Showing papers by "John F. Beacom published in 1998"

Mass signature of supernova muon-neutrino and tau-neutrino neutrinos in Super-Kamiokande

Abstract: The ${\ensuremath{ u}}_{\ensuremath{\mu}}$ and ${\ensuremath{ u}}_{\ensuremath{\tau}}$ neutrinos (and their antiparticles) from a Galactic core-collapse supernova can be observed in a water-\ifmmode \check{C}\else \v{C}\fi{}erenkov detector by the neutral-current excitation of ${}^{16}\mathrm{O}.$ The number of events expected is several times greater than from neutral-current scattering on electrons. The observation of this signal would be a strong test that these neutrinos are produced in core-collapse supernovae, and with the right characteristics. In this paper, this signal is used as the basis for a technique of neutrino mass determination from a future Galactic supernova. The masses of the ${\ensuremath{ u}}_{\ensuremath{\mu}}$ and ${\ensuremath{ u}}_{\ensuremath{\tau}}$ neutrinos can either be measured or limited by their delay relative to the ${\overline{\ensuremath{ u}}}_{e}$ neutrinos. By comparing to the high-statistics ${\overline{\ensuremath{ u}}}_{e}$ data instead of the theoretical expectation, much of the model dependence is canceled. Numerical results are presented for a future supernova at 10 kpc as seen in the SuperKamiokande detector. Under reasonable assumptions, and in the presence of the expected counting statistics, ${\ensuremath{ u}}_{\ensuremath{\mu}}$ and ${\ensuremath{ u}}_{\ensuremath{\tau}}$ masses down to about 50 eV can be simply and robustly determined. The signal used here is more sensitive to small neutrino masses than the signal based on neutrino-electron scattering.

Mass signature of supernova νμ and ντ neutrinos in the Sudbury Neutrino Observatory

Abstract: Core-collapse supernovae emit of order 10^58 neutrinos and antineutrinos of all flavors over several seconds, with average energies of 10–25 MeV. In the Sudbury Neutrino Observatory (SNO), which begins operation this year, neutrinos and antineutrinos of all flavors can be detected by reactions which break up the deuteron. For a future Galactic supernova at a distance of 10 kpc, several hundred events will be observed in SNO. The νμ and ντ neutrinos and antineutrinos are of particular interest, as a test of the supernova mechanism. In addition, it is possible to measure or limit their masses by their delay (determined from neutral-current events) relative to the νe neutrinos (determined from charged-current events). Numerical results are presented for such a future supernova as seen in SNO. Under reasonable assumptions, and in the presence of the expected counting statistics, a νμ or ντ mass down to about 30 eV can be simply and robustly determined. If zero delay is measured, then the mass limit is independent of the distance D. At present, this seems to be the best possibility for direct determination of a νμ or ντ mass within the cosmologically interesting range. We also show how to separately study the supernova and neutrino physics, and how changes in the assumed supernova parameters would affect the mass sensitivity.

Green's function for nonlocal potentials

Abstract: The single-particle nuclear potential is intrinsically nonlocal. In this paper, we consider nonlocalities which arise from the many-body and fermionic nature of the nucleus. We investigate the effects of nonlocality in the nuclear potential by developing the Green's function for nonlocal potentials. The formal Green's function integral is solved analytically in two different limits of the wavelength as compared with the scale of nonlocality. Both results are studied in a quasi-free limit. The results illuminate some of the basic effects of nonlocality in the nuclear medium.

A semiclassical approach to level crossing in supersymmetric quantum mechanics

Abstract: Much use has been made of the techniques of supersymmetric quantum mechanics (SUSY QM) for studying bound-state problems characterized by a superpotential ϕ(x). Under the analytic continuation ϕ(x) → iϕ(x), a pair of superpartner bound-state problems is transformed into a two-state level-crossing problem in the continuum. The description of matter-enhanced neutrino flavor oscillations involves a level-crossing problem. We treat this with the techniques of supersymmetric quantum mechanics. For the benefit of those not familiar with neutrino oscillations and their description, enough details are given to make the rest of the paper understandable. Many other level-crossing problems in physics are of exactly the same form. Particular attention is given to the fact that different semiclassical techniques yield different results. The best result is obtained with a uniform approximation that explicitly recognizes the supersymmetric nature of the system.