A measurement of the crosssection 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 60120GeV/c^2. The crosssection 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 samesign 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 (backgroundsubtracted) data. 
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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. 
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Crosssection for $ p p \rightarrow \rm Z\rightarrow e ^+ e ^ $ at $\sqrt{s}=7\mathrm{\,TeV} $ 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{\,GeV\!/}c}$ and $2<\eta<4.5$ for the leptons and $60<M<120$ $ {\mathrm{\,GeV\!/}c^2}$ for the dilepton. The points show the various theoretical predictions with their uncertainties as described in the text. 
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Differential crosssection for $ p p \rightarrow \rm Z\rightarrow e ^+ e ^ $ as a function of (a) \rm Z rapidity and (b) $\phi^*$. The measurements based on the $\sqrt{s}=7\mathrm{\,TeV} $ LHCb data are shown as the yellow bands where the inner (darker) band represents the statistical uncertainty and the outer the total uncertainty. NNLO QCD predictions are shown as points with error bars reflecting their uncertainties as described in the text. 
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Ratios of various QCD calculations to data for the differential crosssection for $ p p \rightarrow \rm Z\rightarrow e ^+ e ^ $ as a function of $\phi^*$. The measurements based on the $\sqrt{s}=7\mathrm{\,TeV} $ LHCb data are shown as the yellow band centred at unity where the inner (darker) band represents the statistical uncertainty and the outer the total uncertainty. (a) NNLO QCD predictions shown as points with error bars reflecting their uncertainties as described in the text. Small lateral displacements of the theory points are made to improve clarity. (b) Ratios of the predictions of Pythia , R{\sc esbos} and P{\sc owheg} to the data shown as points, with error bars that reflect the statistical uncertainties in the predictions. For most points, these errors are so small that they are not visible. 
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Animated gif made out of all figures. 
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Quantities entering into the crosssection determination, averaged over the range of \rm Z rapidity used. 
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Event yields and measurements for the differential crosssection 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 righthand column gives the values used for the FSR correction factor. 
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Correlation coefficients for the differential crosssection 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. 
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Correlation coefficients for the differential crosssection of $\rm Z\rightarrow e ^+ e ^ $ at 7 TeV between bins of $\phi^*$. Both statistical and systematic contributions are included. 
Table_A.2.pdf [27 KiB] HiDef png [65 KiB] Thumbnail [10 KiB] tex code 
Created on 23 February 2019.Citation count from INSPIRE on 23 February 2019.