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Cross Section Measurement of the Process [gamma Gamma->p Pbar] in Untagged Events at [sqrt](s)

Author : Teresa Barillari

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Page : 129 pages

File Size : 40,31 MB

Release : 2001

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Le collisioneur LEP au CERN est utilisé pour étudier les collisions de deux photons quasi-réels e+e−->e+e−[gamma gamma]->e+e−X. L'échantillon de données pour la réaction e+e−->e+e−[gamma gamma]->e+e− [p pbar] a été collecté par le détecteur OPAL à une énergie dans le centre de masse de [sqrt](s)=183 et 189 GeV. Le processus [gamma gamma]->[p pbar] permet de tester les prédictions fournies par QED et QCD. Les mesures de section efficace obtenues par OPAL couvrent une région du centre de masse de deux photons, "W", entre 2.15 GeV"W"3.95 GeV et l'angle polaire dans le centre de masse du système [gamma gamma]-[p pbar] est restreint à I(cos theta*)I













Determination of the Pi0 Gamma Cross-section

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Page : 21 pages

File Size : 47,83 MB

Release : 1992

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In this memo the authors address the following questions: how the [pi]°[gamma] cross section, which is measured in E760, compares to the expected leakage from the [pi]°[pi]° final states; is it possible to affirm that a substantial fraction of the [pi]°[gamma] events are due to continuum production? Naively, the expected continuum [pi]°[gamma] cross section can be estimated using the Vector Meson Dominance Model (VDM). In that framework, a photon is coupled to a neutral vector meson V by G{sub [gamma]V}. Then [sigma]{sub [pi]°[gamma]} = [sigma]{sub [pi]°[rho]} x G{sub [gamma][rho]}2 with G{sub [gamma][rho]}2 = 1./160 ÷ 1./380 [1]. At E{sub CM} = 2.611 GeV, [sigma]{sub [pi]°[rho]} = (70 ± 30)[mu]b [2] which gives [sigma]{sub [pi]°{gamma}} = 184 ÷ 438 nb. To predict the cross section within a limited acceptance they assume that the angular production of [pi]°{gamma} is similar to the [pi]°[pi]° and [pi]°[rho] ones. To estimate the fraction of events with



A Measurement of the Differential Cross Section for the Reaction $\gamma N \to \pi^{-} P$ from Deuterium

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Page : pages

File Size : 50,96 MB

Release : 2009

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We report a measurement of the differential cross section for the $\gamma n \to \pi^- p$ process from the CLAS detector at Jefferson Lab in Hall B for photon energies between 1.0 and 3.5 GeV and pion center-of-mass (c.m.) angles ($\theta_{c.m.}$) between 50$^\circ$ and 115$^\circ$. We confirm a previous indication of a broad enhancement around a c.m. energy ($\sqrt{s}$) of 2.2 GeV at $\theta_{c.m.}=90^\circ$ in the scaled differential cross section, $s^7 {\frac{d\sigma}{dt}}$. Our data show the angular dependence of this enhancement as the scaling region is approached in the kinematic region from 70$^\circ$ to 105$^\circ$.



Quasi-free Cross Section Measurements at CLAS

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Page : 5 pages

File Size : 48,75 MB

Release : 2014

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Preliminary measurements of the quasi-free differential cross sections of the gD -->pp-(p), gD --> K*(892)0L(p), and gD --> K+S*(1385)-(p) reactions are shown using data from the Jefferson Lab Hall B CLAS g13 experiment. No experimental cross section data have yet been published on gD --> K*(892)0L(p), and the only published cross section data on gD --> K+S*(1385)-(p) are at forward angles, where t-channel K+ and K*+ exchanges are predicted to dominate. These data can be used to contribute to the search for the "missing" N* resonances, some of which are predicted to have non-negligible couplings to the excited strangeness channels. These cross sections are shown to be sizable compared to the ground-state channels, indicating that it is important to include excited channels in coupled-channels analyses used to extract the N* resonances. In addition, the gD --> pp-(p) data provide a significant increase to the world statistics, and will be used to study rescattering effects within the deuteron.