Using Drell-Yan $A_{FB}$ to constrain PDFs

TL;DR

This paper demonstrates that forward-backward asymmetry measurements in Drell-Yan processes at hadron colliders can effectively constrain PDFs, thereby reducing uncertainties in electroweak parameter measurements, including the W boson mass.

Contribution

It introduces a novel method to use $A_{FB}$ measurements to tighten PDF constraints and improve precision in electroweak parameter determinations.

Findings

Constrained PDFs reduce systematic errors in electroweak measurements.

Expected W mass measurement error of ±9 MeV with 200 fb$^{-1}$ at 13 TeV.

$A_{FB}$ measurements provide a new tool for PDF refinement.

Abstract

We show that measurements of the forward-backward charge asymmetry ($A_{FB}(M,y)$) of Drell-Yan dilepton events produced at hadron colliders provide a new powerful tool to constrain Parton Distribution Functions (PDFs). PDF uncertainties are the dominant source of systematic error in precision measurements at hadron colliders (e.g. $\chi^2$ values of fits to extract $\sin^2\theta_{eff}^{lept}(M_Z)$ from $A_{FB}(M,y)$ with different PDF replicas can be used to place additional constraints on PDFs.In turn, using these constrained PDFs significantly reduces the PDF errors in precision measurements of electroweak parameters. The measurement of the on-shell $\sin^2\theta_{W}=1-M_W^2/M_Z^2$ is equivalent to an indirect measurement of the W mass. The errors in this indirect measurement of the W mass are competitive with direct measurements. For example, with 200 fb$^{-1}$ at 13 TeV, the expected error in the indirect measurement of the W mass is $\pm$9 MeV.