1. GADZOOKS! project at Super-Kamiokande M.Ikeda (Kamioka ICRR, U.of Tokyo) for Super-K collaboration 2015,6,9@WIN2015 1 Contents GADZOOKS! project Supernova Relic Neutrino search R&D status and Plan Summary

2. Identify ̄ e p events by neutron tagging with Gadolinium in SK. Gadolinium has large neutron capture cross section and emit 8MeV gamma cascade. γ p n Gd e + 8 MeV ΔT~30μs Vertices within 50cm e GADZOOKS! project Physics targets: (1)Supernova relic neutrino (SRN) (2)Improve pointing accuracy for galactic supernova (3)Precursor of nearby supernova by Si-burning neutrinos (4)Reduce proton decay background (5)Neutrino/anti-neutrino discrimination (6)Reactor neutrinos Captures on Gd Gd in Water 100% 80% 60% 40% 20% 0% 0.0001%0.001%0.01%0.1%1% 0.1% Gd gives ~90% efficiency for n capture In Super-K this means ~100 tons of water soluble Gd 2 (SO 4 ) 3 2 Gadolinium Antineutrino Detector Zealously Outperforming Old Kamiokande, Super! Beacom & Vagins PRL.93, (2004) 171101

3. Supernova Relic Neutrino (SRN) Beginning of the universe NOW １ billion years ago 10 billion years ago S.Ando, Astrophys.J. 607, 20(2004) Theoretical flux prediction : 0.3~1.5 /cm2/s (17.3MeV threshold) 3 Neutrinos from past SNe

4. Supernova Relic Neutrino (SRN) Beginning of the universe NOW １ billion years ago 10 billion years ago S.Ando, Astrophys.J. 607, 20(2004) Theoretical flux prediction : 0.3~1.5 /cm2/s (17.3MeV threshold) 4 Neutrinos from past SNe First goal is discovery of SRN

5. Search for SRN at Super-K Search window for SRN at SK : From ~10MeV to ~30MeV Now SRN search is limited by BG. We need BG reduction by the neutron tagging which can be achieved by GADZOOKS! 5

6. Evaluating Gadolinium’s Action on Detector Systems 200 m 3 tank with 240 PMTs 15m 3 tank to dissolve Gd Gd water circulation system (purify water with Gd) Transparency measurement (UDEAL) 6 EGADS

7. One of main goals for EGADS is to study the Gd water quality with actual detector materials. Thus, the detector fully mimic Super-K detector. : SUS frame, PMT and PMT case, black sheets, etc. Gd dissolving test has been performed since Oct.2014. (see next page) 7 EGADS detector: Baby- Kamiokande

8. 8 The light left at 15 m in the 200m 3 tank was ~75% for 0.2% Gd 2 (SO 4 ) 3, which corresponds to ~92% of SK-IV pure water average. Transparency of Gd water with PMTs

9. Where we are now? Now, we are summarizing the R&D results and making a proposal. A committee which was formed to review and evaluate the proposal has started the review. After the review of the committee, we will start collaboration wide discussion in this June. If the proposal is approved, more detailed plan will be made also with T2K members. 9

10. Summary GADZOOKS! is a project to upgrade Super-K, so that SRN ν̄ e can be tagged by the delayed coincidence signal from a neutron capture of Gd. EGADS detector was build for R&D of Gd water purification system and check Gd effect to Super-K. EGADS has been keeping a good water quality with the target Gd concentration after PMT installation. Collaboration wide discussion to decide the Gd installation to Super-K will start in June (two weeks). 10

11. Improvement for Proton decay 11 Neutron multiplicity for P  e +  0 MC 92.5% Zero n Atmospheric BG Accompany many n If one proton decay event is observed at Super-K after 10 years Current background level: 0.58 events/10 years Background with neutron anti-tag: 0.098 events/10 years Background probability will be decreased from 44% to 9%.

12. Supernova burst case e +p +e e +p +e Improve pointing accuracy e.g. 4~5°  3°(90%C.L.) for 10kpc. 12 By identifying e +p events enhance +e events in angular distribution. Also, it enables us to extract e + x spectrum. W/O n-tagWith n-tag 10 kpc supernova tag eff. = 1.0 tag eff. = 0.8 tag eff. = 0.0 Number of supernovae Pointing accuracy (1000 simulations for 10kpc supernova)

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15. 20-38 degrees38-50 degrees 78-90 degrees E (MeV) SK combined 90% C.L. (SK4 is not included yet) E (MeV) e e+e+ p n (invisible) Signal region 42 o μ, π Low angle events Isotropic region N reconstructed angle near 90 o data ν μ CC ν e CC NC elastic μ / π > C. thr. all background relic 16 MeV) (using LMA model spectrum (Ando et.al, 2005) SRN upper limit from SK PRD 85, 052007 (2012) 15

16. Effect of Star formation rate Nakazato et al. ApJ 804 (2015) 75 16

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