Abstract

We report on the first measurement of exclusive single-photon muoproduction on the proton by COMPASS using 160GeV/cpolarised μ+ and μ- beams of the CERN SPS impinging on a liquid hydrogen target. We determine the dependence of the average of the measured μ+ and μ- cross sections for deeply virtual Compton scattering on the squared four-momentum transfer t from the initial to the final proton. The slope B of the t-dependence is fitted with a single exponential function, which yields B = (4.3 ± 0.6stat+0.1-0.3]sys) (GeV/c)-2. This result can be converted into a transverse extension of partons in the proton, √〈r2〉 = (0.58 ± 0.04stat+0.01-0.02]sys ± 0.04model) fm. For this measurement, the average virtuality of the photon mediating the interaction is 〈Q2〉 = 1.8 (GeV/c)2 and the average value of the Bjorken variable is 〈xBj〉 = 0.056.

Original languageEnglish
Pages (from-to)188-194
Number of pages7
JournalPhysics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
Volume793
DOIs
StatePublished - 10 Jun 2019

Funding

FundersFunder number
Israel Academy of Sciences and Humanities
Bundesministerium für Bildung und Forschung
European Commission
California Department of Fish and Wildlife
National Science Foundation1506416, 1812377
Seventh Framework Programme1506416, 283286
Fundação para a Ciência e a TecnologiaCERN/FIS-NUC/0017/2015
Ministerio de Ciencia y TecnologíaLG13031
Narodowym Centrum Nauki2017/26/M/ST2/00498

    Keywords

    • COMPASS
    • Deep inelastic scattering
    • Deeply virtual Compton scattering
    • Exclusive reactions
    • Generalized Parton Distributions
    • Proton size
    • Quantum chromodynamics

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