fraction range $x \lesssim 10^{-2}$. Meanwhile, there is also a strong tension between these data towards large $x$. We find that this tension fades away if the ATLAS measurement of $W/Z$ production is analyzed together with the ATLAS $W$ + charm data. The $W/Z$ and $W$ + charm data both from ATLAS and CMS experiments agree that the proton strangeness is enhanced towards small momentum fraction $x$ and is smoothly suppressed at large $x$. Furthermore, a strong $x$ dependence of the strange-to-non-strange parton ratio $R_s(x,Q^2)$ is observed.

Highlights

It is well known that nucleons consist of pointlike particles denominated as partons, revealed by lepton nucleon deep inelastic scattering (DIS) experiment [1,2] almost half a century ago
We present a fairly detailed parton distribution functions (PDFs) extraction with the general-purpose PDFs fitting program XFITTER [28] from the following data: HERA I þ II eÆp [14], ATLAS combined inclusive W=Z production cross section [13,15], and W production in association with a charm quark [19]; CMS W-lepton charge asymmetry [20,21] and W production in association with charm quark [22,23], applying variants of different parametrization forms first to clarify whether the same physics processes in ATLAS and CMS experiments give compatible or incompatible distributions of the strange quark and, second, to pin down its exact shape
The shapes of the strange quark PDFs of the proton extracted from LHC data were interpreted in different ways: the ATLAS statement of fully enhanced strangeness and the CMS statement of the suppressed one which supports the same idea obtained from fixed target neutrino-nuclear collision experiments

Summary

INTRODUCTION

It is well known that nucleons consist of pointlike particles denominated as partons, revealed by lepton nucleon deep inelastic scattering (DIS) experiment [1,2] almost half a century ago. The ratio of strange to nonstrange sea quark PDFs, Rs 1⁄4 ðs þ sÞ= ðuþ d Þ, from neutrino-nucleus DIS experiment is approximately 0.5 when evaluated at x 1⁄4 0.023 and energy scale Q 1⁄4 1.6 GeV, whereas the strange to antidown quark ratio, rs 1⁄4 ðs þ sÞ=2d , evaluated at x 1⁄4 0.023 and Q2 1⁄4 1.9 GeV2 from the ATLAS analysis of the inclusive gauge boson production together with the combined HERA I þ II eÆp data [14], rises up to unity. The recently extracted CT18 PDFs series from fixed target and up-to-date collider data by the Coordinated Theoretical-Experimental Project On QCD (CTEQ) group [26] demonstrate that the strange quark density is enhanced over the nominal fit CT18NNLO when the inclusive W=Z data are included Another devoted study on the strangeness of the proton [27], which includes both the lepton-nucleus DIS cross section data from the. We present a fairly detailed PDFs extraction with the general-purpose PDFs fitting program XFITTER [28] from the following data: HERA I þ II eÆp [14], ATLAS combined inclusive W=Z production cross section [13,15], and W production in association with a charm quark [19]; CMS W-lepton charge asymmetry [20,21] and W production in association with charm quark [22,23], applying variants of different parametrization forms first to clarify whether the same physics processes in ATLAS and CMS experiments give compatible or incompatible distributions of the strange quark and, second, to pin down its exact shape

Data description

Theoretial calculation

ANALYSIS SETUP

RESULTS

CONCLUSIONS