Search

Data from the Baksan Underground Scintillation Telescope were used to search for muon neutrinos and antineutrinos with energies above 1 GeV in coincidence with gravitational-wave events detected by the Advanced LIGO and Advanced Virgo observatories in three observing periods. Limits on the integral fluxes of muon neutrinos and antineutrinos from gravitational wave sources were obtained. A way of searching for neutrino events from LIGO/Virgo alerts is presented. An algorithm for data processing and finding coincidences between neutrino and gravitational-wave events in real time is described.

The Carpet-3 array at the Baksan Neutrino Observatory is designed to detect extensive air showers generated by primary cosmic rays of more than 100 TeV in energy. The main aim is to search for cosmic extrahigh-energy gamma rays. In this work, we describe the current state of the facility and the results from searching for extrahigh-energy photons from regions of the localization of candidates for gravitational-wave events detected by LIGO/Virgo during the third observational period.

The Baksan Underground Scintillation Telescope has been used to search for neutrino bursts since the mid-1980s. We use two parts of the telescope with a total mass of 240 tons as a target. The actual observing time from June 30, 1980, to June 30, 2020, was 34.4 years. No neutrino burst candidate events were detected during this period, placing an upper bound of 0.067 g−1 on the average frequency of core collapse supernovas in the Galaxy at a 90% confidence level.

An experiment for measuring the flux of cosmic diffuse gamma rays with energies higher than 100 TeV (the Carpet-3 project) is under preparation at the Baksan Neutrino Observatory. The experiment suggests to increase areas of both the muon detector and the surface shower detectors. The experiment’s sensitivity to the showers initiated by primary gamma rays is estimated in this paper for different configurations of the array. In addition, preliminary estimates of the upper limit on diffuse gamma rays with energy above 700 TeV are presented. They are derived from experimental data of the Carpet-2 array (previous version of the experiment) for the net exposure of 9.2 years of observation.

The search for neutrino bursts at the Baksan Underground Scintillation Telescope began in the middle of 1980. Two parts of the setup with a total mass of 240 t are used as the target. The actual observational time accumulated in the period from June 30, 1980, to December 31, 2017, is 32.1 years. No neutrino burst candidate events were detected, yielding the following upper bound for the mean rate of core-collapse supernovas in the Milky Way: 0.072 yr−1 (90% CL).

The Baksan Underground Scintillation Telescope (BUST) is located in the North Caucasus in an underground laboratory at an effective depth of 850 m.w.e. The BUST began working in 1977, and the installation is still in operation. The successful design of the BUST allows it to be used to solve a number of problems in astrophysics and particle physics. The new data acquisition system is designed to record and analyze experimental data with greatly improved measurement characteristics of digital and analog signals. The data acquisition system is based on the VME interface and provides complete compatibility with existing low-level BUST recording electronics. The hodoscope of pulse channels was completely redeveloped and implemented on field-programmed gate array (FPGA) and LVDS chips.

Carpet-2 is an air-shower array at Baksan Valley, Russia, equipped with a large-area (175 m^2) muon detector, which makes it possible to separate primary photons from hadrons. We report the first results of the search for primary photons with energies E_\gamma>1 PeV, directionally associated with IceCube high-energy neutrino events, in the data obtained in 3080 days of Carpet-2 live time., Comment: 6 pages, 2 figures. V2: minor copy-editing changes. Accepted by JETP Letters

Local sources of muon neutrinos are searched for with the Baksan underground scintillation telescope. In the period from December 1978 through May 2017 (live-time 31.05 yr), 1635 neutrino events with zenith angles between 95° and 180° have been detected. No local sources of muon neutrinos with energies over 1 GeV have been found. Upper limits on the fluxes of muon neutrinos emitted by known astrophysical objects are established.

Matrices of silicon photomultipliers (SiPM) are promising multichannel photosensors for scintillation detectors. They can be used to construct tracks of relativistic particles inside detectors. The first detectors based on the direct contact of the SiPM matrices with the surface of the scintillation detector and with the application of Fresnel lenses are developed; promising variants of large detectors for neutrino astrophysics and geophysics are proposed.

In this work, modernized data acquisition systems of the Andyrchi and Carpet-3 shower facilities with automated data preprocessing and data transmission systems to the observatory of the Terskol Branch of the Institute of Astronomy are described. To solve joint problems on searching transient sources, data from the Andyrchi and Carpet facilities are processed and transmitted to the observatory of the Terskol Branch of the Institute of Astronomy in the form of astronomic coordinates for observations with an optical telescope.

The Baksan Underground Scintillation Telescope has been operating under the program of searching for neutrino bursts since the middle of 1980. The target is two parts of the facility with the total mass of 240 t. The actual observation time over the period from June 30, 1980, to December 31, 2016, is 31.27 years. No candidate for the stellar core collapse has been detected during the observation period. The upper bound for the mean rate of the supernova core collapse in our Galaxy is 0.074 y $$^{{ - 1}}$$ (90% CL).

A prototype scintillation detector with photosensors based on silicon photomultiplier (SiPM) arrays is described. Such a method of data-taking will make it possible to obtain an image (snapshot) of the event and, thereby, to separate different types of events (particle interactions) in the detector. For this purpose, the characteristics of SiPMs have been studied and a calibration measurement technique developed.

An experiment for measuring the flux of cosmic gamma rays with energy above 100 TeV is currently being prepared at the Baksan Neutrino Observatory of the Institute for Nuclear Research, Russian Academy of Sciences. For this purpose, based on the Carpet-2 shower array which has been operating for many years, the Carpet-3 multipurpose shower array is being constructed. In particular, the preparation of the experiment supposes an increase in the area of the muon detector (MD) and ground part of the array. For ground modules of the Carpet-3 array, a scintillation detector with a liquid scintillator in a plastic package has been elaborated. In this work, descriptions of the Carpet-3 array and working characteristics of the new scintillation detector are presented.

An experiment for measuring the flux of diffuse cosmic gamma rays with energies above 100 TeV (the Carpet-3 experiment) is now being prepared at the Baksan Neutrino Observatory, Institute for Nuclear Research, Russian Academy of Sciences. The preparation of the experiment entails an increase in the area both of the muon detector and of the surface part of the air shower array. This work presents an estimate of the experiment sensitivity to showers generated by primary gamma quanta for different configurations of the array. According to experimental data of the Carpet-2 array for 9.2 years of pure data acquisition time, preliminary estimates for the upper limit of the diffuse cosmic gamma ray flux with energies above 930 PeV have been obtained.

The search for neutrino signals from gravitational core collapses in the Milky Way is one of the main lines of research at the Baksan Underground Scintillation Telescope (BUST). Neutrons generated by cosmic-ray muons produce a considerable background in such experiments. The contribution from the elastic scattering of fast neutrons off protons to the overall single-event background rate measured in the inner detector planes is estimated via neutron activation analysis. The resulting value of the fast-neutron flux agrees with one based on the results from FLUKA modeling for the depth of the BUST detector. The same technique can be used to estimate the neutron background in similar experiments focused on rare events.

The mechanisms of origin of ultrahigh-energy gamma radiation are poorly studied. One way to find out is to search for temporal and directional coincidences of high-energy galactic neutrinos with photons of similar energies. The results of such a search could provide indications of the hadronic origin of this radiation. In this paper, we report on the search for photons with energies above 300 TeV in coincidence with high–energy neutrinos. The searches of ultrahigh–energy gammas were carried out at the Carpet–2 EAS array, using three years of data taking.

The LIGO/Virgo collaborations have reported the results of their searches for gravitational-waves from the first half of their third observing run. 39 events were combined into the second Gravitational-Wave Transient Catalog (GWTC-2), reaching the total number of 50. In addition to these, two neutron star - black hole merger events were also confirmed. The search for neutrino counterparts of LIGO/Virgo gravitational-wave events was performed on the Baksan Underground Scintillation Telescope. The processing algorithm and the results of the counterpart search are described.

The characteristics of fast neutrons produced by cosmic-ray muons at the Baksan Underground Scintillation Telescope (BUST) are investigated. A novel approach to the problem consists in estimating the neutron flux by the production rate of the unstable radioactive nuclide 12B in the (n, p) reaction on carbon nuclei of the BUST organic scintillator. The processing of the data collected in 2002–2015 yielded $${N_{{{12}_B}}} = 337 \pm 2.5$$ events consistent with those of the reaction 12C(n, p)12B. For the BUST internal planes, the background of fast neutrons with E > 28.6 MeV is experimentally estimated as Φ ∝ 10−11cm–2 s–1. This is lower than the theoretically predicted total neutron flux by nearly two orders of magnitude. The disagreement with predictions is attributed to the suppression of neutron flux in the external scintillator planes of the detector.

The new cosmic-ray experiment EMMA operates at the depth of 75 m (50 GeV cutoff energy for vertical muons; 210 m.w.e.) in the Pyhasalmi mine, Finland. The underground infrastructure consists of a network of eleven stations equipped with multi-layer, position-sensitive detectors. EMMA is designed for cosmic-ray composition studies around the energy range of the knee, i.e., for primary particles with energies between 1 and 10 PeV. In order to yield significant new results EMMA must be able to record data in the full configuration for about three years. The key to the success of the experiment is the performance of its tracking stations. In this paper we describe the layout of EMMA and construction of the two main detector types used for muon tracking: the high-resolution drift chambers and fast scintillation detector arrays. We also show the measured tracking efficiencies, position and angular resolutions, and sensitivity of drift chambers to the air pressure. The measured angular muon distributions are well reproduced by CORSIKA simulations folded with the known density distribution of the overburden. The single muon flux at the depth of 210 m.w.e. is (1.29 ± 0.06) m − 2 s − 1 . This value was determined from the reconstructed tracks registered by a six-layer array of position-sensitive drift chambers.

Galactic sites of acceleration of cosmic rays to energies of order 10^15 eV and higher, dubbed PeVatrons, reveal themselves by recently discovered gamma radiation of energies above 100 TeV. However, joint gamma-ray and neutrino production, which marks unambiguously cosmic-ray interactions with ambient matter and radiation, was not observed until now. In November 2020, the IceCube neutrino observatory reported an ~150 TeV neutrino event from the direction of one of the most promising Galactic PeVatrons, the Cygnus Cocoon. Here we report on the observation of a 3.1-sigma (post trial) excess of atmospheric air showers from the same direction, observed by the Carpet-2 experiment and consistent with a few-months flare in photons above 300 TeV, in temporal coincidence with the neutrino event. The fluence of the gamma-ray flare is of the same order as that expected from the neutrino observation, assuming the standard mechanism of neutrino production. This is the first evidence for the joint production of high-energy neutrinos and gamma rays in a Galactic source., 7 pages, 3 figures, AASTeX. V2: minor changes; Appendix with more analysis details added. Version accepted by Astrophys. J. Letters. V3: title corrected (text unchanged), matches the published version

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.

The MMIS-32 scaled multichannel measurement system, which is based on 32-channel charge-to-digital converters and has been developed and built, is described here. This system is intended for data acquisition from arrays of silicon photomultipliers used as multichannel photosensors in scintillation detectors. The basic parameters of the measurement system are presented.

An experiment for measuring the flux of cosmic diffuse gamma rays with energies above 100 TeV (the Carpet-3 air shower array) is now being prepared at the Baksan Neutrino Observatory, Institute for Nuclear Research, Russian Academy of Sciences. The preparations entail a substantial increase of the areas of both the muon detector and the surface air shower array. The experiment’s sensitivity to showers generated by primary gamma rays is estimated for different configurations of the array. In addition, preliminary estimates of the upper limit on the flux of diffuse gamma rays with energies higher than 1.3 PeV, derived using experimental data from the old Carpet-2 array, are presented for a net exposure time of 9.2 years.

The Carpet-3 air shower array is being built at the Baksan Neutrino Observatory, which is located near Mount Elbrus (North Caucasus) at an altitude of 1700 m above sea level. The main aim of the experiment is gamma-ray astronomy in the energy range above 100 TeV to search for diffuse gamma radiation and sources and to study the generation mechanisms of this radiation. The paper provides an overview of the current state of the experiment, as well as its prospects.

Preliminary results of a neutron background measurement at the Baksan underground scintillation telescope (BUST) are presented. The external planes of the BUST are fully covered with standard scintillation detectors shielding the internal planes and suppressing thus background events due to cosmogenic and local radioactivity. The shielded internal planes were used as target for the neutron flux registration. The experimental method is based on the delayed coincidences between signals from any of the BUST counters. It is assumed that the first signal is due to inelastic interaction of a neutron with the organic scintillator, while the second signal comes from the decay of an unstable radioactive isotope formed when the fast neutron interacts with the 12C nuclei. Using the Monte-Carlo method (GEANT4) we also simulated propagation of neutrons through a layer of scintillator. The experimentally found muon induced neutron flux is j =1.3-0.3+0.7 ×10-10cm-2s-1 for neutron energies E ≥ 22MeV, which is in a qualitative agreement with similar measurements of other underground laboratories as well as with predictions of the GEANT4.

The current status of the experiment on recording neutrino bursts from core collapse stars is presented. The actual observational time is 29.76 years. An upper bound of the mean frequency of core collapse supernovae in our Galaxy is f col < 0.077 year–1 (90% CL).

A way of estimating a muon-enduced neutron flux has been proposed. The technique is used to estimate the neutron background at the Baksan Underground Scintillation Telescope (BUST). A two-pulse signature (unstable 12B production and its subsequent decay) is used to identify neutron events. The integrated average neutron flux on the external planes of detector is an order of magnitude higher than the one on the internal planes. Within the limits of statistical error, the resulting neutron flux agrees with predictions from simulations for the depth at which the BUST lies using the FLUKA program.

The experiment on recording neutrino bursts operates since the mid-1980. As the target, we use two parts of the facility with the total mass of 240 tons. The current status of the experiment and some results related to the investigation of background events and the stability of facility operation are presented. Over the period of June 30, 1980 to December 31, 2018, the actual observational time is 33.02 years. No candidate for the stellar core collapse has been detected during the observation period. An upper bound of the mean frequency of core collapse supernovae in our Galaxy is 0.070 year$^{-1}$ (90\% CL)., Comment: Submitted to Astropart.Phys

Recently two collaborations (Tibet ASγ and HAWC) almost simultaneously reported about their measurements of ultra-high-energy (> 100 TeV) gamma rays from the Crab Nebula. The Baksan air shower array (BASA) recorded a burst from this very source as long ago as more than 20 years. At the moment the new experiment on gamma ray astronomy (Carpet-3 project) started at Baksan, and it is appropriate to recall old results of BASA to be compared with the new results, already published and expected.

The core collapse of a massive star in the Milky Way will produce a neutrino burst, which will be detected by the Baksan Underground Scintillation Telescope (BUST). The stable and enough low background at the BUST is a clear asset for searching for neutrino bursts. Now two parts of the facility (with the total mass of 242 tons) are used as independent coinciding detectors. Such approach allows us to increase dependability detection of the neutrino signal and the radius of sensitivity of the BUST. The facility has the potential to see a supernova in the Galaxy independently from other detectors. No burst candidate for the core collapse has been detected during the observation period of June 30, 1980, to June 30, 2019. The actual observation time is 33.477 years. This is the longest observation time of our Galaxy with neutrinos at the same facility. An upper bound on the mean frequency of gravitational collapses in the Galaxy is 6.88 per century (at 90% C.L.).

We report on the search of astrophysical gamma rays with energies in the 100 TeV to several PeV range arriving in directional and temporal coincidence with public alerts from HAWC (TeV gamma rays) and IceCube (neutrinos above ~100 TeV). The observations have been performed with the Carpet-2 air-shower detector at the Baksan Neutrino Observatory, working in the "photon-friendly" mode since 2018. Photon candidate showers are selected by their low muon content. No significant excess of the photon candidates have been observed, and upper limits on gamma-ray fluences associated with the alerts are obtained. For events with good viewing conditions, the Carpet-2 effective area for photons is of the order of the IceCube effective area for neutrinos of the same energy, so the constraints start to probe the production of neutrinos in fast flares of Galactic sources., 4 pages paper + 5 pages Supplemental Material. V2: references added, version accepted by JETP Letters

The search for muon neutrinos with energy ≥1 GeV correlated with Gamma-Ray Bursts (GRBs) has been carried out at the Baksan Underground Scintillation Telescope (BUST). Between 1978 December and 2013 December more than 1500 localized gamma-ray bursts occurred in the field of view of the BUST were coincided with the BUST operation periods. No neutrino signal from GRBs was detected. Upper limits on associated gamma-ray burst neutrino production are presented.

The origin of gamma-ray bursts is still one of the unresolved problems in physics. They are short, intense, and non-repeating flashes of MeV gamma-rays with a wide range of spectral and temporal properties. Also these bursts are perhaps sources of neutrino emission. Unlike the photons, which may scatter or be absorbed, the neutrinos, due to their small interaction cross section, arrive at the Earth unaffected. This paper describes experimental methods for detection of low energy neutrinos in the range from 20 MeV to 100MeV at the Baksan Underground Scintillation Telescope. In the analysis we search neutrinos in time coincidence with a gamma-ray burst. We use filtered data collected at the Telescope during 2012. We also use the catalogue of gamma-ray bursts of the SWIFT satellite experiment.

A statistical threshold meter of shaper-discriminators, used in detectors of the Baksan Underground Scintillation Telescope, is described. The device is based on an ATmega103 microprocessor. The principle of operation and block diagram of the device are given. The application of the device reduced the adjustment time of the shaper-discriminators by a factor of dozens, and, in addition, due to the use of statistical methods in the program code of the microprocessor, the threshold adjustment accuracy went up by a factor of 2.5 as compared to the previous adjustment method. The device allows one to diagnose faults in electronics of the anode and 12th dynode circuits and to distinguish photoelectron multiplier tubes with high noise levels.

Early results of the search for E_\gamma>1 PeV cosmic photons from point sources with the data of Carpet-2, an air-shower array equipped with a 175 m^2 muon detector, are presented. They include 95% CL upper limits on PeV photon fluxes from stacked directions of high-energy IceCube neutrino events and from four predefined sources, Crab, Cyg X-3, Mrk 421 and Mrk 501. An insignificant excess of events from Mrk 421 will be further monitored. Prospects of the use of the upgraded installation, Carpet-3 (410 m^2 muon detector), scheduled to start data taking in 2019, for searches of E_\gamma>100 TeV photons, are briefly discussed., Comment: 5 pages, 2 figures, webofc style. Presented at the VLVNT-2018 workshop, Dubna, October 2-4, 2018. V2: minor copy-editing changes