Deep Exclusive Pseudoscalar Meson Production at Jefferson Lab Hall C
Abstract
Measurements of exclusive meson production are a useful tool in the study of hadronic
structure. In particular, one can discern the relevant degrees of freedom at different distance
scales through these studies. In the transition region between low momentum transfer (where
a description of hadronic degrees of freedom in terms of effective hadronic Lagrangians is
valid) and high momentum transfer (where the degrees of freedom are quarks and gluons), the
predictive power of Quantum Chromodynamics (QCD), the theory of the strong interaction,
is limited due to the absence of a complete solution. Thus, one has to rely upon experimental
data from the non-perturbative intermediate-energy regime to thoroughly understand the
onset of perturbative QCD (pQCD) as the momentum transfer is increased.
This work involves two deep exclusive meson electroproduction experiments at Jefferson
Lab (JLab). The p(e, e′π+)n reaction is studied at fixed Q2 and W of 2.5 GeV2 and 2.0
GeV, respectively, while varying the four momentum transfer to the nucleon −t from 0.2
to 2.1 GeV2. As −t is increased, the hadronic interaction scale is reduced independently of
the observation scale of the virtual photon, providing valuable information about the hard-
scattering process in general. The data was taken at JLab Hall C in 2003, as a part of the
experiment E01-004, F -2, using the High Momentum Spectrometer (HMS) and Short Orbit
Spectrometer (SOS), and in this work, the results of the differential cross section analysis
are presented and compared to prior data, as well as two theoretical models. Using these
results over a wide −t range, the transition from hard to soft QCD is also studied.
In addition, the p(e, e′K+) ( 0) reactions are also studied. Despite their importance in
elucidating the reaction mechanism underlying strangeness production, we still do not have
complete understanding of these reactions above the resonance region. The experiment, E12-
09-011, intends to perform, for the first time, a full Rosenbluth (L/T/LT/TT) separation of
p(e, e′K+) ( 0) cross sections above the resonance region using the newly upgraded standard
equipment, Super High Momentum Spectrometer (SHMS) at JLab Hall C. The separated
data will allow us to better understand the Kaon production reaction mechanism and the
hard-soft QCD transition in exclusive processes. The kinematic settings being studied in the
experiment ranges from Q2 of 0.4 to 5.5 GeV2, W of 2.3 to 3.1 GeV, and −t of 0.06 to 0.53
GeV2. Here, the results from some pre-experimental studies with regards to estimations of
singles rates as well as real and accidental coincidence rates are presented, using two different
models. The implications of these projections on the runplan for the experiment are also
discussed.