27 research outputs found
Differential cross sections and spin density matrix elements for the reaction gamma p -> p omega
High-statistics differential cross sections and spin density matrix elements
for the reaction gamma p -> p omega have been measured using the CLAS at
Jefferson Lab for center-of-mass (CM) energies from threshold up to 2.84 GeV.
Results are reported in 112 10-MeV wide CM energy bins, each subdivided into
cos(theta_CM) bins of width 0.1. These are the most precise and extensive omega
photoproduction measurements to date. A number of prominent structures are
clearly present in the data. Many of these have not previously been observed
due to limited statistics in earlier measurements
Exclusive electroproduction on the proton at CLAS
The reaction has been measured, using the 5.754
GeV electron beam of Jefferson Lab and the CLAS detector. This represents the
largest ever set of data for this reaction in the valence region. Integrated
and differential cross sections are presented. The , and
dependences of the cross section are compared to theoretical calculations based
on -channel meson-exchange Regge theory on the one hand and on quark handbag
diagrams related to Generalized Parton Distributions (GPDs) on the other hand.
The Regge approach can describe at the 30% level most of the features
of the present data while the two GPD calculations that are presented in this
article which succesfully reproduce the high energy data strongly underestimate
the present data. The question is then raised whether this discrepancy
originates from an incomplete or inexact way of modelling the GPDs or the
associated hard scattering amplitude or whether the GPD formalism is simply
inapplicable in this region due to higher-twists contributions, incalculable at
present.Comment: 29 pages, 29 figure
Beam-Recoil Polarization Transfer in the Nucleon Resonance Region in the Exclusive and Reactions at CLAS
Beam-recoil transferred polarizations for the exclusive reactions have been measured using the CLAS
spectrometer at Jefferson Laboratory. New measurements have been completed at
beam energies of 4.261 and 5.754 GeV that span a range of momentum transfer
from 0.7 to 5.4 GeV, invariant energy from 1.6 to 2.6 GeV, and
the full center-of-mass angular range of the meson. These new data add to
the existing CLAS measurements at 2.567 GeV, and provide the
first-ever data for the channel in electroproduction. Comparisons
of the data with several theoretical models are used to study the sensitivity
to s-channel resonance contributions and the underlying reaction mechanism.
Interpretations within two semi-classical partonic models are made to probe the
underlying reaction mechanism and the quark-pair creation dynamics.Comment: 48 pages, 22 figure
The extraction of total cross section from
We report on the first measurement of the differential cross section of
-meson photoproduction for the exclusive
reaction channel. The experiment was performed using a
\textcolor{black}{tagged-photon} beam and the CEBAF Large Acceptance
Spectrometer (CLAS) at Jefferson Lab. A combined analysis using data from the
channel and those from a previous publication on
coherent production on the deuteron has been carried out to extract the
total cross section, . The extracted total
cross section favors a value above 20 mb. This value is larger than the value
extracted using vector-meson dominance models for photoproduction on the
proton.Comment: 7 pages 4 figure