2024/12/27 by G. D. Alexeev, Alexeev, G. D., M.G Alexeev +257
Physics and Astronomy · #Particle physics theoretical and experimental studies #High-Energy Particle Collisions Research #Quantum Chromodynamics and Particle Interactions
paper · pdf · doi:10.48550/arxiv.2412.19923
A new and detailed measurement of the cross section for hard exclusive neutral-pion muoproduction on the proton was performed in a wide kinematic region, with the photon virtuality Q2 ranging from 1 to 8 (GeV/c)\rm 2 and the Bjorken variable x\rm Bj ranging from 0.02 to 0.45. The data were collected at COMPASS at CERN using 160 GeV/c longitudinally polarised μ+ and μ- beams scattering off a 2.5 m long 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 the initial and final state proton in the range 0.08 (GeV/c)\rm 2 < |t| < 0.64 (GeV/c)\rm 2. From its angular distribution, the combined contribution of transversely and longitudinally polarised photons are determined, as well as transverse--transverse and longitudinal--transverse interference contributions. They are studied as functions of four-momentum transfer |t|, photon virtuality Q2 and virtual-photon energy ν. The longitudinal--transverse interference contribution is found to be compatible with zero. The significant transverse--transverse interference contribution reveals the existence of a dominant contribution by transversely polarized photons. This provides clear experimental evidence for the chiral-odd GPD ET. In addition, the existence of a non-negligible contribution of longitudinally polarized photons is suggested by the |t|-dependence of the cross section at x\rm Bj < 0.1 . Altogether, these results provide valuable input for future modelling of GPDs and thus of cross sections for exclusive pseudo-scalar meson production. Furthermore, they can be expected to facilitate the study of next-to-leading order corrections and higher-twist contributions.