Neutrino Interaction Rates Research Articles

Neutrino Effects before, during, and after the Freezeout of ther‐Process

We study the effects of neutrino interactions before, during, and after the operation of the r-process in the context of a relativistic hydrodynamic neutrino-energized wind model that includes a Boltzmann solver for the dominant neutrino transport. We also employ newly available charged- and neutral-current interaction rates. Studies are made in a model with a short dynamical timescale that gives a fair reproduction of the solar system r-process abundance curve and hence could be a fair approximation to the true supernova environment. We confirm that charged- and neutral-current interactions can have specific unique effects on the final abundances. Early on, charged-current interactions determine the electron fraction, while later on, neutrino-induced neutron emission can continue to provide a slight neutron exposure even after the freezeout of the r-process. We propose two new potentially observable effects that derive from the use of a more realistic hydrodynamic model and/or new neutrino interaction rates. One is an enhanced odd-even effect in the final abundances, and the other is an enhancement of light A = 68-76 nuclei in the final abundances. These effects are consistent with some recent observations of r-process abundances in metal-poor halo stars and might help to identify the neutrino fluxes present near the freezeout of the r-process.

Update of solar neutrino interaction rate measurements from GNO at LNGS

Update of solar neutrino interaction rate measurements from GNO at LNGS

Update of solar neutrino interaction rate measurements from GNO at LNGS

GNO (Gallium Neutrino Observatory) at LNGS is continuously taking data since may 1998. In this contribution we update the value of the solar neutrino interaction rate R v e ⊙ in the Gallium target as measured by GNO, adding 16 more solar runs to the previously published set of measurements. The updated value from 35 solar runs is 67.7 ± 7.2( stat)± 3.2( syst) SNU. The experimental program is also shortly reviewed.

Determination of solar neutrino oscillation parameters using 1496 days of Super-Kamiokande-I data

A number of different fits to solar neutrino mixing and mass square difference were performed using 1496 days of Super-Kamiokande-I's solar neutrino data. These data select two allowed areas at large neutrino mixing when combined with either the solar 8B flux prediction of the standard solar model or the SNO interaction rate measurements. A global fit combining SK data with the solar neutrino interaction rates measured by Homestake, SNO, Gallex/GNO and SAGE prefers a single allowed area, the Large Mixing Angle solution, at the 98.9% confidence level. The mass square difference Δm 2 between the two mass eigenstates ranges from about 3 to 19×10 −5 eV 2, while the mixing angle θ is in the range of tan 2 θ≈0.25–0.65.

Neutrino opacity in magnetized hot and dense nuclear matter

We study the neutrino interaction rates in hot matter at high densities in the presence of uniform magnetic field. The neutrino cross-sections involving both the charged current absorption and neutral current scattering reactions on baryons and leptons have been considered. We have in particular considered the interesting case when the magnetic field is strong enough to completely polarise the protons and electrons in supernovae and neutron stars. The opacity in such a situation is considerably modified and the cross-section develops anisotropy. This has implications for phenomenon invoked in the literature to explain the observed pulsar kicks.

First results from GNO

GNO is the Gran Sasso experiment devoted to the measurement of the solar neutrino interaction rate in Gallium. It started to take solar data in 1998. Characteristics of the experimental apparatus are reported. The GNO I result from solar runs SR1-SR19 (corresponding to the period May 20, 1998 to January 12, 200) at 1 σ level is 65.8 −9.6 +10.2( stat.) −3.6 +3.4( syst.) or 65.8 −10.2 +10.7 SNU (with errors combined in quadrature). Future plans are also briefly presented.

Effect of a magnetic field on the electron neutrino sphere in pulsars

We study the neutrino interaction rates through charged as well as neutral current weak interactions in hot, dense magnetized matter. At densities near the neutrino sphere, matter in the presence of intense magnetic field is polarized, and electrons and protons typically occupy the lowest Landau level. The weak interaction rates in such a situation are severely modified leading to a sizable change in neutrino opacity and consequently on the location of the neutrino sphere which also gets distorted. This has implications for pulsar velocity explanations.

Methods for neutral-current neutrino detection in the Sudbury neutrino observatory

The Sudbury Neutrino Observatory will permit a comparison of the rate of neutral-current neutrino interactions to charged-current interactions, which is a test of neutrino mixing and mass. The neutral-current process can be measured by: a) comparison of the rate for electron elastic scattering to the pure charged-current rate on deuterium, b) neutron capture on Cl ions added to the heavy water, and, c) neutron capture in an array of 3He-filled proportional counters. The design and construction of suitable proportional counters are described.

Neutral-current detection via 3He(n,p) 3H in the Sudbury Neutrino Observatory

The rate of neutral-current neutrino interactions in SNO can be measured by: a) comparison of the rate for electron elastic scattering to the pure charged-current rate on deuterium, b) neutron capture on Cl ions added to the heavy water, and, c) neutron capture in an array of 3He-filled proportional counters. In the case of proportional counters, the technique described in this paper, extremely low levels of radioactivity are essential to minimize photodisintegration backgrounds. A method for producing ultra-pure nickel counter bodies by chemical vapor deposition from Ni(CO) 4 has been shown to yield purities with respect to U and Th of order 10 −12 by weight. Pulse-shape digitization affords a powerful means for distinguishing between 3He(n,p) 3H events and background alphas or electrons. Novel methods have been developed for deriving the position of events with single-ended readout from counter strings up to 12 m in length.

KARMEN: precision tests of the standard model with neutrinos from muon and pion decay

Neutrinos from pion and muon decay at rest offer unique possibilities for precision tests of the Standard Model at low energies. With typical neutrino interaction rates in this energy domain being only of the order of 10 −42 cm 2 high quality detection methods are required. The spectroscopic quality of neutrino identification in the KARMEN experiment at the pulsed spallation source ISIS allows a high sensitivity search for neutrino oscillations in the appearance channels ν μ → ν ρ and ν μ→ ν ρ . In addition, neutrino spectroscopy is used to look for non-standard (scalar and tensor) amplitudes in weak charged currents, while conservation laws are tested by a search for lepton number violating muon and pion decays allowed in Left - Right symmetric models. We present the results of the KARMEN experiment with regard to tests of the Standard Model obtained from the first three years of data taking.

II. Quasi-elastic neutrino interactions

A series of runs have been recently completed at the Argonne 12.5 GeV proton-synchrotron, the Z. G. S., which were designed to study the elastic scattering of neutrinos via the reaction v + n → μ - + p + . The data provided are expected to give a measure of the momentum transfer dependence or form factor for the axial vector part of the weak interaction as expressed in terms of an axial vector mass or a mean square radius for the axial vector interaction. It was envisaged in the early planning of this experiment that the high intensity of the Argonne Z. G. S. combined with the energy of neutrinos expected to be obtained from 12-5 GeV protons, would combine to make a study of elastic neutrino interactions a desirable and an advantageous type of experiment. In order to obtain a high mass target with neutrino interaction rates of several hundred per day and the possibility of muon sign determination, we used iron as the principal mass. The neutrinos thus interact ‘quasi-elastically’ with neutrons in the iron nucleus providing sufficient momentum transfer is involved so that nuclear physics effects are avoided.