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