LVD Experiment: 25 Years of Operation
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EMENTARY PARTICLES AND FIELDS Experiment
LVD Experiment: 25 Years of Operation N. Yu. Agafonova* , V. V. Ashikhmin, E. A. Dobrynina, R. I. Enikeev, A. S. Malgin, O. G. Ryazhskaya, I. R. Shakiryanova, and V. F. Yakushev (On behalf of the LVD Collaboration) Institute for Nuclear Research, Russian Academy of Sciences, pr. Shestidesyatiletiya Oktyabrya 7a, Moscow, 117312 Russia Received June 20, 2017
Abstract—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. DOI: 10.1134/S1063778818010039
INTRODUCTION
The model validates the possibility of a two-stage collapse such that, at its first stage, the emission of predominantly electron neutrinos with average energies between 30 and 40 MeV occurs, while, at the second stage, there arise all neutrino flavors, in just the same way as in SCM, their mean energy ranging between 10 and 15 MeV. Muons and products of their interactions in the setup materials and in rock are a dominant source of the background in underground experiments. In this respect, nuclear-active particles, such as pions, protons, and especially neutrons, which are able to mimic sought events over a broad energy range, are the greatest danger.
The detection of neutrino radiation from star collapses would make it possible to obtain information about the behavior and properties of matter under extreme conditions arising upon the formation of neutron stars and black holes, which proceeds via processes that are the most fundamental in the Universe. Starting from the late 1970s, Institute for Nuclear Research (INR, Moscow) constructed several large underground scintillation detectors that were able to detect neutrino radiation from the gravitational collapse of stellar cores. These were ASD (Artemovsk scintillation detector, 1977), BUST (Baksan underground scintillation telescope; 1978), LSD (large scintillation detector; USSR–Italy, later, Russia– Italy; 1984 г.), and LVD (large volume detector; Russia–Italy; 1992). Since 1986, Cerenkov detectors have been operating in Japan—Kamiokande (KII) and in the United States of America—IMB (Irvine– Maryland–Brookhaven). A detailed review on the subject was published in [1]. During the explosion of a supernova in the Large Magellanic Cloud on February 23, 1987, KII and IMB detected a signal at 7:35 UT, while LSD detected a signal at 2:52 UT. The signal in LSD proved to be inexplicable [2] within the standard collapse model (SCM) [3]. It was interpreted within the rotating collapsar model (RCM), which was proposed in [4] in ord
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