Hyper-Kamiokande project and R&D status

1. Jan.-2002 @CERN Hyper-Kamiokande project andR&D status Kamioka Observatory Masato Shiozawa For JHF-Kamioka νworking group Hyper-K project Motivation Detector Physics potential study photo-sensor development Summary

2. Jan.-2002 @CERN ｇ４ ｍｐ４ Γ = : τ(p→e+π0) = 1035±1 years ＭＸ４ 　 h４ ｍｐ４ ____ Γ = : τ(p→K+ν) = 1029-35 years 　MHx2ＭＸ2 Next generation proton decay detector Super-K has not found nucleon decays in 3.5 years data • τ/B(p→e+π0) > 5.0 × 1033 years (90% CL) • τ/B(p→ν K+) > 1.9 × 1033 years (90% CL) Predicted lifetime of nucleon • 4 fermion interactions • 2 fermion – 2 sfermion interactions (SUSY models) One or two order of extension of Super-Kamiokande would reveal new physics!!!

3. Jan.-2002 @CERN Hyper-K as a far detector of 2nd JHF ν Same baseline with Super-K (295km) Enable higher statistics physics (22.5 kton  ～1000 kton) • improved sensitivity for θ13 measurement • CP phase measurement in lepton sector • test of the unitarity triangle Detector requirement • good e/π0 separation capability at low energy • No magnetic field is needed

4. R&D Items for Hyper-K Jan.-2002 @CERN • cavity design and assessment • rock stress analysis • excavation cost, time, optimization • physics potential study • optimization of photo-coverage, detector volume • sensitivity for pepi0, nuK+, background estimation • SN, atmospheric nu, and others • long baseline experiment(JHF), pi0 rejection etc. • photo-sensor development • low cost, high sensitivity • mass production rate  automated production • high pressure resistant • other detector improvement • longer light attenuation length? • reducing reflection light?

5. Jan.-2002 @CERN Possible Design of Hyper-Kamiokande Super-K 40m

6. Jan.-2002 @CERN 45m45m46m 41m41m42m 45m45m47m 41m41m43m 2.5 m 3 m 2 m Possible Design of Hyper-Kamiokande (2) Total 800m 16 compartments • PMT Wall 45m  45m  2 planes 16 modules = 64,800 m2 45m  46m  4 planes 4 modules = 33,120 m2 45m  47m  4 planes 12 modules = 101,520 m2 Total 199,440 m2   200,000 PMTs if 1 PMT/m2 • Fiducial Volume 41m  41m  42m 4 modules = 282,408 m3 41m  41m  43m 12 modules = 867,396 m3 Total 1,149,804 m3

7. Jan.-2002 @CERN Possible Design of Hyper-Kamiokande (3) • PMT density should be optimized by • gamma tagging in nuK+ search, pi0 rejection in long baseline experiment • detector volume should be optimized by • physics goals • site, stable cavity design • excavation cost, construction time • photo-sensor cost, production time

8. Detector site candidate Jan.-2002 @CERN Tochibora site Mozumi site Super-K KAMLAND Super-K

9. Jan.-2002 @CERN Analysis for discovery of p→e+π0 Tight momentum cut ⇒ target is mainly free protons efficiency=17.4%, 0.15BG/Mtyr free proton bound proton No Fermi momentum No binding energy No nuclear effect Small systematic uncertainty of efficiency High detection efficiency Perfectly known proton mass and momentum

10. Lifetime sensitivity with tight cut • With 3σ(99.73%) level • 1Mton ×20 years → ～1×1035 years lifetime

11. Jan.-2002 @CERN How the signal looks like Proton mass peak can be observed ! τp/B(p→e+π0) = 1×1035 years S/N = 4 for 1×1035 years ↓ S/N = 1 for 4×1035 years τp/B(p→e+π0) = several×1035 yrs is reachable by a large water Cherenkov detector

12. Jan.-2002 @CERN Backgrounds in p→νK+ searches K.Kobayashi 1. prompt γ ～6 events/Mtyrmost are misfitted vertex events μ spectram 2100 events/Mtyr (single-ring μ,π,proton) π+π0 ～22 events/Mtyr we should reject them by improved vertex fitter 2. K+ production by atmν νN → νN* ΛK+ ～1 events/Mtyr (after pdecay cut) very serious backgrounds if both Λ and K+ are invisible 3. other unknown background?

13. Lifetime sensitivity with reduced BG • With 3σ(99.73%) level • 1Mton ×20 years → ～3×1034 years lifetime Prompt γ tagging is essential

14. Photo-sensor development Jan.-2002 @CERN • improving QE • optimizing cathode materials, production methods • larger (30-40inch) PMTs • glass valve production is a key • hybrid photo-detector (HPD) • photo-cathode + AD(avalanche diode) • simple structure  hopefully low cost • good timing resolution (～1ns) • good single p.e. separation

15. 5 inch HPD prototype Jan.-2002 @CERN electron bombarded gain 1000 ×avalanche gain 50 = 50,000 e sensitive area 80mmφ 5inch APD 3mmφ, GND bias voltage 150V photo-cathode –8kV 100% coll. efficiency cathode 80mmφ -------- 3mm cathode 120mmφ -------- >10mm • need higher voltage • larger AD • spherical cathode

16. 5 inch HPD prototype (2) Jan.-2002 @CERN measured quantum efficiency time response

17. 5 inch HPD prototype (3) Jan.-2002 @CERN pulse height distribution (dark current) • good single p.e. peak • dark rate is 24kHz

18. 5 inch HPD prototype (4) Jan.-2002 @CERN (a) cathode uniformity geomagnetic effect is seen need higher voltage and/or larger AD (b) anode uniformity

19. Spherical HPD Jan.-2002 @CERN light glass photocathode photoelectrons diode-2 Lead and support diode-1 reflector • high efficiency • simple structure •  low cost •  high production • rate • pressure resistant

20. Jan.-2002 @CERN to do list for the new photo-sensor • gain up 　 • 1000(E.B.gain)×50(Av. gain)= 5×104 1×107 • good focusing  higher voltage, spherical shape • good control of AD position • operation of AD in positive high voltage • keep low dark rate • pressure resistant (spherical shape) • larger size

21. Jan.-2002 @CERN Summary of Hyper-K • Rich physics potential • τp/B(p→e+π0) ～ 1×1035 years (3σ CL　with 20Mtyr) • τp/B(p→νK+) ～ 3×1034 years (3σ CL with 20Mtyr) • Atmospheric, Supernova • other physics • 2nd phase of JHF-Kamioka neutrino experiment • R&D’s are in progress • new photo-sensor