Antineutrino spectroscopy with large water Cerenkov 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.     

Upward muon signals at neutrino detectors as a probe of dark matter properties

We study upward muon flux at neutrino detectors such as Super-Kamiokande resulting from high-energy neutrinos produced by the dark matter annihilation/decay at the Galactic center. In particular, we distinguish showering and non-showering muons as their energy loss processes inside the detector, and show that this information is useful for discriminating dark matter models.     

Probing the origins of neutrino mass with supernova data

We study type II supernova signatures of neutrino mass generation via symmetry breaking at a scale in the range from keV to MeV. The scalar responsible for symmetry breaking is thermalized in the supernova core and restores the symmetry. The neutrinos from scalar decays have about half the average energy of thermal neutrinos. The Bose-Einstein distribution of the scalars can be established with a megaton water Cerenkov detector. The discovery of the bimodal neutrino flux is, however, well within the reach of the Super-Kamiokande detector, without a detailed knowledge of the supernova parameters.     

Experimental measurements of atmospheric neutrinos

This talk reports the latest indications of an anomaly in the measurements of atmospheric neutrinos. New results from Soudan-2 and Super-Kamiokande provide evidence that the ratio of ν_μ to ν_e interactions is not as expected. High energy Super-Kamiokande data indicates the cause is a deficit of upward-going ν_μ, and the zenith angle dependence of the effect is consistent with neutrino oscillations. Upward-going muon measurements by several detectors are discussed, but in total they provide inconclusive evidence for the anomaly.     

Low-energy neutrino measurements

Low-energy solar neutrino detection plays a fundamental role in understanding both solar astrophysics and particle physics. After introducing the open questions on both fields, we review here the major results of the last two years and expectations for the near future from Borexino, Super-Kamiokande, SNO and KamLAND experiments as well as from upcoming (SNO+) and planned (LENA) experiments. Scintillator neutrino detectors are also powerful antineutrino detectors which can detect neutrinos emitted by the Earth crust and mantle. First measurements of geoneutrinos have occurred which can bring fundamental contribution in understanding the geophysics of the planet.     

Low-energy anti-neutrinos from the sun

If neutrino conversions within the Sun result in partial polarization of initial solar neutrino fluxes, then a new opportunity arises to observe the 's in future neutrino experiments in the low energy region (such as BOREXINO or HELLAZ) and thus to probe the Majorana nature of the neutrinos. The conversions may take place for low energy solar neutrinos while being unobservable at the Kamiokande and Super-Kamiokande experiments.     

Tau neutrinos favored over sterile neutrinos in atmospheric muon neutrino oscillations

The previously published atmospheric neutrino data did not distinguish whether muon neutrinos were oscillating into tau neutrinos or sterile neutrinos, as both hypotheses fit the data. Using data recorded in 1100 live days of the Super-Kamiokande detector, we use three complementary data samples to study the difference in zenith angle distribution due to neutral currents and matter effects. We find no evidence favoring sterile neutrinos, and reject the hypothesis at the 99% confidence level. On the other hand, we find that oscillation between muon and tau neutrinos suffices to explain all the results in hand.     

Atmospheric Neutrinos as a Tool for Exploring the Earth’s Inner Parts

Investigation of the Earth’s inner parts requires developing new methods. It is well known that atmospheric neutrinos traverse the Earth, undergoing virtually no interaction. The change in the neutrino flux is due exclusively to neutrino oscillations, which are enhanced by the effect of Earth’s matter. At the present time, there are two projects outside Russia (PINGU and ORCA) that are aimed at detecting atmospheric neutrinos that traversed the Earth, which are supposed to be used for purposes of Earth’s tomography. The creation of a large neutrino detector on the basis of a liquid scintillator is planned at the BaksanNeutrino Observatory (Institute for Nuclear Research, Russian Academy of Sciences) in the North Caucasus. After testing this detector, there will arise the possibility of employing it as part of the worldwide network of neutrino detectors for studying the Earth’s inner parts.     

Recording of ultrahigh-energy astrophysical neutrinos

This review is devoted to the problems of recording ultrahigh-energy neutrinos produced in distant astrophysical sources and during the decay of supermassive particles. Prospects for the detection of neutrino fluxes are considered based on peculiarities of the propagation and interaction of ultrahigh-energy neutrinos. The operating and planned facilities designed to investigate neutrinos from various sources are described: neutrino telescopes recording neutrino interactions in natural water and ice volumes; ground-based arrays of detectors and optical telescopes onboard orbital space stations capable of detecting neutrino-triggered horizontal air showers. Instruments based on new principles of recording neutrinos with extremely high energies are considered: radio telescopes designed to observe Cherenkov radio emission from neutrino cascades originating in such radio-transparent natural environments as the atmosphere, salt domes, ice packs, and lunar regolith; underwater acoustic detectors. It is shown that putting new facilities into operation will allow neutrinos from most of the known astrophysical sources with energies differing by more than ten orders of magnitude, from 10¹² to 10²²–10²⁴ eV, to be recorded.     

Theoretical antineutrino detection,direction and ranging at long distances

In this paper we introduce the concept of what we call “NUDAR” (NeUtrino Direction and Ranging), making the point that measurements of the observed energy and direction vectors can be employed to passively deduce the exact three-dimensional location and thermal power of geophysical and anthropogenic neutrino sources from even a single detector. Earlier studies have presented the challenges of long-range detection, dominated by the unavoidable inverse-square falloff in neutrinos, which force the use of kiloton scale detectors beyond a few kilometers. Earlier work has also presented the case for multiple detectors, and has reviewed the background challenges. We present the most precise background estimates to date, all handled in full three dimensions, as functions of depth and geographical location. For the present calculations, we consider a hypothetical 138 kiloton detector which can be transported to an ocean site and deployed to an operational depth. We present a Bayesian estimation framework to incorporate any a priori knowledge of the reactor that we are trying to detect, as well as the estimated uncertainty in the background and the oscillation parameters. Most importantly, we fully employ the knowledge of the reactor spectrum and the distance-dependent effects of neutrino oscillations on such spectra. The latter, in particular, makes possible determination of range from one location, given adequate signal statistics. Further, we explore the rich potential of improving detection with even modest improvements in individual neutrino direction determination. We conclude that a 300 MW_th reactor can indeed be geolocated, and its operating power estimated with one or two detectors in the hundred kiloton class at ranges out to a few hundred kilometers. We note that such detectors would have natural and non-interfering utility for scientific studies of geo-neutrinos, neutrino oscillations, and astrophysical neutrinos. This motivates the development of cost effective methods of constructing and deploying such next generation detectors.     

Oscillation of Dirac and Majorana neutrinos from muon decay in the case of a general interaction

We analyse the possibility of distinguishing Dirac and Majorana neutrinos in future neutrino factory experiments in which neutrinos are produced in muon decay when, in addition to a vector type as in the SM, there are also scalar interactions. We check this possibility in an experiment with a near detector, where the observed neutrinos do not oscillate, and in a far detector, after the neutrino oscillations. Neglecting higher-order corrections, even neutrino observation in the near detector does not give a chance to differentiate their character. However, this possibility appears in the leading-order after the neutrino oscillations observed in far detector.     

Possible violation of the spin-statistics relation for neutrinos: checking through future galactic supernova

We use the detection of neutrinos from a future galactic type-II supernova event in a water Cerenkov detector like Super-Kamiokande to constrain the possible violation of spin-statistics by neutrinos resulting in their obeying a mixed statistics instead of Fermi–Dirac.     

Matter induced neutrino decay and solar antineutrinos

The properties of matter-induced neutrino decay with majoron emission are analysed in some details for the cases of Majorana, ZKM and Dirac neutrinos. The result of such a decay of solarv _e 's in the sun interior could be the appearance of \(\bar \nu _e \) flux. Assuming that the neutrinos have only standard weak interactions, the solar \(\bar \nu _e \) flux can be at the border of detectability for the future large volume detectors like Borex or Super-Kamiokande. However, the \(\bar \nu _e \) signal can be considerably larger, provided the neutrinos have new non-standard interactions with matter.     

Testing the vacuum oscillation and the MSW solutions of the solar neutrino problem

Solar model independent tests of the vacuum oscillation and MSW solutions of the solar neutrino problem are considered. Detailed predictions for time (seasonal) variations of the signals due to neutrino oscillations in vacuum are given for the future solar neutrino detectors (SNO, Super-Kamiokande, BOREXINO, HELLAZ). Results on the distortions of the spectra of ⁸B neutrinos, and of e⁻ from the reaction ν + e⁻ → ν + e⁻ induced by ⁸B neutrinos, are presented in the cases of vacuum oscillations or MSW transitions for a large number of values of the relevant parameters. The possibilities to distinguish between the vacuum oscillation, the MSW adiabatic, and the MSW nonadiabatic transitions in the future solar neutrino experiments are discussed.     

Status of the SNO experiment

The Sudbury Neutrino Observatory (SNO) is a 1-kt heavy water Cherenkov detector sensitive to the flavor content of the ⁸B neutrinos originating in the Sun. The analysis of the second phase, in which salt (NaCl) was added to the heavy water in order to increase the cross section for neutrons and therefore enhance the sensitivity to solar neutrinos, is completed. Results from 391 d of data (June 2001 until September 2003) are summarized and constraints on the neutrino mixing parameters are given. The third phase of operation has started in which ³He proportional counters have been deployed inside the D₂O. These neutral-current detectors will perform a systematically independent measurement of the Solar-neutrino flux on a event-by-event basis. SNO finishes data taking at the end of 2006 and the heavy water will be removed. A new experiment using liquid scintillator to measure the pep solar neutrinos and geoneutrinos is proposed and will be described briefly. for the SNO Collaboration The text was submitted by the author in English.     

Seasonal and energy dependence of solar neutrino vacuum oscillations

We make a global vacuum neutrino oscillation analysis of solar neutrino data, including the seasonal and energy dependence of the recent Super-Kamiokande 708-day results. The best fit parameters for ν_e oscillations to an active neutrino are δm²=4.42×10⁻¹⁰ eV², sin²2θ=0.93. The allowed mixing angle region is consistent with bi-maximal mixing of three neutrinos. Oscillations to a sterile neutrino are disfavored. Allowing an enhanced hep neutrino flux does not significantly alter the oscillation parameters.     

Possible tests of neutrino maximal mixing and comments on matter effects

We show in a simple and general way that matter effects do not contribute to the average value of the transition probabilities of solar ν_e's into other states in the case of maximal mixing of any number of massive neutrinos. We also show that future solar neutrino experiments (Super-Kamiokande and SNO) will allow to test the model with maximal mixing of three massive neutrinos in a way that does not depend on the initial solar neutrino flux.     

Neutrino astronomy: An update

Detecting neutrinos associated with the still enigmatic sources of cosmic rays has reached a new watershed with the completion of IceCube, the first detector with sensitivity to the anticipated fluxes. In this review, we will briefly revisit the rationale for constructing kilometer-scale neutrino detectors and summarize the status of the field.     

Large-volume detector at the Baksan Neutrino Observatory for studies of natural neutrino fluxes for purposes of geo- and astrophysics

At the Baksan Neutrino Observatory (Institute for Nuclear Research, Russian Academy of Sciences, Moscow) deployed in the Caucasus mountains, it is proposed to create, at a depth corresponding to 4760 mwe, a large-volume neutrino detector on the basis of a liquid scintillator with a target mass of 10 kt. The detector in question is intended for recording natural fluxes of neutrinos whose energy may be as low as 100MeV. Neutrino fluxes from various sources are considered in the present study, and the expected effect in the proposed detector is estimated. The detector hat is being developed at the Baksan Neutrino Observatorywill become part of the world network of neutrino detectors for studying natural neutrino fluxes.     

Working group report: Neutrino and astroparticle physics

This is the report of neutrino and astroparticle physics working group at WHEPP-7. Discussions and work on CP violation in long baseline neutrino experiments, ultra high energy neutrinos, supernova neutrinos and water Cerenkov detectors are discussed.