Speaker
Peter Bosted
(William and Mary)
Description
Beam-target double spin asymmetries, beam single-spin asymmetries, and target single-spin asymmetries in exclusive $\pi^+$ and $\pi^0$ electroproduction were obtained from scattering of 1.6 to 6 GeV longitudinally polarized electrons from longitudinally polarized protons using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. The kinematic range covered is final state invariant mass $1.1\lt W \lt 2.7$ GeV and four-momentum transfer squared $0.05\lt Q^2 \lt 5$ GeV$^2$, with good angular coverage in the forward hemisphere. The asymmetry results were divided into approximately 46,000 (6000) kinematic bins for $\pi^+$ ($\pi^0$). The present results are found to be in reasonable agreement with unitary isobar fits to previous world data for $W<1.7$ GeV and $Q^2<0.5$ GeV$^2$, with discrepancies increasing at higher values of $Q^2$, especially for $W>1.5$ GeV. A new preliminary unitary isobar fit is able to provide an adequate description of the $\pi^+$ data to $W=2$ GeV. Very large target-spin asymmetries are observed for $Q^2>1$ GeV$^2$ and $W>2$ GeV and larger values of $t$. In the hadron-nucleon picture, this suggests that nucleon resonances continue to play a significant role for values of $W$ as large as 2.7 GeV. In the quark-parton picture, this suggests that higher-twist contributions cannot be neglected. It is hooped that these experimental results will spark theoretical interest.
Primary author
Peter Bosted
(William and Mary)
