Measurement of the ratio of cross sections for inclusive isolated-photon production in pp collisions at s√=13 and 8 TeV with the ATLAS detector

H. WAHLBERG Y ATLAS COLLABORATION

JOURNAL OF HIGH ENERGY PHYSICS

SPRINGER

Lugar: Berlin; Año: 2019

1126-6708

The ratio of the cross sections for inclusive isolated-photon production in pp collisions atcentre-of-mass energies of 13 and 8 TeV is measured using the ATLAS detector at the LHC.The integrated luminosities of the 13 TeV and 8 TeV datasets are 3.2 fb −1 and 20.2 fb −1 ,respectively. The ratio is measured as a function of the photon transverse energy in differentregions of the photon pseudorapidity. The predictions from next-to-leading-order perturbativeQCD calculations are compared with the measured ratio. The experimental systematicuncertainties as well as the uncertainties affecting the predictions are evaluated taking intoaccount the correlations between the two centre-of-mass energies, resulting in a reduction of upto a factor of 2.5 (5) in the experimental (theoretical) systematic uncertainties. The predictionsbased on several parameterisations of the proton parton distribution functions agree with thedata within the reduced experimental and theoretical uncertainties. In addition, this ratio tothat of the fiducial cross sections for Z boson production at 13 and 8 TeV using the decaychannels Z → e + e − and Z → μ + μ − is made and compared with the theoretical predictions. Inthis double ratio, a further reduction of the experimental uncertainty is obtained because theuncertainties arising from the luminosity measurement cancel out. The predictions describethe measurements of the double ratio within the theoretical and experimental uncertainties.