Hyper-Kamiokande project and R&D status Hyper-K project Motivation Detector Physics potential study photo-sensor development Summary Kamioka Observatory Masato Shiozawa For JHF-Kamioka νworking group

Super-K has not found nucleon decays in 3.5 years data τ/B(p→e + π 0 ) > 5.0 × years (90% CL) τ/B(p→ν K + ) > 1.9 × 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!!! Next generation proton decay detector ｇ ４ ｍ ｐ ４ Γ = : τ(p→e + π 0 ) = 10 35±1 years Ｍ Ｘ ４ h ４ ｍ ｐ ４ ____ Γ = : τ(p→K + ν) = years M Hx 2 Ｍ Ｘ 2

Same baseline with Super-K (295km) Enable higher statistics physics (22.5 kton  ～ 1000 kton) improved sensitivity for θ 13 measurement CP phase measurement in lepton sector test of the unitarity triangle Detector requirement good e/π 0 separation capability at low energy No magnetic field is needed Hyper-K as a far detector of 2 nd JHF ν

R&D Items for Hyper-K 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?

Possible Design of Hyper-Kamiokande Super-K 40m

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

Possible Design of Hyper-Kamiokande (3) #compartmen ts Total volume Fiducial volume PMT density #PMT Case1 8 1Mton0.57Mton 1PMT/m 2 100k Case2 8 1Mton0.57Mton 2PMT/m 2 200k Case3 16 2Mton1.15Mton 1PMT/m 2 200k Case4 16 2Mton1.15Mton 2PMT/m 2 400k 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

Detector site candidate Super-K KAMLAND Mozumi site Tochibora site Super-K

Analysis for discovery of p → e + π 0 Tight momentum cut ⇒ target is mainly free protons efficiency=17.4%, 0.15BG/Mtyr No Fermi momentum No binding energy No nuclear effect Small systematic uncertainty of efficiency High detection efficiency Perfectly known proton mass and momentum free protonbound proton

Lifetime sensitivity with tight cut With 3σ(99.73%) level 1Mton ×20 years → ～ 1×10 35 years lifetime

How the signal looks like τ p /B(p→e + π 0 ) = 1×10 35 years S/N = 4 for 1×10 35 years ↓ S/N = 1 for 4×10 35 years τ p /B(p→e + π 0 ) = several×10 35 yrs is reachable by a large water Cherenkov detector Proton mass peak can be observed !

2. K + production by atmν νN → νN* ΛK + ～ 1 events/Mtyr (after pdecay cut) Backgrounds in p → νK + searches 1. prompt γ ～ 6 events/Mtyr most are misfitted vertex events μ spectram 2100 events/Mtyr (single-ring μ,π,proton) π + π 0 ～ 22 events/Mtyr we should reject them by improved vertex fitter very serious backgrounds if both Λ and K + are invisible K.Kobayashi 3. other unknown background?

Lifetime sensitivity with reduced BG With 3σ(99.73%) level 1Mton ×20 years → ～ 3×10 34 years lifetime Prompt γ tagging is essential

Photo-sensor development 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

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

5 inch HPD prototype (2) measured quantum efficiencytime response

5 inch HPD prototype (3) pulse height distribution (dark current) good single p.e. peak dark rate is 24kHz

5 inch HPD prototype (4) (a) cathode uniformity (b) anode uniformity geomagnetic effect is seen need higher voltage and/or larger AD

Spherical HPD glass photocathode reflector diode-1 diode-2 light photoelectrons Lead and support high efficiency simple structure  low cost  high production rate pressure resistant

to do list for the new photo-sensor gain up 1000(E.B.gain)×50(Av. gain)= 5×10 4  1×10 7 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

Summary of Hyper-K Rich physics potential τ p /B(p → e + π 0 ) ～ 1×10 35 years (3σ CL with 20Mtyr) τ p /B(p → ν K + ) ～ 3×10 34 years (3σ CL with 20Mtyr) Atmospheric, Supernova other physics 2 nd phase of JHF-Kamioka neutrino experiment R&D ’ s are in progress new photo-sensor