Determination of αs and the gluon distribution using direct photon production in pp and pp collisions

G. Ballocchi, A. Bernasconi, R. E. Breedon, L. Camilleri, R. L. Cool, P. T. Cox, P. Cushman, L. Dick, E. C. Dukes, B. Gabioud, F. Gaille, P. Giacomelli, D. Hubbard, J. B. Jeanneret, C. Joseph, W. Kubischta, J. F. Loude, E. Malamud, C. Morel, P. ObersonO. E. Overseth, J. L. Pagès, J. P. Perroud, D. Rüegger, R. W. Rusack, V. Singh, G. R. Snow, G. Sozzi, D. Steiner, L. Studer, M. T. Tran, A. Vacchi, G. Valenti, M. Werlen

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26 Scopus citations


Direct photon cross sections obtained in pp 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, αs, is performed via a measurement of Λ (4) MS. This first measurement of Λ (4) MS using direct photon data yields a value Λ (4) MS = 235 ± 79 (stat.) ± 70 (syst.) MeV. The corresponding value of αs expressed at MZ2 is αs (MZ2) = 0.112±0.006 (stat.)±0.005 (syst.)-0.001+0.009 (theor.). The gluon distribution in the proton for x > 0.2 is determined both from the pp and from the pp data, and the results agree with each other and with previous determinations using the same method.

Original languageEnglish (US)
Pages (from-to)250-256
Number of pages7
JournalPhysics Letters B
Issue number1-2
StatePublished - Nov 4 1993

Bibliographical note

Funding Information:
We are pleased to acknowledge financial support from the "Fonds National Suisse de la Recherche Sci-entifique", the US National Science Foundation, and the US Department of Energy.


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