Neutrino geophysics and astronomy at Baksan Neutrino Observatory: Potential of the spectroscopy of natural antineutrino sources

Prospects for studying, at the Baksan Neutrino Observatory, geoneutrinos, as well as neutrinos from supernovae, by means of a scintillation spectrometer having a target mass of 5000 t are considered. It is shown that the geographical location, a deep position (4800 mwe), and a modest background of antineutrinos from nuclear reactors makes the Baksan Neutrino Observatory one of the best places for performing such investigations. Particular attention is given to the derivation of information about the nature of neutrinos, the possibility of detecting relic neutrinos from supernovae, and the discovery of a hypothetical georeactor.     

Possible explanation of the correlations between events recorded by underground detectors during the Supernova 1987A explosion

A possible explanation of the time correlations between the data from underground detectors (Baksan telescope, LSD, IMB, Kamiokande II) and from the Rome and Maryland gravitational-wave antennas obtained during the Supernova 1987A explosion is proposed. It is shown that the synchronization of the events recorded by various underground facilities could be produced by gravitational radiation from the Supernova.     

Prospects of the search for neutrino bursts from supernovae with Baksan large volume scintillation detector

Observing a high-statistics neutrino signal from the supernova explosions in the Galaxy is a major goal of low-energy neutrino astronomy. The prospects for detecting all flavors of neutrinos and antineutrinos from the core-collapse supernova (ccSN) in operating and forthcoming large liquid scintillation detectors (LLSD) are widely discussed now. One of proposed LLSD is Baksan Large Volume Scintillation Detector (BLVSD). This detector will be installed at the Baksan Neutrino Observatory (BNO) of the Institute for Nuclear Research, Russian Academy of Sciences, at a depth of 4800 m.w.e. Low-energy neutrino astronomy is one of the main lines of research of the BLVSD.     

Supernova 1987A, 30 Years Later

Most supernova theories state that this phenomenon lasts for a few seconds and ends with a big final explosion. However, these theories do not take into account several experimental results obtained with neutrino and gravitational wave detectors during the explosion of SN 1987A, the only supernova observed in a nearby galaxy in modern age. According to these experimental results the phenomenon is much more complex that envisaged by current theories, and has a duration of several hours. Since recent data of the X-ray NASA Satellite NuSTAR show a clear evidence of an asymmetric collapse, we have revisited the experimental data recorded by some underground and gravitational wave detectors running at the time of SN 1987A. New evidence is shown that confirms the previous results, namely that the data recorded by the gravitational wave detectors running in Rome and in Maryland are strongly correlated with the data of both the LSD (Mont Blanc) and the Kamiokande detectors, and that the correlation extends over a long period of time (one or two hours) centered at the Mont Blanc time. In addition, the signals of the GW detectors preceded the signals of the underground detectors by a time of order of one second. This result, obtained by comparing six independent files of data recorded by four different experiments located at intercontinental distances, indicates that also Kamiokande detected neutrinos at theMont Blanc time, but these interactions were not identified because not grouped in a burst. A similar correlation was also found in the data of the underground experiments in Mont Blanc and Baksan.     

Search for neutrino bursts from collapsing stars on the basis of the BUST till 2006

Search for neutrino bursts from collapsing stars with the Baksan underground scintillation telescope has been carried out since 1980. In this study, the experimental data obtained during the period from 2001 to 2005 inclusive are analyzed. The upper limit of the mean frequency of collapses in the Galaxy over the entire period of observations (the total live time is 21.83 yr) was found to be 0.105 yr^?1.     

Neutrino Burst Monitoring in Our Galaxy

Journal of Experimental and Theoretical Physics - Baksan underground scintillation telescope (BUST) operates under the program of neutrino burst search since the middle of 1980. We report the...     

Neutrino geophysics at Baksan I: Possible detection of georeactor antineutrinos

J.M. Herndon in the 1990s proposed a natural nuclear fission georeactor at the center of the Earth with a power output of 3–10 TW as an energy source to sustain the Earth magnetic field. R. S. Raghavan in 2002 pointed out that, under certain conditions, antineutrinos generated in such a georeactor can be detected using massive scintillation detectors. We consider the underground Baksan Neutrino Observatory (4800 m.w.e.) as a possible site for developments in geoneutrino physics. Here, the intrinsic background level of less than 1 event/yr in a liquid scintillation ～1000-t target detector can be achieved and the main source of background is the antineutrino flux from power reactors. We find that this flux is ～10 times lower than at the KamLAND detector site and two times lower than at the Gran Sasso laboratory and thus at Baksan the georeactor hypothesis can be conclusively tested. We also discuss possible searches for the composition of georeactor burning nuclear fuel by analysis of the antineutrino energy spectrum.     

Search for low-energy neutrino radiation accompanying gamma-ray bursts on the Baksan subterranean scintillation telescope

An analysis aimed at finding possible neutrino radiation accompanying gamma-ray bursts in a 24-h period about them is performed on the basis of the data in the 4B BATSE Gamma-Ray Burst Catalog and data from the Baksan scintillation telescope according to a program for finding neutrinos from collapsing stars. Values significantly exceeding the background are not discovered. A lower bound for the distance to the source is established under the assumption that the anticipated radiation has characteristics similar to the characteristics of collapse neutrinos. It attests to the cosmological origin of gamma-ray bursts with a high degree of probability. Zh. éksp. Teor. Fiz. 114, 1921–1929 (December 1998)     

Multiple interactions of muons in BUST

Analysis of the experimental data for a long period of Baksan underground scintillation telescope (BUST) operation to search for very-high-energy muons is presented. The phenomenological parameters and the sensitivity of the method of multiple interactions, based on the concepts of the pair-meter technique, are discussed. The experimental distributions are compared with the results of calculations for a “conventional” muon spectrum, based on 3D simulation of muon passage through the telescope.     

A possibility for studying the fluctuations of the multiplicity in muon bundles

Fluctuations of the multiplicity in muon bundles is another characteristic of these bundles and can provide additional information both about the spectrum and composition of primary cosmic rays and about the model of their interaction. In this paper, the possibility of studying these fluctuations using the data of the Baksan underground scintillation telescope is considered.     

Investigation of the spectrum of high-energy muons by the method of multiple interactions on the basis of data from the Baksan underground scintillation telescope

Experimental data obtained with the aid of the Baksan underground scintillation telescope over a long period of its operation are analyzed with the aim of searches for an excess flux of ultrahigh-energy (≥100 TeV)muons. The multiple-interaction method, which is based on the ideas of the pair-meter technique, is used to analyze the energy spectrum of the muons. The phenomenological parameters of this method and its sensitivity to the shape of the spectrum are discussed. The experimental distributions are compared with the results of calculations for various versions of the muon spectrum. The possibility of separating ultrahigh-energy muons that fly in the vicinity of the axis of extensive air showers is assessed on the basis of the integrated number of recorded and simulated events featuring large energy depositions.     

Total cross sections for ve and ve interactions and search for neutrino oscillations and decay

About 200 and 60 candidates for electron neutrino and antineutrino interactions, respectively, have been analyzed in the heavy liquid bubble chamber Gargamelle exposed to the CERN PS neutrino beam. Evidence for scaling has been found for these interactions, with slopes of the cross sections in good agreement with those obtained for muon neutrino and antineutrino events in the same chamber. No evidence appears for oscillations of neutrinos or antineutrinos, which would induce in the present experiment an excess of electron or positron events. The corresponding limits are given as functions of the mixing parameter, for the finite mass Majorana neutrinos. The possibility of a multiplicative law for the lepton number has also been investigated. A search for isolated electron-positron pairs revealed no excess in the forward direction, in contradiction to the expectation for muonic neutrino and antineutrino decays. The corresponding limits on the c.m. half lifetimes are given.     

Determination of the direction to a source of antineutrinos via inverse beta decay in Double Chooz

To determine the direction to a source of neutrinos (and antineutrinos) is an important problem for the physics of supernovae and of the Earth. The direction to a source of antineutrinos can be estimated through the reaction of inverse beta decay. We show that the reactor neutrino experiment Double Chooz has unique capabilities to study antineutrino signal from point-like sources. Contemporary experimental data on antineutrino directionality is given. A rigorous mathematical approach for neutrino direction studies has been developed. Exact expressions for the precision of the simple mean estimator of neutrinos’ direction for normal and exponential distributions for a finite sample and for the limiting case of many events have been obtained.     

Problems of Neutrino Radiation from SN 1987A: 30 Years Later

Experimental data obtained by means of underground detectors during the explosion of the SN 1987A supernova on February 23, 1987, are discussed. At that time, such data were being collected by two scintillation detectors—the Soviet–Italian liquid scintillation detector (LSD) in a Mont Blanc tunnel and the Baksan underground scintillation telescope (BUST) of the Institute forNuclear Research (Russian Academy of Sciences)—and two Cherenkov detectors—Kamiokande II (Japan) and the Irvine–Michigan–Brookhaven (IMB) detector (USA). Two key instants in SN 1987A evolution that were accompanied by neutrino signals are highlighted. These were 2:52 UT in LSD and 7:35 UT in the other detectors. A group of studies in which correlations between pulses in the different detectors between 1:45 and 3:45 UT and double pulses in LSD between 5:40 and 10:15 UT were observed are also discussed.     

Total cross section for photon-nucleon interaction in the energy range $$\sqrt \mathcal{S} = 40 - 250 GeV$$

Results obtained by directly measuring the total cross section for photon-nucleon interaction through recording photoproduction processes at the Baksan underground scintillation telescope of the Institute for Nuclear Research (Russian Academy of Sciences, Moscow) are presented. The effect of a faster growth of photon-hadron cross sections in relation to hadron-hadron cross sections is confirmed in the energy range \(\sqrt \mathcal{S} = 40 - 130 GeV\). It is shown that an increase in the number of additive quarks in photon-hadronization products may be one of the reasons behind this effect. Experimental data on the cross sections for photon-nucleon and photon-photon interactions are subjected to a comparative analysis, and the status of the results obtained from direct and indirect cross-section measurements in the high-energy region is discussed.     

Oscillation properties of active and sterile neutrinos and neutrino anomalies at short distances

A generalized phenomenological (3 + 2 + 1) model featuring three active and three sterile neutrinos that is intended for calculating oscillation properties of neutrinos for the case of a normal activeneutrino mass hierarchy and a large splitting between the mass of one sterile neutrino and the masses of the other two sterile neutrinos is considered. A new parametrization and a specific form of the general mixing matrix are proposed for active and sterile neutrinos with allowance for possible CP violation in the lepton sector, and test values are chosen for the neutrino masses and mixing parameters. The probabilities for the transitions between different neutrino flavors are calculated, and graphs representing the probabilities for the disappearance of muon neutrinos/antineutrinos and the appearance of electron neutrinos/antineutrinos in a beam of muon neutrinos/antineutrinos versus the distance from the neutrino source for various values of admissible model parameters at neutrino energies not higher than 50 MeV, as well as versus the ratio of this distance to the neutrino energy, are plotted. It is shown that the short-distance accelerator anomaly in neutrino data (LNSD anomaly) can be explained in the case of a specific mixing matrix for active and sterile neutrinos (which belongs to the a₂ type) at the chosen parameter values. The same applies to the short-distance reactor and gallium anomalies. The theoretical results obtained in the present study can be used to interpret and predict the results of ground-based neutrino experiments aimed at searches for sterile neutrinos, as well as to analyze some astrophysical observational data.     

Insight-HXMT observations of the first binary neutron star merger GW170817

Finding the electromagnetic(EM) counterpart of binary compact star merger, especially the binary neutron star(BNS) merger,is critically important for gravitational wave(GW) astronomy, cosmology and fundamental physics. On Aug. 17, 2017,Advanced LIGO and Fermi/GBM independently triggered the first BNS merger, GW170817, and its high energy EM counterpart,GRB 170817 A, respectively, resulting in a global observation campaign covering gamma-ray, X-ray, UV, optical, IR, radio as well as neutrinos. The High Energy X-ray telescope(HE) onboard Insight-HXMT(Hard X-ray Modulation Telescope) is the unique high-energy gamma-ray telescope that monitored the entire GW localization area and especially the optical counterpart(SSS17 a/AT2017 gfo) with very large collection area(~1000 cm~2) and microsecond time resolution in 0.2-5 MeV. In addition,Insight-HXMT quickly implemented a Target of Opportunity(ToO) observation to scan the GW localization area for potential X-ray emission from the GW source. Although Insight-HXMT did not detect any significant high energy(0.2-5 MeV) radiation from GW170817, its observation helped to confirm the unexpected weak and soft nature of GRB 170817 A. Meanwhile,Insight-HXMT/HE provides one of the most stringent constraints(~10~(-7) to 10~(-6) erg/cm~2/s) for both GRB170817 A and any other possible precursor or extended emissions in 0.2-5 MeV, which help us to better understand the properties of EM radiation from this BNS merger. Therefore the observation of Insight-HXMT constitutes an important chapter in the full context of multi-wavelength and multi-messenger observation of this historical GW event.     

Spatial distribution of aligned muons in groups

The phenomenon of alignment along one line for the highest energy secondary particles in the γ-ray-hadron families was observed for the first time in the “Pamir” experiment using the x-ray emulsion chambers and was related to coplanar production of secondary particles at energy E ₀ > 10¹⁶ eV. The distributions of distances between the muon pairs in the muon groups are obtained using the Baksan underground scintillation telescope of the Institute for Nuclear Research (Russian Academy of Sciences) for the threshold energies of 0.85–3.2 TeV for the period of 7.7 years. A difference between spatial distributions of all groups and aligned groups was not detected.     

Sensitivity enhancement of the gravitational detector OGRAN

The gravitational wave antenna OGRAN is installed in the underground laboratory of the Baksan Neutrino Observatory. At the present time, it has a limited sensitivity sufficient only to detect gravitational radiation from sources situated at a distance of about 100 kpc. The calculations presented in this paper demonstrate the increase in the sensitivity by two orders of magnitude with cooling of the acoustical resonator of the antenna to the liquid-nitrogen temperature. The possibility of using the same optical detection scheme as the one under room temperature is discussed. The revised construction of the cryogenic version of the OGRAN antenna is considered. The results of experiments carried out with the pilot model of cryogenic antenna are presented.     

Potential of the ATLAS detector for studying high-energy solar cosmic rays

The ATLAS detector is intended for testing the Standard Model and for seeking new physics at the Large Hadron Collider (LHC). In addition, it permits detecting cosmic-ray muons. At the same time, unusual bursts of the muon intensity that correlate with powerful solar flares were recorded and investigated earlier at the Baksan underground scintillation telescope in the period spanning 1981 and 2006 (2.5 solar cycles). The nature of these muon bursts and their relation to solar cosmic rays have so far remained not quite clear. The ATLAS detector possesses an excellent muon system that allows searches for similar muon bursts. Within the next few years, when the LHC and ATLAS should start operating, one expects an increase in the solar activity in the new 24th cycle. Owing to this, the probability of observing muon bursts may become higher.