24752863
Au photofission cross section by quasimonochromatic photons in the intermediate energy region.
The photofission cross section of Au was determined in the energy range 100--300 MeV by means of a quasimonochromatic photon beam. The nuclear fissility P/sub f/ was calculated using the recently measured total photoabsorption cross sections. The nuclear excitation energy E/sup */, charge and mass of compound nucleus were obtained by means of an intranuclear cascade Monte Carlo calculation. The fissility values determined for Au, Bi, and U were compared with the predictions of the cascade-evaporation model and remarkably fitted by the calculation.
120454281
Energy dependence of the nuclear fissility for Bi, Pb, Au and Pt at photon energies below 1000 MeV
121090511
PHOTOPRODUCTION EXPERIMENTS WITH POLARIZED HD TARGETS
Within the French-Italian GRAAL collaboration, we have constructed a Polarized HD Target Factory (HYDILE), implanted at IPN Orsay. This project is very similar to the SPHICE one existing at BNL, and developed within the LEGS Spill Collaboration. The expected properties of the HD targets and the results already obtained for the polarization of HD samples at Orsay and BNL are given. New possibilities to measure polarization observables oil the proton, the neutron and the deuteron are now opened. Most simple and double polarization measurements for the photoproduction of the low mass pseudoscalar and vector mesons could be performed, by using the high polarization (linear or circular) of the backscattered photon beams and the large effective polarization (longitudinal or tranverse) of the target, resulting essentially, from the good dilution factor. Polarized total cross sections concerning the isovector Drell-Hearn Gerasimov Sum Rule related to the proton neutron difference, could be measured with minimum systematic uncertainties: the target containing both polarized protons and neutrons. By using the available polarized photon beams from LEGS, GRAAL and Spring-8, measurements could be done from the pi meson threshold up to 2.5 Gev, where the pi meson photoproduction cross section is close to its maximum value. Typical examples are given for GRAAL and Spring-8.
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.
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.
10205186
Simultaneous photoproduction of eta and pi0 mesons on the proton.
The analysis of the gammap-->etapi(0)p reaction has been performed using data from the GRAAL experiment. The total and differential cross sections and the beam asymmetry have been obtained from threshold up to 1.5 GeV of beam energy. The two resonances S11(1535) and Delta(1700) are expected to be excited in the intermediate states of this reaction. The results are used to test predictions based on the assumption that both resonances are dynamically generated from the meson-baryon interaction provided by chiral Lagrangians. The term involving the Delta(1700) excitation, followed by the decay into etaDelta(1232), is found to be dominant.
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#