78 research outputs found
Measurement of Deeply Virtual Compton Scattering with a Polarized Proton Target
The longitudinal target-spin asymmetry A_UL for the exclusive
electroproduction of high energy photons was measured for the first time in
p(e,e'p\gamma). The data have been accumulated at Jefferson Lab with the CLAS
spectrometer using 5.7 GeV electrons and a longitudinally polarized NH_3
target. A significant azimuthal angular dependence was observed, resulting from
the interference of the Deeply Virtual Compton Scattering and Bethe-Heitler
processes. The amplitude of the sin(phi) moment is 0.252 +/- 0.042(stat) +/-
0.020(sys). Theoretical calculations are in good agreement with the magnitude
and the kinematic dependence of the target-spin asymmetry, which is sensitive
to the generalized parton distributions H and H-tilde.Comment: Modified text slightly, added reference
Beam Spin Asymmetries in DVCS with CLAS at 4 .8 GeV
We report measurements of the beam spin asymmetry in Deeply Virtual Compton
Scattering (DVCS) at an electron beam energy of 4.8 GeV using the CLAS detector
at the Thomas Jefferson National Accelerator Facility. The DVCS beam spin
asymmetry has been measured in a wide range of kinematics, 1(GeV/c)
(GeV/c), , and 0.1 (GeV/c)
(GeV/c), using the reaction \pEpX. The number of
H and H events are separated in
each bin by a fit to the line shape of the H
distribution. The validity of the method was studied in detail using
experimental and simulated data. It was shown, that with the achieved missing
mass squared resolution and the available statistics, the separation of DVCS-BH
and events can reliably be done with less than 5% uncertainty. The
- and -dependences of the moments of the asymmetry are
extracted and compared with theoretical calculations
Measurement of the N to Delta(1232) Transition at High Momentum Transfer by pi0 Electroproduction
We report a new measurement of the exclusive electroproduction reaction
gamma* p -> pi0 p to explore the evolution from soft non-perturbative physics
to hard processes via the Q2 dependence of the magnetic (M1+), electric (E1+)
and scalar (S1+) multipoles in the N to Delta transition. 9000 differential
cross section data points cover W from threshold to 1.4 eV/c2, 4pi
center-of-mass solid angle, and Q2 from 3 to 6 GeV2/c2, the highest yet
achieved. It is found that the magnetic form factor G*M decreases with Q2 more
steeply than the proton magnetic form factor, the ratio E1+/M1+ is small and
negative, indicating strong helicity non-conservation, and the ratio S1+/M1+ is
negative, while its magnitude increases with Q2
Measurement of unpolarized semi-inclusive pi+ electroproduction off the proton
Semi-inclusive pi+ electroproduction on protons has been measured with the
CLAS detector at Jefferson Lab. The measurement was performed on a
liquid-hydrogen target using a 5.75 GeV electron beam. The complete five-fold
differential cross sections were measured over a wide kinematic range including
the complete range of azimuthal angles between hadronic and leptonic planes,
phi, enabling us to separate the phi-dependent terms. Our measurements of
phi-independent term of the cross section at low Bjorken x were found to be in
fairly good agreement with pQCD calculations. Indeed, the conventional current
fragmentation calculation can account for almost all of the observed cross
section, even at small pi+ momentum. The measured center-of-momentum spectra
are in qualitative agreement with high energy data, which suggests a surprising
numerical similarity between the spectator diquark fragmentation in the present
reaction and the anti-quark fragmentation measured in e+e- collisions. We have
observed that the two phi-dependent terms of the cross section are small.
Within our precision the cos(2phi) term is compatible with zero, except for
low-z region, and the measured cos(phi) term is much smaller in magnitude than
the sum of the Cahn and Berger effects.Comment: 42 pages, 30 figure
Search for the photo-excitation of exotic mesons in the pi+pi+pi- system
A search for exotic mesons in the system
photoproduced by the charge exchange reaction was carried out by the CLAS collaboration at
Jefferson Lab. A tagged-photon beam with energies in the 4.8 to 5.4 GeV range,
produced through bremsstrahlung from a 5.744 GeV electron beam, was incident on
a liquid-hydrogen target. A Partial Wave Analysis (PWA) was performed on a
sample of 83,000 events, the highest such statistics to date in this reaction
at these energies. The main objective of this study was to look for the
photoproduction of an exotic resonant state in the 1 to 2 GeV
mass range. Our PWA analysis, based on the isobar model, shows production of
the and the mesons, but no evidence for the
, nor the exotic state at the expected levels. An
upper limit of 13.5 nb is determined for the exotic cross
section, less than 2% of the production.Comment: 6 pages, 5 figures, to be submitted to Phys.Rev.Let
The Effect of Isoleucine Supplementation on Body Weight Gain and Blood Glucose Response in Lean and Obese Mice
Chronic isoleucine supplementation prevents diet-induced weight gain in rodents. Acute-isoleucine administration improves glucose tolerance in rodents and reduces postprandial glucose levels in humans. However, the effect of chronic-isoleucine supplementation on body weight and glucose tolerance in obesity is unknown. This study aimed to investigate the impact of chronic isoleucine on body weight gain and glucose tolerance in lean and high-fat-diet (HFD) induced-obese mice. Male C57BL/6-mice, fed a standard-laboratory-diet (SLD) or HFD for 12 weeks, were randomly allocated to: (1) Control: Drinking water; (2) Acute: Drinking water with a gavage of isoleucine (300 mg/kg) prior to the oral-glucose-tolerance-test (OGTT) or gastric-emptying-breath-test (GEBT); (3) Chronic: Drinking water with 1.5% isoleucine, for a further six weeks. At 16 weeks, an OGTT and GEBT was performed and at 17 weeks metabolic monitoring. In SLD- and HFD-mice, there was no difference in body weight, fat mass, and plasma lipid profiles between isoleucine treatment groups. Acute-isoleucine did not improve glucose tolerance in SLD- or HFD-mice. Chronic-isoleucine impaired glucose tolerance in SLD-mice. There was no difference in gastric emptying between any groups. Chronic-isoleucine did not alter energy intake, energy expenditure, or respiratory quotient in SLD- or HFD-mice. In conclusion, chronic isoleucine supplementation may not be an effective treatment for obesity or glucose intolerance
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