利用大亚湾中微子实验装置探测超新星中微子

在利用大亚湾中微子实验装置研究超新星中微子探测过程中, 需要考虑到中微子传播过程中受到各种效应的影响, 包括超新星震荡效应、中微子集体效应、 Mikheyev Smirnov Wolfenstein (MSW)效应和地球物质效应等。 由于超新星中微子受到这些效应, 不同味道的中微子之间振荡会发生变化, 因而利用探测某些超新星中微子事例数之比, 就有可能确定中微子的质量层次,得到中微子混合角θ13和中微子绝对质量的信息。 While detecting supernova neutrinos in the Daya Bay neutrino laboratory, several supernova neutrino effects need to be considered, including the supernova shock effects, the neutrino collective effects, the Mikheyev Smirnov Wolfenstein (MSW) effects, and the Earth matter effects. The phenomena of neutrino oscillation is affected by the above effects. Using some ratios of the event numbers of different supernova neutrinos, we propose some possible methods to identify the mass hierarchy and acquire information about the neutrino mixing angle θ13 and neutrino masses.     

Technique for direct eV-scale measurements of the Mu and tau neutrino masses using supernova neutrinos

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, Super-Kamiokande 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. We present the first technique with direct sensitivity to eV-scale mu and tau neutrino masses.     

Plasma-induced neutrino helicity flip in a supernova core and a constraint on the Dirac neutrino magnetic moment

We investigate the neutrino helicity flip under supernova core conditions, where the left-handed neutrinos being produced can be converted into right-handed neutrinos sterile with respect to weak interactions owing to the interaction of the magnetic moments with plasma electrons and protons. In calculating the probability for the conversion neutrino scattering by plasma components, we take into account the polarization effects attributable to both electrons and protons in the photon propagator. Based on realistic models with radial distributions and time evolution of physical parameters in a supernova core, we have obtained upper limits on the Dirac neutrino magnetic moment averaged over flavors and time from the condition that the influence of the right-handed neutrino emission on the total cooling time scale should be limited.     

Detection of neutrinos from supernovae in nearby galaxies

While existing detectors would see a burst of many neutrinos from a Milky Way supernova, the supernova rate is only a few per century. As an alternative, we propose the detection of approximately 1 neutrino per supernova from galaxies within 10 Mpc, in which there were at least 9 core-collapse supernovae since 2002. With a future 1 Mton scale detector, this could be a faster method for measuring the supernova neutrino spectrum, which is essential for calibrating numerical models and predicting the redshifted diffuse spectrum from distant supernovae. It would also allow a > or approximately 10(4) times more precise trigger time than optical data alone for high-energy neutrinos and gravitational waves.     

Effect of Quark Strong Interaction in Phase Transition on Supernova Explosion

The effect of quark interactions perturbatively to order αc on the conversion, from quark matter to strange quark matter, is studied systematically based on a recent set of current quark masses. The process has a significant effect on increasing the core temperature, the neutrino abundance and the neutrino energies even if there is no quark interaction. Furthermore, with the switch of the strong interaction among quarks, these quantities will increase respectively to some further extents with αc increase. Taking αc = 0.47 as an example, the temperature, the neutrino abundance and the total neutrino energies are further raised by about 10%, 7%, and 20% respectively, which is weakly dependent on the initial temperature. Combining the effect of the current quark mass and the effect of the quark strong interaction, the results of the conversions will greatly enhance the probability of success for a supernova explosion and deeply influence the dynamics of the supernova evolution.     

TeV neutrinos and GeV photons from shock breakout in supernovae

We show that as a Type II supernova shock breaks out of its progenitor star, it becomes collisionless and may accelerate protons to energies >10 TeV. Inelastic nuclear collisions of these protons produce an approximately 1 h long flash of TeV neutrinos and 10 GeV photons, about 10 h after the thermal (10 MeV) neutrino burst from the cooling neutron star. A Galactic supernova in a red supergiant star would produce a photon and neutrino flux of approximately 10(-4) erg cm(-2) s(-1). A km(2) neutrino detector will detect approximately 100 muons, thus allowing to constrain both supernova models and neutrino properties.     

Study of Diffuse Supernova Neutrino Background with Modern and Future Detectors

Basic properties of the diffuse supernova neutrino background (DSNB) are reviewed. Current DSNB studies and the limits already set on the DSNB flow by the operating detectors Super-Kamiokande, SNO, and KamLAND are discussed. Prospects of DSNB studies with future high-mass neutrino detectors, such as JUNO and Hyper-Kamiokande, are considered.     

Identifying neutrino mass hierarchy at extremely small theta13 through earth matter effects in a supernova signal

Collective neutrino flavor transformations deep inside a supernova are sensitive to the neutrino mass hierarchy even at extremely small values of theta_(13). Exploiting this effect, we show that comparison of the antineutrino signals from a galactic supernova in two megaton class water Cherenkov detectors, one of which is shadowed by Earth, will enable us to distinguish between the hierarchies if sin(2)theta_(13) < or approximately 10(-5), where long baseline neutrino experiments would be ineffectual.     

Physics opportunities with supernova neutrinos

The high-statistics neutrino signal from the next nearby supernova (SN) would provide a bonanza of astrophysical and particle-physics information. In particular, there are two new developments in this field: (i) The SASI instability can imprint potentially detectable short-time variations on the neutrino signal. (ii) Collective neutrino oscillations strongly modify the previous paradigm of SN neutrino oscillations with potentially detectable consequences.     

K-M Matrix and Fermion Masses

We discuss the relations between the K-M matrix and the masses of the quarks and leptons in the case of four generations, and give the exact expression of the K-M matrix in terms of the masses of quarks and leptons. The requirement that the theoretical and experimental values of the K-M ,matrix are consistent leads to an allowed range of quark masses of the fourth generation m_t'～400-1000 GeV, m_b'～50-130 GeV. In the leptonic sector.in comparison I with the neutrino oscillation experiments and supernova it seems that neutrino masses must have hierarchy as charged leptons.     

Low-mass photinos and supernova 1987A

Photinos or higgsinos with mass O(100) eV are not excluded by cosmological considerations, and their radiative decays could be responsible for the surprisingly large ultra-violet background recently detected at a red-shift z∼4. The agreement of the neutrino data from supernova 1987A with standard expectations severely restricts the energy which could have been emitted via such light photinos or higgsinos, and hence constrains the parameters of models in which they appear. In the low-mass photino case, we find that squark masses between ∼60 GeV and ∼2.5 TeV are excluded. This together with laboratory limits excludes the range of squark masses generally favoured by naturalness arguments. In the low-mass higgsino case, we exclude much of the range of ratios of Higgs VEVs favoured by many models.     

The signal from a galactic supernova: measuring the tau-neutrino mass

We have developed a comprehensive Monte Carlo analysis in order to simulate the neutrino signal from a galactic supernova in a large water Cerenkov detector. This allows us to demonstrate that, by exploiting the various features of the signal in a way which is largely independent of the supernova model, assuming only that the late-time behaviour of the signal is flavor independent, a sensitivity to a tau-neutrino mass down to the cosmologically interesting range of ≈ 25 eV for a medium luminosity burst is possible. This is the case even though the tau signal involves ≈ 50 out of ≈ 10 000 total events in a detector of the size of that proposed for “Super Kamiokande”. In addition, our results allow us to elucidate several aspects of a supernova neutrino signal in water detectors which had not been previously explored, including new results on the observability of the neutrinization burst.     

Resonant neutrino oscillations and the neutrino signature of supernovae

We examine the effects of resonant neutrino oscillations, proposed as a solution to the solar neutrino puzzle, on the neutrino signature of a Type II supernova. We find that, for parameters corresponding to an adiabatic conversion of most of the ⁸B neutrino flux, the supernova neutrino signal in a water-Čerenkov detector is altered in the following way: (1) The isotropic-to-directional event ratio increases; (2) The short time scale neutronization burst signal decreases by a factor 7, perhaps rendering it unobservable. Detection of these changes would allow one to distinguish between neutrino oscillations and solar model alterations as solutions to the solar neutrino problem. We also note that mixing of the higher energy ν_μ and ν_r's to ν_e's will enhance detection of the thermally produced ν-flux.     

Constraining the spectrum of supernova neutrinos from nu-process induced light element synthesis

We constrain energy spectra of supernova neutrinos through the avoidance of an overproduction of the 11B abundance during Galactic chemical evolution. In supernova nucleosynthesis calculations with a parametrized neutrino spectrum as a function of temperature of nu(mu,tau) and nu(mu,tau) and total neutrino energy, we find a strong neutrino temperature dependence of the 11B yield. When the yield is combined with observed abundances, the acceptable range of the nu(mu,tau) and nu(mu,tau) temperature is found to be 4.8 to 6.6 MeV. Nonzero neutrino chemical potentials would reduce this temperature range by about 10% for a degeneracy parameter eta(nu) = mu(nu)/kT(nu) smaller than 3.     

Effect of current quark masses on quark phase transitions in supernovae

The current quark mass model is adopted to study the phase transition of two-flavor quark matter to more stable three-flavor quark matter in the whole core of a supernova. It shows that the timescale of the process is shorter than 10-8 seconds, thatthe u- and d-quark masses can be neglected completely in this model, and that the temperature and the total neutrino energies in the core after the conversion increase nearly by 40% and 20% on the average compared with former results, respectively. The last result can further enhance the probability of success for a supernova explosion significantly.     

Inverted hierarchy of neutrino masses disfavored by supernova 1987A

We discuss the flavor conversion of supernova neutrinos in the three-flavor mixing scheme of neutrinos. We point out that by neutrino observation from supernova one can discriminate the inverted hierarchy of neutrino masses from the normal one if s₁₃²≳a few×10⁻⁴, irrespective of which oscillation solution to the solar neutrino problem is realized in nature. We perform an analysis of data of SN1987A and obtain a strong indication that the inverted mass hierarchy is disfavored unless s₁₃²≲a few×10⁻⁴.     

Can sterile neutrinos be the dark matter?

We use the Ly-alpha forest power spectrum measured by the Sloan Digital Sky Survey and high-resolution spectroscopy observations in combination with cosmic microwave background and galaxy clustering constraints to place limits on a sterile neutrino as a dark matter candidate in the warm dark matter scenario. Such a neutrino would be created in the early Universe through mixing with an active neutrino and would suppress structure on scales smaller than its free-streaming scale. We ran a series of high-resolution hydrodynamic simulations with varying neutrino masses to describe the effect of a sterile neutrino on the Ly-alpha forest power spectrum. We find that the mass limit is m(s) >13 keV at 95% C.L. (9 keV at 99.9%), which is above the upper limit allowed by x-ray constraints, excluding this candidate from being all of the dark matter in this model.     

TeV-scale bileptons, see-saw type II and lepton flavor violation in core-collapse supernova

Electrons and electron neutrinos in the inner core of the core-collapse supernova are highly degenerate and therefore numerous during a few seconds of explosion. In contrast, leptons of other flavors are non-degenerate and therefore relatively scarce. This is due to lepton flavor conservation. If this conservation law is broken by some non-standard interactions, ν _e are converted to ν _μ , ν _τ , and e are converted to μ. This affects the supernova dynamics and the supernova neutrino signal. We consider lepton flavor violating interactions mediated by scalar bileptons, i.e. heavy scalars with lepton number 2. It is shown that in case of TeV-mass bileptons the electron Fermi gas is equilibrated with non-electron species inside the inner supernova core at a time scale ～(1–100) ms. In particular, a scalar triplet which generates neutrino masses through the see-saw type II mechanism is considered. It is found that the supernova core is sensitive to yet unprobed values of masses and couplings of the triplet.     

Effect of current quark masses on quark phase transitions in supernovae

The current quark mass model is adopted to study the phase transition of two-flavor quark matter to more stable three-flavor quark matter in the whole core of a supernova. It shows that the timescale of the process is shorter than 10^－8 seconds, that the u- and d-quark masses can be neglected completely in this model, and that the temperature and the total neutrino energies in the core after the conversion increase nearly by 40% and 20% on the average compared with former results, respectively. The last result can further enhance the probability of success for a supernova explosion significantly.     

Detection of supernova neutrinos at spallation neutron sources

After considering supernova shock effects, Mikheyev-Smirnov-Wolfenstein effects, neutrino collective effects, and Earth matter effects, the detection of supernova neutrinos at the China Spallation Neutron Source is studied and the expected numbers of different flavor supernova neutrinos observed through various reaction channels are calculated with the neutrino energy spectra described by the Fermi-Dirac distribution and the "beta fit"distribution respectively. Furthermore, the numerical calculation method of supernova neutrino detection on Earth is applied to some other spallation neutron sources, and the total expected numbers of supernova neutrinos observed through different reactions channels are given.