Production of W and Z bosons in heavy-ion collisions with CMS

Weak bosons do not participate in the strong interaction, and thus constitute clean probes of the initial state of nucleus–nucleus collisions. The comparison of their production cross sections in pp and in nuclear collisions provides constraints on the nuclear parton distribution functions. Despite the low production cross section of weak bosons, compared to other nuclear processes, the relatively clean signal of their leptonic decay channels allows their detection and reconstruction. A first analysis of PbPb data has confirmed the medium-blind characteristic of the electroweak bosons. This paper reports measurements of Z and W bosons, produced in PbPb and pp collisions at nucleon–nucleon centre of mass energy √(s_NN)=2.76 TeV with the CMS detector. The Z boson yield and the nuclear modification factor (R_AA) corresponding to an integrated luminosity of 150 μb⁻¹ are presented, as a function of the centrality, of the Z rapidity and p_T, both in the muonic and electronic channels. Event centrality and muon pseudorapidity dependencies of the W production yields are presented separately for W⁺ and W⁻