32nd International Cosmic Ray Conference, August , 2011,Beijing 1 R.V. Novoseltseva, M.M. Boliev, I.M. Dzaparova, M.M. Kochkarov,Yu.F. Novoseltsev, V.B. Petkov, P.S. Striganov, G.V. Volchenko, V.I. Volchenko, A.F. Yanin Update for 2010: Search for neutrino bursts from core collapse supernovae at the Baksan Underground Scintillation Telescope (BUST) Institute for Nuclear Research Russian Academy of Sciences Baksan Neutrino Observatory

32nd International Cosmic Ray Conference, August , 2011,Beijing 2 BUST 850 m w.e. The Baksan Neutrino Observatory of Institute for Nuclear Research of RAS

3 BUSTBUSTBUSTBUSTGGNTGGNT 7 LBLLBL 1,7 - LBL 1,7 - LBL 2 - BUST 2 - BUST 3 - Laser interferometer 3 - Laser interferometer 4 - Acoustic gravitational antenna 4 - Acoustic gravitational antenna 5 - Geophysics laboratory 5 - Geophysics laboratory 6 - GGNT(SAGE) 6 - GGNT (SAGE) * - for further projects ~4700 m.w.e. ~5000 m.w.e. ~850 m.w.e. 17m  17m  11m 60m  10m  12m 3.2m  2.4m  2.4m 1.V.B. Petkov “High energy muons in EAS and primary composition around the knee” 2.V.B. Petkov “Temperature variations of high energy muon flux” 3.D.D. Dzhappuev “Study of the PCR’s knee by the method of EAS particles central density” 4. A.N. Gaponenko “Flat air showers as possible signature of PBH evaporation”

32nd International Cosmic Ray Conference, August , 2011,Beijing 4 BUST – the general view ( the effective depth 850 m of w.e.) dimensions m 3 number of tanks 3180 tank size cm 3 low-background concrete the scintillator C n H 2n+2 (n ≈9) the total mass of scintillator is 330 t (3180 tanks) three lower horizontal layers -130 t (1200 tanks) dead time of BUST: ≈ 1 ms a clock: 0.2 ms accuracy of determining the absolute time (signal of GPS) Iron layer (0.8cm)

32nd International Cosmic Ray Conference, August , 2011,Beijing 5 1) an anodic channel provides measuring amplitude and time of a scintillator layer. 2) a pulse channel from 12 th dinode with the energy threshold of 8 MeV. 3) a logarithmic channel from 5 th dinode with the energy threshold 500 MeV. the range: 8 MeV – 600GeV The information from each module is transferred through three channels concurrently: BUST: the upper plane

32nd International Cosmic Ray Conference, August , 2011,Beijing 6 ε, erg τ, s (3-5) Standard model of collapse Imshennik V.S., Nadezhin D.K., Itogi Nauki i Tehniki, ser.Astronomy v.21,1982 A. Burrows, D. Klein, R. Gandhi, Phys. Rev. D 45, 1992 From the theory of the Standard collapse it follows that the total energy carried out by all flavors of neutrinos is equally divided into these 6 components.

32nd International Cosmic Ray Conference, August , 2011,Beijing 7 If the mean antineutrino energy is ≈15 MeV the range of e+ will be included, as a rule, in the volume of one tank. The search for a neutrino burst consists in recording a bunch of single events within time interval of τ. The radiation length for our scintillator is 47 g/cm 2 The Baksan experiment: the method t A

32nd International Cosmic Ray Conference, August , 2011,Beijing 8 The estimation of the expected number of events at BUST from ν burst 1) the distance to the star is 10 kpc (approximately the distance to the Galactic center, but in an arbitrary direction) 2) the total energy radiated in neutrinos is energy radiated in is 3) we leave out a possible influence of oscillations 1 – energy threshold 10 MeV ( yr) 2 – energy threshold 8 MeV (since 1992 yr) detection efficiency of e +

32nd International Cosmic Ray Conference, August , 2011,Beijing 9 The dependence of expected number of neutrino events ( ) on a distance to the star. Curve 1 is for 130 tons, curve 2 is for 330 tons of scintillator. q is the percentage of stars in the Galaxy within a distance R from the Sun. BUST sensitivity curves

32nd International Cosmic Ray Conference, August , 2011,Beijing 10 The registration of SN1987A has given rise to non-standard two-stage scenario of stellar collapse. Imshennik V.S. Space Sci.Rev., 1995, 74: 325 Imshennik V.S., Ryazhskaya O.G. Astronomy Letters, 2004, 30: 17 The mean neutrino energy (during the first stage) in this model is MeV. V.Bajkov, V.M. Suslin, V.M. Chechetkin, V.Bychkov,L.Stenflo, Astronomicheskij jurnal, 2007, 84(4):308 This model has taken into account large-scale convection caused by nonequilibrium neutronization of matter in the central region of protoneutron star. The large-scale convection provides high yield of high energy neutrinos from the central region of presupernova. The average energy of neutrinos is MeV which is more than in the case of diffusion.

32nd International Cosmic Ray Conference, August , 2011,Beijing 11 I f (30-40 MeV) than a noticeable percentage of neutrino reactions will cause triggering of two tanks simultaneously (count rate of two tanks ≈ s -1 ) Iron – additional target Iron, 8mm reaction detection efficiency number of events (e -, e + )

32nd International Cosmic Ray Conference, August , 2011,Beijing 12 Background events radioactivity ghost signals from module cosmic ray muons: a single muon is registered by one module due to spatial gaps between modules of the telescope a muon energy release < 8 MeV radioactivity: natural radioactivity Inelastic muon interaction with the matter of the module. Some part of the background events can be connected with inelastic muon interactions which can produce unstable nuclei whose disintegration brings into operation only one module.

32nd International Cosmic Ray Conference, August , 2011,Beijing 13 Muon group + cascade

32nd International Cosmic Ray Conference, August , 2011,Beijing 14 Study of single events following large energy release (≥ 500 MeV) in the tank Events of type “a”: cascades with one or more tanks with E≥500 MeV (internal planes of BUST) Events of type “b”: single events using these tanks (i.e. tanks after E≥500 MeV) within interval Δt (dead time of BUST ≈ 1 ms) events “b”

32nd International Cosmic Ray Conference, August , 2011,Beijing 15 N tot = 205 Na-b/Ntot = Afterpulses related to inelastic muon interactions have been studied: discrimination of such afterpulses does not lead to noticeable reduction of the background. Amplitude spectrum of single events following large energy release (≥ 500 MeV in the tank) 2007 year, 3d horizontal plane events ‘b’, amplitude spectrum absence of single event bunches following cascades calibration of energy release

32nd International Cosmic Ray Conference, August , 2011,Beijing 16 The number of bunches with k single events within time interval of τ =20s f in = 0.02 Hz is for internal planes (three lower horizontal layers) f = 1 Hz is for external ones. The cluster of events at BUST would be considered to be a serious candidate for collapse detection if nine or more single events were observed within 20 s sliding time interval in the internal planes of the facility (130 tons of scintillator). Squares are experimental data, the curve is the expected number according to the expression (P). T = 8,3 yr

32nd International Cosmic Ray Conference, August , 2011,Beijing 17 CONCLUSIONS Investigations of BUST’s response to neutrinos of 30 – 40 MeV have been performed. The number of events induced by neutrino in BUST has been found to be increased by ≈ 50%. Afterpulses related to inelastic muon interactions have been studied. The single event bunches following cascades has been not observed. The total livetime for the period of to is T = 26.2 years. No burst candidate for the core collapse in the Galaxy has been detected during this period. year LIVE TIME (years) UPPER BOUND (90%CL) /yr /yr /yr up /yr An upper bound on the mean frequency of gravitational collapses in the Galaxy for BUST’s data (at 90% CL)