The nuclear matter effect on parton distribution functions

TL;DR

This paper investigates how nuclear matter influences parton distribution functions by introducing nucleon pair PDFs, which help explain the EMC effect and impact measurements of the weak mixing angle.

Contribution

It introduces nucleon pair PDFs to model nuclear effects on PDFs, providing a new approach to understanding the EMC effect and related measurements.

Findings

Nuclear PDFs can be expressed as a sum of PDFs and nucleon pair PDFs.

Nucleon pair PDFs are proportional to nucleon PDFs but suppressed.

dPDFs can explain the EMC effect behavior.

Abstract

Parton distribution functions (PDFs) are important quantities in describing nucleon structures. They are universal and process-independent. As a matter of fact, nucleon PDFs are inevitably affected by nuclear matter during nuclear scattering process. In order to study the nuclear PDFs (nPDFs), in this paper, we introduce the nucleon pair PDFs (dPDFs) to describe parton distributions in the nucleon pair which is confined to a nucleus. We first of all construct the nuclear state in terms of the nucleonic states and calculate the operator definition of nPDFs. Neglecting the higher order corrections or multi-nucleon correlations, we find that nPDFs can be written as a sum of two terms which respectively correspond to PDFs and dPDFs. Nucleon pair PDFs which stem from nucleon-nucleon correlation are proportional to common nucleon PDFs but suppressed by a factor. Compared with the experimental data, we find that dPDFs can explain the behaviour of the EMC effect. We further calculate the Paschos-Wolfenstein ratio to study the nuclear matter effect on the extraction of weak mixing angle or $\sin^2\theta_W$ by using dPDFs.