A new determination of αs using direct photon production cross sections in pp and collisions at GeV

Abstract

Direct photon production cross sections obtained in high statisticspp and pp collisions at √ s = 24.3 GeV at the CERN SPS are used in a next-to-leading order QCD analysis. From the cross section difference σ(pp → γX) − σ(pp → γX) and quark distributions measured in deep inelastic scattering, a determination of the strong coupling constant, α s , is performed via a measurement of Λ (4) MS. This measurement yields a value Λ (4) MS = 210 ± 22 (stat.) ± 44 (syst.) +105 −36 (theo.) MeV. The corresponding value of α s expressed at M 2 Z is α s (M 2 Z) = 0.1112 ± 0.0016 (stat.) ± 0.0033 (syst.) +0.0077 −0.0034 (theo.).

Recent critical study of photon production in hadronic collisions

“…The disagreement cannot be due to the 'low' center of mass energy, ( √ s = 31.6, 38.8 GeV), of the E706 experiment since the WA70 and UA6 fixed target data at even lower energies, √ s = 23 and 24.3 GeV respectively, (and higher x T ) are in good agreement with theory. Let us note that a reasonably accurate determination of α s , in good agreement with determinations from other processes,was performed by the UA6 collaboration [40].…”

Measurement of the inclusive isolated prompt photon cross section inppcollisions ats=7 TeVwith the ATLAS detector

“…Subsequent studies, for example [16][17][18], further established prompt photons as a useful probe of parton interactions. More recent measurements at hadron colliders were performed at the Tevatron, in p " p collisions at a center-of-mass energy ffiffi ffi s p ¼ 1:96 TeV.…”

Photon Physics at the LHC

“…[36,37] Subsequent studies, for example [38,39,40], further established prompt photons as a useful probe of parton interactions.…”

“…Barrel Endcap Barrel Endcap Barrel Endcap unconverted γ [15,20) 4.1 ± .6 3.9 ± .9 1.4 ± .4 2 ± .7 3.6 ± .6 2.7 ± .8 [20,25) 3.6 ± .2 2.6 ± .3 0.1 ± .1 0.6 ± .2 3.6 ± .2 2.2 ± .3 [25,30) 2.7 ± .3 1.5 ± .4 0.0 ± .1 0.6 ± .3 2.8 ± .3 1.1 ± .4 [30,35) 2 ± .3 1.2 ± .6 0.0 ± .1 0.1 ± .4 2.0 ± .3 1.4 ± .5 [35,40) 1.7 ± .4 0.0 ± .8 0.0 ± .2 0.5 ± .6 1.8 ± .4 0.5 ± .6 [40,50) 1.3 ± .4 0.6 ± .8 0.4 ± .2 1.0 ± .6 1.0 ± .4 1.6 ± .6 [50,60) 0.3 ± .6 2 ± 1 0.1 ± .3 2 ± .1 0.4 ± .5 0.9 ± .9 [60, 100) 0.6 ± .6 0 ± .1 0.2 ± .3 1 ± .1 0.4 ± .5 1.1 ± .9 converted γ [15,20) 7.7 ± .9 7.6 ± .9 6.2 ± .9 3.2 ± .9 8 ± 1 9 ± .1 [20,25) 5.4 ± .3 8.1 ± .3 0.8 ± .3 1.4 ± .3 6.1 ± .4 8.9 ± .3 [25,30) 4.7 ± .5 6.9 ± .4 1.1 ± .4 0.9 ± .4 4.8 ± .4 7.6 ± .4 [30,35) 4.0 ± .6 6.0 ± .6 0.5 ± .5 0.8 ± .5 4.3 ± .5 6.5 ± .5 [35,40) 4.3 ± .8 5.5 ± .8 1.9 ± .7 1.1 ± .7 3.2 ± .6 5.6 ± .7 [40,50) 3.6 ± .8 5.3 ± .8 1.5 ± .7 1.8 ± .7 2.7 ± .6 4.7 ± .6 [50, 60) 20) 5.8 ± .5 7.5 ± .7 3.6 ± .4 4.0 ± .6 4.4 ± .6 6.3 ± .7 [20,25) 4.6 ± .2 6.8 ± .2 0.7 ± .1 1.8 ± . 0.8 ± .6 3.3 ± .9 0.8 ± .4 2.8 ± .8 0.13 ± .4 0.9 ± .6 Table 6.3: Uncertainties on photon reconstruction ("Reco") and offline identification extracted from a photon+jet sample with an artificially inflated material distribution in the inner tracker.…”