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
StatePublished - 10 Jun 2019


FundersFunder number
National Science Foundation1812377, PHY-1506416
National Science Foundation
California Department of Fish and Wildlife
Seventh Framework Programme283286
Seventh Framework Programme
Bundesministerium für Bildung und Forschung
Israel Academy of Sciences and Humanities
Narodowym Centrum Nauki2017/26/M/ST2/00498
Narodowym Centrum Nauki
Ministerio de Ciencia y TecnologíaLG13031
Ministerio de Ciencia y Tecnología


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


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