Observed Neutrino Events Research Articles

Supernova signatures of neutrino mass ordering

A suite of detectors around the world is poised to measure the flavor-energy-time evolution of the ten-second burst of neutrinos from a core-collapse supernova occurring in the Milky Way or nearby. Next-generation detectors to be built in the next decade will have enhanced flavor sensitivity and statistics. Not only will the observation of this burst allow us to peer inside the dense matter of the extreme event and learn about the collapse processes and the birth of the remnant, but the neutrinos will bring information about neutrino properties themselves. This review surveys some of the physical signatures that the currently-unknown neutrino mass pattern will imprint on the observed neutrino events at Earth, emphasizing the most robust and least model-dependent signatures of mass ordering.

Estimating the core compactness of massive stars with Galactic supernova neutrinos

We suggest the future detection of neutrinos from a Galactic core-collapse supernova can be used to infer the progenitor’s inner mass density structure. We present the results from 20 axisymmetric core-collapse supernova simulations performed with progenitors spanning initial masses in the range 11–, and focus on their connections to the progenitor compactness. The compactness is a measure of the mass density profile of the progenitor core and recent investigations have suggested its salient connections to the outcomes of core collapse. Our simulations confirm a correlation between the neutrinos emitted during the accretion phase and the progenitor’s compactness, and that the ratio of observed neutrino events during the first hundreds of milliseconds provides a promising handle on the progenitor’s inner structure. Neutrino flavor mixing during the accretion phase remains a large source of uncertainty.

Indirect searches for dark matter particles with the Super-Kamiokande detector

A search for dark matter (DM) induced neutrinos from the Milky Way has been performed based on data collected with the Super-Kamiokande detector in the years 1996–2014. Dark matter density is expected to be largely enhanced in the area of the Galactic Center (GC) which may result in increased annihilation/deacy of relic particles in that region. The analysis focuses on the search for angular anisotropy in the number of observed neutrino events between the GC and the other part of the sky where the expected flux of dark matter annihilation/ decay products is low. No excess of neutrinos from the GC region has been observed with respect to atmospheric neutrino background. Upper limits on the self-annihilation cross-section and lower limits on the lifetime have been obtained for dark matter particle masses ranging from 1GeV to 10TeV for various dark matter halo models.

Erratum: ‘How many of the observed neutrino events can be described by cosmic ray interactions in the Milky Way?’

Cosmic rays diffuse through the interstellar medium and interact with matter and radiations as long as they are trapped in the Galactic magnetic field. The IceCube experiment has detected some TeV-PeV neutrino events whose origin is yet unknown. We study if all or a fraction of these events can be described by the interactions of cosmic rays with matter. We consider the average target density needed to explain them for different halo sizes and shapes, the effect of the chemical composition of the cosmic rays, the impact of the directional information of the neutrino events, and the constraints from gamma ray bounds and their direction. We do not require knowledge of the cosmic ray escape time or injection for our approach. We find that, given all constraints, at most 0.1 of the observed neutrino events in Ice-Cube can be described by cosmic ray interactions with matter. In addition, we demonstrate that the currently established chemical composition of the cosmic rays contradicts a peak of the neutrino spectrum at PeV energies.

Reconciling neutrino flux from heavy dark matter decay and recent events at IceCube

The IceCube detector has recently reported the observation of 28 events at previously unexplored energies. While the statistics of the observed events are still low, these events hint at the existence of a neutrino flux over and above the atmospheric neutrino background. We investigate the possibility that a significant component of the additional neutrino flux originates due to the decay of a very heavy dark matter (VHDM) particle via several possible channels into standard model particles. We show that a combination of a power law astrophysical neutrino spectrum and the neutrino flux from the decay of a DM species of mass in the range $150-400$ TeV improves the fit to the observed neutrino events than that obtained from a best-fit astrophysical flux alone. Assuming the existence of an astrophysical background described by the IC best-fit, we also show that, for the decay of even heavier DM particles ($m_{\text{DM}} \sim 1$ PeV), the same observations impose significant constraints on the decay lifetimes. Allowing the astrophysical flux normalization to vary leads to modifications of these limits, however, there is still a range of dark matter mass and lifetime that is excluded by the IC results.

How many of the observed neutrino events can be described by cosmic ray interactions in the Milky Way?

Cosmic rays diffuse through the interstellar medium and interact with matter and radiations as long as they are trapped in the Galactic magnetic field. The IceCube experiment has detected some TeV–PeV neutrino events whose origin is yet unknown. We study if all or a fraction of these events can be described by the interactions of cosmic rays with matter. We consider the average target density needed to explain them for different halo sizes and shapes, the effect of the chemical composition of the cosmic rays, the impact of the directional information of the neutrino events, and the constraints from gamma-ray bounds and their direction. We do not require knowledge of the cosmic ray escape time or injection for our approach. We find that, given all constraints, at most 0.1 of the observed neutrino events in IceCube can be described by cosmic ray interactions with matter. In addition, we demonstrate that the currently established chemical composition of the cosmic rays contradicts a peak of the neutrino spectrum at PeV energies.

Measurements of the T2K neutrino beam properties using the INGRID on-axis near detector

Precise measurement of neutrino beam direction and intensity was achieved based on a new concept with modularized neutrino detectors. INGRID (Interactive Neutrino GRID) is an on-axis near detector for the T2K long baseline neutrino oscillation experiment. INGRID consists of 16 identical modules arranged in horizontal and vertical arrays around the beam center. The module has a sandwich structure of iron target plates and scintillator trackers. INGRID directly monitors the muon neutrino beam profile center and intensity using the number of observed neutrino events in each module. The neutrino beam direction is measured with accuracy better than 0.4mrad from the measured profile center. The normalized event rate is measured with 4% precision.

STATUS OF THE MINOS EXPERIMENT

The MINOS experiment is designed to search for neutrino oscillations. A neutrino beam from Fermilab is observed by the Near and Far detectors, separated by 735km. A comparison of the observed neutrino events at the two locations allows a measurement of the oscillation parameters to be made. Commissioning of the Near detector is underway and the Far detector is collecting cosmic ray and atmospheric neutrino data. Analysis of the atmospheric neutrino events has begun and neutrino, antineutrino event separation has been achieved. Data collection with the NuMI beam will begin in December 2004.

Atmospheric neutrinos in Super-Kamiokande

In this paper I will present the updated results from the Super-Kamiokande atmospheric neutrino analysis. We have now completed the analysis of 1144 live days of data corresponding to an exposure of 70 kt-years. I will discuss our measurements of contained, partially contained and entering events and the flavor ratio and angular distribution of the observed neutrino events. Using these observations, we calculate the neutrino oscillation parameters that best represent the data and our limits on a sterile neutrino interpretation of the oscillation.

Resonant helicity flip of the electron neutrino due to the magnetic moment and the dynamics of the supernova

It is argued that the magnetic moment of the electron neutrino ω≈10 −11 μ B is most likely to induce a adiabatic resonant (i.e. complete) helicity flip of the neutrino in the layer of the supernova core with density ϱ≈10 12g cm −3. Therefore contrary to previous claims such a value of μ does not lead to an inconsistency with the observed neutrino events from the supernova SN1987A. Moreover, the process proposed gives rise to a rapid energy transfer from the inner core to the outer layers which can explain the mechanism of blowing off the supernovas envelope.

Supernova theory and the neutrinos from SN1987a

A summary of the physical processes occurring in gravitational collapse supernovae is presented. Special emphasis is placed on those areas of nuclear physics in which experimental results will play the biggest role. The character of neutrino emissions in a supernova event is also detailed. Studies of the afternath of a supernova explosion, the birth of a neutron star, are examined: this is the phase in which most of the neutrino emissions occur. Finally, an analysis of the observed neutrino events is presented. The general conclusion is that the standard supernova and neutron star cooling calculations are in remarkably good agreement with experiment. There seems to be no reason to assume the observed bunching in the data is real. The observed low energy neutrinos, and the signal duration of several seconds, attest to the diffusion, not streaming, of the neutrinos from the lepton-rich neutron star. The deduced total energy emitted is about 3 × 10 53 ergs to within 50% or so, just what is expected for a 1.4 M⊙ neutron star.