1. Prospects of the search for neutrino bursts from Supernovae with Baksan Large Volume Scintillation Detector V.B. Petkov Institute for Nuclear Research of RAS, Institute of Astronomy of RAS

2. The experiment to search for neutrino bursts from supernovae is carried out at the BUST during many years. It is the longest duration experiment (June 1980 - December 2014, T live = 29.76 years) with best upper limit on the rate of core-collapse and failed supernova explosions in the Galaxy: f < 0.077 y –1. When can we expect the next Galactic supernova? Plausible estimates give a rate between 1 every 10 years and 1 every 100 years. Expected rate of the ccSN in the Galaxy: 3.2 +7.3 -2.6 per century. (S.M. Adams et al., Observing the next Galactic supernova. AJ, 778,164, 2013) "The expected rate of stellar deaths in the Galaxy (~ 0.1 per year) is computed using a detailed model of the distribution of stars in the disk and standard values for Population I stellar evolutionary lifetimes." (John.N. Bahcall and Tsvi Piran, Stellar collapses in the Galaxy. AJ, 267, L77, 1983) If a ccSN in the Galaxy appears soon the supernova will not be missed, as many independent detectors are working now. But we need next generation detectors to measure with appropriate accuracy all flavors of neutrinos.

3. Neutrinos carry about 99% of the binding energy released during the collapse of the star. Precise measurements of all flavors of neutrinos can provide much information about a supernova. Next Galactic core collapse Supernova: What should the new neutrino detector to measure? 1. The different neutrino flavors must be distinguished. → It is necessary to consider the several interaction processes. 2. Large statistic must be collected to study spectra (and time profiles) of all six neutrino flavors. → Detector should have large target mass. 3. For follow-up optical observations it is critical to get the directional information out as soon as possible. Now - SK only. Large (10 kt and more) liquid scintillation detectors are under consideration now. JUNO – 20 kton, RENO-50 – 18 kton, LENA – 50 kton

4. Baksan Large Volume Scintillation Detector A large volume detector filled with liquid scintillator at the Baksan neutrino observatory is discussed during many years. The main research directions of the BLVSD are neutrino geophysics and neutrino astrophysics. Estimation of target mass of future detector is changed over time: ~1 kton target mass of LS: G.V. Domogatsky et al., Phys.Atom.Nucl., 68, 69, 2005. ~5 kton target mass of LS: G.V. Domogatsky et al., Phys.Atom.Nucl., 70, 1081, 2007; I.R. Barabanov et al., arXiv:0908.1466v2 [hep-ph] At present a complex of research and development aimed at the creation of a new-generation geoneutrino detector using an extra-pure scintillator of 10-20 kiloton mass is discussed.

5. – Gallium-Germanium B – Gallium-Germanium Neutrino Telescope D D D D D of muons Schematic view of a section of the Andyrchy slope along the adit (right scale) and dependence of underground muon flux on the laboratory location depth (left scale). General view of underground objects of the Baksan neutrino observatory

6. Underground Laboratories of the BNO INR RAS OGRAN’s hall GGNT’s hall Entrance BUST’s hall Low Bkg Lab1 «НИКА» Low Bkg Lab3 «DULB-4900» Low Bkg Lab2 + Laser Interferom. 620 m – 1000 m w.e. GeoPhys Lab1 GeoPhys Lab2 4000 m BLVSD

7. Interaction channels, CC processes (double-signal events) IBD, E th = 1.8 MeV τ ≈ 200 μs, E γ = 2.2 MeV The double coincidence signal of e + and n means that these events can be individually identified (assuming 99% capture efficiency of neutrons in large detector).

8. Interaction channels, CC processes (double-signal events) E th = 14.4 MeV τ B = 29.1 ms, Q = 12.9 MeV E th = 17.3 MeV τ N = 15.9 ms, Q = 16.8 MeV It will be important to distinguish between the final states interactions with 12 C. Pulse shape distortion produced by positron can be used to distinguish between these interactions. As the electron antineutrino spectrum will be known to ~ 2% precision from the IBD, it can be used to predict the electron antineutrino + 12 C signal.

9. In the Elastic Scattering on electrons all the flavors participate, but the cross section is slightly different for the different flavors. Interaction channels, NC processes (single-signal events): all neutrino flavors participate ES on protons inelastic scattering de-excitation line E γ = 15.11 MeV ES on electrons

10. Expected numbers of events in a 20 kton liquid scintillator detector for a Galactic supernova for different values of the neutrino average energy. The total energy is assumed to be 3×10 53 erg, divided equally among all flavors, at distance of 10 kpc. The detection threshold: 0.2 MeV. R. Laha et al., arXiv:1412.8425v1 [hep-ph]

11. Observed energy distribution in a 20 kton liquid scintillator detector for a Galactic supernova at 10 kpc. The total energy carried by each flavor is 5 × 10 52 erg. R. Laha et al., arXiv:1412.8425v1 [hep-ph]

12. Observed energy distribution in a 20 kton liquid scintillator detector for a Galactic supernova.The total energy carried by each flavor is 5 × 10 52 erg. Recoil spectra of electrons and positrons from interactions with 12 C. R. Laha et al., arXiv:1412.8425v1 [hep-ph] It is possible to distinguish even close average energies.

13. Importance of neutrino detection from the point of view of astronomers: the pointing is necessary. Optical/near-IR observations will remain a crucial component of studies of Galactic SNe. Schematic time sequence for the stages of a ccSN. The core-collapse releases ∼ 10 4 times more energy in neutrinos in ∼ 10 s than is released in the electromagnetic signal of the supernova over its entire duration. [S.M. Adams et al., AJ, 778,164, 2013]

14. Determination of direction to ccSN: water Cherenkov detectors. Using neutrino-electron scattering, ν e + e - → ν e + e -. These events are forward-peaked, so a narrow cone contains the majority of them. This technique is used at Super-Kamiokande with electron neutrinos from short (~10 ms) neutronization burst. → Benefits of SK as water Cherenkov detector, a few- degree error circle. [M. Ikeda et al., AJ, 669, 519, 2007]

15. Determination of direction to ccSN: large liquid scintillation detectors. IBD reaction: The direction of the outgoing positron is nearly isotropic because of the small recoil energy of the nucleon. But there is a neutron displacement: the angle with respect to the incoming neutrino direction is limited to values below ~55°. 5000 neutrino interactions was generated in an experiment with the same geometry, the same position resolution and the same target (Gd- loaded liquid scintillator) as the CHOOZ experiment. Uncertainty: 8.8° for all events and 8.4° for events with positron-neutron distance to be larger than 20 cm. [M. Apllonio et al., Phys. Rev. D61, 012001, 1999.] This method is under further development in INR RAS. Ya. Nikitenko. Inverse beta decay reaction for determination of direction to antineutrino source. Talk at this conference (Thursday, February 5)

16. Determination of direction to ccSN: new techniques. Water-based Liquid Scintillator Detector combines the benefits of both water Cherenkov detection and pure liquid scintillator in a single detector (high light yield and low threshold of scintillator with the directionality of a Cherenkov detector). [arXiv:1409.5864v3]

17. Scintillator + SiPM matrices with optical collector Determination of direction to ccSN: new techniques. Scintillation detector with a photodetector based on SiPM matrices with appropriate optical collector gives a possibility to obtain an image of an event. Benefits: determination of direction(s) of the particle(s), measurement of the energy release along the tracks, separation of different classes of events. [INR RAS, under development] Large LS detectors: absorption? scattering?

18. Conclusion Liquid scintillation detectors of the 20-kton scale are acceptable to detect all flavors of neutrinos (to measure the total and average energy in each). Possible detection strategies to measure the total and average energy of all supernova neutrino flavors with appropriate precision are being developed. There are different methods of determination of direction to ccSN. New experimental technique is under development. Thank you for attention!