Measurement of the cross-section for Z0→ e+e− production in pp collisions at √s = 7 TeV

The paper is available here.

J. High Energy Phys. 02 (2013) 106

arXiv:1212.4620

More detailed information: ANA note 2012-078

Abstract

A measurement of the cross-section for pp→Z→e+e- is presented using data at √s = 7 TeV corresponding to an integrated luminosity of 0.94 fb-1. The process is measured within the kinematic acceptance pT>20 GeV/c and 2<η <4.5 for the daughter electrons and dielectron invariant mass in the range 60-120 GeV/c2. The cross-section is determined to be σ(pp→Z→e+e-)=76.0±0.8±2.0±2.6 pb 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.

Figures

(Note, eps versions are available under attachments).

Caption Figure
Fig.1 Invariant mass distribution of Z→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 Z→e+e- simulated distribution has been normalised to the (background-subtracted) data. Fig1.png
Fig.2 Distribution of pT for the ``tag'' electron in cases where an isolated cluster of energy of high ET is found in the electromagnetic calorimeter. This is fitted with two components obtained from data, the Z→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. Fig2.png
Fig.3 Cross-section for pp→Z→e+e- measured in LHCb at √s = 7 TeV, 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, pT>20 GeV/c and 2<η <4.5 for the leptons and 60<M<120 GeV/c2 for the dilepton. The points show the various theoretical predictions with their uncertainties as described in the text. Fig3.png
Fig.4(a) Differential cross-section for pp→Z→e+e- as a function of Z rapidity. The measurements based on the √s = 7 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. Fig4a.png
Fig.4(b) Differential cross-section for pp→Z→e+e- as a function of φ*. The measurements based on the √s = 7 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. Fig4b.png
Fig.5(a) Ratios of various QCD calculations to data for the differential cross-section for pp→Z→e+e- as a function of φ*. The measurements based on the √s = 7 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. 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. Fig5a.png
Fig.5(b) Ratios of the predictions of PYTHIA, RESBOS and POWHEG 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. Fig5b.png

-- DavidWard - 20-Dec-2012

Topic attachments
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Unknown file formateps Fig1.eps r1 manage 326.5 K 2012-12-20 - 17:21 DavidWard  
PNGpng Fig1.png r1 manage 28.8 K 2012-12-20 - 17:21 DavidWard  
Unknown file formateps Fig2.eps r1 manage 314.3 K 2012-12-20 - 17:21 DavidWard  
PNGpng Fig2.png r1 manage 26.1 K 2012-12-20 - 17:21 DavidWard  
Unknown file formateps Fig3.eps r1 manage 253.7 K 2012-12-20 - 17:21 DavidWard  
PNGpng Fig3.png r1 manage 19.0 K 2012-12-20 - 17:21 DavidWard  
Unknown file formateps Fig4a.eps r1 manage 328.1 K 2012-12-20 - 17:21 DavidWard  
PNGpng Fig4a.png r1 manage 35.8 K 2012-12-20 - 17:21 DavidWard  
Unknown file formateps Fig4b.eps r1 manage 253.6 K 2012-12-20 - 17:21 DavidWard  
PNGpng Fig4b.png r1 manage 33.2 K 2012-12-20 - 17:23 DavidWard  
Unknown file formateps Fig5a.eps r1 manage 255.5 K 2012-12-20 - 17:23 DavidWard  
PNGpng Fig5a.png r1 manage 33.7 K 2012-12-20 - 17:23 DavidWard  
Unknown file formateps Fig5b.eps r1 manage 252.0 K 2012-12-20 - 17:23 DavidWard  
PNGpng Fig5b.png r1 manage 38.3 K 2012-12-20 - 17:23 DavidWard  
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