Abstract
The COMPASS experiment at CERN uses hadron and lepton beams for nucleon structure studies. Most of the data collected so far with a muon beam and either proton or deuteron polarised target were analysed in terms of longitudinally or transversely polarised parton distribution functions and transverse momentum-dependent distributions in the nucleon. A negative hadron beam is used to perform Drell-Yan measurements. The COMPASS large polarised target gives access to several momentum-dependent singlespin asymmetries and provides a stringent test of the fundamental QCD factorisation assumptions. With positive and negative muon beams COMPASS also studies Generalised Parton Distributions using exclusive deeply virtual Compton scattering and meson production experiments. An overview of the most recent COMPASS results is given. The expected physics outcome of the forthcoming measurements is discussed.
Highlights
The COMPASS fixed-target experiment at CERN [1] uses the SPS secondary and tertiary beams for nucleon structure and spectroscopy studies
The data were collected with a positive, naturally-polarised muon beam, and either proton or deuteron longitudinally polarised target
The range of solutions resulting from the different assumptions for the shape of the Δg(x) distribution clearly show that the inclusive data are unable to determine neither the shape, nor even the sign of Δg
Summary
The COMPASS fixed-target experiment at CERN [1] uses the SPS secondary and tertiary beams for nucleon structure and spectroscopy studies. An important share of the beam time was dedicated to measurements with a transversely polarised target. The DIS and SIDIS data are mainly used to evaluate the polarised parton distribution functions (PDF) and transverse-momentum dependent (TMD) distributions. A negative hadron beam is used to perform Drell-Yan measurements on polarised nucleon and unpolarised nuclear targets. Positive and negative muons beams scattered off an unpolarised proton target will allow measurements of both beam charge and spin sum and difference. The results will provide a determination of the transverse nucleon size as a function of the parton longitudinal momentum
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