Transverse extension of partons in the proton probed in the sea-quark range by measuring the DVCS cross section (vol 793, pg 188, 2019)
Abstrakt
We report on the first measurement of exclusive single-photon muoproduction on the proton by COMPASS using 160 GeV/c polarised 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 +- 0.6 stat + 0.1- 0.3 DIVIDESDIVIDESsys) (GeV/c)-2. This result can be converted into a transverse extension of partons in the proton, SQUARE ROOT〈r2 UP TACK 〉 = (0.58 +- 0.04 stat + 0.01 - 0.02DIVIDES DIVIDESsys +- 0.04 model) fm.
For this measurement, the average virtuality of the photon mediating the interaction is 〈Q 2〉 = 1.8 (GeV/c)2 and the average value of the Bjorken variable is 〈xBj〉 = 0.056.