Selected topics on parton distribution functions

TL;DR

This paper reviews recent research on nucleon and nuclear structure functions, including clustering effects in Be-9, tensor-polarized quark distributions, and the CDF dijet anomaly's relation to strange-quark distributions, highlighting new experimental and theoretical insights.

Contribution

It presents novel analyses of clustering effects, tensor polarization in quark distributions, and the impact of strange-quark PDFs on collider anomalies, advancing understanding of parton distribution functions.

Findings

Clustering effects may explain unusual nuclear corrections in Be-9.

Finite tensor polarization for antiquark distributions is suggested.

Strange-quark distribution modifications can partially explain the CDF dijet anomaly.

Abstract

We report recent studies on structure functions of the nucleon and nuclei. First, clustering effects are investigated in the structure function F_2 of Be-9 for explaining an unusual nuclear correction found in a JLab experiment. We propose that high densities created by formation of clustering structure like 2*alpha+neutron in Be-9 is the origin of the unexpected JLab result by using the antisymmetrized molecular dynamics (AMD). There is an approved proposal at JLab to investigate the structure functions of light nuclei including the cluster structure, so that much details will become clear in a few years. Second, tensor-polarized quark and antiquark distributions are obtained by analyzing HERMES measurements on the structure function b_1 for the deuteron. The result suggests a finite tensor polarization for antiquark distributions, which is an interesting topic for further theoretical and experimental investigations. An experimental proposal exists at JLab for measuring b_1 of the deuteron as a new tensor-structure study in 2010's. Furthermore, the antiquark tensor polarization could be measured by polarized deuteron Drell-Yan processes at hadron facilities such as J-PARC and GSI-FAIR. Third, the recent CDF dijet anomaly is investigated within the standard model by considering possible modifications of the strange-quark distribution. We find that the shape of a dijet-mass spectrum changes depending on the strange-quark distribution. It indicates that the CDF excess could be partially explained as a PDF effect, particularly by the strangeness in the nucleon, within the standard model if the excess at m_{jj}~140 GeV is not a sharp peak.