TOP-13-011 Measurement of the top-quark pair + photon production cross section in the muon + jets channel in pp collisions at 8 TeV

Abstract

The production cross section of top-quark pairs associated with a photon is measured in pp-collisions at a centre-of-mass energy of at 8 TeV, with the CMS detector at LHC, using data corresponding to an integrated luminosity of L=19.7/fb. The measurement is performed in the muon + jets decay channel. The signal region is defined by the final state of the process p p => W+ W- b ~b gamma, with a transverse energy of the photon of ET(gamma)>20 GeV and a distance between the photon and the b-quark in eta-phi space, DR(gamma, b) > 0.1. The normalized cross-section is measured to be R = sigma(t ~t + gamma} / sigma(t ~t) = (1.07 +- 0.07 stat +- 0.27 syst)*10^-2. Using a CMS cross section measurement of inclusive top quark pair production at 8 TeV, sigma(t ~t) = 227 +- 15 pb, the top-quark pair + photon production cross section is sigma(t ~t + gamma) = 2.4 +- 0.2 stat +- 0.6 syst pb. The result agrees with the standard model expectation of sigma(t ~t + gamma) = 1.8 +- 0.5pb.

Document

The document can be found here: link

Figures

Distributions of relevant observables used in the photon selection (N-1 plots)

Figure Caption
Photon transverse energy of selected candidates. All other selection requirements are applied. Get pdf version
Eta distribution of selected photon candidates. All selection requirements are applied. The cut on abs(eta)<1.444 requires the photons being in the barrel region. Get pdf version
Distribution of neutral hadron isolation of photon cadidates. Neutral hadron isolation accounts for the sum of pT of all neutral particles in a cone of DR < 0.4 around the reconstructed photon candidates. All other selection requirements are applied. Get pdf version
Distribution of charged hadron isolation of photon cadidates. Charged hadron isolation accounts for the sum of pT of all charged particles in a cone of DR < 0.4 around the reconstructed photon candidates. All other selection requirements are applied. Get pdf version

Template fit

Binned template fit to charged hadron isolation: The real and fake photon templates are normalized to the integral of the distribution. Get pdf version
Binned template fit to charged hadron isolation. The plot shows the fit result, where the templates are scaled to the fit parameters, N_{real} and N_{fake}, respectively. Get pdf version

Result

Final result. Reminder of the signal region: process p p => W+ W- b ~b gamma; ET(gamma)>20\GeV; DR(gamma, b) > 0.1; Get pdf version

-- HeikoGeenen - 04 Dec 2013

Topic attachments
I Attachment History Action Size Date Who Comment
PNGpng CrtlPlotPosteta_histo.png r1 manage 31.6 K 2013-12-06 - 12:03 HeikoGeenen  
PNGpng Nm1PlotchargedHadronIsoEB_histo.png r1 manage 31.6 K 2013-12-06 - 12:03 HeikoGeenen  
PNGpng Nm1Plotetcut_histo.png r1 manage 37.6 K 2013-12-06 - 12:01 HeikoGeenen  
PNGpng Nm1PlotneutralHadronIsoEB_histo.png r1 manage 36.4 K 2013-12-06 - 11:53 HeikoGeenen  
PDFpdf TemplateChHadIsofake_TemplateFitToolChHadIsoSBIDInputBkg_000.pdf r1 manage 7.5 K 2013-12-06 - 13:15 HeikoGeenen  
PNGpng TemplateFitToolChHadIsoSBIDInputBkg.png r1 manage 24.9 K 2013-12-06 - 11:53 HeikoGeenen  
PNGpng TemplateFitToolChHadIso_historebin.png r1 manage 16.4 K 2013-12-06 - 11:53 HeikoGeenen  
PDFpdf nm1_log_Nm1PlotchargedHadronIsoEB_histo.pdf r1 manage 12.1 K 2013-12-06 - 13:15 HeikoGeenen  
PDFpdf nm1_log_Nm1Plotetcut_histo.pdf r1 manage 12.7 K 2013-12-06 - 13:15 HeikoGeenen  
PDFpdf nm1_log_Nm1PlotneutralHadronIsoEB_histo.pdf r1 manage 12.1 K 2013-12-06 - 13:15 HeikoGeenen  
PDFpdf overlay_int_TemplateFitToolChHadIsoSBID_chhadiso__fake.pdf r1 manage 3.8 K 2013-12-06 - 13:15 HeikoGeenen  
PDFpdf post_lin_CrtlPlotPosteta_histo.pdf r1 manage 10.7 K 2013-12-06 - 13:15 HeikoGeenen  
PDFpdf ttgam_result.pdf r1 manage 82.7 K 2013-12-06 - 15:56 HeinerTholen  
PNGpng ttgam_result.png r1 manage 23.2 K 2013-12-06 - 15:57 HeinerTholen  
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Topic revision: r10 - 2014-03-26 - AndreasMeyer
 
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