Measurement of the cross section for hard exclusive π0 muoproduction on the proton

The COMPASS Collaboration

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We report on a measurement of hard exclusive π0 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. From the average of the measured μ+ and μ cross sections, the virtual-photon proton cross section is determined as a function of the squared four-momentum transfer between initial and final proton in the range 0.08(GeV/c)2<|t|<0.64(GeV/c)2. The average kinematics of the measurement are 〈Q2〉=2.0(GeV/c)2, 〈ν〉=12.8GeV, 〈xBj〉=0.093 and 〈−t〉=0.256(GeV/c)2. Fitting the azimuthal dependence reveals a combined contribution by transversely and longitudinally polarised photons of (8.2±0.9stat −1.2 +1.2|sys)nb/(GeV/c)2, as well as transverse-transverse and longitudinal-transverse interference contributions of (−6.1±1.3stat −0.7 +0.7|sys)nb/(GeV/c)2 and (1.5±0.5stat −0.2 +0.3|sys)nb/(GeV/c)2, respectively. Our results provide important input for modelling Generalised Parton Distributions. In the context of the phenomenological Goloskokov-Kroll model, the statistically significant transverse-transverse interference contribution constitutes clear experimental evidence for the chiral-odd GPD E‾T.

Original languageEnglish (US)
Article number135454
JournalPhysics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
StatePublished - Jun 10 2020


  • Generalised Parton Distributions
  • Hard exclusive meson production
  • Muoproduction
  • Quantum chromodynamics

ASJC Scopus subject areas

  • Nuclear and High Energy Physics


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