Weak boson production measured in PbPb and pp collisions by CMS

TL;DR

This paper reports on measurements of electroweak boson production in PbPb and pp collisions at the LHC, providing insights into initial state conditions and nuclear PDFs with no observed modifications in Z boson yields.

Contribution

It presents the first measurements of W and Z boson production in heavy-ion collisions at the LHC, comparing them to pp collisions and theoretical predictions.

Findings

No modification observed in Z boson yields compared to predictions.

First observation of W d7 a0 in heavy ion collisions.

Results help constrain nuclear PDFs and serve as a standard candle.

Abstract

The unprecedented center-of-mass energy available at the LHC offers unique opportunities for studying the properties of the strongly-interacting QCD matter created in PbPb collisions at extreme temperatures and very low parton momentum fractions. Electroweak boson production is an important benchmark process at hadron colliders. Precise measurements of Z production in heavy-ion collisions can help to constrain nuclear PDFs as well as serve as a standard candle of the initial state in PbPb collisions at the LHC energies. The inclusive and differential measurements of the Z boson yield in the muon decay channel will be presented, establishing that no modification is observed with respect to next-to-leading order pQCD calculations, scaled by the number of incoherent nucleon-nucleon collisions. The status of the Z measurement in the electron decay channel, as well as the first observation of W \rightarrow \mu {\nu} in heavy ion collisions will be given. The heavy-ion results will be presented in the context of those obtained in pp collisions with the CMS detector.