Next-Generation Water Cherenkov Detectors (1) Hyper-Kamiokande

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1 Next-Generation Water Cherenkov Detectors (1) Hyper-Kamiokande Kenzo NAKAMURA KEK C.N. Yang Institute for Theoretical Physics Conference Neutrinos and Implications for Physics Beyond the Standard Model October 11-13, 2002 SUNY

2 3 Generations of Kamioka Nucleon Decay Experiments Kamiokande Super-Kamiokande Hyper-Kamiokande Mass 3,000 t 50,000 t 1,000,000 t (+1,500 t) Photosensitive 20 % 40 % (SK-1)? Coverage Observation ? Started Cost (Oku-Yen) * ? ** * 1 Oku-Yen 1M$ ** Target cost; No realistic estimate yet

3 Hyper-Kamiokande: A Multi Purpose Detector Proton decay νk + e + π 0 and other modes Reach: τ p (νk + )/B yr τ p (e + π 0 )/B yr Supernova neutrino (~10 5 neutrinos for a SN at the center of the galaxy.) JHF-Kamioka long baseline neutrino oscillation experiment: 2nd phase, CP violation If the θ 13 measurement in the 1 st phase gives only an upper limit, the 2 nd phase will enhance the reach. Why water Cherenkov? Common topics to Hyper-K and UNO Next talk The primary reason for Super-Kamiokande to have been successful is that it is only one order of magnitude extension of the well-proven Kamiokande. One order of magnitude extension of well-proven Super-Kamiokande will not cause any serious difficulty both in construction and in operation. (We now know how to avoid an accident caused by the implosion of a PMT under water pressure.) Water is the cheapest detector material.

4 Overview of the JHF-to to-kamioka Experiment ν µ beam of ~1GeV Super-K: 50 kton Water Cherenkov ~Mt Hyper Kamiokande Kamioka 1st Phase νµ νx disappearance ν µ νe appearance NC measurement 2nd Phase CPV proton decay JAERI (Tokai-mura) 0.75 MW 50 GeV PS 4MW 50 GeV PS

5 sin 2 2θ 13 from ν e Appearance (JHFν 1 st Phase) m 2 m 2 (ev 2 ) % C.L. sensitivities 20 improvement Work in progress Off axis 2 deg, 5 years 10-3 JHF 5year WBB OAB 2deg. NBB 2GeVπ CHOOZ excluded sin 2 2θ µe 0.5 sin 2 2θ 13 sin 2 2θ 13 ν µ Background in Super-K ν e ν µ ν e total Signal Signal + BG

6 Sensitivity to sin 2 2θ 13 as a function of exposure 0.5 sin 2 2θ 13 sensitivity m 2 = ev 2 Phase 1 Phase 2 SK unit JHF yr

7 JHF-Kamioka Neutrino Project: Phase-II MW beam power Hyper-Kamiokande (1 Mt FV) ν: _ 2 yr ν: 6.8 yr 10 6 events CP Violation m 21 =5x10-5 ev 2 θ 12 =π/8 m 32 = m 31 =3x10-3 ev 2 θ 23 =π/4

8 Sensitivity (3σ) to CPV (JHFν 2 nd Phase) Chooz m 31 ~3x10-3 ev 2 4MW, 1Mt Fid.Vol. 2yr for ν µ 6.8yr for ν µ δ>~14deg Preliminary JHF1 3σ discovery δ>~27deg m 21 =5x10-5 ev 2 θ 12 =π/8 m 32 = m 31 =3x10-3 ev 2 θ 23 =π/4

9 Conceptual Design 48m 50m 500m, Total mass = 1 Mton

10 Fiducial Size of the detector / Total Fiducial volume: 39mφ 45m 10 sections = 0.54 Mton Total Inner detector volume: 43mφ 49m 10 sections = 0.72 Mton Total detector volume: 1 Mton Total number of PMTs: 200,000 (if 2/m 2 )

11 Any other way to start Hyper-K earlier? Wished Construction Plan JHF-I Discovery of θ13? HK construction HK experiment

12 2 Detector Hyper-Kamiokande? 2 detectors 48m 50m 250m, Total mass = 1 Mton

13 Wished Construction Plan (2 Detector Hyper-K) JHF-I Discovery of θ13? ½ HK construction Half HK experiment ½ HK construction Full HK experiment

14 R&D Items Site selection Cavity design and assessment Rock stress analysis Cost analysis, optimization Detector tank design and study of construction method Simulation studies for Proton decay K + ν e + p 0 Long baseline neutrino oscillation experiment Development of new photo-detectors PMT? Larger size? High QE? Not very successful Flat & thin? Not very active.. Hybrid Photo-detector? Present focus Other technique? Not active How to improve S/N Optimize photocathode coverage Initially some R&D, but no more after the SK accident

15 Plan to Develop 40-inch PMT Was Given up due to the SK Accident

16 Super-K (Depth: 2700mwe) Candidate Site 8km 295km JHF Hyper-K (Depth: mwe, not decided yet ) (Tochibora-mine of the Kamioka mining company) North-south Candidate place About m.

17 Mozumi Mine Geology is not preferable for excavation of a very large cavity. Large-scale blastings should be avoided near the Super-K and KamLAND detectors. Limestone Hyper-Kamiokande? Gneiss KamLAND Super-Kamiokande

18 Tochibora Mine

19 Decay Pipe Common for SK/HK Possible site for Hyper-K Beam eye DV center SK 2 HK SK ~10km Best ) Fit 3.43 (OAB2.3 Beam Axis) Decay pipe (OAB2 beam axis) 3.64 (OAB2.5 ) 4.16 (OAB3 ) HK 3 must cover p/π beam axis -(3~4) deg corresponding to m 2 =(2.2~3.2) 10-3 ev 2

20 Finite Element Is it possible Analysis to construct of the cavity? Hyper-K Cavity Using the Onsite Rock Condition Safety factor VERY Preliminary Experts say: Regions with the safety factor < 1.3 need supports (rock bolt or wire) The depth of the region with safety factor < 1.3 is similar to that in Super-K. presure ( horizontal) presure ( vertical) = 0.45 = 1.0 It seems possible to excavate the Hyper-K cavity. Need more detailed studies.

21 Design of PMT Support Structure

22 Construction Plan for the Water Tank and PMT Support Frame Movable scaffolding Panel Reinforced concrete Upper deck Movable scaffolding For building PMT support frame PMT support frame

23 Development of Large Spherical Hybrid Photo Detectors (HPD) glass light photocathode diode-1 photoelectrons support diode-2 reflector high efficiency simple structure low cost high production rate pressure resistant (no chain-reaction of explosion) 5-inch HPD prototype tested. 13-inch HPD prototype to be developed. Design of a 20-inch spherical HPD.

24 5-inch HPD Prototype Tested electron bombarded gain 1000 avalanche gain 50 = 50,000 e photocathode 8kV Avalanche diode 3mmφ, bias150v

25 Characteristics of 5-inch HPD Prototype (1) size Effective area Rise time Fall time Dark rate Avalanche gain HV value Bombarded gain Total gain P/V 5inch 80mm φ 24(%) Hz 8500Hz 380Hz 50-8kV -16kV x x Due to non-spherical glass bulb and small(3mm) APD ~10ns@Super-K ~16ns@Super-K First measurement(~3000hz@super-k) paint a conductor of electricity (outside of photo-sensitive area) paint wholly a conductor Bias 150V 300/kV at >-8kV 10 ~2@Super-K

26 Hyper-K R&D: Summary Site: Tochibora mine is seriously considered as a candidate site. Cavity excavation: FEA in progress. Geological survey to be done; boring, in situ measurement of initial stress, rock sample taken from the candidate site for mechanical tests, etc. Water tank and PMT support: Conceptual design started. Spherical HPD: 5-inch prototype tested, larger HPD to be developed. Further physics simulation: to be done.