Search results for "meson"
showing 10 items of 1548 documents
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…
Predictions for the ${\vec{\Lambda }_b \rightarrow J/\psi ~ \Lambda (1405)}$ Λ b → J / ψ Λ ( 1405 ) decay
2015
We calculate the shape of the [Formula: see text] and [Formula: see text] invariant mass distributions in the [Formula: see text] and [Formula: see text] decays that are dominated by the [Formula: see text] resonance. The weak interaction part is the same for both processes and the hadronization into the different meson-baryon channels in the final state is given by symmetry arguments. The most important feature is the implementation of the meson-baryon final-state interaction using two chiral unitary models from different theoretical groups. Both approaches give a good description of antikaon-nucleon scattering data, the complex energy shift in kaonic hydrogen and the line shapes of [Formu…
T-odd andCP-odd triple momentum correlations in the exclusive semi-leptonic charm meson decayD→K *(Kπ)lv l
1992
We studyT-odd andCP-odd triple momentum correlations in exclusive semi-leptonic charm meson decaysD→K*(Kπ)lvl. We define asymmetry ratios that measure the trueCP-violating effects, andT-odd triple momentum correlation effects from unitarity contributions. Possible newCP-violating contributions are parametrized in terms of an effective four-fermion Hamiltonian whereCP-violating effects should come from new non-standard sources. A detailed analysis of the left-right model and the Weinberg Higgs-boson model ofCP-violation is carried out.
Lepton hadron angular correlations in semileptonic ? decays
1994
We studyT-odd triple momentum correlations in exclusive semileptonic ∋-decays into three pseudoscalar mesons. We define asymmetry ratios that measure theseT-odd correlations and show how to separate the unitarity contribution from the trueCP-violating contributions. TheCP-violating contributions to the asymmetry ratios would have to come from new non-Standard Model sources as theCP-violating Standard Model contributions to the asymmetry ratios are zero. We discuss two extensions of the Standard Model that give rise to nonvanishingCP-violating triple momentum correlations, namely a left-right symmetric model and a multi Higgs boson model. Numerical results on triple momentum correlations are…
Exclusive non-leptonic charm baryon decays
1992
We present a spectator quark model calculation of the Cabibbo-enhanced non-leptonic decays of the lowest lying charm baryons Λc, Ξc and Ωc decaying into non-charm ground state baryons and mesons. We employ covariant quark model wave functions to describe the ground state baryons and mesons. They are obtained by boosting rest frame wave functions to equal velocity frames. The non-leptonic decay amplitudes are then obtained in terms of two wave function overlap parameters which we fit to the experimental data. We discuss general features of the flavour and helicity composition of the final states in the quark model approach. We emphasize thatW-exchange contributions are of crucial importance …
CP violation in decay rates of charged bottom mesons
1981
In the standard theory we discuss a mechanism of interference between two different tree-level charged current amplitudes to induce CP violation. The asymmetry between conjugate Cabibbo disfavoured modes of charged bottom meson decays is considered. Estimates for two-body decays ofB u andB c are presented. We find thatB u − →D −+D 0 * , for instance, can give a big CP asymmetry with values ≈1–50%, depending on the angle and phase parameters.
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…
Beam-Helicity Asymmetries in Double-Pion Photoproduction off the Proton
2009
Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz in the three isospin channels $\vec{\gamma}p\to \pi^{+}\pi^0n$, $\vec{\gamma}p\to \pi^{0}\pi^0p$ and $\vec{\gamma}p\to \pi^{+}\pi^{-}p$ . The circularly polarized photons, produced from bremsstrahlung of longitudinally polarized electrons, were tagged with the Glasgow magnetic spectrometer. Charged pions and the decay photons of $\pi^0$ mesons were detected in a $~4\pi$ electromagnetic calorimeter which combined the Crystal Ball detector with the TAPS detector. The precisely measured asymmetries are very sensitive to details of the production processes and are thus key observables in the modeling of the reaction d…
ϕ meson transparency in nuclei from ϕN resonant interactions
2017
We investigate the $\ensuremath{\phi}$ meson nuclear transparency using some recent theoretical developments on the $\ensuremath{\phi}$ in medium self-energy. The inclusion of direct resonant $\ensuremath{\phi}N$ scattering and the kaon decay mechanisms leads to a $\ensuremath{\phi}$ width much larger than in most previous theoretical approaches. The model has been confronted with photoproduction data from CLAS and LEPS and the recent proton induced $\ensuremath{\phi}$ production from COSY finding an overall good agreement. The results support the need of a quite large direct $\ensuremath{\phi}N$-scattering contribution to the self-energy.