Abstract
The production of Z0 bosons at large rapidities in Pb–Pb collisions at sNN=5.02TeV is reported. Z0 candidates are reconstructed in the dimuon decay channel (Z0→μ+μ−), based on muons selected with pseudo-rapidity −4.0<η<−2.5 and pT>20GeV/c. The invariant yield and the nuclear modification factor, RAA, are presented as a function of rapidity and collision centrality. The value of RAA for the 0–20% central Pb–Pb collisions is 0.67±0.11(stat.)±0.03(syst.)±0.06(corr. syst.), exhibiting a deviation of 2.6σ from unity. The results are well-described by calculations that include nuclear modifications of the parton distribution functions, while the predictions using vacuum PDFs deviate from data by 2.3σ in the 0–90% centrality class and by 3σ in the 0–20% central collisions.
Highlights
Z0 bosons are weakly interacting probes formed early in the evolution of hadronic collisions (t f ∼ 1/M 0.01 fm/c), with a typical decay time td ∼ 0.1 fm/c
The uncertainty on the model include the uncertainty on the next-to-leading order (NLO) calculations and of the measurements considered in the Parton Distribution Functions (PDFs) fit
The nPDFs are obtained by fitting the nuclear data in a similar way as done for free proton data, but using a parameterisation that depends on the atomic mass of the nucleus
Summary
Z0 bosons are weakly interacting probes formed early in the evolution of hadronic collisions (t f ∼ 1/M 0.01 fm/c), with a typical decay time td ∼ 0.1 fm/c. Their leptonic decays are of particular interest in heavy-ion collisions, since leptons do not interact strongly and their in-medium energy loss by bremsstrahlung is negligible [1]. Ing efficiency is 3%, obtained from the comparison of the efficiency estimated in data and MC by exploiting the redundancy of the tracking chamber information [51].
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