Spin and Azimuthal Asymmetries in Electroproduction at CLAS
Abstract
The orbital angular momentum of partons has become of central interest since the EMC measurements implied that quark helicities account for only a small fraction of the nucleon spin. The single-spin asymmetries (SSA) that have been reported in semi-inclusive DIS from longitudinally polarized target (HERMES), transversely polarized target (SMC), and in polarized beam measurements (CLAS), have emerged as a powerful tool to access observables directly related to the orbital motion of quarks. SSA enable measurements of some essentially unexplored physical observables, including transversity, time-reversal odd distribution and fragmentation functions. Different azimuthal moments contain combinations of unknown distribution and fragmentation functions. Thus, extraction of relevant quantities require a set of measurements with unpolarized, and longitudinally and transversely polarized targets. This contribution presents recent results from Jefferson Lab's CLAS detector on beam and target SSA in single pion electroproduction in the DIS kinematics (Q^2>1GeV^2,W>2GeV) off a longitudinally polarized NH3 and off unpolarized hydrogen targets. Significant target spin asymmetry is measured for the first time in the sin2φ dependent moment of the cross section providing an indication of a non-zero Collins fragmentation. Kinematic dependence of SSAs are also compared with model predictions.
- Publication:
-
APS Division of Nuclear Physics Meeting Abstracts
- Pub Date:
- October 2003
- Bibcode:
- 2003APS..DNP.BB013A