Electroweak probes with ATLAS

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 colour 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 $1.08\pm0.06$ above the inclusive. To make the measurement ATLAS solves the technical problem of measuring the underlying event in high pileup condition.