229 research outputs found
Longitudinal Target-Spin Asymmetries for Deeply Virtual Compton Scattering
A measurement of the electroproduction of photons off protons in the deeply inelastic regime was performed at Jefferson Lab using a nearly 6 GeV electron beam, a longitudinally polarized proton target, and the CEBAF Large Acceptance Spectrometer. Target-spin asymmetries for ep. e\u27p\u27gamma. events, which arise from the interference of the deeply virtual Compton scattering and the Bethe-Heitler processes, were extracted over the widest kinematics in Q(2), x(B), t, and phi, for 166 four-dimensional bins. In the framework of generalized parton distributions, at leading twist the t dependence of these asymmetries provides insight into the spatial distribution of the axial charge of the proton, which appears to be concentrated in its center. These results also bring important and necessary constraints for the existing parametrizations of chiral-even generalized parton distributions
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Preliminary site report for the 2005 ICDP-USGS deep corehole in the Chesapeake Bay impact crater
First report for the ICDP-USGS 1.7-km-deep corehole drilled into the central part of the Chesapeake Bay impact crater during 2005
Design and Performance of SiPM-Based Readout of PbF\u3csub\u3e2\u3c/sub\u3e Crystals for High-Rate, Precision Timing Applications
We have developed a custom amplifier board coupled to a large-format 16-channel Hamamatsu silicon photomultiplier device for use as the light sensor for the electromagnetic calorimeters in the Muon g - 2 experiment at Fermilab. The calorimeter absorber is an array of lead-fluoride crystals, which produces short-duration Cherenkov light. The detector sits in the high magnetic field of the muon storage ring. The SiPMs selected, and their accompanying custom electronics, must preserve the short pulse shape, have high quantum efficiency, be non-magnetic, exhibit gain stability under varying rate conditions, and cover a fairly large fraction of the crystal exit surface area. We describe an optimized design that employs the new-generation of thru-silicon via devices. The performance is documented in a series of bench and beam tests
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
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
Studies of an array of PbF2 Cherenkov crystals with large-area SiPM readout
The electromagnetic calorimeter for the new muon (g-2) experiment at Fermilab
will consist of arrays of PbF2 Cherenkov crystals read out by large-area
silicon photo-multiplier (SiPM) sensors. We report here on measurements and
simulations using 2.0 -- 4.5 GeV electrons with a 28-element prototype array.
All data were obtained using fast waveform digitizers to accurately capture
signal pulse shapes versus energy, impact position, angle, and crystal
wrapping. The SiPMs were gain matched using a laser-based calibration system,
which also provided a stabilization procedure that allowed gain correction to a
level of 1e-4 per hour. After accounting for longitudinal fluctuation losses,
those crystals wrapped in a white, diffusive wrapping exhibited an energy
resolution sigma/E of (3.4 +- 0.1) % per sqrt(E/GeV), while those wrapped in a
black, absorptive wrapping had (4.6 +- 0.3) % per sqrt(E/GeV). The
white-wrapped crystals---having nearly twice the total light
collection---display a generally wider and impact-position-dependent pulse
shape owing to the dynamics of the light propagation, in comparison to the
black-wrapped crystals, which have a narrower pulse shape that is insensitive
to impact position.Comment: 14 pages, 19 figures, accepted to Nucl.Instrum.Meth. A. In v2, edited
Figures 14,15, and 17 for clarity, improved explanation of energy resolution
systematics, added reference to SiP
Target and beam-target spin asymmetries in exclusive pion electroproduction for Q2>1GeV2 . I. epâeÏ+n
Beam-target double-spin asymmetries and target single-spin asymmetries were measured for the exclusive
Ï
+
electroproduction reaction
Îł
â
p
â
n
Ï
+
. The results were obtained from scattering of 6-GeV longitudinally polarized electrons off longitudinally polarized protons using the CEBAF Large Acceptance Spectrometer at Jefferson Laboratory. The kinematic range covered is
1.1
<
W
<
3
GeV and
1
<
Q
2
<
6
GeV
2
. Results were obtained for about 6000 bins in
W
,
Â
Q
2
,
Â
cos
(
Ξ
â
)
, and
Ï
â
. Except at forward angles, very large target-spin asymmetries are observed over the entire
W
region. Reasonable agreement is found with phenomenological fits to previous data for
W
<
1.6
GeV, but very large differences are seen at higher values of
W
. A generalized parton distributions (GPD)-based model is in poor agreement with the data. When combined with cross-sectional measurements, the present results provide powerful constraints on nucleon resonance amplitudes at moderate and large values of
Q
2
, for resonances with masses as high as 2.4 GeV
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
Measurement of the neutron F2 structure function via spectator tagging with CLAS
We report on the first measurement of the F2 structure function of the
neutron from semi-inclusive scattering of electrons from deuterium, with
low-momentum protons detected in the backward hemisphere. Restricting the
momentum of the spectator protons to < 100 MeV and their angles to < 100
degrees relative to the momentum transfer allows an interpretation of the
process in terms of scattering from nearly on-shell neutrons. The F2n data
collected cover the nucleon resonance and deep-inelastic regions over a wide
range of Bjorken x for 0.65 < Q2 < 4.52 GeV2, with uncertainties from nuclear
corrections estimated to be less than a few percent. These measurements provide
the first determination of the neutron to proton structure function ratio
F2n/F2p at 0.2 < x < 0.8 with little uncertainty due to nuclear effects.Comment: 6 pages, 3 page
A comparison of forward and backward pp pair knockout in 3He(e,e'pp)n
Measuring nucleon-nucleon Short Range Correlations (SRC) has been a goal of
the nuclear physics community for many years. They are an important part of the
nuclear wavefunction, accounting for almost all of the high-momentum strength.
They are closely related to the EMC effect. While their overall probability has
been measured, measuring their momentum distributions is more difficult. In
order to determine the best configuration for studying SRC momentum
distributions, we measured the He reaction, looking at events
with high momentum protons ( GeV/c) and a low momentum neutron
( GeV/c). We examined two angular configurations: either both protons
emitted forward or one proton emitted forward and one backward (with respect to
the momentum transfer, ). The measured relative momentum distribution
of the events with one forward and one backward proton was much closer to the
calculated initial-state relative momentum distribution, indicating that
this is the preferred configuration for measuring SRC.Comment: 8 pages, 9 figures, submitted to Phys Rev C. Version 2 incorporates
minor corrections in response to referee comment
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