47 research outputs found
Comment on the narrow structure reported by Amaryan et al
The CLAS Collaboration provides a comment on the physics interpretation of
the results presented in a paper published by M. Amaryan et al. regarding the
possible observation of a narrow structure in the mass spectrum of a
photoproduction experiment.Comment: to be published in Physical Review
Differential cross sections and recoil polarizations for the reaction gamma p -> K+ Sigma0
High-statistics measurements of differential cross sections and recoil
polarizations for the reaction have been
obtained using the CLAS detector at Jefferson Lab. We cover center-of-mass
energies () from 1.69 to 2.84 GeV, with an extensive coverage in the
production angle. Independent measurements were made using the
() and () final-state topologies,
and were found to exhibit good agreement. Our differential cross sections show
good agreement with earlier CLAS, SAPHIR and LEPS results, while offering
better statistical precision and a 300-MeV increase in coverage.
Above GeV, - and -channel Regge scaling behavior
can be seen at forward- and backward-angles, respectively. Our recoil
polarization () measurements represent a substantial increase in
kinematic coverage and enhanced precision over previous world data. At forward
angles we find that is of the same magnitude but opposite sign as
, in agreement with the static SU(6) quark model prediction of
. This expectation is violated in some mid- and
backward-angle kinematic regimes, where and are of
similar magnitudes but also have the same signs. In conjunction with several
other meson photoproduction results recently published by CLAS, the present
data will help constrain the partial wave analyses being performed to search
for missing baryon resonances.Comment: 23 pages, 17 figure
Differential cross section and recoil polarization measurements for the gamma p to K+ Lambda reaction using CLAS at Jefferson Lab
We present measurements of the differential cross section and Lambda recoil
polarization for the gamma p to K+ Lambda reaction made using the CLAS detector
at Jefferson Lab. These measurements cover the center-of-mass energy range from
1.62 to 2.84 GeV and a wide range of center-of-mass K+ production angles.
Independent analyses were performed using the K+ p pi- and K+ p (missing pi -)
final-state topologies; results from these analyses were found to exhibit good
agreement. These differential cross section measurements show excellent
agreement with previous CLAS and LEPS results and offer increased precision and
a 300 MeV increase in energy coverage. The recoil polarization data agree well
with previous results and offer a large increase in precision and a 500 MeV
extension in energy range. The increased center-of-mass energy range that these
data represent will allow for independent study of non-resonant K+ Lambda
photoproduction mechanisms at all production angles.Comment: 22 pages, 16 figure
Absorption of the and Mesons in Nuclei
Due to their long lifetimes, the and mesons are the ideal
candidates for the study of possible modifications of the in-medium
meson-nucleon interaction through their absorption inside the nucleus. During
the E01-112 experiment at the Thomas Jefferson National Accelerator Facility,
the mesons were photoproduced from H, C, Ti, Fe, and Pb targets. This
paper reports the first measurement of the ratio of nuclear transparencies for
the channel. The ratios indicate larger in-medium widths compared
with what have been reported in other reaction channels.Comment: 6 pages, 4 figure
Coherent Photoproduction of pi^+ from 3^He
We have measured the differential cross section for the
He reaction. This reaction was studied using
the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. Real photons
produced with the Hall-B bremsstrahlung tagging system in the energy range from
0.50 to 1.55 GeV were incident on a cryogenic liquid He target. The
differential cross sections for the He
reaction were measured as a function of photon-beam energy and pion-scattering
angle. Theoretical predictions to date cannot explain the large cross sections
except at backward angles, showing that additional components must be added to
the model.Comment: 11 pages, 16 figure
Near-threshold Photoproduction of Phi Mesons from Deuterium
We report the first measurement of the differential cross section on
-meson photoproduction from deuterium near the production threshold for a
proton using the CLAS detector and a tagged-photon beam in Hall B at Jefferson
Lab. The measurement was carried out by a triple coincidence detection of a
proton, and near the theoretical production threshold of 1.57 GeV.
The extracted differential cross sections for the initial
photon energy from 1.65-1.75 GeV are consistent with predictions based on a
quasifree mechanism. This experiment establishes a baseline for a future
experimental search for an exotic -N bound state from heavier nuclear
targets utilizing subthreshold/near-threshold production of mesons
Measurement of the nuclear multiplicity ratio for hadronization at CLAS
The influence of cold nuclear matter on lepto-production of hadrons in
semi-inclusive deep inelastic scattering is measured using the CLAS detector in
Hall B at Jefferson Lab and a 5.014 GeV electron beam. We report the
multiplicity ratios for targets of C, Fe, and Pb relative to deuterium as a
function of the fractional virtual photon energy transferred to the
and the transverse momentum squared of the . We find that the
multiplicity ratios for are reduced in the nuclear medium at high
and low , with a trend for the transverse momentum to be
broadened in the nucleus for large .Comment: Submitted to Phys. Lett.
Transverse Polarization of in Photoproduction on a Hydrogen Target in CLAS
Experimental results on the hyperon transverse polarization
in photoproduction on a hydrogen target using the CLAS detector at Jefferson
laboratory are presented. The was reconstructed in the
exclusive reaction via the
decay mode. The was reconstructed in the
invariant mass of two oppositely charged pions with the identified in
the missing mass of the detected final state. Experimental data
were collected in the photon energy range = 1.0-3.5 GeV
( range 1.66-2.73 GeV). We observe a large negative polarization of
up to 95%. As the mechanism of transverse polarization of hyperons produced in
unpolarized photoproduction experiments is still not well understood, these
results will help to distinguish between different theoretical models on
hyperon production and provide valuable information for the searches of missing
baryon resonances.Comment: pages 1
Cross sections for the γp→K*+Λ and γp→K*+Σ0 reactions measured at CLAS
The first high-statistics cross sections for the reactions γp→K*+Λ and γp→K*+Σ0 were measured using the CLAS detector at photon energies between threshold and 3.9 GeV at the Thomas Jefferson National Accelerator Facility. Differential cross sections are presented over the full range of the center-of-mass angles, and then fitted to Legendre polynomials to extract the total cross section. Results for the K*+Λ final state are compared with two different calculations in an isobar and a Regge model, respectively. Theoretical calculations significantly underestimate the K*+Λ total cross sections between 2.1 and 2.6 GeV, but are in better agreement with present data at higher photon energies
Precision measurements of of the proton and the deuteron with 6 GeV electrons
The inclusive polarized structure functions of the proton and deuteron, g1p
and g1d, were measured with high statistical precision using polarized 6 GeV
electrons incident on a polarized ammonia target in Hall B at Jefferson
Laboratory. Electrons scattered at lab angles between 18 and 45 degrees were
detected using the CEBAF Large Acceptance Spectrometer (CLAS). For the usual
DIS kinematics, Q^2>1 GeV^2 and the final-state invariant mass W>2 GeV, the
ratio of polarized to unpolarized structure functions g1/F1 is found to be
nearly independent of Q^2 at fixed x. Significant resonant structure is
apparent at values of W up to 2.3 GeV. In the framework of perturbative QCD,
the high-W results can be used to better constrain the polarization of quarks
and gluons in the nucleon, as well as high-twist contributions