Development of early warning method incorporating pre-supernova neutrino light curves

October 2nd, 2025 XXI Workshop on Neutrino telescopes Development of early warning method incorporating pre-supernova neutrino light curves A Research Center for Neutrino Science, Tohoku University B School of Physics & Astronomy, University of Glasgow C Kavli Institute for the Physics and Mathematics of the Universe, University of Tokyo D Institute for Cosmic Ray Research, University of Tokyo E Department of Physics, Kyoto University *K.SaitoA (e-mail: [email protected]), K.IchimuraA, K.IshidoshiroA, L.N.MachadoB, L.MartiC, M.IkedaD, N.KawadaA, Roger A. WendellEand Z.HuE Pre-supernova neutrino (1/2) 02/10/2025 XXI Workshop on Neutrino telescopes 2 •All flavor neutrinos are predominantly emitted thorough thermal pair productions and nuclear interactions (β decay, electron/positron capture) during the last stage of massive stars. ▸early warning to a core collapse supernova explosion. 𝐿ν[erg/s] Time before core collapse 𝐸ν[MeV] O shell burning Si shell burning Neutrino luminosity and its average energy (from Odrzywolek et al.(2010), 15 M⊙star) SiOCHe H Fe 𝜈തν Minit ≳8 M⊙ Core collapse supernovae a few days later •The observation of pre-supernova (pre-SN) neutrino provides: NASA Images Luminosity of pre-SN തν𝑒 Average energy of pre-SN തν𝑒 ▸direct insight of the physical state into the star. Pre-supernova neutrino (2/2) 02/10/2025 XXI Workshop on Neutrino telescopes 3 •Pre-SN neutrinos are emitted before core collapse. •Alarm distance ≲1 kpc ▸restrict number of supernova candidate stars to ~ 30. ▸neutrino and GW detectors prepare to detect supernova burst. ▸EM detectors observe stars before and during core collapse due to stelar evolution. Pre-SN neutrinos issue alarm to neutrino, gravitational wave (GW) and electromagnetic (EM) supernova telescopes. ▸By aligning telescopes worldwide, we can monitor all potential supernova candidates. ref) K.Nakamura et al. (2016) KamLAND(since 2002) 02/10/2025 XXI Workshop on Neutrino telescopes 4 Inner detector (Neutrino detector) •1 kiloton liquid scintillator detector (80% Dodecan, 20% Psedocumene and 1.36 g/L PPO) •1,325 17inch + 554 20inch PMT Outer detector (veto detector) •3.2 kiloton water Cherenkov detector •~140 20inch PMT KamLAND is liquid scintillator neutrino detector located in Kamioka, Japan (~1,000 m underground). 13m Kamioka Liquid scintillator Anti-Neutrino Detector • Inner balloon (r=1.90 m) for 0νββ decay search (KamLAND-Zen experiment) →This region is not used for my analysis. Super-Kamiokande (since 1996) 02/10/2025 XXI Workshop on Neutrino telescopes 5 Super-Kamiokande is water Cherenkov neutrino detector located in Kamioka, Japan (~1,000 m underground). 39.3 m 41.4 m Inner detector (Neutrino detector) •~11,000 20inch PMT Outer detector (veto detector) •Water Cherenkov detector •1885 8inch PMT •22.5 kiloton (fiducial volume) water Cherenkov detector SK-Gd experiment 0.03 wt% Gadolinium is loaded into water. Neutron capture fraction on Gd is 75%. 0.03wt% ~75% ref) Ll. Marti, et al, (2020) Nuclear Inst. and Methods in Physics Research, A 959 163549 Detection of Pre-SN Neutrino 02/10/2025 XXI Workshop on Neutrino telescopes 6 •KamLAND and SK-Gd detect pre-SN ഥ 𝝂𝒆from nearby stars (~𝒪(100)pc from Earth) through inverse beta decay reaction. തν𝑒𝑝𝑒+ n𝑝തν𝑒𝑝𝑒+ n Gd KamLAND SK-Gd •Delayed coincidence between prompt positron event and delayed neutron capture event •Event selection based on machine learning (Boosted decision tree) γ: 2.2 MeV γcascade: ~8 MeV •Visible pre-SN തν𝑒energy: 0.9–4.0 MeV 𝑒− Please see Dr. Lucas’s talk for more details. Title: Enhancing Low-Energy Neutrino Sensitivity in Super-Kamiokande with the Wide-band Intelligent Trigger γ: 511 keV ΔR<200 cm 0.5<ΔT<1,000 μs ΔR<300 cm ΔT< 80 μs •Fiducial cut: R<6 m •Likelihood cut Background 02/10/2025 XXI Workshop on Neutrino telescopes 7 Expected BG rate KamLAND: 0.19 /day (Assumption: current reactor operational status) *Expected reactor ഥ 𝝂𝒆rate depends on its operational status. Online alarm system calculates the expected reactor തν𝑒rate by obtaining real-time electric power data and monitoring the operational status of the reactor. Dominant background (BG) contribution KamLAND: •Reactor തν𝑒* •Geo തν𝑒 •Accidental coincidence •13C(α,n)16O •Reactor തν𝑒* •Geo തν𝑒 •Accidental coincidence •Radioactivre contamination SK-Gd: SK-Gd: 12.4 /day Conventional alarm system 02/10/2025 XXI Workshop on Neutrino telescopes 8 KamLAND[1] and SK-Gd[2] issues alarm based on statistical excess of observed event rate over the BG rate (Rate analysis) Target star: 15 M⊙star at 150 pc from Earth (Betelgeuse-like star [3]) [1] K. Asakura et al 2016 ApJ 818 91 [2] L. N. Machado et al 2022 ApJ 935 40 [3] Meridith Joyce et al 2020 ApJ 902 63 In order to issue an earlier alarm than conventional system, We develop alarm method incorporating time evolution of pre-SN ഥ 𝝂𝒆rate. (Rate+Time analysis) KamLAND SK-Gd Combined alarm system 02/10/2025 XXI Workshop on Neutrino telescopes 9 Ref) S. Abe et al 2024 ApJ 973 140 •Lower BG rate + Lower energy threshold ▸Earlier warning for supernovae •Larger target mass ▸Rapid increase of alarm significance KamLAND SK-Gd Combined combine Combined alarm system benefits advantages from both detectors and improve the alarm sensitivity. We evaluate alarm performance of Rate+Time analysis in KamLAND and SK-Gd and its combined case. alarm webpage: https://www.lowbg.org/presnalarm/ Expected neutrino flux at Kamioka 02/10/2025 XXI Workshop on Neutrino telescopes 16 Expected തν𝑒flux at Kamioka Neutrino energy [MeV] തν𝑒flux [/MeV/cm2/sec] Concept of combined alarm 02/10/2025 XXI Workshop on Neutrino telescopes 17 Likelihood function 𝐿 𝑛KL obs,𝑛SK obs =Pois(𝑛KL obs,𝑛KL BG)×Pois(𝑛SK obs,𝑛SK BG) The alarm system is triggered based on statistical excess of BG level of both KamLAND and SK (Not Rate+Shape analysis) 𝑛obs: number of candidates 𝑛BG: number of expected BG The system provides warning when the combinations of 𝑛KL obs and 𝑛SK obs are in blue region (≦1 FAR/century). False alarm rate (FAR) •Frequency of false positive alarms based on BG number •It is calculated with toy MC simulation assuming BG only Online combined alarm system (2023~2024) 02/10/2025 XXI Workshop on Neutrino telescopes 18 •The system outputs every 5 minutes. If FAR ≦1/century, An alarm will be sent Gamma-ray Coordinate Network. •Combined alarm system was running in both KamLAND and SK side (redundancy system). •BG number is average one over a past period. (KamLAND: 90 days, SK: 30 days) •Total latency time is approximately 6 minutes. Alarm methodology 02/10/2025 XXI Workshop on Neutrino telescopes 19 Pre-SN തν𝑒 Time profile from reference model 1 Time profile from reference model 2 Time profile from reference model k … FAR1FAR2FAR𝑘 (False alarm rate) =M𝑖𝑛 FAR1,FAR2⋯FAR𝑘 Simulation Star’s mass[𝑴⨀] Odrzywolek [1] 15, 25 Kato [2] 15 Patton [3] 15 Alarms using various reference models are set in parallel. We set Pre-SN model with various numerical simulations and mass as a reference model. Assumption: Signal pre-SN model does not match reference models in this talk. [1] Odrzywolek & Heger, Acta Phys.Pol. B , 41 (2010) [2] Chinami Kato et al 2017 ApJ 848 48 [3] Kelly M. Patton et al 2017 ApJ 851 6 False alarm rate 02/10/2025 XXI Workshop on Neutrino telescopes 20 Time Significance Time 1. We generate a time-series of ToyMC events assuming BG only for 100 years. 2. We simulate what the alerm system does. 3. We count how many times we issue false positive alarm. We count the number of times it crosses over from below to above. Significance Time Alarm performance (KamLAND) 02/10/2025 XXI Workshop on Neutrino telescopes 21 Alarm performance (SK) 02/10/2025 XXI Workshop on Neutrino telescopes 22 Alarm performance (Combined) 02/10/2025 XXI Workshop on Neutrino telescopes 23