A new determination of αs using direct photon production cross sections in pp and p̄p collisions at s=24.3 GeV

Abstract Direct photon production cross sections obtained in high statistics p p 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( p p → 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. ) .