Search results for "Cross Section"
showing 10 items of 3111 documents
Development of a PbWO 4 detector for single-shot positron annihilation lifetime spectroscopy at the GBAR experiment
2020
International audience; We have developed a PbWO 4 (PWO) detector with a large dynamic range to measure the intensity of a positron beam and the absolute density of the ortho-positronium (o-Ps) cloud it creates. A simulation study shows that a setup based on such detectors may be used to determine the angular distribution of the emission and reflection of o-Ps to reduce part of the uncertainties of the measurement. These will allow to improve the precision in the measurement of the cross section for the (anti) hydrogen formation by (anti) proton-positronium charge exchange and to optimize the yield of antihydrogen ion which is an essential parameter in the GBAR experiment.
Ratio of Isolated Photon Cross Sections in pp¯ Collisions at √s=630 and 1800 GeV
2001
The inclusive cross section for production of isolated photons has been measured in p (p) over bar collisions at roots = 630 GeV with the DO detector at the Fermilab Tevatron Collider. The photons span a transverse energy (E-T) range from 7-49 GeV and have pseudorapidity \eta\ s = 1800 GeV to form a ratio of the cross sections. Comparison of next-to-leading-order QCD with the measured cross section at 630 GeV and the ratio of cross sections show satisfactory agreement in most of the E-T range.
Quark effects, meson-exchange currents and background in the d(e,e'p)delta reaction
1994
[EN] We have studied in detail the cross section for the d(e, e'p)Delta reaction leading to the emission of a fast nucleon and a Delta at rest, which has been advocated as a tool to investigate quark effects in nuclei. We find that ordinary meson-exchange currents mechanisms dominate the quark-exchange effects in the region of excitation of the Delta and could be competitive at higher energies. Furthermore, at these higher energies, the small cross sections for the quark signal, together with the presence of a background about one order of magnitude bigger than the quark signal, make in any case the extraction of information about quark-exchange currents effects extraordinarily difficult.
Implications for relic neutralinos of the theoretical uncertainties in the neutralino-nucleon cross section
1999
We discuss the effect induced on the neutralino-nucleon cross-section by the present uncertainties in the values of the quark masses and of the quark scalar densities in the nucleon. We examine the implications of this aspect on the determination of the neutralino cosmological properties, as derived from measurements of WIMP direct detection. We show that, within current theoretical uncertainties, the DAMA annual modulation data are compatible with a neutralino as a major dark matter component, to an extent which is even larger than the one previously derived. We also comment on implications of the mentioned uncertainties for experiments of indirect dark matter detection.
Studies of inelastic cross-section in Rb(7S) + Rb(5S) collisions
1996
The cross section σ = (8 ± 4) × 10−15 cm2 was determined for the Rb(7S) + Rb(5S) → Rb(5D) + Rb(5S) excitation energy transfer process, and the quenching cross section σq = (2 ± 1) × 10−14 cm2 for the Rb(5D) state in collisions with ground state Rb atoms. Applying rubidium quasimolecular asymptotic potential curves at relatively large internuclear distances, a qualitative interpretation of the experimental results is presented. It is shown that the quenching of the Rb(5D) atoms in collisions may be explained by a reversed energy pooling process Rb(5D) + Rb(5S) → Rb(5P) + Rb(5P).
Determination of ion-induced K-shell ionization cross sections by comparison with nuclear Coulomb excitation
1979
Abstract A new method for the determination of cross sections for K-shell ionization of heavy atoms by charged particles is proposed. The method is based on a comparison of photon lines due to K X-rays and low-energy γ-rays, the latter ones being produced in nuclear Coulomb excitation with accurately known cross sections. This procedure applies within a limited energy range to the study of targets comprising deformed even nuclei, but can also be extended to other targets having Z≳30. A test of the new technique has been carried out for Gd, W, Th and U natural targets irradiated by 4.75 MeV protons. For Th, also energies of 6.80–10.10 MeV were used. The results are briefly discussed with ref…
Energy transfer reaction K(4s) + K(7s) → K(4s) + K(5f), theory compared with experiment
2019
Abstract A comparison between theory and experiment, concerning the K(4 s) + K(7s)→K(4 s) + K(5f) reaction of excitation energy transfer in thermal collisions, is presented. The cross sections for this process are calculated for the potassium vapour temperatures in the range of 310–1000 K. The calculations are based on the theoretical adiabatic K2 potential energy curves and on the use of the multicrossing Landau-Zener model. The experiment was carried out using the method of spectroscopy with resolution in time. The signals of the direct-fluorescence decay from pulsed-laser-excited 7s state, and of the sensitized-fluorescence from 5f state, were registered and analysed. In the temperature …
Electro-kinetics of charged-sphere suspensions explored by integral low-angle super-heterodyne laser Doppler velocimetry
2012
We investigated the flow behaviour of colloidal charged-sphere suspensions using a newly designed integral low-angle super-heterodyne laser Doppler velocimetry instrument, which combines the advantages of several previous approaches. Sample conditions ranged from strong electrostatic interactions with pronounced short-range order to individual particles with no spatial correlations. The obtained power spectra correspond to diffusion broadened velocity distributions across the complete sample cross section. The excellent performance of the instrument is highlighted in detail by the example of electro-kinetic flow of suspensions in a closed cell of a rectangular cross section. We demonstrate …
Near-threshold $\pi^-$ photoproduction on the deuteron
2018
The first experimental investigation of the near-threshold cross section for incoherent $\pi^-$ photoproduction on the deuteron $\gamma$ d -> $\pi^-$ pp is presented. The experimental technique involved detection of the ~131 MeV gamma ray resulting from the radiative capture of photoproduced $\pi^-$ in the target. The total cross section has been measured using an unpolarized tagged-photon beam, a liquid-deuterium target, and three very large NaI(Tl) spectrometers. The data are compared to theoretical models that give insight into the elementary reaction $\gamma$ n -> $\pi^-$ p and pion-nucleon and nucleon-nucleon final-state interactions.
Total photoabsorption cross section for4He from 200 to 800 MeV
1997
The total photoabsorption cross section for ${}^{4}$He has been measured for the first time over a wide photon energy range (200 MeV$l~{E}_{\ensuremath{\gamma}}l~$800 MeV). By using the large acceptance detector DAPHNE at the tagged photon facility of the MAMI microtron in Mainz high precision results with small systematic errors were obtained. This measurement shows that ${}^{4}$He has a behavior similar to heavy nuclei and, in particular, a reduction of the cross section with respect to the lighter nuclei is found for ${E}_{\ensuremath{\gamma}}g$600 MeV.