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Speaker | Title | ||
Akihiro Haga
|
Relativistic and
non-relativistic
description of nuclear
polarization in electronic
and muonic atoms
| ||
Abstract | |||
We present the electronic and muonic nuclear-polarization corrections, which provide level shifts due to the two-photon exchange process between a bound lepton and a nucleus. The nuclear excitations are constructed by two nuclear models: the relativistic and non-relativistic random-phase approximations. We give the nuclear-polarization energies with non-relativistic nuclear model for electronic and muonic $^{208}$Pb and with relativistic nulcear model for muonic $^{16}$O. Present calculation is the first gauge-invariant calculation using the microscopic nuclear model, in both electronic and muonic atoms. In electronic $^{208}$Pb the transverse interaction contributes fairly large if the contributions from the positive- and negative-energy electron states are separately considered. However, since the large cancellations between them occur, the total nuclear-polarization is small and similar to the result with the Coulomb interaction only. It is also found that the nuclear polarization from the ladder and cross diagrams considered commonly, is very sensitive to the photon propagator employed. In the two-photon exchange diagrams, the seagull term, which consists of the square of the transverse photon field should be involved when the nuclear structure is constructed non-relativistically. The seagull diagram is shown to be quite important to attain the gauge invariance of nuclear-polarization energy. In muonic $^{208}$Pb, in contrast, the transverse interaction is weaker than the Coulomb one, so that the effect of the seagull diagram is correspondingly small and the nuclear polarization is insensitive to the choice of the gauge. The transverse interaction, however, is significant for the estimation of muonic transition energies because the transverse interaction gives rise to nuclear-polarization energies with different muon-spin dependences from those of the Coulomb interaction in addition to the facts that the electric transverse interaction interferes coherently with the Coulomb interaction. It is found that the transverse contribution reduces the discrepancies between theory and experiment in the 2p and 3p fine-structure splitting energies of muonic $^{208}$Pb considerably. We also present the nuclear polarization in muonic $^{16}$O with the relativistic random-phase approximation including the negative-energy states. The transverse current have large couplings between positive- and negative-energy nuclear states. As a result, the contribution from the negative-enegy states to the nuclear-polarization correction is found to be significant and also essential to achieve gauge invariance as well as the seagull diagram in non-relativistic model. We find that the non-relativistic nuclear model with the effective mass provides similar results as the relativistic one. | |||
Speaker | Title | ||
Maria Laura Costantini
(marialaura.costantini@aqui
la.infn.it) in
collaboration with Aldo
Ianni and Francesco Vissani |
SN1987A and the
properties of neutrino
burst
| ||
Abstract | |||
We reanalyze the neutrino events from SN1987A in IMB and Kamiokande-II (KII) detectors, and compare them with the expectations from simple theorethical models of neutrino emission. Both angular distributions are peaked in forward direction: the average cosines are 2 sigma from the predicted ones, and furthermore, the average energy in KII is low compared with the indications. On the other hand, the assumption that a few (probably one) events at KII have been caused by elastic scattering is not in contrast with the 'standard' picture of the collapse, and yields a more satisfactory distributions in angle and (marginally) in energy. The observations give useful hints on the astrophysical parameters of the collapse: in our evaluations, the mean energy of electron antineutrinos is E=11-16 MeV and the total energy radiated around 2.5*10^53 erg. These values are not in disagreement with those suggested by current theoretical paradigm, but leave wide space to non-standard pictures, especially when neutrino oscillations are included. | |||
Speaker | Title | ||
Krzysztof Kurek
|
Tau polarization in
neutrino induced quasi
elastic and resonce
reactions.
| ||
Abstract | |||
The Fermi motion and nucleon binding energy effect are taken into account in calculations of tau polarization in neutrino induced quasi elastic and Delta (resonance) tau production. Special attention is paid to neutrino energy region close to the reaction threshold. | |||
Speaker | Title | ||
Hiroshi Yokoya
|
Open fortran code for tau
production.
| ||
Abstract | |||
We introduce an open fortran code for tau production cross section and its spin polarization produced in nu_tau-nucleon scattering. Quasi-elastic scattering, delta resonance production, and deep inelastic scattering are included in the program. We explain the physical context, algorithm, and how to use it. | |||
Speaker | Title | ||
Nicola Farina
|
Neutrino-nucleus
scattering in the impulse
approximation regime
| ||
Abstract | |||
The Fermi gas model, while providing a reasonable qualitative description of the continuum nuclear response, does not include the effects of dynamical nucleon-nucleon correlations in the initial and final states,that have long been recognized to play a critical role in electron-nucleus scattering.We discuss the results of a calculation of the neutrino-oxygen cross section in which these effects are consistently taken into account. | |||
Speaker | Title | ||
Vadim Naumov
|
Tau lepton polarization
in quasielastic
neutrino-nucleon
scattering.
| ||
Abstract | |||
A numerical analysis of the polarization vector of tau leptons produced through quasielastic neutrino and antineutrino scattering off free nucleons is given for different models for electromagnetic nucleon form factors, the standard dipole model and the extended model by Gari and Kruempelmann recently updated by Lomon. We study the uncertainties in the calculation of the lepton polarization vector due to indetermination in the axial mass. Next we investigate possible impact of second class currents (SCC). In the absence of a specific model for the vector and axial SCC, we adopt simple phenomenological parametrizations for the nonstandard (in general complex) scalar and tensor nucleon form factors. Our choice of the unknown parameters is made to ensure the limits obtained in the BNL AGS muon neutrino experiment as well as restrictions on SCC derived from the nuclear structure studies. | |||
Speaker | Title | ||
Vadim Naumov
|
Extended Rein-Sehgal
model for tau lepton
production.
| ||
Abstract | |||
The polarization density matrix of leptons produced in neutrino-nucleon collisions is derived by applying a covariant method. The general formalism is employed to include the final lepton mass and spin into the popular model by Rein and Sehgal (RS) for single pion neutrinoproduction. We investigate the effect of the lepton mass on the total and differential cross sections. The lepton polarization evaluated within the extended RS model is compared against that follows from the single resonance production model based upon the phenomenological transition form factors of the nucleon. Our calculations are embedded into a FORTRAN code available upon request from one of the authors (V.V.Lyubushkin, <lvv@nusun.jinr.ru>). | |||
Speaker | Title | ||
Chiara Maieron
|
Final State Interaction
effects in neutrino-nucleus
quasielastic scattering
| ||
Abstract | |||
I will consider the quasielastic scattering of muon neutrinos on an Oxygen 16 target, described within a relativistic shell model and, for comparison, the relativistic Fermi gas. Final state interactions are described in the distorted wave impulse approximation, using a relativistic optical potential, with and without imaginary part. I will present results for inclusive cross sections at fixed neutrino energies in the range E_nu = 200 MeV - 1 GeV, showing that final state interaction effects can remain sizeable even at large energies. | |||
Speaker | Title | ||
Krzysztof Graczyk
|
Tau polarization in
neutrino charge current
Deep Inelastic Scattering
in the threshold region.
| ||
Abstract | |||
Numerical calculations of polarization of tau produced in neutrino charge current deep inelastic scattering are presented. We consider the process in the threshold region. We compare calculations obtained by adopting GRV98 structure functions with results given by adopting GRV98 PDF’s with corrections due to Bodek at al.” |