Abstract

Measurements are presented of the triple-differential cross section for inclusive isolated-photon+jet events in mathrm{p}mathrm{p} collisions at sqrt{s} = 8 TeV as a function of photon transverse momentum (p_{mathrm {T}} ^{{upgamma {}{}}}), photon pseudorapidity (eta ^{{upgamma {}{}}}), and jet pseudorapidity (eta ^{text {jet}}). The data correspond to an integrated luminosity of 19.7{,text {fb}^{-1}} that probe a broad range of the available phase space, for |eta ^{{upgamma {}{}}} |<1.44 and 1.57<|eta ^{{upgamma {}{}}} |<2.50, |eta ^{text {jet}} |<2.5, 40< p_{mathrm {T}} ^{{upgamma {}{}}}<1000,text {GeV}, and jet transverse momentum, p_{mathrm {T}} ^{text {jet}}, > 25,text {GeV}. The measurements are compared to next-to-leading order perturbative quantum chromodynamics calculations, which reproduce the data within uncertainties.

Highlights

  • Direct photons produced in the hard scattering of partons in proton–proton collisions are sensitive probes of the perturbative regime of quantum chromodynamics [1,2] and provide useful constraints on the parton distribution function (PDF) of gluons [3–5]

  • To separate signal photons from this background, photons are selected by requiring a narrow transverse shower shape in the electromagnetic calorimeter (ECAL), no matching reconstructed track candidates, and minimal energy measured in the hadronic calorimeter (HCAL) region matched to the ECAL shower

  • Measurements of the triple-differential inclusive isolatedphoton+jet cross section were performed as a function of photon transverse momentum, photon pseudorapidity c(ηaγrr)i,eadnodujtetinpspepudcoorllaipsiiodnityat(η√jest).=Th8eTmeVeasuusrinemg e1n9t.s7wfbe−re1 of data collected by the CMS detector covering a kinematic range of |ηγ| < 1.44 and 1.57 < |ηγ| < 2.50, |ηjet| < 2.5, 40 < pTγ < 1000 GeV, and jet transverse momentum, pTjet, >25 GeV

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Summary

Introduction

Direct photons produced in the hard scattering of partons in proton–proton collisions are sensitive probes of the perturbative regime of quantum chromodynamics (pQCD) [1,2] and provide useful constraints on the parton distribution function (PDF) of gluons [3–5]. A good understanding of isolated photon production indirectly impacts all jet measurements at the LHC, because photon+jet events are commonly used to determine the absolute jet energy-scale. This paper presents measurements of the triple-differential inclusive isolated-photon+jet cross sections using data collected by the CMS experiment during the 2012 run at √s = 8 TeV corresponding to an integrated luminosity of 19.7 fb−1. Given the photon transverse momentum range of pTγ = 40–1000 GeV, the measurement probγes√Q2 = ( pTγ) in the range 103–106 GeV2, and xT = 2 pT/ s in the range 0.01–0.25, where xT is an approximation to the parton momentum fraction when both photon and jet are produced centrally.

The CMS detector
Event reconstruction and selection
Experimental measurement
Signal templates
Background templates
Fit and systematic uncertainties
Unfolding
Findings
Summary
Full Text
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