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