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Register a new userTechnique for Direct eV-Scale Measurements of the Mu and Tau Neutrino Masses Using Supernova Neutrinos
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J.F. Beacom
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Early black hole formation in a core-collapse supernova will abruptly truncate the neutrino fluxes. The sharp cutoff can be used to make model-independent time-of-flight neutrino mass tests. Assuming a neutrino luminosity of $10^{52}$ erg/s per flavor at cutoff and a distance of 10 kpc, SuperKamiokande can detect an electron neutrino mass as small as 1.8 eV, and the proposed OMNIS detector can detect mu and tau neutrino masses as small as 6 eV. This {it Letter} presents the first technique with direct sensitivity to eV-scale mu and tau neutrino masses.
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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), a future Galactic supernova at a distance of 10 kpc would cause several hundred events. The $ u_mu$ and $ u_tau$ 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 $bar{ u}_e$ 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 $ u_mu$ or $ u_tau$ mass down to about 30 eV can be simply and robustly determined. This seems to be the best technique for direct measurement of these masses.
Sterile neutrinos with mass in the eV-scale and large mixings of order $theta_0simeq 0.1$ could explain some anomalies found in short-baseline neutrino oscillation data. Here, we revisit a neutrino portal scenario in which eV-scale sterile neutrinos have self-interactions via a new gauge vector boson $phi$. Their production in the early Universe via mixing with active neutrinos can be suppressed by the induced effective potential in the sterile sector. We study how different cosmological observations can constrain this model, in terms of the mass of the new gauge boson, $M_phi$, and its coupling to sterile neutrinos, $g_s$. Then, we explore how to probe part of the allowed parameter space of this particular model with future observations of the diffuse supernova neutrino background by the Hyper-Kamiokande and DUNE detectors. For $M_phi sim 5-10$~keV and $g_s sim 10^{-4}-10^{-2}$, as allowed by cosmological constraints, we find that interactions of diffuse supernova neutrinos with relic sterile neutrinos on their way to the Earth would result in significant dips in the neutrino spectrum which would produce unique features in the event spectra observed in these detectors.
We discuss the importance of observing supernova neutrinos. By analyzing the SN1987A observations of Kamiokande-II, IMB and Baksan, we show that they provide a 2.5{sigma} support to the standard scenario for the explosion. We discuss in this context the use of neutrinos as trigger for the search of the gravity wave impulsive emission. We derive a bound on the neutrino mass using the SN1987A data and argue, using simulated data, that a future galactic supernova could probe the sub-eV region.
We report in detail on searches for eV-scale sterile neutrinos, in the context of a 3+1 model, using eight years of data from the IceCube neutrino telescope. By analyzing the reconstructed energies and zenith angles of 305,735 atmospheric $ u_mu$ and $bar{ u}_mu$ events we construct confidence intervals in two analysis spaces: $sin^2 (2theta_{24})$ vs. $Delta m^2_{41}$ under the conservative assumption $theta_{34}=0$; and $sin^2(2theta_{24})$ vs. $sin^2 (2theta_{34})$ given sufficiently large $Delta m^2_{41}$ that fast oscillation features are unresolvable. Detailed discussions of the event selection, systematic uncertainties, and fitting procedures are presented. No strong evidence for sterile neutrinos is found, and the best-fit likelihood is consistent with the no sterile neutrino hypothesis with a p-value of 8% in the first analysis space and 19% in the second.
Assuming the Majorana nature of massive neutrinos, we generalize the Friedberg-Lee neutrino mass model to include CP violation in the neutrino mass matrix M_ u. The most general case with all the free parameters of M_ u being complex is discussed. We show that a favorable neutrino mixing pattern (with theta_12 approx 35.3^circ, theta_23=45^circ, theta_13 eq 0^circ and delta=90^circ) can naturally be derived from M_ u, if it has an approximate or softly-broken mu-tau symmetry. We also point out a different way to obtain the nearly tri-bimaximal neutrino mixing pattern with delta=0^circ and non-vanishing Majorana phases.
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