Search results for "Partial"
showing 10 items of 1477 documents
Nucleon resonances inπNscattering up to energiess⩽2.0GeV
2007
A meson-exchange model for pion-nucleon scattering was previously constructed using a three-dimensional reduction scheme of the Bethe-Salpeter equation for a model Lagrangian involving $\ensuremath{\pi},\ensuremath{\eta},N,\ensuremath{\Delta},\ensuremath{\rho}$, and \ensuremath{\sigma} fields. We thereby extend our previous work by including the $\ensuremath{\eta}N$ channel and all the $\ensuremath{\pi}N$ resonances with masses $~2$ GeV, up to the $F$ waves. The effects of the $\ensuremath{\pi}\ensuremath{\pi}N$ channels are taken into account by introducing an effective width in the resonance propagators. The extended model gives an excellent fit to both $\ensuremath{\pi}N$ phase shifts an…
Spectral distribution for the decay τ→ντKπ
2006
Abstract With the newly available data sets on hadronic τ decays from the B -factories BaBar and BELLE, and future data from BESIII, precise information on the decay distributions will soon become available. This calls for an improvement of the decay spectra also on the theoretical side. In this work, the distribution function for the decay τ → ν τ K π will be presented with the relevant Kπ vector and scalar form factors being calculated in the framework of the resonance chiral theory, also taking into account additional constraints from dispersion relations and short-distances. As a by-product the slope and curvature of the vector form factor F + K π ( s ) are determined to be λ + ′ = 25.6…
Meson-meson interactions in a nonperturbative chiral approach
1999
A non-perturbative method which combines constraints from chiral symmetry breaking and coupled channel unitarity is used to describe the meson-meson interaction up to about 1.2 GeV. The approach uses the O(p^2) and O(p^4) chiral Lagrangians. The seven free parameters of the O(p^4) Lagrangian are fitted to the data. The results are in good agreement with a vast amount of experimental analyses. The amplitudes develop poles in the complex plane corresponding to the f0, a0, rho, K*, phi, sigma and kappa resonances; the latter two, very broad. The total and partial decay widths of the resonances are also well reproduced. Further extensions and applications of this chiral non-perturbative scheme …
Truncated partial-wave analysis of a complete experiment for photoproduction of two pseudoscalar mesons on a nucleon
2013
A truncated partial wave analysis for the photoproduction of two pseudoscalar mesons on a nucleon is discussed with respect to the determination of a complete set of observables. For the selection of such a set we have applied a criterion previously developed for photo- and electrodisintegration of a deuteron, which allows one to find a 'minimal' set of observables for determining the partial wave amplitudes up to possible discrete ambiguities. The question of resolving the remaining ambiguities by invoking additional observables is discussed for the simplest case, when the partial wave expansion is truncated at the lowest total angular momentum of the final state $J_{max}=1/2$. The resulti…
Kaon-antikaon nuclear optical potentials and the kappa meson in the nuclear medium
2004
We study the properties of the kappa meson in the nuclear medium, starting from a chiral unitary model of S-wave, I=1/2 K-pi scattering, which describes the elastic K-pi phase shifts and generates a pole in the amplitude. Medium effects are considered by including pion and kaon selfenergies. We explore the changes in the kappa pole position and in the K-pi scattering amplitude at finite density, with two different models for the kaon selfenergy.
Dispersion relation analysis of neutral pion photoproduction and electroproduction at threshold
2002
Neutral pion photoproduction and electroproduction at threshold is analyzed in the framework of dispersion relations. For this purpose, we evaluate the real threshold amplitudes in terms of Born contributions and dispersion integrals determined by the imaginary parts of the multipoles of the unitary isobar model (MAID) and the phenomenological partial-wave analysis (SAID). The results show considerable cancellations between Born terms and resonance contributions. Good agreement with the data is found for photoproduction. While our dispersion analysis suggests considerable discrepancies for electroproduction, the present state of the experimental multipole analysis at finite ${Q}^{2}$ does n…
Constraints from lepton universality at the z-peak on unified theories
1995
We suggest the use of a universality-breaking observable based on lepton asymmetries as derived from the left-right asymmetry and the $\tau$ polarization at the $Z$ peak, which can efficiently constrain the parameter space of unified theories. The new observable is complementary to the leptonic partial width differences and it depends critically on the chirality of a possible non-universal $Z$-boson coupling to like-flavour leptons. The LEP/SLC potential of probing universality violation is discussed in representative low-energy extensions of the Standard Model (SM) that could be derived by supersymmetric grand unified theories, such as the SM with left-handed and/or right-handed neutral is…
Radiative decay of the
2007
Abstract Electromagnetic properties provide information about the structure of strongly interacting systems and allow for independent tests of hadronic models. The radiative decay of the Δ ∗ ( 1700 ) is studied, which appears dynamically generated in a coupled channel approach from the rescattering of the ( 3 / 2 + ) decuplet of baryons with the ( 0 − ) octet of pseudoscalar mesons. The radiative decay is predicted from the well-known couplings of the photon to the mesons and baryons which constitute this resonance in the dynamical picture.
Amplitude analysis of the decayD0→K−K+π0
2007
Using 385 fb^-1 of e^+e^- collisions at the CM energies of around 10.6 GeV recorded by the BaBar experiment, we study the amplitudes of the singly Cabibbo-suppressed decay D^0 --> K^- K^+ pi^0. We measure the strong phase difference between the D0bar and D0 decays to the K^*(892)^+ K^- state to be -35.5 +/- 1.9 (stat) +/- 2.2 (syst) degrees, and their amplitude ratio to be 0.599 +/- 0.013 (stat) +/- 0.011 (syst). We observe significant contributions from the Kpi and K^-K^+ scalar and vector amplitudes, and analyze the moments of the cosine of the helicity angle in these systems. We find no evidence for charged, scalar kappa(800) state, nor for higher spin states. We also perform a model-ind…
Numerical treatment of the long-range Coulomb potential with Berggren bases
2010
The Schrodinger equation incorporating the long-range Coulomb potential takes the form of a Fredholm equation whose kernel is singular on its diagonal when represented by a basis bearing a continuum of states, such as in a Fourier-Bessel transform. Several methods have been devised to tackle this difficulty, from simply removing the infinite-range of the Coulomb potential with a screening or cut function to using discretizing schemes which take advantage of the integrable character of Coulomb kernel singularities. However, they have never been tested in the context of Berggren bases, which allow many-body nuclear wave functions to be expanded, with halo or resonant properties within a shell…