Azimuthal asymmetries in lepton-pair production at a fixed-target experiment using the LHC beams (AFTER)

TL;DR

This paper investigates the potential to measure azimuthal asymmetries in lepton-pair production at a proposed fixed-target experiment using LHC beams, aiming to access three-dimensional parton distributions.

Contribution

It provides theoretical estimates of azimuthal asymmetries in dilepton production, demonstrating the feasibility of studying TMDs at the AFTER experiment.

Findings

Azimuthal asymmetries can be measured at AFTER.

Feasibility of extracting 3dPDFs and TMDs from these measurements.

Predicted asymmetries around Z-resonance and continuum regions.

Abstract

A multi-purpose fixed-target experiment using the proton and lead-ion beams of the LHC was recently proposed by Brodsky, Fleuret, Hadjidakis and Lansberg, and here we concentrate our study on some issues related to the spin physics part of this project (referred to as AFTER). We study the nucleon spin structure through $pp$ and $pd$ processes with a fixed-target experiment using the LHC proton beams, for the kinematical region with 7 TeV proton beams at the energy in center-of-mass frame of two nucleons $\sqrt{s}=115$ GeV. We calculate and estimate the $\cos2\phi$ azimuthal asymmetries of unpolarized $pp$ and $pd$ dilepton production processes in the Drell--Yan continuum region and at the $Z$-pole. We also calculate the $\sin(2\phi-\phi_S)$, $\sin(2\phi+\phi_S)$ and $\sin2\phi$ azimuthal asymmetries of $pp$ and $pd$ dilepton production processes with the target proton and deuteron longitudinally or transversally polarized in the Drell--Yan continuum region and around $Z$ resonances region. We conclude that it is feasible to measure these azimuthal asymmetries, consequently the three-dimensional or transverse momentum dependent parton distribution functions (3dPDFs or TMDs), at this new AFTER facility.