Measurement of the cross-section for Z→ e+e− production in pp collisions at √s = 8 TeV

The paper is available here.

arXiv:1503.00963, LHCB-PAPER-2015-003, JHEP 05 (2015) 109, DOI: 10.1007/JHEP05(2015)109

More detailed information: ANA note 2014-086

Abstract

A measurement of the cross-section for Z-boson production in the forward region of pp collisions at 8 TeV centre-of-mass energy is presented. The measurement is based on a sample of Z → e+e- decays reconstructed using the LHCb detector, corresponding to an integrated luminosity of 2.0 fb-1. The acceptance is defined by the requirements 2.0 < η < 4.5 and pT > 20 GeV for the pseudorapidities and transverse momenta of the leptons. Their invariant mass is required to lie in the range 60120 GeV. The cross-section is determined to be

σ(pp → Z → +e ) = 93.81 0.41(stat) 1.48(syst) 1.14(lumi) pb ,

where the first uncertainty is statistical and the second reflects all systematic effects apart from that arising from the luminosity, which is given as the third uncertainty. Differential cross-sections are presented as functions of the Z-boson rapidity and of the angular variable φ∗ , which is related to the Z-boson transverse momentum.

Figures

(Note, eps versions are available under attachments).

Caption Figure
Figure 1: Overall detection efficiency, , determined from a combination of data and simulation as described in the text, shown as a function of (left) yZ and (right) φ∗. Fig1a.png Fig1b.png
Figure 2: Comparison between data and simulation for the distribution of min(pT(e+), pT(e- )), used in the assessment of uncertainties in ekin. 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 Z →e+e- simulation is added in yellow (light shading). The simulated distribution is normalised to the background-subtracted data. The τ+ τ- background is also included (green), though barely visible. The dashed line indicates the threshold applied in the event selection. The small plot at the top shows the pulls (i.e. deviations divided by statistical uncertainties) between the data and the expectation. Fig2.png
Figure 3: Measured cross-section for Z →+e- shown as the shaded band, with the inner →(orange) band indicating the statistical error and the outer (yellow) band the total uncertainty. For comparison, the NNLO predictions of Fewz are shown using five different sets of PDFs. The uncertainties on these predictions include the PDF uncertainties and the variation of the factorisation and normalisation scales, as well as the errors arising from numerical integration. Fig3.png
Figure 4: (left) Differential cross-section dσ/dyZ and (right) normalised differential cross-section (1/σ)dσ/dyZ as a function of yZ. The measured data are shown as the shaded bands, with the inner (orange) bands indicating the statistical error and the outer (yellow) bands the total uncertainty. For comparison, the NNLO predictions of Fewz using five different sets of PDFs are shown on the left-hand plot. The same data are compared with leading log calculations in the right-hand plot. To aid clarity, small horizontal displacements are applied to some of the predictions. Fig4a.pngFig4b.png
Figure 5: (left) Normalised differential cross-section (1/σ)dσ/dφ∗ as a function of φ∗. The measured data are shown as the shaded bands, with the inner (orange) bands indicating the statistical error and the outer (yellow) bands the total uncertainty. For comparison, the predictions of the leading-log calculations described in the text are shown. (right) The same data and predictions normalised to the measurement in data, so that the measurements are shown as the shaded bands at unity. To aid clarity, small horizontal displacements are applied to some of the predictions. Fig5a.pngFig5b.png
Figure 6 (supplementary): Comparison between data and simulation for the distribution of M (+e -). The opposite-sign 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 Z →e+e -simulation is added in yellow (light shading). The simulated distribution is normalised to the background-subtracted data. The τ+τ background is also included (green), though not visible. Fig6.png
-- KatharinaMueller - 2015-03-03
Topic attachments
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Unknown file formateps Fig1a.eps r1 manage 9.0 K 2015-03-03 - 15:01 KatharinaMueller  
PDFpdf Fig1a.pdf r1 manage 14.8 K 2015-03-03 - 15:01 KatharinaMueller  
PNGpng Fig1a.png r1 manage 14.0 K 2015-03-03 - 15:01 KatharinaMueller  
Unknown file formateps Fig1b.eps r1 manage 9.5 K 2015-03-03 - 15:01 KatharinaMueller  
PDFpdf Fig1b.pdf r1 manage 14.7 K 2015-03-03 - 15:01 KatharinaMueller  
PNGpng Fig1b.png r1 manage 12.2 K 2015-03-03 - 15:01 KatharinaMueller  
Unknown file formateps Fig2.eps r1 manage 27.1 K 2015-03-03 - 15:01 KatharinaMueller  
PDFpdf Fig2.pdf r1 manage 24.6 K 2015-03-03 - 15:01 KatharinaMueller  
PNGpng Fig2.png r1 manage 20.2 K 2015-03-03 - 15:01 KatharinaMueller  
Unknown file formateps Fig3.eps r1 manage 9.2 K 2015-03-03 - 15:02 KatharinaMueller  
PDFpdf Fig3.pdf r1 manage 13.9 K 2015-03-03 - 15:02 KatharinaMueller  
PNGpng Fig3.png r1 manage 9.7 K 2015-03-03 - 15:02 KatharinaMueller  
Unknown file formateps Fig4a.eps r1 manage 15.8 K 2015-03-03 - 15:02 KatharinaMueller  
PDFpdf Fig4a.pdf r1 manage 19.0 K 2015-03-03 - 15:02 KatharinaMueller  
PNGpng Fig4a.png r1 manage 22.5 K 2015-03-03 - 15:02 KatharinaMueller  
Unknown file formateps Fig4b.eps r1 manage 12.7 K 2015-03-03 - 15:02 KatharinaMueller  
PDFpdf Fig4b.pdf r1 manage 16.9 K 2015-03-03 - 15:02 KatharinaMueller  
PNGpng Fig4b.png r1 manage 17.1 K 2015-03-03 - 15:02 KatharinaMueller  
Unknown file formateps Fig5a.eps r1 manage 11.8 K 2015-03-03 - 15:02 KatharinaMueller  
PDFpdf Fig5a.pdf r1 manage 16.4 K 2015-03-03 - 15:02 KatharinaMueller  
PNGpng Fig5a.png r1 manage 14.8 K 2015-03-03 - 15:02 KatharinaMueller  
Unknown file formateps Fig5b.eps r1 manage 12.0 K 2015-03-03 - 15:02 KatharinaMueller  
PDFpdf Fig5b.pdf r1 manage 16.6 K 2015-03-03 - 15:02 KatharinaMueller  
PNGpng Fig5b.png r1 manage 15.9 K 2015-03-03 - 15:02 KatharinaMueller  
Unknown file formateps Fig6.eps r1 manage 25.9 K 2015-03-03 - 15:02 KatharinaMueller  
PDFpdf Fig6.pdf r1 manage 24.2 K 2015-03-03 - 15:02 KatharinaMueller  
PNGpng Fig6.png r1 manage 18.8 K 2015-03-03 - 15:02 KatharinaMueller  
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