Measurement of Z${}^0$-boson production at large rapidities in Pb-Pb collisions at $\sqrt{s_{\mathrm{N}\mathrm{N}}}=5.02$ TeV

The production of Z${}^0$ bosons at large rapidities in Pb-Pb collisions at $\sqrt{s_{\mathrm{N}\mathrm{N}}}=5.02$ TeV is reported. Z${}^0$ candidates are reconstructed in the dimuon decay channel (${\mathrm{Z}}^0\to {\mu }^{+}{\mu }^{-}$), based on muons selected with pseudo-rapidity $-4.0<\eta <-2.5$ and $p_{\mathrm{T}}>20$ GeV/$c$. The invariant yield and the nuclear modification factor, $R_{\mathrm{A}\mathrm{A}}$, are presented as a function of rapidity and collision centrality. The value of $R_{\mathrm{A}\mathrm{A}}$ for the 0-20% central Pb-Pb collisions is $0.67 \pm 0.11 , \mbox{(stat.)} , \pm 0.03 , \mbox{(syst.)} , \pm 0.06 , \mbox{(corr. syst.)}$,exhibitingadeviationof$2.6 \sigma$ 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 $2.3\sigma$ in the 0-90% centrality class and by $3\sigma$ in the 0-20% central collisions.