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.     

LVD Experiment: 25 Years of Operation

The current status of the LVD (large volume detector) experiment aimed at search for neutrinos from the gravitational collapse of stellar cores is described. Within the period of observations from June 1992 to February 2017, no gravitational collapse was found in the Milky Way Galaxy and Magellanic Clouds, including hidden ones (not ejecting the envelope). The LVD collects data for 99% of the live time. A limit on the frequency of supernova bursts within a distance of 25 kpc was set at a level of 0.1 event/yr. The most recent results obtained by studying the muon component of cosmic rays are presented.     

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.     

Cosmic-ray muon and atmospheric neutrino fluxes at very high energies

Estimates of cosmic-ray muon and atmospheric neutrino fluxes at TeV energies are obtained taking into account a “prompt” production of muons and neutrinos through charmed-particle decays and a “direct” lepton-pair production through the Drell-Yan mechanism and resonances. It is found that the contribution of charmed particles to the muon flux is equal to that from the conventional sources (pion and kaon decays) at 60 TeV, and the same equality can take place at 10 and 1 TeV for muon and electron neutrinos, respectively (for particles coming to sea level in the vertical direction). This “direct” production contribution to muon and neutrino fluxes is estimated very arbitrarily, but it cannot be excluded that this contribution is equal to that from the conventional source at energies of 0.5 and 0.05 PeV for muons and muon neutrinos, respectively. Currently, the estimates of the “prompt” and the “direct” contributions to cosmic-ray muons and atmospheric neutrinos are only qualitative. This is true especially for the “direct” contribution. Nevertheless, it seems reasonable to attract attention to these potentially important sources of atmospheric muons and neutrinos.     

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.     

Muons and neutrinos in the cosmic radiation

Summary This report covers 86 papers presented in HE4 and HE5 sessions of the XXIV ICRC. The topics of the papers are atmospheric muons and neutrinos, muon bundles, horizontal air showers, ?muon astronomy?, neutrino oscillations, high-energy neutrinos and neutrinos from collapsing stars. Rapporteur talk given at the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

High energy neutrinos from galactic sources

Analytical expressions are derived which allow to calculate flux densities of energetic neutrinos from hypothetical galactic sources, consisting of a proton accelerator and a dilute gas beam dump. The same formalism is used to calculate atmospheric muon and μ-neutrino fluxes. From the results, rates of upward going muons, both from the atmosphere and galactic sources, are computed and detection limits for neutrino emitters in the sky are established. Finally, the background in a surface detector, caused by scattered muons and charm decays in the rock, is estimated for the case of a flat surrounding.     

Search for neutrino emission from supernovae using the Large Volume Detector

The basic task of the Large Volume Detector LVD situated at the underground Gran Sasso National Laboratory (Italy) is the search for neutrino bursts from gravitational stellar collapses in our Galaxy. At present, the algorithm for determining neutrino bursts has been developed. It is based on the identification of event clusters in fixed time intervals, special attention is paid not only to the inverse β decay reaction which has a characteristic signature, but also to the neutrino-iron interaction. The data for of 3.5 years of LVD operation have been processed. No candidates for neutrino bursts are found.     

Cosmic ray muons at a depth of 754 hg/cm2 in the Kolar gold Mines

A telescope of area 4 m², consisting of horizontal layers of plastic scintillators, neon flash tubes and absorbers was operated at a depth of 754 hg/cm² in the Kolar Gold Mines. New values for the vertical intensities of muons have been obtained from observations of the angular distribution over the slant depths ∼ 750–2300 hg/cm² and are compared with the existing measurements. From the angular distribution observed, we conclude that muons are produced wholly through the decay of pions and kaons up to energies of the order of 1 TeV. A value of 0.3±0.2 is estimated for theK/π ratio at production, for muon energies around 500 GeV. A decoherence distribution has been obtained for parallel muon events up to distances of the order of 10 m. From this we conclude that the averageP _t of the parents of muons of energy ∼ 250 GeV is of the order of 0.3 GeV/c. From an analysis of rock showers, we obtain the cross section for inelastic interaction of muons of mean energy 100 GeV as (3.8±1.5)×10⁻³⁰ cm²/nucleon.     

Physics prospects of the Jinping neutrino experiment

The China Jinping Underground Laboratory(CJPL), which has the lowest cosmic-ray muon flux and the lowest reactor neutrino flux of any laboratory, is ideal to carry out low-energy neutrino experiments. With two detectors and a total fiducial mass of 2000 tons for solar neutrino physics(equivalently, 3000 tons for geo-neutrino and supernova neutrino physics), the Jinping neutrino experiment will have the potential to identify the neutrinos from the CNO fusion cycles of the Sun, to cover the transition phase for the solar neutrino oscillation from vacuum to matter mixing, and to measure the geo-neutrino flux, including the Th/U ratio. These goals can be fulfilled with mature existing techniques. Efforts on increasing the target mass with multi-modular neutrino detectors and on developing the slow liquid scintillator will increase the Jinping discovery potential in the study of solar neutrinos,geo-neutrinos, supernova neutrinos, and dark matter.     

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.     

Study of single muons with the Large Volume Detector at the Gran Sasso Laboratory

The present study is based on the sample of 2.9×10⁶ single muons observed by the Large Volume Detector (LVD) at the underground Gran Sasso Laboratory during 36 500 live hours from June 1992 to February 1998. We have measured the muon intensity at slant depths from 3 to 20 km w.e. Most events are high-energy downward muons produced by meson decay in the atmosphere. The analysis of these muons has revealed the power index γ of the π and K spectrum: γ=2.76±0.05. The remainders are horizontal muons produced by the neutrino interactions in the rock surrounding the LVD. The value of this flux near 90° is (6.1±2.7)×10⁻¹³ cm⁻² s⁻¹ sr⁻¹. The results are compared with the Monte Carlo simulations and the world data. From Yadernaya Fizika, Vol. 66, No. 1, 2003, pp. 125–132. Original English Text Copyright ? 2003 by Aglietta, Alyea, Antonioli, Badino, Bari, Basile, Berezinsky, Bersani, Bertaina, Bertoni, Bruni, Cara Romeo, Castagnoli, Castellina, Chiavassa, Chinellato, Cifarelli, Cindolo, Contin, Dadykin, Dos Santos, Enikeev, Fulgione, Galeotti, Ghia, Giusti, Gomez, Granella, Grianti, Gurentsov, Iacobucci, Inoue, Kemp, Khalchukov, Korolkova, P. Korchaguin, V. Korchaguin, Kudryavtsev, Luvisetto, Malguin, Massam, Mengotti Silva, Morello, Nania, Navarra, Periale, Pesci, Picchi, Pless, Ryazhskaya, Saavedra, Saitoh, Sartorelli, Selvi, Taborgna, Talochkin, Trinchero, Tsuji, Turtelli, Vallania, Vernetto, Vigorito, Votano, Wada, Weinstein,Widgoff, Yakushev, Yamamoto, Zatsepin, Zichichi. The authors represent the LVD Collaboration This article was submitted by the authors in English.     

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.     

Determination of the atmospheric neutrino spectra with the Fréjus detector

The combined analysis of the final event set of data on neutrino interactions inside the detector, upward going stopping muons and horizontal muons recorded in the Fréjus experiment is presented. The absolute atmospheric neutrino spectra in the energy range for electron neutrinos and for muon neutrinos are determined. Based on the parameterization of Volkova for thev ^µ a spectral index of =2.66±0.05 is obtained from the ratio of horizontal muons over upward going stopping muons and from the measurement of the energy loss of horizontal muons inside the detector. The neutrino spectra are compared with various flux calculations. They do not show any evidence for neutrino oscillations in agreement with earlier analyses of the Fréjus data.Now atUniversity of Michigan, Ann Arbor, USA     

Very high energy neutrinos

A sky survey with neutrinos may considerably extend our understanding of cosmic phenomena. Due to the low interaction cross section of neutrinos with matter and due to the high cosmic ray background the detector must be very large (of the order of 1 km³) and must be shielded. These new devices consist of a network of photo-tubes which are deployed in the depth of the ocean, of a lake or of the ice of South Pole. The detection of the Cherenkov light emitted by muons produced in muon neutrino interactions with the matter surrounding the detector will allow the reconstruction of the neutrino direction with an angular resolution of the order or lower than one degree. Several projects are underway. Their status will be reviewed in this paper.     

Probing pseudo-Dirac neutrino through detection of neutrino-induced muons from gamma ray burst neutrinos

The possibility to verify the pseudo-Dirac nature of neutrinos is investigated here via the detection of ultra-high energy neutrinos from distant cosmological objects like γ-ray bursts (GRBs). The very long baseline and the energy range from ∼TeV to ∼EeV for such neutrinos invoke the likelihood to probe very small pseudo-Dirac splittings. The expected secondary muons from such neutrinos that can be detected by a kilometer scale detector such as ICECUBE is calculated and compared with the same in the case of mass-flavour oscillations and for no oscillation cases. The calculated muon yields indicate that to probe such small pseudo-Dirac splittings one needs to look for a nearby GRB (red shift z ∼ 0.03 or less) whereas for a distant GRB (z ∼ 1) the flux will be much depleted and such phenomenon cannot be distinguished. Also calculated are the muon-to-shower ratios.      

High-energy neutrinos from gamma ray bursts

We treat high-energy neutrino production in gamma ray bursts (GRBs). Detailed calculations of photomeson neutrino production are presented for the collapsar model, where internal nonthermal synchrotron radiation is the primary target photon field, and the supranova model, where external pulsar-wind synchrotron radiation provides important additional target photons. Detection of greater, similar 10 TeV neutrinos from GRBs with Doppler factors > or approximately 200, inferred from gamma-ray observations, would support the supranova model. Detection of < or approximately 10 TeV neutrinos is possible for neutrinos formed from nuclear production. Only the most powerful bursts at fluence levels > or approximately 3 x 10(-4) erg cm(-2) offer a realistic prospect for detection of nu(mu).     

Single and multiple muons and the generation of neutrons in the LVD experiment

The large geometric factor and good spatial resolution of the Large Volume Detector (LVD) ensures statistically significant and highly accurate measurements of muon trajectories and determination of the multiplicity of muon groups. The developed algorithm allows us to reconstruct 2 × 10⁶ muon events (single muons and muon groups). Characteristics of muon groups are obtained and the specific yield of neutrons produced by single muons, muon groups, and showers is determined.     

Measurement of Seasonal Variations of Horizontal Muons with Underground LVD Setup

The Large-Volume scintillation Detector commonly known as LVD and located at the Gran Sasso Laboratory at an average depth of 3650 m w.e. measures muons of intensity $$3.31\times 10^{-4}$$ m$${}^{-2}$$ s$${}^{-1}$$. The results obtained from an analysis of the properties of seasonal variations of the horizontal and vertical muon fluxes are presented in this article. Horizontal muons detected in LVD mostly correspond to rock depths of about 5 km w.e. and zenith angles $$\theta$$ of about $$75^{\circ}$$, while vertical muons ($$\theta\approx 13^{\circ}$$) correspond to depths of about 4.6 km w.e.