Vector-boson production in p--Pb collisions with ALICE at the LHC

ALICE (A Large Ion Collider Experiment) is designed and optimized to study ultra-relativistic heavy-ion collisions at the LHC, in which a hot and dense, strongly-interacting medium is created. Vector bosons (W and Z) are produced in hard scattering processes and interact weakly with the medium formed in heavy-ion collisions. Thus, they present a suitable reference for processes which are heavily affected by the medium. In proton-nucleus collisions their production can be used to study the modification of parton distribution functions in the nucleus and to test the validity of binary-collision scaling for hard processes. The production of W and Z bosons is studied in p--Pb collisions at a centre-of-mass energy of $\sqrt {s_{\rm NN}}$ = 5.02 TeV with the ALICE muon spectrometer at forward ($2.03 < \mathit{y}^{\mu}_{\textrm{cms}} < 3.53$) and backward ($-4.46< \mathit{y}^{\mu}_{\textrm{cms}} <-2.96$) rapidity. W bosons are studied via the inclusive single muon differential $p_{\rm T}$ spectrum whereas the Z-boson signal is observed in the invariant mass distribution of unlike-sign muon pairs as a peak around the Z-boson mass. In this presentation the measured cross sections of W and Z bosons and the W-boson yield per centrality interval will be discussed. The cross-sections are compared to theoretical calculations.