Reduction of the electroweak correlation in the PDF updating by using the forward-backward asymmetry of Drell-Yan process

TL;DR

This paper introduces a new observable based on the gradient of the forward-backward asymmetry spectrum in Drell-Yan processes to reduce the correlation bias between electroweak parameter measurements and PDF updates at hadron colliders.

Contribution

A novel observable related to the gradient of the $A_{FB}$ spectrum is proposed to decouple electroweak measurements from PDF updates, reducing bias.

Findings

The gradient of $A_{FB}$ is insensitive to $ heta_W$, unlike its average value.

The new observable significantly reduces bias in $ heta_W$ determination during PDF updates.

The approach improves the precision of electroweak parameter measurements.

Abstract

We propose a new observable for the measurement of the forward-backward asymmetry $(A_{FB})$ in Drell-Yan lepton production. At hadron colliders, the $A_{FB}$ distribution is sensitive to both the electroweak (EW) fundamental parameter $\sin^2 \theta_{W}$, the weak mixing angle, and the parton distribution functions (PDFs). Hence, the determination of $\sin^2 \theta_{W}$ and the updating of PDFs by directly using the same $A_{FB}$ spectrum are strongly correlated. This correlation would introduce large bias or uncertainty into both precise measurements of EW and PDF sectors. In this article, we show that the sensitivity of $A_{FB}$ on $\sin^2 \theta_{W}$ is dominated by its average value around the $Z$ pole region, while the shape (or gradient) of the $A_{FB}$ spectrum is insensitive to $\sin^2 \theta_{W}$ and contains important information on the PDF modeling. Accordingly, a new observable related to the gradient of the spectrum is introduced, and demonstrated to be able to significantly reduce the potential bias on the determination of $\sin^2 \theta_{W}$ when updating the PDFs using the same $A_{FB}$ data.