Abstract
After successfully running since several years with polarized muon and hadron beams to study the spin structure of the nucleon and spectroscopy of hadrons, the COMPASS (Common Muon and Proton Apparatus for Structure and Spectroscopy) experiment enters a second phase with a new extended physics program to obtain deeper insight in the partonic structure of matter. These future plans include a measurement of deep virtual Compton scattering in order to determine generalized parton distributions and the study of the polarized DrellYan process giving access to transverse momentum dependent (TMD) parton distributions. Recent results and these future plans will be presented in this document.
Highlights
Another extension of the simple collinear quark parton model is to consider the transverse position of a quark inside the nucleon. This effect is described by generalized parton distributions accessible in deep virtual Compton scattering
From the definitions above one can read off the relation between generalized parton distributions (GPDs) and from factors (F1(t)) and parton distributions: 2.1 The COMPASS Experiment
COMPASS is a fixed target experiment at CERN using hadron and muon beams to study the structure of the nucleon and spectroscopy of hadrons
Summary
Most of our knowledge about the internal structure of the nucleon comes from lepton-nucleon scattering experiment. At high momentum transfers from the lepton to the nucleon the nucleon can be described in terms of parton distribution functions. At leading twist and after integration over the transverse momentum of the quarks inside the nucleon the nucleon is fully described by three parton distributions, the unpolarized parton distributions q(x) and g(x), the helicity distributions ∆q(x) and ∆g(x) and the transversity distribution ∆T q(x). The unpolarized distributions q(x)dx equals the number of quarks of type q carrying a longitudinal momentum fraction in the interval [x, x + dx] inside the nucleon. The transversity distribution is related to a single spin Collinsasymmetry on a transversally polarized target
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