112 research outputs found
Photoproduction of Pseudoscalar Mesons
Experiments that study the photoproduction of pseudoscalar mesons; pions,
etas and kaons, have the potential to increase our knowledge of baryon and
hyperon resonance properties. Recent experiments at JLab, Mainz, GRAAL, and
Bonn are beginning to produce results in the form of polarization and asymmetry
measurements and determinations of the differential and integrated cross
sections. These new data are essential to the performance of Partial-Wave
Analyses that are less model dependent and coupled-channels calculations that
incorporate unitarity dynamically,combining hadronic reaction channels together
with electromagnetic processes. This approach is necessary to extract resonance
properties and may lead to the identification of missing, but predicted,
resonances. Some recent experimental and phenomenological results for single
and double pseudoscalar meson photoproduction are discussed.Comment: 4 pages, 4 figures, Proceedings of Particles and Nuclei, PANIC2002,
Osaka, Japan, Sept.30-Oct.4, 200
Progress on Neutron-Target Multipoles above 1 GeV
We report a new extraction of nucleon resonance couplings using pi-
photoproduction cross sections on the neutron. The world database for the
process gn-->pi-p above 1 GeV has quadrupled with the addition of new
differential cross sections from the CEBAF Large Acceptance Spectrometer (CLAS)
at Jefferson Lab in Hall B. Differential cross sections from CLAS have been
improved with a new final-state interaction determination using a diagrammatic
technique taking into account the SAID phenomenological NN and piN final-state
interaction amplitudes. Resonance couplings have been extracted and compared to
previous determinations. With the addition of these new cross sections,
significant changes are seen in the high-energy behavior of the SAID cross
sections and amplitudes.Comment: 4 pages, 3 figures, 1 table; talk given at 12th International
Workshop on Meson Production, Properties and Interaction (MESON2012), 31 May
- 5 June 2012, Krakow, Poland; will be published online in European Journal
Web of Conference
Properties of the Lambda(1520) Resonance from High-Precision Electroproduction Data
High-resolution spectrometer measurements of the reaction H(e,e'K+)X at small
Q2 are used to extract the mass and width of the Lambda(1520). We investigate
the influence of various assumptions used in the extraction. The width appears
to be more sensitive to the assumptions than the mass. To reach a width
uncertainty about 1 MeV or better, one needs to know the structure of the
non-resonant background. Based on the new Jefferson Lab Hall A data, our final
values for the Breit-Wigner parameters are M = 1520.4 +- 0.6 (stat) +- 1.5
(syst) MeV, Gamma = 18.6 +- 1.9 (stat) +- 1 (syst) MeV. For the first time, we
also estimate the pole position for this resonance and find that both the pole
mass and width seem to be smaller than the Breit-Wigner values.Comment: 7 pages, 3 figures; corresponds to the published versio
The as a resonance in the system
We study the system by solving the Faddeev equations, for which
the input two-body -matrices are obtained by solving the Bethe-Salpeter
equation in the coupled channel formalism. The potentials for the ,
sub-systems and their coupled channels are obtained from chiral
Lagrangians, which have been earlier used to study resonances in these systems
successfully. In this work, we find a resonance in the system with a
mass of MeV and with quantum numbers , .
We identify this state with the . This peak is found where the
energies of the sub-system fall in the region of the
resonance. We do not find evidence for the Roper resonance in our study
indicating a more complex structure for this resonance, nor for any state with
total isospin or
Observation of exclusive DVCS in polarized electron beam asymmetry measurements
We report the first results of the beam spin asymmetry measured in the
reaction e + p -> e + p + gamma at a beam energy of 4.25 GeV. A large asymmetry
with a sin(phi) modulation is observed, as predicted for the interference term
of Deeply Virtual Compton Scattering and the Bethe-Heitler process. The
amplitude of this modulation is alpha = 0.202 +/- 0.028. In leading-order and
leading-twist pQCD, the alpha is directly proportional to the imaginary part of
the DVCS amplitude.Comment: 6 pages, 5 figure
Complete measurement of three-body photodisintegration of 3He for photon energies between 0.35 and 1.55 GeV
The three-body photodisintegration of 3He has been measured with the CLAS
detector at Jefferson Lab, using tagged photons of energies between 0.35 GeV
and 1.55 GeV. The large acceptance of the spectrometer allowed us for the first
time to cover a wide momentum and angular range for the two outgoing protons.
Three kinematic regions dominated by either two- or three-body contributions
have been distinguished and analyzed. The measured cross sections have been
compared with results of a theoretical model, which, in certain kinematic
ranges, have been found to be in reasonable agreement with the data.Comment: 22 pages, 25 eps figures, 2 tables, submitted to PRC. Modifications:
removed 2 figures, improvements on others, a few minor modifications to the
tex
Measurement of the Deuteron Structure Function F2 in the Resonance Region and Evaluation of Its Moments
Inclusive electron scattering off the deuteron has been measured to extract
the deuteron structure function F2 with the CEBAF Large Acceptance Spectrometer
(CLAS) at the Thomas Jefferson National Accelerator Facility. The measurement
covers the entire resonance region from the quasi-elastic peak up to the
invariant mass of the final-state hadronic system W~2.7 GeV with four-momentum
transfers Q2 from 0.4 to 6 (GeV/c)^2. These data are complementary to previous
measurements of the proton structure function F2 and cover a similar
two-dimensional region of Q2 and Bjorken variable x. Determination of the
deuteron F2 over a large x interval including the quasi-elastic peak as a
function of Q2, together with the other world data, permit a direct evaluation
of the structure function moments for the first time. By fitting the Q2
evolution of these moments with an OPE-based twist expansion we have obtained a
separation of the leading twist and higher twist terms. The observed Q2
behaviour of the higher twist contribution suggests a partial cancellation of
different higher twists entering into the expansion with opposite signs. This
cancellation, found also in the proton moments, is a manifestation of the
"duality" phenomenon in the F2 structure function
eta-prime photoproduction on the proton for photon energies from 1.527 to 2.227 GeV
Differential cross sections for the reaction gamma p -> eta-prime p have been
measured with the CLAS spectrometer and a tagged photon beam with energies from
1.527 to 2.227 GeV. The results reported here possess much greater accuracy
than previous measurements. Analyses of these data indicate for the first time
the coupling of the etaprime N channel to both the S_11(1535) and P_11(1710)
resonances, known to couple strongly to the eta N channel in photoproduction on
the proton, and the importance of j=3/2 resonances in the process.Comment: 6 pages, 3 figure
First measurement of direct photoproduction on the proton
We report on the results of the first measurement of exclusive
meson photoproduction on protons for GeV and GeV. Data were collected with the CLAS detector at the Thomas
Jefferson National Accelerator Facility. The resonance was detected via its
decay in the channel by performing a partial wave analysis of the
reaction . Clear evidence of the meson
was found in the interference between and waves at GeV. The -wave differential cross section integrated in the mass range of
the was found to be a factor of 50 smaller than the cross section
for the meson. This is the first time the meson has been
measured in a photoproduction experiment
Measurement of the beam-helicity asymmetry in photoproduction of Ï0η pairs on carbon, aluminum, and lead
The beam-helicity asymmetry was measured, for the first time, in photoproduction of
Ï0η pairs on carbon, aluminum, and lead, with the A2 experimental setup at MAMI. The results are compared to an earlier measurement on a free proton and to the corresponding theoretical calculations. The Mainz model is used to predict the beam-helicity asymmetry for the nuclear targets. The present results indicate that the photoproduction mechanism for Ï0η pairs on nuclei is similar to photoproduction on a free nucleon. This process is dominated by the D33 partial wave with the ηÎ(1232) intermediate state
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