Searching for neutrino bursts in the galaxy: 36 years of exposure
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, PARTICLES, FIELDS, GRAVITATION, AND ASTROPHYSICS
Searching for Neutrino Bursts in the Galaxy: 36 Years of Exposure Yu. F. Novoseltseva*, M. M. Bolieva, V. I. Volchenkoa, G. V. Volchenkoa, I. M. Dzaparovaa,b, M. M. Kochkarova, R. V. Novoseltsevaa, V. B. Petkova,b, and A. F. Yanina aInstitute
for Nuclear Research, Russian Academy of Sciences, pr. 60-letiya Oktyabrya 7a, Moscow, 117312 Russia b Institute of Astronomy, Russian Academy of Sciences, ul. Pyatnitskaya 48, Moscow, 119017 Russia *e-mail: [email protected] Received November 20, 2016
Abstract—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. DOI: 10.1134/S1063776117070226
et al. [12] showed that strange-quark contributions to the neutrino scattering by nucleons reduces (approximately by 15%) the neutrino opacity of matter in the stellar core. This leads to amplification of the neutrino energy deposition behind the stalled shock and to an increase in the shock energy and provides a canonical SN explosion. This result underlines that an accurate knowledge of neutrino–nucleon interaction rates, in particular also for neutral-current scattering, is of crucial importance for assessing the viability of the neutrino-driven explosion mechanism. Since light (and generally electromagnetic radiation) can be partially or completely absorbed by dust in the Galactic plane, large neutrino detectors are the most suitable instrument for the detection of core-collapse SNe. Several such detectors have searched for neutrino bursts in the last decades: the Baksan Underground Scintillation Telescope [13–15], SuperKamiokande [16], MACRO [17], LVD [18, 19], AMANDA [20], and SNO [21]. At present, a new generation of detectors that are capable of recording the neutrino burst from an SN has been added to the facilities listed above: IceCube [22], Borexino [23, 24], KamLAND [25], and others. The search for neutrino bursts at the Baksan Underground Scintillation Telescope has been conducted since the mid-1980s. In this time (more than 35 years) our views and knowledge of the structure and
1. INTRODUCTION The detection of neutrinos from SN1987A [1–4] was an experimental confirmation of a critical role of neutrinos in the explosion of massive stars (the birth of supernovae (SNe)), as was suggested more than 50 years ago [5–7]. Owing to their great penetrability, neutrinos deliver information about the physical conditions in the core of a star at the instant of its gravitational collapse. The SN19
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