Abstract
A measurement of the cross section for the inclusive production of isolated prompt photons in pp collisions at a centre-of-mass energy sqrt(s) = 7TeV is presented. The measurement covers the pseudorapidity ranges |eta|<1.37 and 1.52<|eta|<1.81 in the transverse energy range 15 < E_T <100 GeV. The results are based on an integrated luminosity of 880 nb-1, collected with the ATLAS detector at the Large Hadron Collider. Photon candidates are identified by combining information from the calorimeters and from the inner tracker. Residual background in the selected sample is estimated from data based on the observed distribution of the transverse isolation energy in a narrow cone around the photon candidate. The results are compared to predictions from next-to-leading order perturbative QCD calculations.
Highlights
Prompt photon production at hadron colliders provides a handle for testing perturbative QCD predictions [1,2]
This paper describes the extraction of a signal of isolated prompt photons using 880 nbÀ1 of data collected with the ATLAS detector at the Large Hadron Collider (LHC)
A set of loose identification criteria for photons is defined based on independent requirements on three quantities: (i) the leakage Rhad in the first layer of the hadronic compartment beyond the electromagnetic cluster, defined as the ratio between the transverse energy deposited in the first layer of the hadronic calorimeter and the transverse energy of the photon candidate; (ii) the ratio R between the energy deposits in 3 Â 7 and 7 Â 7 cells in the second layer of the electromagnetic calorimeter; (iii) the root mean square (RMS) width w2 of the energy distribution along in the second layer of the electromagnetic calorimeter
Summary
Prompt photon production at hadron colliders provides a handle for testing perturbative QCD (pQCD) predictions [1,2]. Photon identification is important for many physics signatures, including searches for Higgs boson [5] and graviton decays [6] to photon pairs, decays of excited fermions [7], and decays of pairs of supersymmetric particles characterized by the production of two energetic photons and large missing transverse energy [8,9,10] Prompt photons include both ‘‘direct’’ photons, which take part in the hard scattering subprocess D0 and CDF measure an isolated prompt photon cross section in agreement with next-to-leading-order (NLO).
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