Electroweak boson-tagged jet event asymmetries at the Large Hadron Collider

TL;DR

This paper calculates the transverse momentum asymmetry and momentum imbalance of electroweak boson-tagged jets at the LHC, incorporating perturbative QCD and medium effects, to understand jet production in heavy-ion collisions.

Contribution

First calculation of jet event asymmetries in heavy-ion collisions combining perturbative QCD with medium-induced modifications.

Findings

Strong asymmetry and imbalance observed in central Pb+Pb collisions

Results show little sensitivity to soft background fluctuations

Model predictions for shape and magnitude of asymmetries

Abstract

Tagged jet measurements provide a promising experimental channel to quantify the similarities and differences in the mechanisms of jet production in proton-proton and nucleus-nucleus collisions. We present the first calculation of the transverse momentum asymmetry of $Z^0/\gamma^*$-tagged jet events and the momentum imbalance of $\gamma$-tagged jet events in $\sqrt{s}=2.76$ TeV reactions at the LHC. Our results combine the ${\cal O}(G_F\alpha_s^2)$, ${\cal O}(G_F\alpha_s^2)$ perturbative cross sections with the radiative and collisional processes that modify parton showers in the presence of dense QCD matter. We find that strong asymmetry momentum and imbalance, respectively, are generated in central Pb+Pb reactions that have little sensitivity to the fluctuations of the underlying soft hadronic background. We present theoretical model predictions for their shape and magnitude.