Diffuse Supernova Neutrino Background Research Articles

The Diffuse Supernova Neutrino Background

The diffuse supernova neutrino background (DSNB) is the weak glow of megaelectronvolt neutrinos and antineutrinos from distant core-collapse supernovae. The DSNB has not been detected yet, but the Super-Kamiokande (SK) 2003 upper limit on the [Formula: see text] flux is close to predictions, now quite precise, that are based on astrophysical data. If SK is modified with dissolved gadolinium to reduce detector backgrounds and increase the energy range for analysis, then it should detect the DSNB at a rate of a few events per year, providing a new probe of supernova neutrino emission and the cosmic core-collapse rate. If the DSNB is not detected, then new physics will be required. Neutrino astronomy, although uniquely powerful, has proven extremely difficult—only the Sun and the nearby Supernova 1987A have been detected to date—so the promise of detecting new sources soon is exciting indeed.

Synoptic sky surveys and the diffuse supernova neutrino background: Removing astrophysical uncertainties and revealing invisible supernovae

The cumulative (anti)neutrino production from all core-collapse supernovae within our cosmic horizon gives rise to the diffuse supernova neutrino background (DSNB), which is on the verge of detectability. The observed flux depends on supernova physics, but also on the cosmic history of supernova explosions; currently, the cosmic supernova rate introduces a substantial (+/-40%) uncertainty, largely through its absolute normalization. However, a new class of wide-field, repeated-scan (synoptic) optical sky surveys is coming online, and will map the sky in the time domain with unprecedented depth, completeness, and dynamic range. We show that these surveys will obtain the cosmic supernova rate by direct counting, in an unbiased way and with high statistics, and thus will allow for precise predictions of the DSNB. Upcoming sky surveys will substantially reduce the uncertainties in the DSNB source history to an anticipated +/-5% that is dominated by systematics, so that the observed high-energy flux thus will test supernova neutrino physics. The portion of the universe (z < 1) accessible to upcoming sky surveys includes the progenitors of a large fraction (~ 87%) of the expected 10-26 MeV DSNB event rate. We show that precision determination of the (optically detected) cosmic supernova history will also make the DSNB into a strong probe of an extra flux of neutrinos from optically invisible supernovae, which may be unseen either due to unexpected large dust obscuration in host galaxies, or because some core-collapse events proceed directly to black hole formation and fail to give an optical outburst.

Mimicking diffuse supernova antineutrinos with the sun as a source

Measuring the \( \bar \nu _e \) component of the cosmic diffuse supernova neutrino background (DSNB) is the next ambitious goal for low-energy neutrino astronomy. The largest flux is expected in the lowest accessible energy bin. However, for E ≲ 15 MeV a possible signal can be mimicked by a solar \( \bar \nu _e \) flux that originates from the usual 8B neutrinos by spin-flavor oscillations. We show that such an interpretation is possible within the allowed range of neutrino electromagnetic transition moments and solar turbulent field strengths and distributions. Therefore, an unambiguous detection of the DSNB requires a significant number of events at E ≳ 15 MeV.

Shock waves in supernovae: New implications on the diffuse supernova neutrino background

We investigate shock wave effects upon the diffuse supernova neutrino background using dynamic profiles taken from hydrodynamical simulations and calculating the neutrino evolution in three flavors with the S-matrix formalism. We show that the shock wave impact is significant and introduces modifications of the relic fluxes by about $20 \%$ and of the associated event rates at the level of $10-20 \%$. Such an effect is important since it is of the same order as the rate variation introduced when different oscillation scenarios (i.e. hierarchy or $\theta_{13}$) are considered. In addition, due to the shock wave, the rates become less sensitive to collective effects, in the inverted hierarchy and when $\sin^2 2 \theta_{13}$ is between the Chooz limit and $10^{-5}$. We propose a simplified model to account for shock wave effects in future predictions.

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.

Diffuse supernova neutrino background is detectable in Super-Kamiokande

The diffuse supernova neutrino background (DSNB) provides an immediate opportunity to study the emission of MeV thermal neutrinos from core-collapse supernovae. The DSNB is a powerful probe of stellar and neutrino physics, provided that the core-collapse rate is large enough and that its uncertainty is small enough. To assess the important physics enabled by the DSNB, we start with the cosmic star formation history of Hopkins and Beacom (2006) and confirm its normalization and evolution by cross-checks with the supernova rate, extragalactic background light, and stellar mass density. We find a sufficient core-collapse rate with small uncertainties that translate into a variation of $\ifmmode\pm\else\textpm\fi{}40%$ in the DSNB event spectrum. Considering thermal neutrino spectra with effective temperatures between 4--6 MeV, the predicted DSNB is within a factor 4--2 below the upper limit obtained by Super-Kamiokande in 2003. Furthermore, detection prospects would be dramatically improved with a gadolinium-enhanced Super-Kamiokande: the backgrounds would be significantly reduced, the fluxes and uncertainties converge at the lower threshold energy, and the predicted event rate is $1.2--5.6\text{ }\text{ }\mathrm{events}\text{ }{\mathrm{yr}}^{\ensuremath{-}1}$ in the energy range 10--26 MeV. These results demonstrate the imminent detection of the DSNB by Super-Kamiokande and its exciting prospects for studying stellar and neutrino physics.

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.

Hanohano – deep ocean observatory for particle physics and geological studies

An undersea antineutrino observatory being developed in Hawaii presents excellent potential for neutrino science. The observatory is a 10-kT monolithic, scintillating organic liquid detector for deployment in the deep ocean. Its design allows for relocation from one site to another. Positioning the observatory 50-60 km distant from a nuclear reactor complex enables precision measurement of neutrino mixing parameters Δm221, θ12, and, for non-zero θ13, Δm231 and Δm232, possibly leading to determination of neutrino mass hierarchy. At a mid-Pacific location the observatory can measure the flux of neutrinos from the decay series of uranium and thorium primarily in earth's mantle, and performs a sensitive search for a hypothetical natural fission reactor in earth's core. Subsequent deployments at other mid-ocean locations would test lateral heterogeneity of uranium and thorium in earth's mantle. Sites with depth greater than ∼ 5 km allow a relatively background-free measurement of pep and CNO solar neutrinos, probing the energy region marking the transition between matter- and vacuum-dominated oscillations. The observatory provides sensitivity to galactic supernova neutrinos and their potential to reveal neutrino mass hierarchy, and to the diffuse supernova neutrino background. Initial engineering and design studies for this project are complete, an international collaboration of physicists and geologists continues to grow, and a demonstration deployment is in progress.

Low Energy Neutrino Astronomy in the future large-volume liquid-scintillator detector LENA

The recent successes in neutrino physics prove that liquid-scintillator detectors allow to combine high energy resolution, efficient means of background reduction, and a large detection volume. In the planned LENA (Low Energy Neutrino Astronomy) experiment, a target mass of 50 kt will enable the investigation of a variety of terrestrial and astrophysical neutrino sources. The high-statistics spectroscopy of geoneutrinos, solar neutrinos and supernova neutrinos will provide new insights in the heat production processes of Earth and Sun, and the workings of a gravitational collapse. The same measurements will as well investigate neutrino properties as oscillation parameters and mass hierarchy. A first spectroscopic measurement of the low flux of diffuse supernova neutrino background is within the sensitivity of the LENA detector. Finally, a life-time limit of several 1034 years can be set to the proton decay into proton and anti-neutrino, testing the predictions of SUSY theory. The present contribution includes a review of the scientific studies that were performed in the last years as well as a report on currently on-going R&D activities.

The effect of collective flavor oscillations on the diffuse supernova neutrino background

Collective flavor oscillations driven by neutrino–neutrino interactions inside core-collapsesupernovae have now been shown to drastically alter the resultant neutrino fluxes. Thiswould in turn significantly affect the diffuse supernova neutrino background (DSNB),created by all core-collapse supernovae that have exploded in the past. In view of thesecollective effects, we re-analyze the potential for detecting the DSNB in currently runningand planned large scale detectors meant for detecting both and νe. We find that the event rate can be different from previous estimates by up to50%, depending onthe value of θ13. The next generation detectors should be able to observe DSNB fluxes. Under certainconducive conditions, one could learn about neutrino parameters. For instance, it might bepossible to determine the neutrino mass hierarchy, even if .

Low-energy neutrino observation at Super-Kamiokande-III

Super-Kamiokande-III (SK-III) has been started its observation in July 2006. The main targets of low-energy neutrinos are the solar neutrinos and the diffuse supernova neutrino background. In this paper, the current status of the solar neutrino observation in SK-III is reported.

Neutrino spectrum from SN 1987A and from cosmic supernovae

The detection of neutrinos from SN 1987A by the Kamiokande-II and Irvine-Michigan-Brookhaven detectors provided the first glimpse of core collapse in a supernova, complementing the optical observations and confirming our basic understanding of the mechanism behind the explosion. One long-standing puzzle is that, when fitted with thermal spectra, the two independent detections do not seem to agree with either each other or typical theoretical expectations. We assess the compatibility of the two data sets in a model-independent way and show that they can be reconciled if one avoids any bias on the neutrino spectrum stemming from theoretical conjecture. We reconstruct the neutrino spectrum from SN 1987A directly from the data through nonparametric inferential statistical methods and present predictions for the diffuse supernova neutrino background based on SN 1987A data. We show that this prediction cannot be too small (especially in the 10--18 MeV range), since the majority of the detected events from SN 1987A were above 18 MeV (including 6 events above 35 MeV), suggesting an imminent detection in operational and planned detectors.

A Search for Neutrinos from the SolarhepReaction and the Diffuse Supernova Neutrino Background with the Sudbury Neutrino Observatory

A search has been made for neutrinos from the hep reaction in the Sun and from the diffuse supernova neutrino background (DSNB) using data collected during the first operational phase of the Sudbury Neutrino Observatory, with an exposure of 0.65 kilotonne-years. For the hep neutrino search, two events are observed in the effective electron energy range of 14.3 MeV <T_eff< 20 MeV where 3.1 background events are expected. After accounting for neutrino oscillations, an upper limit of 2.3x10^4 cm^-2s^-1 at the 90% confidence level is inferred on the integral total flux of hep neutrinos. For DSNB neutrinos, no events are observed in the effective electron energy range of 21 MeV <T_eff< 35 MeV and, consequently, an upper limit on the nu_e component of the DSNB flux in the neutrino energy range of 22.9 MeV <E_nu< 36.9 MeV of 70 cm^-2s^-1 is inferred at the 90% confidence level. This is an improvement by a factor of 6.5 on the previous best upper limit on the hep neutrino flux and by two orders of magnitude on the previous upper limit on the $\nu_e$ component of the DSNB flux.

New test of supernova electron neutrino emission using Sudbury Neutrino Observatory sensitivity to the diffuse supernova neutrino background

Supernovae are rare nearby, but they are not rare in the Universe, and all past core-collapse supernovae contributed to the Diffuse Supernova Neutrino Background (DSNB), for which the near-term detection prospects are very good. The Super-Kamiokande limit on the DSNB electron {\it antineutrino} flux, $\phi(E_\nu > 19.3 {\rm MeV}) < 1.2$ cm$^{-2}$ s$^{-1}$, is just above the range of recent theoretical predictions based on the measured star formation rate history. We show that the Sudbury Neutrino Observatory should be able to test the corresponding DSNB electron {\it neutrino} flux with a sensitivity as low as $\phi(22.5 < E_\nu < 32.5 {\rm MeV}) \simeq 6 $ cm$^{-2}$ s$^{-1}$, improving the existing Mont Blanc limit by about three orders of magnitude. While conventional supernova models predict comparable electron neutrino and antineutrino fluxes, it is often considered that the first (and forward-directed) SN 1987A event in the Kamiokande-II detector should be attributed to electron-neutrino scattering with an electron, which would require a substantially enhanced electron neutrino flux. We show that with the required enhancements in either the burst or thermal phase $\nu_e$ fluxes, the DSNB electron neutrino flux would generally be detectable in the Sudbury Neutrino Observatory. A direct experimental test could then resolve one of the enduring mysteries of SN 1987A: whether the first Kamiokande-II event reveals a serious misunderstanding of supernova physics, or was simply an unlikely statistical fluctuation. Thus the electron neutrino sensitivity of the Sudbury Neutrino Observatory is an important complement to the electron antineutrino sensitivity of Super-Kamiokande in the quest to understand the DSNB.

A search for neutrinos from the solar hep reaction and the diffuse supernova neutrino background with the Sudbury Neutrino Observatory

A search for neutrinos from the solar hep reaction and the diffuse supernova neutrino background with the Sudbury Neutrino Observatory

The concordance cosmic star formation rate: implications from and for the supernovaneutrino and gamma ray backgrounds

We constrain the cosmic star formation rate (CSFR) by requiring that massive starsproduce the observed UV, optical, and IR light and at the same time not overproduce thediffuse supernova neutrino background as bounded by Super-Kamiokande. With themassive star component so constrained we then show that a reasonable choice of stellarinitial mass function and other parameters results in SNIa rates and iron yields in goodagreement with data. In this way we define a ‘concordance’ CSFR that predicts the opticalSNII rate and the SNIa contribution to the MeV cosmic gamma ray background. TheCSFR constrained to reproduce these and other proxies of intermediate and massivestar formation is more clearly delineated than if it were measured by any onetechnique and has the following testable consequences: (1) SNIa contribute onlya small fraction of the MeV cosmic gamma ray background, (2) massive starcore collapse is nearly always accompanied by a successful optical SNII, and (3)the diffuse supernova neutrino background is tantalizingly close to detectability.

Antineutrino Spectroscopy with Large Water Čerenkov Detectors

We propose modifying large water C erenkov detectors by the addition of 0.2% gadolinium trichloride, which is highly soluble, newly inexpensive, and transparent in solution. Since Gd has an enormous cross section for radiative neutron capture, with summation operatorE(gamma)=8 MeV, this would make neutrons visible for the first time in such detectors, allowing antineutrino tagging by the coincidence detection reaction nu (e)+p-->e(+)+n (similarly for nu (mu)). Taking Super-Kamiokande as a working example, dramatic consequences for reactor neutrino measurements, first observation of the diffuse supernova neutrino background, galactic supernova detection, and other topics are discussed.