44 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
photoproduction on the proton for photon energies from 0.725 to 2.875 GeV
Differential cross sections for the reaction have been
measured with the CEBAF Large Acceptance Spectrometer (CLAS) and a tagged
photon beam with energies from 0.725 to 2.875 GeV. Where available, the results
obtained here compare well with previously published results for the reaction.
Agreement with the SAID and MAID analyses is found below 1 GeV. The present set
of cross sections has been incorporated into the SAID database, and exploratory
fits have been made up to 2.7 GeV. Resonance couplings have been extracted and
compared to previous determinations. With the addition of these cross sections
to the world data set, significant changes have occurred in the high-energy
behavior of the SAID cross-section predictions and amplitudes.Comment: 18 pages, 10 figure
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
A measurement of the differential cross section for the reaction from deuterium
We report a measurement of the differential cross section for the process from the CLAS detector at Jefferson Lab in Hall B for
photon energies between 1.0 and 3.5 GeV and pion center-of-mass (c.m.) angles
() between 50 and 115. We confirm a previous
indication of a broad enhancement around a c.m. energy () of 2.2 GeV
at in the scaled differential cross section, . Our data show the angular dependence of this enhancement
as the scaling region is approached in the kinematic region from 70 to
105.Comment: 6 pages, 3 figures. submitted to PR
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
First measurement of target and double spin asymmetries for polarized e- polarized p --> e p pi0 in the nucleon resonance region above the Delta(1232)
The exclusive channel polarized proton(polarized e,e prime p)pi0 was studied
in the first and second nucleon resonance regions in the Q2 range from 0.187 to
0.770 GeV2 at Jefferson Lab using the CEBAF Large Acceptance Spectrometer
(CLAS). Longitudinal target and beam-target asymmetries were extracted over a
large range of center-of-mass angles of the pi0 and compared to the unitary
isobar model MAID, the dynamic model by Sato and Lee, and the dynamic model
DMT. A strong sensitivity to individual models was observed, in particular for
the target asymmetry and in the higher invariant mass region. This data set,
once included in the global fits of the above models, is expected to place
strong constraints on the electrocoupling amplitudes A_{1/2} and S_{1/2} for
the Roper resonance N(1400)P11, and the N(1535)S11 and N(1520)D13 states.Comment: 13 pages, 13 figure