Probing the Proton’s Quark Dynamics in Semi-inclusive Pion Electroproduction

Measurements of pion electro-production in semi-inclusive deep inelastic scattering (SIDIS) have been performed. Data were taken with the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab using a 5.498 GeV longitudinally polarized electron beam and an unpolarized liquid hydrogen target during the E1-f run period in 2003. All three pion channels (π+, π0 and π-) were measured simultaneously over a large range of kinematics (Q2~1-4 GeV2 and x~0.1-0.5). Single-spin azimuthal asymmetries from all three pion channels were measured as functions of x, z, PT, and Q2, from which A_LU^sin(phi) was extracted. This new high statistical data could provide access to transverse-momentum dependent parton distribution functions (TMD's), which are thought to be important for understanding the physics underlying the spin structure of the nucleon.