Speaker
Description
Hard Exclusive Meson Production is a very promising reaction to access Generalized Parton Distributions. Measurement of the cross section for hard exclusive neutral pion muoproduction on the proton was performed at COMPASS in 2016 at the M2 beamline of the CERN SPS using 160 GeV/c longitudinally polarised positive and negative muon beams scattering off a 2.5 m long liquid hydrogen target. Results were obtained in a wide kinematic region with the photon virtuality Q2 up to 8 (GeV/c)$^2$ and the Bjorken variable xBj ranging from 0.016 to 0.45. We will report on the virtual-photon proton cross section averaged over the µ+ and µ- cross sections and on its dependence on the squared four-momentum transfer between initial and final proton in the range 0.08 (GeV/c)$^2$ < |t|< 0.64 (GeV/c)$^2$ and on the azimuthal angle between the scattering plane and the π0 production plane. Fitting the azimuthal dependence yields the sum of the contributions by transversely and longitudinally polarised photons as well as transverse-transverse and longitudinal-transverse interference contributions. They are studied as functions of four-momentum transfer, photon virtuality and virtual-photon energy. The COMPASS results provide input to constrain Generalized Parton Distributions, in particular chiral-odd (“transversity”) ones.
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