Results and perspective on TMDs and GPDs at COMPASS

Abstract

Abstract. COMPASS is a fixed target experiment at the CERN SPS dedicated to the study of the nucleon structure in the framework of the most complete descriptions based on transverse momentum dependent parton distribution functions (TMDs) and generalised parton distributions (GPDs). TMDs have been accessed so far with semi-inclusive deep inelastic reactions using a 160 GeV muon beam off transversely polarized targets and they will be further investigated with Drell-Yan reactions using a 190 GeV pion beam off a transversely polarized proton target. GPDs will be studied with deeply virtual Compton scattering and hard exclusive meson production using muon beams. A selection of the results as well as the projections for the future program are discussed.

Nuclear effects in neutrino production of pions

“…Right now all the information on GPDs comes from electron-proton and positron-proton measurements done at JLAB and HERA, in particular the deeply virtual Compton scattering (DVCS) and deeply virtual meson production (DVMP) [1][2][3][4][5][6][7][8][9][10][12][13][14][15][16][17]. A planned CLAS12 upgrade at JLAB [17] and ongoing experiments at COMPASS [18] will help to improve our understanding of the GPDs, and in particular the ability to polarize both the beam and the target will allow to measure a large number of polarization asymmetries, providing various constraints for phenomenological GPD parametrizations. However, in practice the extraction of GPDs from modern experimental data is still aggravated by uncertainties, such as large BFKL-type logarithms in next-to-leading order (NLO) corrections [19] at HERA kinematics, higher-twist components of GPDs and pion distribution amplitudes (DAs) at JLAB kinematics [20][21][22][23], and vector meson DAs in the case of ρ-and φ-meson production.…”