Terrestrial Neutrino Detectors Research Articles

Neutrino spin-flavour precession in magnetized white dwarf

Due to notoriously small value of the neutrino magnetic moment, the phenomena of neutrino spin flavour precession (SFP) require a very high magnetic field. This makes only a handful of systems suitable to study this phenomenon. By the observation of SFP, the Dirac and Majorana nature of neutrinos is expected to be distinguished. In this work, we point out the potential of the white dwarf (WD) system in studying the spin-flavour oscillation of neutrinos. From recent analysis, it has been found that young isolated WDs may harbour very strong internal magnetic field, even without exhibiting any surface magnetic field. The presence of a magnetic field enhances the cooling process and along with that, renders the spin-flavour oscillation of neutrinos emitted in the neutrino cooling process. Employing the standard WD specifications, we analyse whether a magnetized WD is a suitable environment to distinguish between the Dirac and Majorana nature of the neutrino. Higher value of spin flavour transition probability implies reduced active neutrino flux which is possible to be estimated in terrestrial neutrino detectors. We find that for the current upper bound on the neutrino magnetic moment, the spin flavour transition probability of Dirac neutrinos is much higher in comparison to the Majorana neutrino which converts the active neutrino flavours to sterile in a significant amount. We also examine the sensitivity of the spin flavour transition probability to the neutrino magnetic moment.

Supernova neutrino signals based on long-term axisymmetric simulations

ABSTRACT We study theoretical neutrino signals from core-collapse supernova (CCSN) computed using axisymmetric CCSN simulations that cover the post-bounce phase up to ∼4 s. We provide basic quantities of the neutrino signals such as event rates, energy spectra, and cumulative number of events at some terrestrial neutrino detectors, and then discuss some new features in the late phase that emerge in our models. Contrary to popular belief, neutrino emissions in the late phase are not always steady, but rather have temporal fluctuations, the vigour of which hinges on the CCSN model and neutrino flavour. We find that such temporal variations are not primarily driven by proto-neutron star convection, but by fallback accretion in exploding models. We assess the detectability of these temporal variations, and find that IceCube is the most promising detector with which to resolve them. We also update fitting formulae first proposed in our previous paper for which the total neutrino energy emitted at the CCSN source is estimated from the cumulative number of events in each detector. This will be a powerful technique with which to analyse real observations, particularly for low-statistics data.

Pulsational Pair-instability Supernovae. II. Neutrino Signals from Pulsations and Their Detection by Terrestrial Neutrino Detectors

Abstract A Pulsational Pair-instability supernova (PPISN) evolves from a massive star with a mass ∼80–140 M ⊙ that develops electron–positron pair-instability after hydrostatic He-burning in the core has finished. In Leung et al. (Paper I), we examined the evolutionary tracks and the pulsational mass-loss history of this class of stars. In this paper, we analyze the thermodynamical history to explore the neutrino observables of PPISNe. We compute the neutrino light curves and spectra during pulsation. We then study the detailed neutrino emission profiles of these stars and estimate the expected neutrino detection count for different terrestrial neutrino detectors, including, e.g., KamLAND and Super-Kamiokande. Finally, we compare the neutrino pattern of PPISN with other types of supernovae based on a canonical 10 kt detector. The predicted neutrino signals can provide an early warning for telescopes to trace for the early time optical signals. The implications of neutrino physics on the expected detection are also discussed.

Neutrino Emissions in All Flavors up to the Pre-bounce of Massive Stars and the Possibility of Their Detections

Abstract This paper is a sequel to our 2015 paper, Kato et al., which calculated the luminosities and spectra of electron-type anti-neutrinos ( ν ¯ e ) from the progenitors of core-collapse supernovae. Expecting that the capability to detect electron-type neutrinos ( ν e ) will increase dramatically with the emergence of liquid-argon detectors such as DUNE, we broaden the scope in this study to include all flavors of neutrinos emitted from the pre-bounce phase. We pick up three progenitor models of electron capture supernovae (ECSNe) and iron-core collapse supernovae (FeCCSNe). We find that the number luminosities reach ∼1057 s–1 and ∼1053 s–1 at maximum for ν e and ν ¯ e , respectively. We also estimate the numbers of detection events at terrestrial neutrino detectors including DUNE, taking flavor oscillations into account and assuming the distance to the progenitors to be 200 pc. It is demonstrated that ν ¯ e from the ECSN progenitor will be undetected at almost all detectors, whereas we will be able to observe ≳15,900 ν e at DUNE for the inverted mass hierarchy. From the FeCCSN progenitors, the number of ν ¯ e events will be largest for JUNO, 200–900 ν ¯ e , depending on the mass hierarchy, whereas the number of ν e events at DUNE is ≳ 2100 for the inverted mass hierarchy. These results imply that the detection of ν ¯ e is useful to distinguish progenitors of FeCCSNe from those of ECSNe, while ν e will provide us with detailed information on the collapse phase regardless of the type and mass of the progenitor.

DETECTING THE SUPERNOVA BREAKOUT BURST IN TERRESTRIAL NEUTRINO DETECTORS

ABSTRACT We calculate the distance-dependent performance of a few representative terrestrial neutrino detectors in detecting and measuring the properties of the ν e breakout burst light curve in a Galactic core-collapse supernova. The breakout burst is a signature phenomenon of core collapse and offers a probe into the stellar core through collapse and bounce. We examine cases of no neutrino oscillations and oscillations due to normal and inverted neutrino-mass hierarchies. For the normal hierarchy, other neutrino flavors emitted by the supernova overwhelm the ν e signal, making a detection of the breakout burst difficult. For the inverted hierarchy (IH), some detectors at some distances should be able to see the ν e breakout burst peak and measure its properties. For the IH, the maximum luminosity of the breakout burst can be measured at 10 kpc to accuracies of ∼30% for Hyper-Kamiokande (Hyper-K) and ∼60% for the Deep Underground Neutrino Experiment (DUNE). Super-Kamiokande (Super-K) and Jiangmen Underground Neutrino Observatory (JUNO) lack the mass needed to make an accurate measurement. For the IH, the time of the maximum luminosity of the breakout burst can be measured in Hyper-K to an accuracy of ∼3 ms at 7 kpc, in DUNE to ∼2 ms at 4 kpc, and JUNO and Super-K can measure the time of maximum luminosity to an accuracy of ∼2 ms at 1 kpc. Detector backgrounds in IceCube render a measurement of the ν e breakout burst unlikely. For the IH, a measurement of the maximum luminosity of the breakout burst could be used to differentiate between nuclear equations of state.

The status of the study of solar CNO neutrinos in the Borexino experiment

Although less than 1% of solar energy is generated in the CNO cycle, it plays a critical role in astrophysics, since this cycle is the primary source of energy in certain more massive stars and at later stages of evolution of solar-type stars. Electron neutrinos are produced in the CNO cycle reactions. These neutrinos may be detected by terrestrial neutrino detectors. Various solar models with different abundances of elements heavier than helium predict different CNO neutrino fluxes. A direct measurement of the CNO neutrino flux could help distinguish between these models and solve several other astrophysical problems. No CNO neutrinos have been detected directly thus far, and the best upper limit on their flux was set in the Borexino experiment. The work on reducing the background in the region of energies of CNO neutrinos (up to 1.74 MeV) and developing novel data analysis methods is presently under way. These efforts may help detect the CNO neutrino flux in the Borexino experiment at the level predicted by solar models.

Large-scale calculations of supernova neutrino-induced reactions inZ=8–82 target nuclei

Background: In the environment of high neutrino fluxes provided in core-collapse supernovae or neutron star mergers, neutrino-induced reactions with nuclei contribute to the nucleosynthesis processes. A number of terrestrial neutrino detectors are based on inelastic neutrino-nucleus scattering and modeling of the respective cross sections allow predictions of the expected detector reaction rates.Purpose: To provide a self-consistent microscopic description of neutrino-nucleus cross sections involving a large pool of $Z=8$--82 nuclei for the implementation in models of nucleosynthesis and neutrino detector simulations.Methods: Self-consistent theory framework based on relativistic nuclear energy density functional is employed to determine the nuclear structure of the initial state and relevant transitions to excited states induced by neutrinos. The weak neutrino-nucleus interaction is employed in the current-current form and a complete set of transition operators is taken into account.Results: We perform large-scale calculations of charged-current neutrino-nucleus cross sections, including those averaged over supernova neutrino fluxes, for the set of even-even target nuclei from oxygen toward lead ($Z=8$--82), spanning $N=8$--182 (OPb pool). The model calculations include allowed and forbidden transitions up to $J=5$ multipoles.Conclusions: The present analysis shows that the self-consistent calculations result in considerable differences in comparison to previously reported cross sections, and for a large number of target nuclei the cross sections are enhanced. Revision in modeling $r$-process nucleosynthesis based on a self-consistent description of neutrino-induced reactions would allow an updated insight into the origin of elements in the Universe and it would provide the estimate of uncertainties in the calculated element abundance patterns.

Postbounce Evolution of Core‐Collapse Supernovae: Long‐Term Effects of the Equation of State

We study the evolution of supernova core from the beginning of gravitational collapse of a 15Msolar star up to 1 second after core bounce. We present results of spherically symmetric simulations of core-collapse supernovae by solving general relativistic neutrino-radiation-hydrodynamics in the implicit time-differencing. We aim to explore the evolution of shock wave in a long term and investigate the formation of protoneutron star together with supernova neutrino signatures. These studies are done to examine the influence of equation of state (EOS) on the postbounce evolution of shock wave in the late phase and the resulting thermal evolution of protoneutron star. We make a comparison of two sets of EOS, that is, by Lattimer and Swesty (LS-EOS) and by Shen et al.(SH-EOS). We found that, for both EOSs, the core does not explode and the shock wave stalls similarly in the first 100 milliseconds after bounce. The revival of shock wave does not occur even after a long period in either cases. However, the recession of shock wave appears different beyond 200 milliseconds after bounce, having different thermal evolution of central core. A more compact protoneutron star is found for LS-EOS than SH-EOS with a difference in the central density by a factor of ~2 and a difference of ~10 MeV in the peak temperature. Resulting spectra of supernova neutrinos are different to the extent that may be detectable by terrestrial neutrino detectors.

On detecting stellar collapse with neutrinos

view Abstract Citations (31) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On detecting stellar collapse with neutrinos Burrows, A. Abstract The author estimates the distances out to which various terrestrial neutrino detectors can see a stellar collapse. With these ranges, neutrino burst detection rates are obtained. The mean time between detections is expected to be rather long. A realistic estimate for this time is ≡50 - 100 years. Whether this is indeed the case depends sensitively on the as yet unknown mean energy of the emitted neutrinos and the galactic collapse rate. Publication: The Astrophysical Journal Pub Date: August 1984 DOI: 10.1086/162371 Bibcode: 1984ApJ...283..848B Keywords: Gravitational Collapse; Neutrinos; Stellar Radiation; Supernovae; Bursts; Radiation Detectors; Radiation Measurement; Astrophysics full text sources ADS |