Differential measurements of the Drell--Yan process in the muon channel in pPb collisions at $\sqrt{s_{_{\text{NN}}}}=8.16~\mathrm{TeV}$

Measurements of differential cross sections for the Drell--Yan process, including Z boson production, in proton-lead (pPb) collisions at a nucleon-nucleon centre-of-mass energy of $8.16~\textrm{TeV}$ are presented, in the muon channel. A data sample recorded with the CMS detector at the LHC is used, corresponding to an integrated luminosity of $173.4 \pm 6.1 \textrm{nb}^{-1}$. The differential cross section $\textrm{d}\sigma / \textrm{d}m_{\mu\mu}$ in the dimuon mass range $15 < m_{\mu\mu} < 600~\textrm{GeV}$ is measured with the CMS detector, for the first time in heavy ion collisions, and reported before and after correction to the full phase space, given by the dimuon rapidity $y_{\rm{CM}}$ in the centre-of-mass frame from $-2.87$ to $1.93$. The differential cross section $\textrm{d}\sigma/\textrm{d}y_{\rm{CM}}$ is also measured over the mass ranges $15-60$ and $60-120$$~\textrm{GeV}$, and same dimuon rapidity range. Ratios of dimuon yields for the proton-going over the Pb-going beam directions are built in the range $|y_{\rm{CM}}|<1.93$. In both mass ranges, the differential cross sections $\textrm{d}\sigma / \textrm{d}p_{\rm{T}}$ and $\textrm{d}\sigma / \textrm{d}\phi^{*}$ are measured, where the kinematic observable $\phi^{*}$ correlates with the dimuon transverse momentum but only depends on angular quantities. Results are compared to predictions at next-to-leading order, including nuclear modifications of parton distribution functions, which they could help better constrain.