447730
eta meson photoproduction on hydrogen near threshold.
The total cross section for {gamma}{ital p}{r_arrow}{eta}{ital p} near threshold has been measured using the PHOENICS tagging system at the ELSA electron facility of the Physikalisches Institut der Universitaet Bonn. The photons are created by bremsstrahlung, and are tagged by measuring the momentum of each electron after the photon has been emitted. The recoil proton from {gamma}{ital p}{r_arrow}{eta}{ital p} is detected by the AMADEUS counter setup in coincidence with the tagging system. Data were taken with AMADEUS at 3.3{degree} in the laboratory, where the large Jacobian increases our event rate so that we obtain the cross section from threshold ({ital E}{sub {gamma}}=707.2 MeV) to {ital E}{sub {gamma}}{congruent}720 MeV with adequate statistics. The {gamma}{ital p}{r_arrow}{eta}{ital p} events are identified by kinematics, {ital dE}/{ital dx}, and timing information. We find that in our energy region the production cross section is consistent with {ital S}-wave production.
120150278
Results from CEBAF experiment E89-012: Measurements of deuteron photo-disintegration up to 4 GeV
The first measurements of differential cross sections for deuteron photo-disintegration at photon energies up to 4 GeV were performed at the Thomas Jefferson National Accelerator Facility early in 1996. Cross section results for D(γ,p)n at proton center of mass angle of 35°, 53° and 90° will be presented. These results are in good agreement with previous measurements at low energy and extend to higher energies where data were previously unavailable. The 90° degree data show behavior consistent with the constituent counting rules up to 4 GeV and are also in fair agreement with the asymptotic meson exchange model. The 37° and 53° data do not show clear signs of counting rule behavior, although a threshold in transverse momentum for the onset of scaling cannot be excluded.
53627708
Measurement of beam-spin asymmetries for π+ electroproduction above the baryon resonance region
We report the first evidence for a nonzero beam-spin azimuthal asymmetry in the electroproduction of positive pions in the deep-inelastic kinematic region. Data for the reaction ep→e'pi(+)X have been obtained using a polarized electron beam of 4.3 GeV with the CEBAF Large Acceptance Spectrometer at the Thomas Jefferson National Accelerator Facility. The amplitude of the sin phi modulation increases with the momentum of the pion relative to the virtual photon, z. In the range z=0.5-0.8 the average amplitude is 0.038+/-0.005+/-0.003 for a missing mass M-X gt 1.1 GeV and 0.037+/-0.007+/-0.004 for M-X gt 1.4 GeV
2754667
The Neutral Decay Modes of the Eta-Meson
The neutral decay modes of the η meson are reviewed. The most recent results obtained with the Crystal Ball multiphoton detector at BNL are incorporated. This includes a new, precise result for the slope parameter α of the Dalitz plot in η → 3π0 decay and a new, lower branching ratio for η → π0γγ which is consistent with chiral perturbation theory. Recently-obtained limits are given for novel tests of CP and C invariance based on several rare η decays.
621293
Observation of an exotic S = +1 baryon in exclusive photoproduction from the deuteron.
In an exclusive measurement of the reaction gammad-->K(+)K(-)pn, a narrow peak that can be attributed to an exotic baryon with strangeness S=+1 is seen in the K(+)n invariant mass spectrum. The peak is at 1.542+/-0.005 GeV/c(2) with a measured width of 0.021 GeV/c(2) FWHM, which is largely determined by experimental mass resolution. The statistical significance of the peak is (5.2+/-0.6)sigma. The mass and width of the observed peak are consistent with recent reports of a narrow S=+1 baryon by other experimental groups.
126150572
First measurement of the double spin asymmetry in polarized-e polarized-p —> e-prime pi+ n in the resonance region
16181352
Escape of gravitational radiation from the field of massive bodies.
We consider a compact source of gravitational waves of frequency omega in or near a massive spherically symmetric distribution of matter or a black hole. Recent calculations have led to apparently contradictory results for the influence of the massive body on the propagation of the waves. We show here that the results are in fact consistent and in agreement with the 'standard' viewpoint in which the high-frequency compact source produces the radiation as if in a flat background, and the background curvature affects the propagation of these waves.