Search results for "Particle physics"
showing 10 items of 6826 documents
Measurement of the Parity Violation in Quasi-Elastic Electroweak Electron-Scattering from 9Be
1986
In the energy range of about 300 MeV, available at the Mainz- Linac, quasi-elastic scattering dominates the total cross section at backward scattering angles. This process can therefore be detected efficiently by a gas Cerenkov-counter with large solid angle. This is a prerequisit for experiments on parity violation due to the very small asymmetry effect being of the order of 1|10-5 at these energies [1]. The counting system built, consists of 12 elliptical mirrors, imaging the Cerenkov photons seen in target direction onto photomultipliers. The mirrors cover the full azimuth for polar angles 115°≦ϑ≦145°, thus covering 20% of 4π (Fig. 1). The detector has been proved to yield a statistical …
Chiral perturbation theory study of the axial N -> Delta(1232) transition
2008
We have performed a theoretical study of the axial Nucleon to Delta(1232) ($N\to\Delta$) transition form factors up to one-loop order in covariant baryon chiral perturbation theory within a formalism in which the unphysical spin-1/2 components of the $\Delta$ fields are decoupled.
One-photon transitions between heavy baryons in a relativistic three-quark model
1998
We study one-photon transitions between heavy baryon states in the framework of a relativistic three-quark model. We calculate the one-photon transition rates for ground-state to ground-state transitions and for some specific excited state to ground-state transitions. Our rate predictions for the most important transitions are: $\Gamma(\Sigma^{+}_{c}\to \Lambda_c^+\gamma)= 60.7\pm 1.5 $ KeV, $\Gamma(\Xi^{'+}_{c}\to \Xi_c^+\gamma) = 12.7\pm 1.5$ KeV, $\Gamma(\Lambda_{c1}(2593)\to\Lambda_c^+\gamma)=104.3\pm 1.3$ KeV.
Moments of nucleon structure functions at next-to-leading order in baryon chiral perturbation theory
2014
We obtain leading- and next-to-leading-order predictions of chiral perturbation theory for several prominent moments of nucleon structure functions. These parameter-free results turn out to be in overall agreement with the available empirical information on nearly all of the considered moments, in the region of low momentum transfer $({Q}^{2}l0.3\phantom{\rule{4pt}{0ex}}{\mathrm{GeV}}^{2})$. Especially surprising is the situation for the spin polarizability ${\ensuremath{\delta}}_{LT}$, which thus far was not reproducible in chiral perturbation theory for proton and neutron simultaneously. This problem, known as the ``${\ensuremath{\delta}}_{LT}$ puzzle,'' is not seen in the present calcula…
The S01 − Λ(1405) and − Λ(1670) resonances in meson-baryon unitarized coupled channel chiral perturbation theory
2003
Abstract The s-wave meson-baryon system with strangeness S = −1 and isospin I = 0 is studied using the Bethe-Salpeter coupled channel formalism incorporating Chiral Symmetry. The needed two particle irreducible potential is taken from lowest order Chiral Perturbation Theory in a relativistic formalism. The K N, πΣ, νΛ , and KΞ two-body channels have been included. Off-shell behavior is parameterized in terms of low energy constants, which outnumber those assumed in previous works and provide a better fit to the data. The masses, widths and branching ratios of the Λ(1405) and Λ(1670) resonances are determined. In our model, we find no one but two resonances in the Λ(1405) region.
Polarization effects in the cascade decayΛb→Λ(→pπ−)+J/ψ(→ℓ+ℓ−)in the covariant confined quark model
2013
We calculate the invariant and helicity amplitudes for the nonleptonic decay ${\ensuremath{\Lambda}}_{b}\ensuremath{\rightarrow}\ensuremath{\Lambda}+J/\ensuremath{\psi}$, $\ensuremath{\psi}(2S)$ in the covariant confined quark model. We discuss joint angular decay distributions in the cascade decay ${\ensuremath{\Lambda}}_{b}\ensuremath{\rightarrow}\ensuremath{\Lambda}(\ensuremath{\rightarrow}p{\ensuremath{\pi}}^{\ensuremath{-}})+J/\ensuremath{\psi}$, $\ensuremath{\psi}(2S)(\ensuremath{\rightarrow}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}})$ and calculate some of the asymmetry parameters that characterize the joint angular decay distribution. We confirm expectations from th…
Radiative decay of theΛ*(1520)
2006
A recently developed nonperturbative chiral approach to dynamically generate the 3/2{sup -} baryon resonances has been extended to investigate the radiative decays {lambda}*(1520){yields}{gamma}{lambda}(1116) and {lambda}*(1520){yields}{gamma}{sigma}{sup 0}(1193). We show that the {lambda}*(1520) decay into {gamma}{lambda} is an ideal test for the need of extra components of the resonance beyond those provided by the chiral approach since the largest meson-baryon components give no contribution to this decay. The case is different for {gamma}{sigma} decay, where the theory agrees with experiment, though the large uncertainties of these data call for more precise measurements. Some estimates…
New calculations of grossβ-decay properties for astrophysical applications: Speeding-up the classicalrprocess
2003
Recent compilations of experimental gross $\ensuremath{\beta}$-decay properties, i.e., half-lives ${(T}_{1/2})$ and neutron-emission probabilities ${(P}_{\mathrm{n}}),$ are compared to improved global macroscopic-microscopic model predictions. The model combines calculations within the quasiparticle (QP) random-phase approximation for the Gamow-Teller (GT) part with an empirical spreading of the QP strength and the gross theory for the first-forbidden part of ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay. Nuclear masses are either taken from the 1995 data compilation of Audi et al., when available, otherwise from the finite-range droplet model. Especially for spherical and neutron-(sub-)mag…
Chiral approach to antikaons- andp-wave interactions in dense nuclear matter
2006
The properties of the antikaons in nuclear matter are investigated from a chiral unitary approach which incorporates the $s$- and $p$-waves of the $\overline{K}N$ interaction. To obtain the in-medium meson-baryon amplitudes we include, in a self-consistent way, Pauli blocking effects, meson self-energies corrected by nuclear short-range correlations and baryon binding potentials. We pay special attention to investigating the validity of the on-shell factorization, showing that it cannot be applied in the evaluation of the in-medium corrections to the $p$-wave amplitudes. In nuclear matter at saturation energy, the \ensuremath{\Lambda} and \ensuremath{\Sigma} develop an attractive potential …
Heavy baryon spectroscopy with relativistic kinematics
2014
We present a comparative Faddeev study of heavy baryon spectroscopy with nonrelativistic and relativistic kinematics. We show results for different standard hyperfine interactions with both kinematics in an attempt to learn about the light quark dynamics. We highlight the properties of particular states accessible in nowadays laboratories that would help in discriminating between different dynamical models. The advance in the knowledge of light quark dynamics is a key tool for the understanding of the existence of exotic hadrons.