Galactic and extragalactic core-collapse supernova neutrino flux detection in the LEGEND muon veto
Abstract
Parallel talk presented at the XXI International Workshop on Neutrino Telescopes - Padova 29 September - 3 October 2025 (https://agenda.infn.it/event/44606/) On behalf of the LEGEND Collaboration Abstract: The LEGEND Collaboration advances an experimental program to search for the neutrinoless double-beta decay of 76 Ge.It has recently released the first results on the decay search based on 61 kg yr of data collected by the first stage of the experiment, LEGEND-200. It operates high-purity germanium (HPGe) detectors enriched in 76 Ge immersed in a cryostat filled with pure liquid argon. The cryostat is deployed in a tank filled with 590 m3 of purifiedwater, instrumented with photomultiplier tubes to tag cosmic-ray induced muon events, and to passively shield the detectors against environmental radioactivity.The second stage of the experiment, LEGEND-1000, aims to operate up to one ton of HPGe detectors enriched in 76 Ge with different proposals to optimize the water tank features.In this presentation, we explore the detection capabilities and sensitivity of the LEGEND muon veto in both phases of the experiment to the neutrino flux from core-collapse supernovae. The ability to identify the time of black hole formation is also discussed. This work is supported by the U.S. DOE, and the NSF, the LANL, ORNL and LBNL LDRD programs; the European ERC and Horizon programs; the German DFG, BMBF, and MPG; the Italian INFN; the Polish NCN and MNiSW; the Czech MEYS; the Slovak RDA; the Swiss SNF; the UK STFC; the Canadian NSERC and CFI; the LNGS and SURF facilities.
Full text
Galactic and extragalactic core-collapse supernova neutrino flux detection in the LEGEND muon veto Valentina Biancacci on behalf the LEGEND Collaboration 02.10.25
Valentina Biancacci Core-collapse SN neutrino flux detection in the LEGEND muon veto 02.10.25 2 LEGEND = Large Enriched Germanium Experiment for Neutrinoless Double-Beta Decay “The collaboration aims to develop a phased 76Ge based double beta decay experimental program with discovery potential at a half-life significantly longer than 1028 years, using existing resources as appropriate to expedite physics results.” LEGEND mission: 13 countries, 60 institutions, ~ 300 members, Collaboration formed in October 2016 Qββ= 2039 keV 2
Valentina Biancacci Core-collapse SN neutrino flux detection in the LEGEND muon veto 02.10.25 3 The project First Stage: LEGEND-200 ●~200 kg of detector mass: 35 kg from GERDA + 30 kg from MJD + 140 kg which are new, distributed to 14 strings ●Current data taking since March 2023 with ~142 kg of detectors deployed in LAr ●Total planned exposure 10 times larger than GERDA, up to 1 ton yr Further Stage: LEGEND-1000 ●Staged installation of 1000 kg detector mass (ICPC) ●Detector strings immersed in radiopure underground LAr (UGLAr) ●Pending funding approval > 1028 yrs < 10-20 meV < 10-5 cts/(keV⋅kg⋅yr) B m > 1027 yrs < 30-70 meV < 2⋅10-4 cts/(keV⋅kg⋅yr) B m 3
Valentina Biancacci Core-collapse SN neutrino flux detection in the LEGEND muon veto 02.10.25 After the success of our main research… 4 …what else can LEGEND do beyond 0nbb? look at K. Gusev’s talk
Valentina Biancacci Core-collapse SN neutrino flux detection in the LEGEND muon veto 02.10.25 Why should we care about SNv in LEGEND? ●Cherenkov veto network for SN neutrino at LNGS among COSINUS, LEGEND and XENON ○great bkg reduction thanks to coincidences ●Potential involvement on the SNEWS network ●Measurement of the BH time formation, which can be used in VIRGO detector and future Einstein Telescope to look for the gravitational wave counterpart to the neutrino signal ○smallest uncertainty thanks to the very small distance between the LNGS facility and the Virgo gravitational wave interferometer 5 Dr. G. Pagliaroli @ LNGS-INFN
1. Supernova and pre-Supernova neutrinos 6 Prompt signal discovery sensitivity
Valentina Biancacci Core-collapse SN neutrino flux detection in the LEGEND muon veto 02.10.25 Supernova and pre-supernova neutrinos ●Core-Collapse Supernovae (CCSN) are the end of life of heavy stars whose core collapses in a fraction of a second with a powerful explosion ●1058 neutrinos are emitted with a average energy of the order of 10 MeV. ●The detection of 25 neutrinos from SN 1987A marked the beginning of neutrino astronomy ●Several experiments sensitive to SN neutrinos are currently in operation or under preparation ●The detection of the neutrino burst would provide invaluable information on the CCSN mechanism and neutrino properties. 7 from here
Valentina Biancacci Core-collapse SN neutrino flux detection in the LEGEND muon veto 02.10.25 SN and pre-SN neutrino interactions in LEGEND LEGEND is uniquely sensitive to many SN neutrino interaction channels thanks to the combination of Ge, LAr, and water shield. The potential interactions in LEGEND are: ●Neutrino-electron elastic scattering (νeES) ●Charged current neutrino-nuclear scattering (νNCC) ●Coherent elastic neutrino-nuclear scattering (CEνNS) ●Inverse Beta Decay (IBD) in water tank 8 Some qualitative estimates already made by CJ Nave and Sam Watkins
Valentina Biancacci Core-collapse SN neutrino flux detection in the LEGEND muon veto 02.10.25 SuperNova neutrinos - e+ detection efficiency The number of detected supernova events are given by: ● is the threshold energy for the interaction x ● is the number of targets ● is the supernova neutrino flux ● is the interaction cross-section ● is the detection efficiency 9
Valentina Biancacci Core-collapse SN neutrino flux detection in the LEGEND muon veto 02.10.25 Sensitivity horizon - counting method - L1000 ●Events vs distance from supernova with PMT multiplicity = 10 ●Significance computed from likelihood ratio method and counting method: 16 4 events are required from the likelihood ratio method 9 events are required to get a significance of 3σ with counting method 0.06Hz*10s preliminary 3σ (kpc) LRT (kpc) NO 57+10 -8 70+12 -11 IO 70+12 -10 95+24 -19 MW centre MW edge LMC sMC
1. Supernova and pre-Supernova neutrinos 17 Efficiency and discrimination techniques of the delayed signal
Valentina Biancacci Core-collapse SN neutrino flux detection in the LEGEND muon veto 02.10.25 Neutron capture 18 ●The IBD delayed coincidence allows the selection of a BG-free sample, giving a clear signature of a SN burst ●The generated gammas gives an energy spectrum with a peak at 2.2 MeV from p and a showers up to ~8 MeV from Gd ●With 0.2% Gd2(SO4)3 dissolved in water, >90% of the neutrons are captured by 155/157Gd (from here) with 14.8% and 15.7% abundances, respectively. Supernova neutrinos fluence has a specific shape over time, easy to discriminate from the low and constant background Pre-supernova neutrinos are much lesser and distributed in a longer time interval Neutron capture is a great help in the bkg discrimination especially for pre-supernova events
Valentina Biancacci Core-collapse SN neutrino flux detection in the LEGEND muon veto 02.10.25 Gamma detection efficiency 19 157Gd 155Gd Grabmayr’s ANNRI-Gd Grabmayr’s ANNRI-Gd 10 PMT 96.2% 96.1% 97.4% 96.4% ●Geant4 doesn’t reproduce the neutron capture well, ANNRI-Gd and Grabmayr’s models are used instead to simulate the gammas from n capture in 155/157Gd ●Detection efficiency for γ at 2.2MeV with multiplicity of 10 PMTs is 43.2% ●Extracting 10k events randomly from the two model distributions for Gd ●LEGEND-1000 can see the released gammas. We can then combine positron Cherenkov shower with the delayed neutron capture Work in progress! Results for L1000
2. Failed Supernova neutrino 20
Valentina Biancacci Core-collapse SN neutrino flux detection in the LEGEND muon veto 02.10.25 Failed SN - Black hole 21 see https://arxiv.org/abs/2403.06678 ●In case of massive stars, with M ≳ 20M⊙ , the explosion mechanism can fails with the generation of a black hole (BH) very shortly after the core bounce. ●In this failed SN, neutrino and gravitational wave emissions stop abruptly when the BH is created, while the emission of electromagnetic signal is very faint. ●Neutrino detectors can identify the time of black hole formation providing an important timing to look for the gravitational counterpart of such events. ●In the absence of the electromagnetic counterpart, LNGS can provide this timing in real time to the VIRGO the future Einstein Telescope without the need to know the sky position of the SN, thanks to the proximity of the sites and so the negligible time of fly.
Valentina Biancacci Core-collapse SN neutrino flux detection in the LEGEND muon veto 02.10.25 BH time formation uncertainty 22 Work in progress! ●Capability to identify the BH formation time of experiments at LNGS for the two Models ●Total uncertainty on time formation in Virgo/Einstein Telescope with Model 2 8 ms with LEGEND time info Better estimations of the uncertainties are expected from the more precise simulations of the detection efficiency LEGEND with LNGS time info with SuperK time info Model 1 Model 2
Valentina Biancacci Core-collapse SN neutrino flux detection in the LEGEND muon veto 02.10.25 BH Horizon for L-200 and L-1000 L-200 23 L-1000 MW centre MW edge LMC sMC MW centre MW edge LMC sMC ●The sensitivity horizon for BH is obtained via counting method
Valentina Biancacci Core-collapse SN neutrino flux detection in the LEGEND muon veto 02.10.25 Conclusions ●LEGEND has a great potential to join the SNv research experiment crew and SNEWS ●IBD is our strongest channel for SN neutrinos in LEGEND ●Extremely high e+ detection efficiency for LEGEND-1000 ●Horizon sensitivity even up to the Small Magellanic Cloud under some conditions ●Nice capability for the neutron capture tagging ●LEGEND could provide one of the best uncertainties on the black hole time formation for the gravitation counterpart seen by Virgo/Einstein Telescope Outlook ●Better estimation of BH time formation using the obtained detection efficiency ●Tagging delayed coincidence to prompt signal 24
Valentina Biancacci Core-collapse SN neutrino flux detection in the LEGEND muon veto 02.10.25 backup 25