1,994 research outputs found
Q^2-Dependence of the Drell-Hearn-Gerasimov integral
The energy and four-momentum (Q^2) dependence of the photo-absorption cross
section on the proton is calculated for helicity -1/2 and -3/2 states. An
effective Lagrangian model is used, formulated in terms of meson and baryon
degrees of freedom, which obeys crossing symmetry, unitarity, Lorentz and gauge
invariance. The difference in the cross sections for the two helicity states,
the Drell-Hearn-Gerasimov integral , is evaluated at different
. We find that at small momentum transfer the absolute value of
first increases to reach a maximum at
before decreasing at higher .Comment: 8 pages, 3 figures, revte
On electromagnetic off-shell effects in proton-proton bremsstrahlung
We study the influence of the off-shell structure of the nucleon
electromagnetic vertex on proton-proton bremsstrahlung observables. Realistic
choices for these off-shell effects are found to have considerable influences
on observables such as cross sections and analyzing powers. The rescattering
contribution diminishes the effects of off-shell modifications in
negative-energy states.Comment: 7 pages, 3 figure
Channel coupling effects in -meson photoproduction
We investigate -meson photoproduction in a coupled-channels
formulation. It is shown that channel coupling effects are large and account
for discrepancies observed in several single-channel treatments.Comment: 8 pages, 5 figures; small textual corrections and notation change
K-Lambda and K-Sigma photoproduction in a coupled channels framework
A coupled channels analysis, based on the K-matrix approach, is presented for
photo-induced kaon production. It is shown that channel coupling effects are
large and should not be ignored. The importance of contact terms in the
analysis, associated with short range correlations, is pointed out. The
extracted parameters are compared with SU(3)-model predictions.Comment: 15 pages, 10 figures; Submitted to Physical Review C. v2: A figure
showing the effect of P13(1900) added v3: Small spelling corrections, one
reference update
Semi-inclusive cross sections for deep-inelastic neutrino scattering on hydrogen and deuterium
The production of low energy protons observed in recent deep-inelastic (anti-)neutrino scattering on hydrogen and deuteron targets is interpreted in terms of fragmentation of the spectator di-quark and emission of nuclear spectators
Photoproduction of eta meson within a coupled-channels K-matrix approach
We investigate photoproduction of eta mesons off protons and neutrons within
a coupled-channels effective-Lagrangian method which is based on the K-matrix
approach. The two-body final channels included are pi-N, eta-N, phi-N, rho-N,
gamma-N, K-Lambda, and K-Sigma. Non-resonant meson-baryon interactions are
included in the model via nucleon intermediate states in the s- and u-channels,
meson exchanges in the t-channel amplitude and the u-channel resonances. The
nucleon resonances S_{11}(1535), S_{11}(1650), S_{31}(1620), P_{11}(1440),
P_{11}(1710), P_{13}(1720), P_{33}(1232), P_{33}(1600), D_{13}(1520),
D_{13}(1700), and D_{33}(1700) are included explicitly in calculations. Our
model describes simultaneously the available data as well on total and
differential cross sections as on beam and target asymmetries. This holds for
the p(gamma,eta)p reaction for photon energies ranging from very close to
threshold to up to 3 GeV. The polarization observables show strong sensitivity
to resonances that otherwise contribute only weakly to the total cross section.
It is found that the pronounced bump-like structure seen in the excitation
function of the n(gamma,eta)n cross section at gamma energies around 1 GeV, can
be explained by the interference effects of S_{11}, P_{11} and P_{13} resonance
contributions.Comment: 36 pages, 14 figures, one new figure added, discussions revised,
version to appear in Phys. Rev.
Measurement of the average shape of longitudinal profiles of cosmic-ray air showers at the Pierre Auger Observatory
The profile of the longitudinal development of showers produced by ultra-high energy cosmic rays carries information related to the interaction properties of the primary particles with atmospheric nuclei. In this work, we present the first measurement of the average shower pro file in traversed atmospheric depth at the Pierre Auger Observatory. The shapes of profiles are well reproduced by the Gaisser-Hillas parametrization within the range studied, for E > 10(17.8) eV. A detailed analysis of the systematic uncertainties is performed using ten years of data and a full detector simulation. The average shape is quantified using two variables related to the width and asymmetry of the profile, and the results are compared with predictions of hadronic interaction models for different primary particles.</p
Observation of inclined EeV air showers with the radio detector of the Pierre Auger Observatory
With the Auger Engineering Radio Array (AERA) of the Pierre Auger Observatory, we have observed the radio emission from 561 extensive air showers with zenith angles between 60 degrees and 84 degrees. In contrast to air showers with more vertical incidence, these inclined air showers illuminate large ground areas of several km(2) with radio signals detectable in the 30 to 80 MHz band. A comparison of the measured radio-signal amplitudes with Monte Carlo simulations of a subset of 50 events for which we reconstruct the energy using the Auger surface detector shows agreement within the uncertainties of the current analysis. As expected for forward-beamed radio emission undergoing no significant absorption or scattering in the atmosphere, the area illuminated by radio signals grows with the zenith angle of the air shower. Inclined air showers with EeV energies are thus measurable with sparse radio-antenna arrays with grid sizes of a km or more. This is particularly attractive as radio detection provides direct access to the energy in the electromagnetic cascade of an air shower, which in case of inclined air showers is not accessible by arrays of particle detectors on the ground.</p
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