EPPS16: nuclear parton distributions with LHC data

Kari J Eskola,Petja Paakkinen,Hannu Paukkunen,Carlos A Salgado

doi:10.1140/epjc/s10052-017-4725-9

Abstract

We introduce a global analysis of collinearly factorized nuclear parton distribution functions (PDFs) including, for the first time, data constraints from LHC proton–lead collisions. In comparison to our previous analysis, EPS09, where data only from charged-lepton–nucleus deep inelastic scattering (DIS), Drell–Yan (DY) dilepton production in proton–nucleus collisions and inclusive pion production in deuteron–nucleus collisions were the input, we now increase the variety of data constraints to cover also neutrino–nucleus DIS and low-mass DY production in pion–nucleus collisions. The new LHC data significantly extend the kinematic reach of the data constraints. We now allow much more freedom for the flavor dependence of nuclear effects than in other currently available analyses. As a result, especially the uncertainty estimates are more objective flavor by flavor. The neutrino DIS plays a pivotal role in obtaining a mutually consistent behavior for both up and down valence quarks, and the LHC dijet data clearly constrain gluons at large momentum fraction. Mainly for insufficient statistics, the pion–nucleus DY and heavy-gauge-boson production in proton–lead collisions impose less visible constraints. The outcome – a new set of next-to-leading order nuclear PDFs called EPPS16 – is made available for applications in high-energy nuclear collisions.

Highlights

The original idea of having nuclear effects in parton distribution functions (PDFs) was data-driven as the early deep inelastic scattering (DIS) experiments unexpectedly revealed significant nuclear effects in the cross sections [7,8]
It was demonstrated [9,10] that such effects in DIS and fixed nuclear-target Drell–Yan (DY) cross sections can be consistently described by modifying the free nucleon PDFs at low Q2 and letting the Dokshitzer–Gribov– Lipatov–Altarelli–Parisi (DGLAP) evolution [11,12,13,14,15,16,17] take care of the Q2 dependence
The data were in line with a concept that the measured nuclear effects are of non-perturbative origin but at sufficiently high Q2 there is no fundamental difference in the scattering off a nucleon or off a nucleus

Summary

Introduction

The original idea of having nuclear effects in PDFs was data-driven as the early deep inelastic scattering (DIS) experiments unexpectedly revealed significant nuclear effects in the cross sections [7,8]. The data were in line with a concept that the measured nuclear effects are of non-perturbative origin but at sufficiently high Q2 there is no fundamental difference in the scattering off a nucleon or off a nucleus. These ideas eventually led to the first global fit and the EKS98 set of leading-order nuclear PDFs [18,19]. The constraints on the gluon distribution are weak in these analyses, and it is only along with the RHIC pion data [31] that an observable carrying direct information on the nuclear gluons has been

Objectives

Methods

Results

Conclusion