26374785
K+ Emission in Symmetric Heavy Ion Reactions at Subthreshold Energies.
Subthreshold {ital K}{sup +} production cross sections have been measured in symmetric Ne+NaF, Ni+Ni, and Au+Au collisions at 1.0{ital A} GeV. The mass dependence is strong, close to {ital A}{sup 2}. The angular distributions are nonisotropic in the center-of-mass system. Introducing rescattering seems to explain this effect to a large extent. {copyright} {ital 1996 The American Physical Society.}
126121197
Compton scattering at GRAAL
Preliminary results on the Compton scattering on the proton are presented in energy region around 1 GeV. Data are from the GRAAL facility: where a polarized γ—beam in the energy range of 500–1600 MeV is combined with a 4π detector having a very good energy resolution for photons.
122151633
Monte Carlo calculation of energy spectrum and spatial distribution of photons from positron annihilation
Abstract A Monte Carlo computing program has been used to calculate the photon spectrum and emittance from positron annihilation and bremsstrahlung. The positron energy spread, the energy loss and the multiple scattering in the annihilation target have been taken into account. Moreover, the positron emittance, the positron incidence angle and the finite angular acceptance of the photon collimation channel have been explicitly considered. Experimental results, obtained with a pair spectrometer and a beam profile monitor are in good agreement with calculations. In particular, it is shown that the positron emittance has a crucial influence on the shape of the photon spectrum and on the absolute value of the photon flux.
123367441
Meson photoproduction at GRAAL and baryon resonances
Differential cross sections and polarised photon beam asymmetries for eta, pi(0) and pi(1) photoproduction on the proton, produced by the GRAAL Collaboration, are presented. The results cover wide angular and enegy ranges of 40-170degrees and 550-1496 MeV (707-1496 MeV for eta) respectively, and exhibit an unprecedented level of accuracy. The results are compared with predictions of several models.
20890367
Limits on light-speed anisotropies from Compton scattering of high-energy electrons.
The possibility of anisotropies in the speed of light relative to the limiting speed of electrons is considered. The absence of sidereal variations in the energy of Compton-edge photons at the European Synchrotron Radiation Facility's GRAAL facility constrains such anisotropies representing the first nonthreshold collision-kinematics study of Lorentz violation. When interpreted within the minimal standard-model extension, this result yields the two-sided limit of 1.6×10(-14) at 95% confidence level on a combination of the parity-violating photon and electron coefficients (κ(o+))(YZ), (κ(o+))(ZX), c(TX), and c(TY). This new constraint provides an improvement over previous bounds by 1 order of magnitude.
53709037
GEM tracker for high luminosity experiments at the JLab Hall A
A new large-area, lightweight tracker based on the GEM technology is under development for the upcoming experiments in Hall A at Jefferson Lab, where a longitudinally polarized electron beam of 11 GeV will be available in late 2013. This beam, combined with innovative polarized targets, will provide luminosity up to 1039/(s⋅cm2) opening exciting opportunities to investigate unexplored aspects of the inner structure of the nucleon and the dynamics of its constituents. The GEM tracker design is presented in this paper.
38212869
Stochastic approach to inflation: Classicality conditions.
The stochastic approach to inflation relies on one key assumption, the emergence of a long-wave classical field that drives the inflation and is subject to a shortwave classical noise. In this work we consider explicitly the potential that acts on the inflaton field, and analyze classicality conditions that must be satisfied to have an effective classical stochastic approach. When these hold, the dynamics is given by a two-dimensional classical Fokker-Planck equation. We develop some examples, already widely considered in different approaches, and find a very suggestive result, which is the damping of the quantum fluctuations by the effect of the inflaton interaction potential. @S0556-2821~96!01624-4#