Search results for "Nucleon"
showing 10 items of 1041 documents
Pion Photo- and Electroproduction on the Proton
1999
Using a unitary isobar model a new operator for pion photo- and electroproduction has been developed for nuclear applications at photon equivalent energies up to 1 GeV. The model contains Born terms, vector mesons and nucleon resonances (P 33(1232), P 11(1440), D 13(1520), S 11(1535), F 15(1680), and D 33(1700)). Within this model we have obtained good agreement with the experimental data for pion photo- and electroproduction on the nucleon for both differential cross sections and polarization observables.
Measurement of the transverse target and beam-target asymmetries in η meson photoproduction at MAMI
2014
We present new data for the transverse target asymmetry T and the very first data for the beam-target asymmetry F in the $\vec \gamma \vec p\to\eta p$ reaction up to a center-of-mass energy of W=1.9 GeV. The data were obtained with the Crystal-Ball/TAPS detector setup at the Glasgow tagged photon facility of the Mainz Microtron MAMI. All existing model predictions fail to reproduce the new data indicating a significant impact on our understanding of the underlying dynamics of $\eta$ meson photoproduction. The peculiar nodal structure observed in existing T data close to threshold is not confirmed.
Nucleon resonance contributions to unpolarised inclusive electron scattering
2019
The first CLAS12 experiments will provide high-precision data on inclusive electron scattering observables at a photon virtuality Q2 ranging from 0.05 to 12GeV2 and center-of-mass energies W up to 4 GeV. In view of this endeavor, we present the modeling of the resonant contributions to the inclusive electron scattering observables. As input, we use the existing CLAS electrocoupling results obtained from exclusive meson electroproduction data off protons, and evaluate for the first time the resonant contributions based on the experimental results on the nucleon resonance electroexcitation. The uncertainties are given by the data and duly propagated through a Monte Carlo approach. In this way…
Meson Properties in Nuclear Medium
2003
In this paper, we report on the properties of meson resonances in the nuclear medium, in the scalar and vector sectors. First of all, the ρ meson is studied by looking at the pion-pion scattering amplitude in the vector-isovector channel, following a chiral unitary framework in free space and in the medium. The pious are modified in the medium by means of p-h and Δ-h excitations, and the p meson couples to these components as well as to N*(1520)-h excitations. Second, the Φ meson spectrum due to the kaon channel is obtained in terms of the Φ selfenergy provided by a chiral SU(3) dynamics model. The medium effects are considered in the properties of K and K mesons which are renormalized by S…
Electroweak interaction in muonic atoms
1992
The parity non-conserving effective neutral current interaction between charged leptons and nucleons is studied in its implications for atomic physics. Present results on heavy electronic atoms are discussed within the standard electroweak theory and beyond. The new features provided by muonic atoms open the way to the nuclear-spin-dependent parity non-conserving effects. Different observables proposed to study these effects in muonic atoms are reviewed.
Nucleon form factors, B-meson factories and the radiative return
2004
The feasibility of a measurement of the electric and magnetic nucleon form factors at $B$-meson factories through the radiative return is studied. Angular distributions allow a separation of the contributions from the two form factors. The distributions are presented for the laboratory and the hadronic rest frame, and the advantages of different coordinate systems are investigated. It is demonstrated that $Q^2$ values up to 8 or even 9 GeV$^2$ are within reach. The Monte Carlo event generator PHOKHARA is extended to nucleon final states, and results are presented which include Next-to-Leading Order radiative corrections from initial-state radiation. The impact of angular cuts on rates and d…
In-Medium Properties of theD13(1520) Nucleon Resonance
2001
The in-medium properties of the ${\mathrm{D}}_{13}(1520)$ nucleon resonance were studied via photoproduction of ${\ensuremath{\pi}}^{0}$ mesons from nuclei (C, Ca, Nb, Pb) with the TAPS detector at the Mainz Microton accelerator. The inclusive (single and multiple pion production) data disagree with model predictions which explain the disappearance of the second resonance bump in total photoabsorption via a medium modification of the ${\mathrm{D}}_{13}\ensuremath{\rightarrow}\mathrm{N}\ensuremath{\rho}$ decay. The exclusive single ${\ensuremath{\pi}}^{0}$ production data show no broadening of the resonance structure beyond Fermi smearing. Both results together cast doubt on attempts to expl…
Experiments on threshold pion photoproduction γp → pπ 0
2008
An update is given on the experimental results for neutral pion photo-production on the nucleon. Also ideas for future experiments are presented.
Where Do Diffractive Nucleons Go?
1974
Nucleon and pion-nucleon distributions from the diffractive component in pp collisions are analysed. Diffractive events are assumed to come from a mechanism pp → N*p, in which a proton is diffractively excited to a nova N*. The decay properties of N* are determined by assuming that a Pomeron-proton collision behaves as a proton-proton collision. Correlations within the diffractive component are computed and seen to be numerically small. Even interference with the pionization component does not reproduce the observed pattern of pion (in the plateau)-proton (in the fragmentation region) correlations. This may imply the existence of long-range correlations within the pionization component.
Low-energy doubly virtual Compton scattering from dilepton electroproduction on a nucleon
2020
We propose a new way to experimentally determine the subleading low-energy structure constant of doubly virtual Compton scattering on a proton. Such empirical determination will reduce the theoretical model error in estimates of the hadronic correction to the muonic hydrogen Lamb shift. We demonstrate that the dilepton forward-backward asymmetry in the e−p→e−pe−e+ process, which can be accessed at electron scattering facilities, yields a large sensitivity to this so far unknown low-energy constant.