# Measurement of the cross-section for $Z\to e^+e^-$ production in $pp$ collisions at $\sqrt{s} =7$ TeV

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## Abstract

A measurement of the cross-section for pp->Z->e+e- is presented using data at sqrt{s}=7TeV corresponding to an integrated luminosity of 0.94 fb^{-1}. The process is measured within the kinematic acceptance pT>20GeV/c and 2<\eta<4.5 for the daughter electrons and dielectron invariant mass in the range 60--120GeV/c^2. The cross-section is determined to be \sigma(pp->Z->e+e-)=76.0+-0.8+-2.0+-2.6pb where the first uncertainty is statistical, the second is systematic and the third is the uncertainty in the luminosity. The measurement is performed as a function of Z rapidity and as a function of an angular variable which is closely related to the Z transverse momentum. The results are compared with previous LHCb measurements and with theoretical predictions from QCD.

 Invariant mass distribution of $\rm Z\rightarrow e ^+ e ^-$ candidates. The data are shown as points with error bars, the background obtained from same-sign data is shown in red (dark shading), to which the expectation from signal simulation is added in yellow (light shading). The $\rm Z\rightarrow e ^+ e ^-$ simulated distribution has been normalised to the (background-subtracted) data. Z0_M_1[..].pdf [21 KiB] HiDef png [181 KiB] Thumbnail [155 KiB] *.C file Distribution of $p_{\rm T}$ for the "tag" electron in cases where an isolated cluster of energy of high $E_{\rm T}$ \ is found in the electromagnetic calorimeter. This is fitted with two components obtained from data, the $\rm Z\rightarrow e ^+ e ^-$ signal whose shape is taken from those candidates where the cluster is associated with an identified electron track, and background whose shape is obtained from candidates where the cluster is not isolated. TrackE[..].pdf [15 KiB] HiDef png [139 KiB] Thumbnail [122 KiB] *.C file Cross-section for $p p \rightarrow \rm Z\rightarrow e ^+ e ^-$ at $\sqrt{s}=7\mathrm{ Te V}$ measured in LHCb , shown as the yellow band. The inner (darker) band represents the statistical uncertainty and the outer the total uncertainty. The measurement corresponds to the kinematic acceptance, $p_{\rm T} >20$ ${\mathrm{ Ge V /}c}$ and $2<\eta<4.5$ for the leptons and $60 ## Tables and captions  Quantities entering into the cross-section determination, averaged over the range of \rm Z rapidity used. Table_1.pdf [54 KiB] HiDef png [100 KiB] Thumbnail [49 KiB] tex code Event yields and measurements for the differential cross-section of$ p p \rightarrow \rm Z\rightarrow e ^+ e ^- $at$\sqrt{s}=$7 TeV as a function of \rm Z rapidity,$y_{\rm Z}$, and of$\phi^*$. The first uncertainty is statistical, the second and third are the uncorrelated and correlated experimental systematic uncertainties respectively, and the fourth is the uncertainty in the FSR correction. The common luminosity uncertainty of 3.5% is not explicitly included here. The results are given for the combined data sample. The right-hand column gives the values used for the FSR correction factor. Table_2.pdf [45 KiB] HiDef png [93 KiB] Thumbnail [41 KiB] tex code Correlation coefficients for the differential cross-section of$\rm Z\rightarrow e ^+ e ^- $at 7 TeV between bins of \rm Z rapidity,$y_{\rm Z}$. Both statistical and systematic contributions are included. Table_3.pdf [27 KiB] HiDef png [61 KiB] Thumbnail [29 KiB] tex code Correlation coefficients for the differential cross-section of$\rm Z\rightarrow e ^+ e ^- $at 7 TeV between bins of$\phi^*\$. Both statistical and systematic contributions are included. Table_4.pdf [27 KiB] HiDef png [65 KiB] Thumbnail [30 KiB] tex code

Created on 17 August 2019.Citation count from INSPIRE on 20 August 2019.