# Measurement of $Z$ production cross-sections in proton-lead collisions at $\sqrt{s_\rm{NN}}=8.16\ \rm{TeV}$

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## Abstract

This document describes a measurement of the $Z\rightarrow \mu^+\mu^-$ production cross-sections in proton-lead collisions at a centre-of-mass energy per nucleon pair of $\sqrt{s_\mathrm{NN}}=8.16 \mathrm{TeV}$, using data collected by the LHCb detector in 2016. The dataset corresponds to an integrated luminosity of $30.8 \mathrm{nb}^{-1}$, with $12.2 \mathrm{nb}^{-1}$ for the forward ($p$Pb) configuration and $18.6 \mathrm{nb}^{-1}$ for the backward (Pb$p$) configuration. The $Z$ candidates are reconstructed from two opposite-sign muons with transverse momentum greater than $20 \mathrm{GeV}$, pseudorapidity from 2.0 to 4.5, and an invariant dimuon mass between 60 and 120 GeV. The measured cross-section in the LHCb acceptance is \begin{equation*} \sigma_{Z\rightarrow \mu^+\mu^-,\:p\mathrm{Pb}} = 28.5 \pm 1.7(\mathrm{stat}) \pm 1.2(\mathrm{syst}) \pm 0.7(\mathrm{lumi}) \mathrm{nb}, \end{equation*} in the case when the proton propagates in the positive z-direction and \begin{equation*} \sigma_{Z\rightarrow \mu^+\mu^-,\:\mathrm{Pb}p} = 13.4 \pm 1.0(\mathrm{stat}) \pm 1.4(\mathrm{syst}) \pm 0.3(\mathrm{lumi}) \mathrm{nb}, \end{equation*} in the case when it is traveling in the opposite direction.

## Figures and captions

 Control plots of the dimoun system after the offline selection, which includes the dimuon invariant mass ($m_{\mu ^+\mu ^- }$) distributions for $p \mathrm{Pb}$ (a) and $\mathrm{Pb} p$ (b) configurations, the $p_{\mathrm{T}}$ of the $Z$ candidates ($p_{\mathrm{T}} (Z)$) for $p \mathrm{Pb}$ (c) and $\mathrm{Pb} p$ (d) configurations, and the rapidity of the dimuon system in the centre-of-mass frame ($y^*_Z$) for $p \mathrm{Pb}$ (e) and $\mathrm{Pb} p$ (f) configurations. The red line shows the distributions from simulation generated using Pythia 8 with CTEQ6L1 PDF set, normalised to the number of observed candidates. ppb_se[..].pdf [15 KiB] HiDef png [148 KiB] Thumbnail [149 KiB] *.C file pbp_se[..].pdf [15 KiB] HiDef png [155 KiB] Thumbnail [161 KiB] *.C file ppb_se[..].pdf [14 KiB] HiDef png [146 KiB] Thumbnail [143 KiB] *.C file pbp_se[..].pdf [14 KiB] HiDef png [156 KiB] Thumbnail [159 KiB] *.C file ppb_se[..].pdf [14 KiB] HiDef png [130 KiB] Thumbnail [136 KiB] *.C file pbp_se[..].pdf [14 KiB] HiDef png [132 KiB] Thumbnail [139 KiB] *.C file (color online) Measured fiducial cross-sections of $Z$ production and theoretical calculations using various PDF sets with or without nuclear modification. plot_x[..].pdf [14 KiB] HiDef png [152 KiB] Thumbnail [127 KiB] *.C file Comparison of LHCb 8.16 $\text{ Te V}$ results with previous 5.02 $\text{ Te V}$ results from ATLAS , CMS , ALICE , and LHCb . The uncertainties on the data over theory ratios include only the experimental statistical and systematic uncertainties; the PDF uncertainties are shown separately on the line at one. The central values of the LHCb and ALICE results at 5.02 $\text{ Te V}$ are shifted to left and right by 0.1 units in rapidity, respectively, for better visibility. [Failure to get the plot] Animated gif made out of all figures. CONF-2019-003.gif Thumbnail

## Tables and captions

 Summary of the relative uncertainties of the cross-section measurements for the $p \mathrm{Pb}$ and $\mathrm{Pb} p$ configurations. Table_1.pdf [63 KiB] HiDef png [77 KiB] Thumbnail [35 KiB] tex code Summary of the inputs to the fiducial cross-sections calculated in the common rapidity range $2.5<|y^*|<4.0$ for the forward-backward ratio $R_\mathrm{FB}$. Table_2.pdf [80 KiB] HiDef png [60 KiB] Thumbnail [29 KiB] tex code

Created on 06 March 2021.