Neutral Current Forward-Backward Asymmetry: from $\theta_W$ to PDF Determinations

TL;DR

This paper explores how the forward-backward asymmetry in neutral-current Drell-Yan processes at the LHC can be used not only to measure the weak mixing angle but also to constrain parton distribution functions, especially quark and antiquark flavors.

Contribution

It demonstrates, for the first time at LHC Run-II, that the reconstructed forward-backward asymmetry can effectively constrain PDFs, complementing existing methods and extending to high-luminosity scenarios.

Findings

Forward-backward asymmetry constrains quark PDFs.

Selection cuts improve flavor disentanglement.

Potential for high-luminosity LHC constraints.

Abstract

Measurements of the forward-backward asymmetry in neutral-current Drell-Yan di-lepton production have primarily been used for determinations of the weak mixing angle $\theta_W$. We observe that, unlike the case of Run-I of the Large Hadron Collider (LHC Run-I), for the first time at the LHC Run-II the reconstructed forward-backward asymmetry has the capability of placing useful constraints on the determination of the parton distribution functions (PDFs). By examining the statistical and the PDF uncertainties on the reconstructed forward-backward asymmetry, we investigate its potential for disentangling the flavour content of quark and antiquark PDFs. Access to the valence/sea $u$-quark and to the sea up-type antiquark PDFs, in particular, may be gained by the appropriate use of selection cuts in the rapidity of the emerging lepton pair in regions both near the $Z$-boson peak and away from it, in a manner complementary, though more indirect, to the case of the charged-current asymmetry. We study the extension of these results for the planned high-luminosity (HL) LHC.