Content-type: text/html NuInt04 - Poster Abstracts

Poster Abstracts

SpeakerTitle
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.
 



SpeakerTitle
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.
 

SpeakerTitle
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.
 

SpeakerTitle
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.
 

SpeakerTitle
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.
 

SpeakerTitle
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. 
SpeakerTitle
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>). 
SpeakerTitle
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.
 

SpeakerTitle
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.”