Twenty years of Galactic observations in searching for bursts of collapse neutrinos with the Baksan underground scintillation telescope

The results of twenty-year-long Galactic observations in neutrino radiation are summarized. Except for the recording of a neutrino signal from the supernova SN 1987A, no Galactic bursts of collapse neutrinos have been detected. An upper bound on the mean frequency of gravitational collapses in our Galaxy was obtained, f _collapse (at 90% confidence) <0.13 yr^?1.     

The LVD experiment at Gran Sasso

Summary The Large-Volume Detector (LVD) in the Gran Sasso underground Laboratory is a multipurpose detector consisting of a large volume of liquid scintillator (at present 562 tons are in data taking) interleaved with limited-streamer tubes. Several physical problems are investigated with LVD, the major being the search for neutrino bursts from gravitational stellar collapses in our Galaxy. In this paper we discuss some results on cosmic neutrinos and cosmic-ray muons obtained with the first of the five towers of LVD (operational since June 1992) and part of the second tower (operational since June 1994). The results of the search for supernovae neutrinos show that LVD is a neutrino observatory able to detect neutrinos of different flavours from gravitational stellar collapses in all our Galaxy, over a wide range of burst durations. Indeed, the carbon-based liquid-scintillator target gives a unique possibility to directly detect neutral- and charged-currents neutrino interactions with a very good signature. This characteristic of LVD allows us to make an indirect estimate of the neutrino rest mass and of neutrino oscillations from supernovae in our Galaxy. No evidence for burst candidates has been found in the data recorded from June 1992 to March 1995, for a total live time of 682 days and a total exposure of 613 tons per year. We present the results of a time coincidence analysis between low-energy signals, eventually due to neutrinos of different flavours, and γ-ray bursts (GRBs) detected by the BATSE experiment. This search covers the period from June 1993 to March 1995, during which 41 GRBs have been selected from the BATSE data. Since no excess of events in LVD has been found, upper limits on the neutrino fluxes are reported for (ν_e, p), and for neutral- and charged-currents neutrino interactions of different flavours with the C-nuclei of the scintillator. The muon intensity as a function of slant depth is presented. These measurements, obtained during a live time period of 11.556 hours, cover a slant depths range from about 3000 to about 20 000 hg/cm² of standard rock and extend over five decades of intensity. An interesting result is that the muon flux is independent of slant depth beyond a depth of about 14 000 hg/cm² of standard rock, and corresponds to near horizontal muons. This is direct evidence that this flux is due to atmospheric neutrinos interacting in the rock surrounding LVD.     

Status of the LVD experiment

The large-volume detector operating at the Gran Sasso National Laboratory, Italy, is intended primarily for detecting neutrinos from gravitational collapses in the Galaxy. The apparatus consisting of scintillation detectors, with a total scintillator mass of ～1 kt, interleaved with iron (～1 kt) has been collecting data since 1992. No candidates for neutrino bursts from collapsing stars have been found. The new upper limit of the frequency of supernova bursts in the Galaxy is reported. The results of the investigation of the space distribution of muon-produced neutrons are presented, and the possibilities for determining the charge composition of muon fluxes with energies E _μ > 5 TeV are considered.     

The search for neutrino bursts from core collapse Supernovae at the Baksan Underground Scintillation Telescope

The current status of the experiment on recording neutrino bursts from core collapse stars is presented. The actual observational time T (from June 30, 1980 until December 31, 2009) is 25.58 years. An upper bound of the mean frequency of gravitational collapse in our Galaxy f _col < 0.090 year^?1 at a 90% confidence level. The results of studying single events at the facility in the case of muon inelastic interaction of cosmic rays with the matter of the detector are presented.     

Search for stellar gravitational collapses with the MACRO detector

We present the final results of the search for stellar gravitational collapses obtained by the MACRO experiment. The detector was active for a stellar collapse search for more than 11 years and it was sensitive to collapses occurring all over in our galaxy for 8.6 years. A real time system for a prompt recognition of neutrino bursts was developed and was operating on-line for almost the whole life of the experiment. No signal compatible with a neutrino burst from a galactic supernova was observed.Received: 18 February 2003, Revised: 25 March 2004, Published online: 14 September 2004     

The large volume detector and neutrinos from collapsing stars

The major purpose of the experiments performed on the Russian-Italian Large Volume Detector (LVD) located at the Gran Sasso Underground Laboratory (Italy) is to search for neutrino bursts from gravitational collapses of stars in our Galaxy. The estimates obtained for the numbers of neutrino interactions occurring in the LVD structure in the case of collapses developing by different scenarios at the center of the Galaxy and the efficiencies of detection of these interactions for different neutrino energies are presented.     

Probing the violation of equivalence principle at a muon storage ring via neutrino oscillation

We examine the possible tests of violation of the gravitational equivalence principle (VEP) at a muon storage ring via neutrino oscillation experiments. If the gravitational interactions of the neutrinos are not diagonal in the flavour basis and the gravitational interaction eigenstates have different couplings to the gravitational field, this leads to the neutrino oscillation. If one starts with μ⁺ beam then appearance of τ^±, e⁺ and μ⁻ in the final state are the signals for neutrino oscillation. We have estimated the number of μ⁻ events in this scenario in ν_μ–N deep inelastic scattering. Final state lepton energy distribution can be used to distinguish the VEP scenario from the others. A large area of VEP parameter space can be explored at a future muon storage ring facility with moderate beam energy.     

Results from the MUNU experiment on neutrino-electron scattering

The MUNU experiment studies electron antineutrino-electron elastic scattering. The detector is a time projection chamber surrounded by an anti-Compton detector. The distance between the reactor (serving as the neutrino source) and the detector is 18 m. Here, data are presented corresponding to 66.6-d live time reactor on and 16.7-d reactor off. The electron recoil spectrum obtained by using a visual scanning procedure is presented. The upper limit on the neutrino magnetic moment ν_π<1.0×10^?10π_B is derived.     

Searching for neutrino bursts in the galaxy: 36 years of exposure

The Baksan Underground Scintillation Telescope has operated within the program of searching for neutrino bursts since the mid-1980s. We present the current status of the experiment and some results related to the investigation of background events and the stability of facility operation. Over the period from June 30, 1980, to December 31, 2016, the pure observation time was 31.27 years. No neutrino burst candidate event from the explosion of a core-collapse supernova in the Galaxy was recorded in this time. This sets an upper bound of 0.074 yr^–1 on the mean frequency of gravitational stellar collapses in the Galaxy at a 90% confidence level.     

Search for Neutrino Bursts from Collapsing Stars by Means of the LVD and BUST Detectors

A long-term and stable operation of the LVD and BUST detectors in searches for neutrino bursts from gravitational star collapses is demonstrated, and a random origin of background pulses in the detectors is confirmed thereby. The experimental results obtained by means of the LSD and BUST detectors on February 23, 1987, are considered in detail. The probability for the possible backgroundmimicked coincidences of clusters of pulses recorded in the LSD detector at 2 : 52 UT with a group of correlations of pulses within 1 s between LSD and BUST in the interval from 1 : 45 to 3 : 45 UT is estimated. Also, coincidences of the background pulses in the LVD and BUST detectors over the period of about eight years are analyzed. The results obtained in this way give sufficient grounds to conclude that the cluster of pulses recorded by the LSD detector on February 23, 1987, at 2 : 52 UT and the coincidences of individual pulses in the LSD and BUST detectors are events associated with the gravitational collapse of SN 1987A.     

Double-beta-decay experiments: Present status and prospects for the future

The present status of experiments seeking double-beta decay is surveyed. The results of the most sensitive experiments are discussed. Particular attention is given to describing the NEMO-3 detector, which is intended for seeking the neutrinoless double-beta decay of various isotopes (¹⁰⁰Mo, ⁸²Se, etc.) with a sensitivity as high as T _1/2 ～ 10²⁵ yr, which corresponds to a sensitivity to the Majorana neutrino mass at a level of 0.1 to 0.3 eV. The first results obtained with the NEMO-3 detector are presented. A review of the existing projects of double-beta-decay experiments where it is planned to reach a sensitivity to the Majorana neutrino mass at a level of 0.01 to 0.1 eV is given.     

The search for different neutrino flavors from collapsing stars using the LVD detector

The main goal of the Large Volume Detector (LVD) is to search for neutrino burst from gravitational stellar collapses in our Galaxy. The apparatus is shown to be able to register stellar collapse even if there is none of the antineutrino emission specific to the standard scenario. The data from more than nine years of detector operation have been processed, and no candidate events for neutrino bursts have been detected. This implies the existence of an experimental limit to the galactic stellar collapse rate in those cases where collapse is not accompanied by electron antineutrino emission: less than one event per 4.1 yr at the 90% confidence level.     

C2GT: intercepting CERN neutrinos to Gran Sasso in the Gulf of Taranto to measure θ13

Today’s greatest challenge in accelerator-based neutrino physics is to measure the mixing angle θ₁₃ which is known to be much smaller than the solar mixing angle θ₁₂ and the atmospheric mixing angle θ₂₃. A non-zero value of the angle θ₁₃ is a prerequisite for observing CP violation in neutrino mixing. In this paper, we discuss a deep-sea neutrino experiment with 1.5 Mt fiducial target mass in the Gulf of Taranto with the prime objective of measuring θ₁₃. The detector is exposed to the CERN neutrino beam to Gran Sasso in off-axis geometry. Monochromatic muon neutrinos of ≈ 800 MeV energy are the dominant beam component. Neutrinos are detected through quasi-elastic, charged-current reactions in sea water; electrons and muons are detected in a large-surface, ring-imaging Cherenkov detector. The profile of the seabed in the Gulf of Taranto allows for a moveable experiment at variable distances from CERN, starting at 1100 km. From the oscillatory pattern of the disappearance of muon neutrinos, the experiment will measure sin²θ₂₃ and especially Δm² ₂₃ with high precision. The appearance of electron neutrinos will be observed with a sensitivity to P(ν_μ→ν_e) as small as 0.0035 (90% CL) and sin²θ₁₃ as small as 0.0019 (90% CL; for a CP phase angle δ=0° and for normal neutrino mass hierarchy).     

Oscillations of three generations of neutrinos and the solar neutrino problem

The resonant neutrino oscillations in matter are assumed to be responsible for the observed reduction in the capture rate for the ³⁷Cl detector. The expression of the probability that a solar v_e reaches the Earth as a v_e is given in the case of three generations. In the small mixing angle approximation, we describe all the regions of neutrino parameters which give rise to a capture rate of 2.1 SNU for ³⁷Cl and we give the corresponding prediction for the ⁷¹Ga detector.     

Detector lens as a new tool for solar neutrino spectroscopy

The LENS detector is a ν _e-flavor real-time detector for measurement of low-energy solar neutrino flux and spectral shape, specifying the pp and ⁷Be neutrinos individually. It will complement future low-energy neutrino experiments (BOREXINO, HELLAZ, GENIUS), all of which are scattering experiments. The main goal of the LENS collaboration is to develop final formulation of Yb-and In-loaded liquid scintillators and to build a prototype of suitable volume to study the backgrounds and detector performance.     

Gemma experiment: Three years of the search for the neutrino magnetic moment

The result of the 3-year neutrino magnetic moment measurement at the Kalinin Nuclear Power Plant (KNPP) with the GEMMA spectrometer is presented. Antineutrino-electron scattering is investigated. A high-purity germanium detector of 1.5 kg placed at a distance of 13.9 m from the 3 GW_th reactor core is exposed to the antineutrino flux of 2.7 × 10¹³ cm⁻² s⁻¹. The scattered electron spectra taken in (5184 + 6798) and (1853 + 1021) h for the reactor ON and OFF periods are compared. The upper limit for the neutrino magnetic moment μ_v < 3.2 × 10⁻¹¹μ _B at 90% CL is derived from the data processing.     

Einstein-Weyl space-times with geodesic and shear-free neutrino rays: Asymptotic behaviour

We consider a neutrino field with goodesic and shear-free rays, in interaction with a gravitational field according to the Einstein-Weyl field equations. Furthermore we suppose that there exists a Killing vector r^μ whose magnitude is almost everywhere bounded at the future and past endpoints of the neutrino rays. The implications of the asymptotic behavior of r^μ on the structure of space-time are investigated and a useful set of reduced equations is obtained. It is found that under these hypothesis the space-time cannot be asymptotically flat if the neutrino field is nonvanishing. All the Demianski-Kerr-NUT-like space-times as well as the space-times which admit a covariantly constant null vector are explicitly obtained.     

Recent neutrino oscillation results from T2K

The Tokai-to-Kamioka (T2K) experiment studies neutrino oscillations in a ~600 MeV muon neutrino beam sent at 295 km from the Japan Proton Accelerator Complex (J-PARC) to the Super Kamiokande (SK) detector in Kamioka. The primary goals of T2K are to search for the appearance of electron neutrinos at SK resulting from ?? ₁₃?>?0 and to precisely measure ?? ₂₃ and $\Delta m^2_{32}$ via ?? _?? disappearance. We report on T2K results obtained from neutrino data taken in 2010 and 2011.     

First result for the neutrino magnetic moment from measurements with the GEMMA spectrometer

The first result obtained in the measurements of the neutrino magnetic moment at the Kalinin nuclear power plant with the GEMMA spectrometer is presented. A high-purity germanium detector of mass 1.5 kg placed at a distance of 13.9 m from the reactor core is used in the spectrometer. The antineutrino flux at the detector position is 2.73 × 10¹³ $ \bar \nu The first result obtained in the measurements of the neutrino magnetic moment at the Kalinin nuclear power plant with the GEMMA spectrometer is presented. A high-purity germanium detector of mass 1.5 kg placed at a distance of 13.9 m from the reactor core is used in the spectrometer. The antineutrino flux at the detector position is 2.73 × 10¹³ /(cm² s). The differential method is used to select events of electromagnetic antineutrino-electron scattering. The spectra taken in the reactor-on and reactor-off modes over 6200 and 2064 h, respectively, are compared. On the basis of a data analysis, an upper limit of 5.8 × 10⁻¹¹ μB was set on the neutrino magnetic moment μ _ν at a 90% C.L. Original Russian Text ? A.G. Beda, V.B. Brudanin, E.V. Demidova, C.Vylov, M.G. Gavrilov, V.G. Egorov, A.S. Starostin, M.V. Shirchenko, 2007, published in Yadernaya Fizika, 2007, Vol. 70, No. 11, pp. 1925–1935.     

The TEXONO research program on low-energy neutrino and astroparticle physics

This article reviews the research program and efforts of the TEXONO Collaboration on neutrino and astroparticles. The main program is on reactor-based low-energy neutrino physics at the Kuo-Sheng Power Plant in Taiwan. The facilities of the laboratory are described. A limit on the neutrino magnetic moment of μ_ν( ) < 1.3 × 10⁻¹⁰ μ_B at 90% C.L. has been achieved from measurements with a high-purity germanium detector. Other research programs at Kuo-Sheng are surveyed. The text was submitted by the authors in English.