Electroweak probes with ATLAS

TL;DR

This paper reviews ATLAS measurements of electroweak bosons in various collision systems, highlighting their role in probing the quark-gluon plasma and initial collision geometry, including novel two-particle correlation analysis in pp collisions.

Contribution

It introduces a new method to analyze initial collision geometry in pp collisions using Z bosons and two-particle correlations, expanding electroweak probes' application.

Findings

Electroweak bosons are unaffected by the quark-gluon plasma, preserving early collision information.

First measurement constraining initial geometry in pp collisions via Z boson correlations.

Successful measurement of underlying event in high pileup conditions.

Abstract

Measuring electroweak bosons in relativistic heavy ion collisions at high energy provide an opportunity to understand temporal evolution of the quark-gluon plasma created in such collisions by constraining the initial state of the interaction. Due to lack of color charges the bosons and or particles produced in their leptonic decays are unaffected by the quark-gluon plasma and therefore preserve the information about the very early stage of the collision when they were born. This singles electroweak bosons as a unique and very interesting class of observables in heavy ion collisions. The ATLAS experiment at LHC measures production of electroweak bosons in pp, p+Pb, and Pb + Pb collisions systems. A review of the existing results is given in this proceeding that includes studies made with isolated photons to constraint kinematic properties and flavour composition of associated jets, measurements of W and Z bosons used to estimate nuclear modification of parton distribution function and the production rates of the bosons used to verify geometric models implied to estimate event centrality. A novel analysis on measuring two-particle correlations in pp collisions where the Z boson is registered is also discussed in the proceeding. This is the first attempt to break into the initial geometry of the pp collisions by constraining the impact parameter with a hard scattering process. It shows that the strength of the two particle correlations in such collision is 1.08+/-0.06 above the inclusive. To make the measurement ATLAS solves the technical problem of measuring the underlying event in high pileup condition.