Supernova Relic Neutrinos Research Articles

Implications of the pseudo-Dirac scenario for ultra high energy neutrinos from GRBs

The source of Ultra High Energy Cosmic Rays (UHECR) is still an unresolved mystery. Up until recently, sources of Gamma Ray Bursts (GRBs) had been considered as a suitable source for UHECR. Within the fireball model, the UHECR produced at GRBs should be accompanied with a neutrino flux detectable at the neutrino telescope such as IceCube. Recently, IceCube has set an upper bound on the neutrino flux accompanied by GRBs about 3.7 times below the prediction. We investigate whether this deficit can be explained by the oscillation of the active neutrinos to sterile neutrinos en route from the source to the detectors within the pseudo-Dirac scenario. We then discuss the implication of this scenario for diffuse supernova relic neutrinos.

Search for Supernova Relic Neutrinos at Super-Kamiokande

The search for a supernova relic neutrino (SRN) signal at the Super-Kamiokande detector is limited by irreducible backgrounds. New work has improved our cuts to dramatically improve efficiency, lower energy threshold, and better control our backgrounds, and a new likelihood method has been developed for our limit extraction.

GADZOOKS!

The method of adding a soluble gadolinium [Gd] compound into water Cherenkov dectectors at minimal loadings will allow for a high percentage of free neutrons to capture on the Gd. The immediate positron signal follwed by the delayed 8 MeV gamma cascade will give a handle on inverse beta decays coming from the interaction of an antielectron neutrino and a proton. This handle will allow for greater background reduction, most notably needed for the detection of supernova relic neutrinos and also allows for a more precise measurement of Japanʼs reactor anti-neutrino flux and spectrum. Research and developement is now underway, in both Japan and The US, to investigate if Gd can be safely introduced into water Cherenkov detectors and if the required physics can be done.

Identification of Neutron Produced from v Interactions with Water and Its Physics Application at Super-Kamiokande IV

With the electronics upgrade in 2008, the fourth phase of Super-Kamiokande(SK) is now capable of identifying neutrons from neutrino interactions with water. A detailed study has been conducted in determining the detection efficiency and background probability. An analysis of neutron production in atmospheric neutrino data is presented, together with a preliminary result of background study for the supernova relic neutrino(SRN) study. Also discussed are prospects of future SRN searches and possible improvement of background rejection for proton decay searches with neutron identification - potentially gadolinium-enhanced - in SK and beyond.

Supernova relic neutrinos at Super-Kamiokande

The diffuse supernova relic neutrino signal has never been observed. Currently the world's best upper flux limit comes from a search for inverse beta decay of anti-neutrinos in the Super-Kamiokande (SK) detector. A new SK study utilizes a novel method of spallation tagging, improved event selection, and an expanded data set to lower the analysis energy threshold and improve overall accuracy. Full results of this new study (including a combined upper flux limit of 2.8−3.1 ν̄e events cm−2 s−1 Eν > 17.3 MeV) are presented, as well as a short update on the research and development of using Gadolinium for neutron tagging.

Supernova relic neutrino search at super-Kamiokande

A new Super-Kamiokande (SK) search for Supernova Relic Neutrinos (SRNs) was conducted using 2853 live days of data. Sensitivity is now greatly improved compared to the 2003 SK result, which placed a flux limit near many theoretical predictions. This more detailed analysis includes a variety of improvements such as increased efficiency, a lower energy threshold, and an expanded data set. New combined upper limits on SRN flux are between 2.8 and 3.0 nu_e cm^-2 s^-1 > 16 MeV total positron energy (17.3 MeV E_nu).

Research and Development for a Gadolinium Doped Water Cherenkov Detector

The proposed introduction of a soluble gadolinium (Gd) compound into water Cherenkov detectors can result in a high efficiency for the detection of free neutrons capturing on the Gd. The delayed 8 MeV gamma cascades produced by these captures, in coincidence with a prompt positron signal, serve to uniquely identify electron antineutrinos interacting via inverse beta decay. Such coincidence detection can reduce backgrounds, allowing a large Gd-enhanced water Cherenkov detector to make the first observation of supernova relic neutrinos and high precision measurements of Japan's reactor antineutrino flux, while still allowing for all current physics studies to be continued. Now, a dedicated Gd test facility is operating in the Kamioka Mine. This new facility houses everything needed to successfully operate a Gd doped water Cherenkov detector. Successful running of this facility will demonstrate that adding Gd salt to SK is both safe for the detector and is capable of delivering the expected physics benefits

A Search for supernova relic neutrinos at Super-Kamiokande

Supernova relic neutrinos (SRN) are the diffuse supernova neutrino background from all past supernovae. No experiment has succeeded in detecting SRN yet. Currently, the Super-Kamiokande experiment has the world's best flux upper limit of 1.2 ν̄e/cm2/sec for Ev < 19.3MeV. We have worked to improve this value by improving the data analysis. We have achieved better reduction efficiency and lowered the analysis energy threshold by developing a new spallation cut as well as optimizing other cuts.

Search for supernova relic neutrino at Super-Kamiokande

Supernova relic neutrinos (SRN) is diffuse supernova neutrino background from all past supernova. No experiments has succeeded in detecting SRN yet. In this paper a search for SRN was conducted using Super-Kamiokande (SK) data. SK is a large water Cherenkov detecter in Kamioka, Japan.In this analysis, 791 days' data taken in the second phase of SK (SK-II) was used and antineutrino signals in the neutrino energy range above 19.3MeV were searched. The observed spectrum is consistent with the expected background spectrum and a flux upper limit of 3.68 /cm^2 /sec was obtained with 90% confidence level. A similar search using SK-I data gave a flux upper limit of >1.25 /cm^2 /sec. By the combined analysis of SK-I and SK-II, a flux upper limit of > 1.08 /cm^2/sec was obtained.For future we are planning to improve this analysis. As a first try of the improvement, we started study of fiducial volume enlargement. Now the volume within 2m from the inner detector wall is not used for this analysis. If we can expand 1m from current boarder line, 20% larger volume can be obtained. We show the status of this improvement too.

Supernova detection

The detection of supernova neutrinos is reviewed, focusing on the current status of experiments to detect supernova burst neutrinos and supernova relic neutrinos. The capabilities of each detector currently operating and in development are assessed and the likely neutrino yield for a future supernova is estimated. It is expected that much more information will be obtained if a supernova burst were to occur in our Galaxy than was obtained for supernova SN1987A. The detection of supernova relic neutrinos is considered and it is concluded that a large volume detector with a neutron tagging technique is necessary.

Neutron tagging technique for relic supernova neutrinos in Super-Kamiokande

One of the physics goals in Super-Kamiokande (SK) is observing relic supernova neutrinos through the identification of their electron anti-neutrino component. Delayed coincidence method is capable of selecting e's in inverse β-decay together with making a large background reduction. It is therefore motivated to establish tagging technique of neutrons produced in this reaction as well as positrons in SK. Experiments were conducted to mimic inverse β-decay reactions using 0.2 % GdCl3-water solution. The solution was filled in 2.4 liters of acrylic cylindrical vessel, and an Am/Be-embedded 5 cm cube of BGO scintillator was installed in the middle of this transparent case. The whole apparatus was deployed at the detector center in SK to investigate the neutron tagging efficiency. This poster presents results of this study and discusses a feasibility of lowering an analysis threshold in SK down to ∼ 10 MeV in neutrino energy for relic supernova neutrino observation.

Neutrino Burst from Supernovae and Neutrino Oscillation

Core-collapse driven supernovae are the most luminous neutrino source in the universe. SK (Super-Kamiokande) and SNO (Sudbury Neutrino Observatory showed that neutrinos have finite masses and convert each other from the solar and atmospheric neutrino observations. The time profile and energy spectrum of neutrino burst from supernovae should be greatly modified by this effect. We review how this conversion happens in a supernova mantle and how the burst will be detected by SK and SNO. We show that implications for neutrino parameters (mass hierarchy and the mixing angle between mass eigenstate ν 1 , ν 3 ), are obtained if a supernova appears at Galactic Center. We also discuss effects of neutrino oscillation on the supernova relic neutrino observations.

Ultrahigh-energy neutrino flux as a probe of large extra dimensions

A suppression in the spectrum of ultrahigh-energy (UHE, eV) neutrinos will be present in extra-dimensional scenarios, due to enhancedneutrino–anti-neutrino annihilation processes with the supernova relic neutrinos. In then>4 scenario, n being the number of extra dimensions, neutrinos cannot be responsible for the highestenergy events observed in the UHE cosmic ray spectrum. A direct implication of theseextra-dimensional interactions would be the absence of UHE neutrinos in ongoing andfuture neutrino telescopes.

Probing late neutrino mass properties with supernova neutrinos

Models of late-time neutrino mass generation contain new interactions of the cosmic background neutrinos with supernova relic neutrinos (SRNs). Exchange of an on-shell light scalar may lead to significant modification of the differential SRN flux observed at earth. We consider an Abelian U(1) model for generating neutrino masses at low scales, and show that there are cases for which the changes induced in the flux allow one to distinguish the Majorana or Dirac nature of neutrinos, as well as the type of neutrino mass hierarchy (normal or inverted or quasidegenerate). In some region of parameter space the determination of the absolute values of the neutrino masses is also conceivable. Measurements of the presence of these effects may be possible at the next-generation water Cerenkov detectors enriched with Gadolinium, or a 100 kton liquid argon detector.

Neutrino Physics around MeV Energies

We present a brief informative overview of a broad ranges of subjects, the solar, the reactor, the geo and the supernova neutrinos (but without excluding possible biases), the topics which consist of the session “Neutrino Physics around MeV Energies” in NOW2006. Contrary to the naive expectation, the field is found to be very active in improving the performance of existing detectors, and in preparation for the development coming in the near future. The former includes excellent performance of SNO 3 He detector, successful reconstruction of SK III, and KamLAND's new “4 π ” calibration. The next data release from these experiments will be very exciting. The latter includes effort for lowering threshold in SK III, KamLAND's purification by which geo-neutrino observation becomes much cleaner, and the forthcoming 7 Be neutrino measurement by BOREXINO and KamLAND. Possible detection of relic supernova neutrinos and non-zero effect of θ 13 would bring us great excitement. Furthermore, improved new measurement of heavy element abundance in the solar atmosphere resulted in a solar model with much lower CNO ν flux and with disagreement with helioseismology, thereby bringing us a new solar puzzle.

DARK ENERGY MODELS AND SUPERNOVA RELIC NEUTRINOS

Recent cosmological observations show that the unknown energy element called dark energy dominates in the universe. In this letter, we investigate to what extent dark energy models influence supernova relic neutrino (SRN) spectra when the supernova rate could be determined by direct counting and discuss the possibility to distinguish dark energy models using future observation of SRN. We found that the total number of SRN events in GCG model will be larger than those in ΛCDM and holographic dark energy models by 20%. As a result, we find a possibility to distinguish GCG model from ΛCDM and holographic dark energy models using observation of SRN. SRN should be a unique probe into dark energy models and will play complementary roles to other observables.

A Proposal for Detecting Supernova Relic Neutrino in Super Kamiokande

We propose new trigger logic for detection of ν ¯ e with energy above 10 MeV, by identifying the inverse beta decay ν ¯ e + p → e + + n in Super Kamiokande III. This fully restored detector starts commissioning in 2006. The proposed trigger logic is intended to implement the present online system, to record the emitted 2.2 MeV γ candidates from neutron capture in pure water without increasing much online trigger rate.

Mini Z′ burst from relic supernova neutrinos and late neutrino masses

In models in which neutrinos are light, due to a low scale of symmetry breaking, additional light bosons are generically present. We show that the interaction between diffuse relic supernova neutrinos (RSN) and the cosmic background neutrinos, via exchange of these light scalars, can result in a dramatic change of the supernova (SN) neutrinos flux. Measurement of this effect with current or future experiments can provide a spectacular direct evidence for the low scale models. We demonstrate how the observation of neutrinos from SN1987A constrains the symmetry breaking scale of the above models. We also discuss how current and future experiments may confirm or further constrain the above models, either by detecting the ``accumulative resonance'' that diffuse RSN go through or via a large suppression of the flux of neutrinos from nearby < O(Mpc) SN bursts.

Neutrino signatures from the first stars

Evidence from the WMAP polarization data indicates that the Universe may have been reionized at very high redshift. It is often suggested that the ionizing UV flux originates from an early population of massive or very massive stars. Depending on their mass, such stars can explode either as type II supernovae or pair-instability supernovae, or may entirely collapse into a black hole. The resulting neutrino emission can be quite different in each case. We consider here the relic neutrino background produced by an early burst of Population III stars coupled with a normal mode of star formation at lower redshift. The computation is performed in the framework of hierarchical structure formation and is based on cosmic star formation histories constrained to reproduce the observed star formation rate at redshift z \la 6, the observed chemical abundances in damped Lyman alpha absorbers and in the intergalactic medium, and to allow for an early reionization of the Universe at z \sim 10-20. We find that although the high redshift burst of Population III stars does lead to an appreciable flux of neutrinos at relatively low energy (E_\nu \approx 1 MeV), the observable neutrino flux is dominated by the normal mode of star formation. We also find that predicted fluxes are at the present level of the SuperK limit. As a consequence, the supernova relic neutrino background has a direct impact on models of chemical evolution and/or supernova dynamics.

Neutrino decay and the supernova relic neutrino background

Future experiments will be able to observe the neutrinos coming from all the past supernovae in the universe, the so-called Supernova Relic Neutrino Background (SRNB). These neutrinos have travelled from cosmological distances before reaching the Earth. The measure of this background would be possible in the next generation of neutrino detectors. We show that the measure of the SRNB flux could give information on very long-life neutrino decays, in particular for “invisible decays”, such as ν decay into Majoron.