https://doi.org/10.1051/epjconf/201819200012
Recent results from COMPASS on the GPD program
National Institute for Nuclear Research, Division of High Energy Physics,
PL 00-681 Warsaw,
Poland
* Work supported by the Polish NCN Grant 2017/26/M/ST2/00498.
** e-mail: andrzej.sandacz@ncbj.gov.pl
Published online: 14 November 2018
The dedicated COMPASS GPD program started in 2012 with a short pilot ’DVCS run’ and the first results from this run on DVCS, exclusive π0 and exclusive ω channels have been obtained. From the sum of cross sections measured with positive and negative beam polarities the DVCS cross-section and its dependence on the squared four-momentum transfer t have been extracted. It allowed a first estimate of the transverse size of the partonic distribution of the nucleon √〈r2⊥〉 i in a range of intermediate xBj with a mean xBj value of 0.056. We report also on the absolute value of the cross section for exclusive π0 production and its dependence on t and azimuthal angle ϕ between the scattering plane and π0 production plane. These measurements are aiming to constrain the GPDs, in particular chiral-odd (transversity) GPDs. Further, we present results on the spin density matrix elements for exclusive ω meson production and discuss the contributions from unnaturaly parity exchanges and from transitions that do not conserve helicity.
© The Authors, published by EDP Sciences, 2018
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