The 20th Lomonosov Conference on Elementary Particle Physics, MSU, August 19-25, 2021 - online

Gravitational Stellar Collapses are astrophysical events of great interest.
Because of the complexity of the problem, the modelling of the physicalprocesses is still in evolution, but it is in general accepted that the role ofneutrinos is critical to allow the supernova to form out of a collapse.
The detection of the neutrino signal from the SN 1987A marked thebeginning of a new era in neutrino astrophysics and, in spite of someunresolved controversies, opened the way to the Neutrino Astronomy.
N.Yu.Agafonova1, M.Aglietta2,3, P.Antonioli4 , V.V. Ashikhmin1, G.Bari4,G.Bruno5,6, E.A. Dobrynina1, R.I. Enikeev1, W.Fulgione3,7, P.Galeotti2,3,M.Garbini4,8, P.L.Ghia9 , P.Giusti4 , E.Kemp10, A.S.Malgin1 , A.Molinario2,3,R.Persiani4 , I.A.Pless11, O.G.Ryazhskaya1 , G.Sartorelli4 , I.R.Shakiryanova1 , M.
Selvi4 , G.C.Trinchero2,3, C.F.Vigorito2, V.F.Yakushev1 and A. Zichichi4,81 Institute for Nuclear Research, Russian Academy of Sciences, Moscow, Russia; 2 University ofTorino and INFN-Torino, Italy; 3 INAF, Osservatorio Astrofisico di Torino, Italy; 4University of
Bologna and INFN-Bologna, Italy; 5 INFN, Laboratori Nazionali del Gran Sasso, Assergi,L’Aquila, Italy; 6 New York University Abu Dhabi, NYUAD, United Arab Emirates; 7 INFN,Laboratori Nazionali del Gran Sasso, Assergi, L’Aquila, Italy; 8 Centro Enrico Fermi, 00184
Roma, Italy; 9 Institut de Physique Nucleaire, CNRS, 91406 Orsay, France; 10 University ofCampinas, Campinas, Brazil; 11 Massachusetts Institute of Technology, Cambridge, USA.

The coordinates of the LNGS:
13.5333E, 42.4275N.

Length Width Height

22.713.210 m

Iron mass
1020 t
Scintillator mass (CnH2n, n~10)1008 tAmount of scintillation
840
counters
Average depth
3650 m w.e.
Minimal depth
3000 m w.e.
LVD@LNGS
Mean muon energy
280 GeVЕµ on see level (min.)
1.3 TeV
Muon rate (on 1 tower)~ 120 h-1
The main goal of LVD is searching for
Average counting rate (7MeV) 2x10-4 s-1 count-1
neutrino radiation from stellar core collapse.
Threshold EHET (ELET,)
4 MeV (0.5 MeV)

Tower1 Tower2Tower3

LVD duty cycle and active mass as afunction of time from 1992, June 9th
1992 to 2021, May 5th .

The detector maintenance can be done during data acquisition by stopping only the part that needs to bemaintained, even a single counter. This peculiarity allows a dynamic active mass and a high duty cycle.

Bunch detection with N
pulses in a short timeinterval T

А

t

10kps
5 MeV
0.8 MeVt

window: t=500ms

Eth = 1.8 MeV

n + p → d + .
n + Fe → Fe + .

E= 2.2 MeV
E  7 MeV

CnH2n, n~ 101 kt CnH2n1 kt Fe
840 countersTte + p → e+ + nt

300 ev.
in LVD

Fe….. O C He H

The SN outburst is triggered by the gravitational
collapse of the “iron” core of a mass MFe=1.22
Mc into a neutron star. About (10  15)% MFec2
is radiated in the form of  and of all theflavors (e, m, t): E = (3 - 5) 1053 erg. The totalenergy is assumed to be equally distributed
among the six neutrino species: Ei ~ 0.5×1053 erg.

eem,tm,t

E νe  = 9.5 MeV,
 Eνe = 12 MeV,
 E νx  = 15.6MeV
Neutrino spectra, 100ms after bounce e + p → e+ + n

Main reaction:
e+n + p → d +  (E = 2.2 MeV)n + 56Fe → 57Fe +  (E = 10.16 MeV)

The search for neutrino bursts isbased on the identification of event
clusters with a low probability oft 150ms
event imitation. These events arebackground fluctuations..

Reaction with Iron and Carbon:

e + 56Fe → 56Co* + e−,

56Co*→ 56Co + , E  7 MeVi + 12C → 12C* + i, (i = e, m, t); 12C*→ 12C + , E = 15.1 MeV

N.Y. Agafonova et al. (LVD Collaboration) "Implication for the core-collapse
supernova rate from 21 years of data of the Large Volume Detector" The
Astrophysical Journal, 802:47 (9pp), 2015 March 20

Registered clusters with Fim <1 day − 1.
Clusters with high significance are markedin red.
6

1 “Good” counters with average counting rate is E ≥ 7MeV: R=210−4 s −1 counter −12 Imitation frequency:mminP(k, fbki∆ti) is the Poisson probability to have k events in the time window ∆ti∆tmax - maximum cluster duration chosen for the analysis,fbk, fbki is the background and instantaneous background frequency

7 MeV, fbk = 0.2 Hz
10 MeV, fbk = 0.03 Hz

LVD Collaboration. The Astrophysical Journal, 802:47 (9pp), 2015
LVD Collaboration. Astroparticle Physics 28 (2008) 516-522

7 MeV

10 MeVOn-line trigger
efficiency versus
distance (lowerscale) andpercentage ofSN1987A signal at
10 kpc (upper scale)and Mact = 330 tons(dotted) and 1000
tons (continuous).

lg Fim [Ev/year]
Minimum cluster multiplicity (m ) vs. the imitation frequency
3 (F ). The lines represent the F min
imim thresholds of 1 candidate per
100 year (off-line) and of 1 per month (on-line).

sliding window ∆tmax=20 second
sliding window ∆tmax=100 second

HALO

DayaBay

IceCubeSNEWS - Supernova
Alert Program. Since
2015 includes: HALO,
DayaBay, KamLAND,
Super-K, LVD, IceCube,
Borexino

SNEWS

SNEWS aims to provide the astronomical community with early warning ofa supernova explosion in our Galaxy, so that experimenters can observe theastronomical consequences of a star's gravitational collapse.

The detectors send reports of a possiblesupernova to a computer at Brookhaven NationalLaboratory to identify a supernova. If the SNEWS
computer has signals from two detectors within 10seconds, the computer will send a supernova alert
to observatories around the world to study thesupernova. The SNEWS mailing list is opensubscription, and the general public is allowed tosign up. https://snews.bnl.gov/alert.html

Fim = 1/100 year

Fim = 1/ year

Detected clusters withFim <1 day−1. Clusters with highsignificance are marked in red.

All clusters with Fim < 1/yr have been checked in terms of energy spectra and low
energy signals that may be the signature of the IBD interactions. They are fullycompatible with chance coincidence among background signals.

Cluster date andtime
16.04.1994
10:40:49.263
27.08.1995
16:18:10.478
07.10.1998
15:41:41.775
18.07.2009
07:39:20.510
25.05.2014
03:54:14.555
18.12.2014
20:21:28.787

Cluster
multiplicity
7Duration
ti, s
18.88

EnergyE, MeV
26.5Frequency
1/F, y-1
1.06

7

5.49

36.2

11.16

12

90.05

32.2

1.76

12

42.71

14.6

4.02

14

61.56

22.6

1.49

8

9.98

18.8

3.22

Characteristics of clusters with significance Fim < 1 year-1.

The detection of neutrino radiation has been
carried out with the help of an LVD (LNGS, Italy)
since 1992. A technique has been developed forobserving neutrino bursts in our galaxy in on-line
and off-line modes.
According to the data of the LVD neutrino
telescope for 29 years of operation (1992 - 2021),
an experimental limitation on the frequency ofneutrino bursts from gravitational collapses ofstars in the Galaxy was obtained: less than 1 eventin 12.6 years (f = 0.08 y-1) at a 90% confidence
level.