Detection of supernova neutrinos at Super-Kamiokande M. Nakahata - PowerPoint PPT Presentation

Detection of supernova neutrinos at Super-Kamiokande M. Nakahata Kamioka Observatory, ICRR, Kavli IPMU, Univ. of Tokyo The sixth Astrophysical Multimessenger Observatory Network(AMON) Workshop 1 May 22, 2019

Core-collapse supernova Scenario of the core-collapse supernova Core-collapse Neutrino trapping Core bounce C+O He ν Si ν H Fe ν ν ν ν ν Supernova burst Shock wave propagation Shock wave at core ν ν ν Neutron star ν ν Figure from K.Sato 2

Expected neutrinos from core-collapse supernova Released total energy: ~3x10 53 erg (E tot ) Neutrino emission is ~ several seconds Neutrinos carry out 99% of the energy Burst kinetic energy: ~10 51 erg （ 1% of E tot ) Neutronization burst Optical energy: ~10 49 erg （ 0.01% of E tot ) Luminosity Iron core  neutron star / black hole Mean neutrino energy (x= µ,τ) S. Nakazato et al., APJ supp.205:2(2013) T.Totani et al., ApJ.496,216(1998) 3

Neutrino and optical signals in supernova Collapsed star Neutrinos Travel with speed of light (3x10 5 km/sec) Shock wave travels with ~1/30 of speed of light (~10 4 km/sec). Optical signals are produced when the shock wave arrives at surface. core envelop surface So, neutrinos arrive earlier than optical signals. Type II: a few hours - several tens of hours earlier Type Ib/Ic: several minutes earlier 4

SN1987A: supernova at LMC(50kpc) Kamiokande-II IMB-3 BAKSAN Russia Baksan tunnel 330ton in 3150tanks USA Ohio state Morton mine Liquid scintillator ~5000ton Fiducial Japan Kamioka mine Observed events Water Charenkov 2140ton fiducial Water Cherenkov Kam-II (11 evts.) IMB-3 (8 evts.) Although the observed number of events Baksan (5 evts.) was only 24 in total, energy released by ν ̅ e 24 events total was measured to be ~5x10 52 erg. It is consistent with core-collapse scenario. But, no detailed information of burst process was obtained because of the low statistics. We need next supernova with large number of neutrino events. 5

Super-Kamiokande detector • 50 kton water LINAC Electronics hut Water and air purification system • ~2m OD viewed by 8-inch PMTs Control room Atotsu entrance • 32kt photo- sensitive volume ID 41.4m • 22.5kt fid. vol. (2m from wall) OD • SK-I: April 1km Ikeno-yama 1996~ Kamioka-cho, Gifu (2700 mwe ) Japan 3km 2km • SK-V is running Mozumi SK Atotsu 39.3m Inner Detector (ID) PMT: ~11,000 20-inch PMTs Outer Detector (OD) PMT: 1885 8-inch PMTs 6

The Super-Kamiokande Collaboration Kamioka Observatory, ICRR, Univ. of Tokyo, Japan INFN Padova, Italy University of Sheffield, UK RCCN, ICRR, Univ. of Tokyo, Japan INFN Roma, Italy Shizuoka University of Welfare, Japan University Autonoma Madrid, Spain Kavli IPMU, The Univ. of Tokyo, Japan Sungkyunkwan University, Korea University of British Columbia, Canada KEK, Japan Stony Brook University, USA Boston University, USA Kobe University, Japan Tokai University, Japan University of California, Irvine, USA Kyoto University, Japan The University of Tokyo, Japan California State University, USA University of Liverpool, UK Tokyo Institute of Technology, Japan Chonnam National University, Korea LLR, Ecole polytechnique, France Tokyo University of Science, japan Duke University, USA Miyagi University of Education, Japan University of Toronto, Canada Fukuoka Institute of Technology, Japan ISEE, Nagoya University, Japan TRIUMF, Canada Gifu University, Japan NCBJ, Poland Tsinghua University, Korea GIST, Korea Okayama University, Japan The University of Winnipeg, Canada University of Hawaii, USA Osaka University, Japan Yokohama National University, Japan Imperial College London, UK University of Oxford, UK INFN Bari, Italy Queen Mary University of London, UK INFN Napoli, Italy Seoul National University, Korea ~175 collaborators from 44 institutes in10 countries 7

Typical low-energy event Electron/positron OD • Timing information vertex position ID • Ring pattern direction • Number of hit PMTs energy (color: time) E e,total = 9.1 MeV ~6 hit / MeV Resolutions (for 10 MeV electrons) Direction: 23 o Energy: 14% Vertex: 55cm 8

Event reconstruction in water Cherenkov detector Timing and pulse height of each PMT are recorded. Reconstruct vertex position (i.e. interaction position) using timing information of PMTs Reconstruct particle direction using the Chrenkov pattern (ring pattern with 42 deg. opening angle) . 9

Neutrino interaction in water Angular distributions Cross section (for H 2 O) ν ｅ ＋ｐ→ｅ + +n +n Supernova ν ν＋ e － →ν＋ｅ － ν ｅ + １６ O → e - + １６ F ν ｅ + １６ O→e + + １６ N COS θ SN 10

Super-K: Number of events Number of events vs. distance 32kton water Cherenkov For each interaction Livermore Nakazato ν ̅ e p  e + n 7300 3100 ν +e -  ν +e - 320 170 16 O CC 110 57 Directional info. Supernova at 10 kpc Ethr=3.5MeV(kin) 32kton SK volume 4.5MeV(kin) threshold No oscillation case. Livermore simulation T.Totani, K.Sato, H.E.Dalhed and J.R.Wilson, ApJ.496,216(1998) Nakazato et al. K.Nakazato, K.Sumiyoshi, H.Suzuki, T.Totani, H.Umeda, and S.Yamada, 11 ApJ.Suppl. 205 (2013) 2, (20M sun , trev=200msec, z=0.02 case)

Super-K: directional information Reconstructed direction Distance vs. pointing accuracy (Simulation of a 10kpc supernova) ν ̅ e +p ν +e Livermore Model 3.1-3.8 deg. for 10kpc Nakazato model ν +e ν ̅ e +p 4.3-5.9 deg. for 10kpc 12

Sensitivity of Super-K for the model discrimination 10kpc supernova Time variation of mean energy Time variation of event rate High statistics enough to discriminate models Cooperation: H. Suzuki 13

Real time supernova monitor in Super-K Real Time Process Raw data SK shift people always keep Quickly analyze watch whether the events. processes are running. Reconstruct vertex, energy and direction. Processed data Supernova Watch If significant time-clustered Search for time- events are found, send e-mails clustered events. Get to experts (PC and portable initial result within 200 phone e-mails.) sec after a burst. Also, send signal to SNEWS. Details in K. Abe et al., Astropart. Phys. 81 (2016) 39-48 14

Flowchart of action for a event cluster with >7MeV is found! supernova in Super-K No Is vertex distribution uniform? (i.e. not spllation?) Yes No cluster size > 100 ? cluster size > 25 ? Yes Yes No Issue Normal Alarm Issue Silent Alarm Issue Golden Alarm Discuss among relevant people Just send e-mail to Discuss among experts. with TV conference. Hold a TV conference. experts. (happens ~2 If real, send information times per day.) (including direction, if possible) to ATEL, GCN, IAU-CBAT within one hour. 15

Detection efficiency of the real time SN monitor Solid: Golden alarm Dotted: Normal alarm Color: model dependence 100% efficient for our galaxy and LMC for various models. K. Abe et al., Astropart. Phys. 81 (2016) 39-48 16

Gadolinium project at Super-K: SK-Gd Identify ν e p events by neutron tagging with Gadolinium. Gadolinium has large neutron capture cross section and emit 8MeV gamma cascade. 0.1% Gd gives ν e ~90% efficiency n 100% Captures on Gd for n capture In Super-K this means p Gd ~100 tons of water soluble e + 80% Gd 2 (SO 4 ) 3 γ 60% 8 MeV Δ T~30 μs 0.01% Gd gives Vertices within 50cm ~50% efficiency. 40% 20% 0% 0.0001% 0.001% 0.01% 0.1% 1% Gd in Water 17

Physics with SK-Gd project • Observation of Supernova Relic Neutrinos (SRN) • (also called Diffuse Supernova Neutrino Background (DSNB)) • First observation is expected at SK-Gd • Improve observation of supernova burst neutrinos • Improve pointing accuracy • ν e (+ ν x ) spectrum measurement • Possible detection of neutrinos from Si burning. • Reduce neutrino background for proton decays • Anti-tag neutrons to reduce atmospheric neutrino background • Discriminate neutrino and anti-neutrino events for T2K • Using neutron multiplicity • Reactor neutrinos • precise determination of θ 12 and ∆ m 2 12 with high statistics measurement, if Japanese reactors restart 18

Supernova Relic Neutrinos （ SRN) 10 22-23 stars in the universe （～ 10 11 galaxies, ~10 11-12 stars/galaxy ） At present, we are getting neutrinos from 10 8 supernovae every year. Horiuchi,Beacom(2010) Star Formation Rate Initial Mass Function Burst neutrino spectrum 2 E ' dN tot E 120 1 ν = ν ν e e π 4 2 E ' / T dE ' 6 7 T + ν ν e 1 e e ν ν e e We can study star formation history and averaged neutrino spectrum. 19

SK-Gd: Expected SRN signal and its significance preliminary SRN flux from Horiuchi, Beacom and Dwek, PRD, 79, 083013 (2009) BG assumption BG can be reduced by neutron tagging as follows  ν µ CC BG 1/4  ν e CC BG 2/3  NC elastic BG 1/3 （ require only one neutron) 10 12 14 16 18 20 22 24 26 28 Position Energy (MeV) Model 10-16MeV 16-28MeV Total (10-28MeV) Significance (evts/10yrs) (evts/10yrs) (/10yrs) (2 energy bin) 5.3 σ HBD 8MeV 11.3 19.9 31.2 4.3 σ HBD 6MeV 11.3 13.5 24.8 2.5 σ HBD 4MeV 7.7 4.8 12.5 2.1 σ HBD SN1987a 5.1 6.8 11.9 BG 10 24 34 ---- 20