Sub-threshold J/u photoproduction
Date
2009-10-15T10:56:44Z
Authors
Lee, Claire Alexandra
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Jefferson Lab experiment E03-008 aimed to measure the J/ψ photoproduc-
tion cross section at energies sub-threshold to a free nucleon. Prior data ex-
tended only to just above threshold; the closest-to-threshold measurements
come from Cornell and SLAC and provide data in the 9.3 to 21 GeV region.
For E03-008, a mixed real and quasi-real bremsstrahlung photon beam with
an endpoint energy of 5.76 GeV incident on a solid carbon target was used,
allowing measurement for the first time in the sub-threshold region. The
sub-threshold energy of the beam required momentum contributions from
the nucleon target to bring the energy of the reaction up to threshold, thus
providing an opportunity to probe higher order nucleon correlations within
the nucleus as well as exotic mechanisms that may enhance the cross section.
The aim of the analysis was to study the parametrization of the cross section
near threshold and comment on the predictions made by theoretical models
of the J/ψ photoproduction reaction mechanism. No J/ψ events were ob-
served, a result which is consistent with predictions under the assumption
of quasi-free photoproduction, and places restictions on exotic mechanisms
that would strongly enhance quasi-free production.