Jan.-2002 @CERN

Hyper-Kamiokande project andR&D status

Hyper-K project Motivation Detector Physics potential study photo-sensor development

Summary

Kamioka Observatory Masato ShiozawaFor JHF-Kamioka νworking group

Jan.-2002 @CERN

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!!!

Next generation proton decay detector

　ｇ４ ｍｐ４

Γ = : τ(p→e+π0) = 1035±1 years ＭＸ

４

h ４ ｍｐ４ ____

Γ = : τ(p→K+ν) = 1029-35 years MHx

2 　ＭＸ2

Jan.-2002 @CERN

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 requirementgood e/π0 separation capability at low energyNo magnetic field is needed

Hyper-K as a far detector of 2nd JHF ν

Jan.-2002 @CERN

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 pepi0, 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?

Jan.-2002 @CERNPossible Design of Hyper-Kamiokande

Super-K

40m

Jan.-2002 @CERNPossible Design of Hyper-Kamiokande (2)

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

2.5 m2 m

3 m

45m45m46m

41m41m42m

45m45m47m

41m41m43m

Total 800m 16 compartments

Jan.-2002 @CERNPossible Design of Hyper-Kamiokande (3)

#compartments

Total volume

Fiducial volume

PMT density #PMT

Case1 8 1Mton

0.57Mton

1PMT/m2 100k

Case2 8 1Mton

0.57Mton

2PMT/m2 200k

Case3 16 2Mton

1.15Mton

1PMT/m2 200k

Case4 16 2Mton

1.15Mton

2PMT/m2 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

Jan.-2002 @CERN

Detector site candidate

Super-K

KAMLAND

Mozumi site Tochibora site

Super-K

Jan.-2002 @CERN

Analysis for discovery of p→e+π0

Tight momentum cut ⇒ target is mainly free protons efficiency=17.4%, 0.15BG/Mtyr

No Fermi momentumNo binding energyNo nuclear effect

Small systematic uncertainty of efficiency High detection efficiency Perfectly known proton mass and momentum

free proton bound proton

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Jan.-2002 @CERN

How the signal looks like

τp/B(p→e+π0) = 1×1035 years

S/N = 4 for 1×1035 years ↓ S/N = 1 for 4×1035 yearsτp/B(p→e+π0) = several×1035 yrs

is reachable by a large water Cherenkov detector

Proton mass peak can be observed !

Jan.-2002 @CERN

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+π0 ～ 22 events/Mtyr

we should reject them by improved vertex fitter

very serious backgrounds if both Λ and K+ are invisible

K.KobayashiK.Kobayashi

3. other unknown background?

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Jan.-2002 @CERN

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

Jan.-2002 @CERN

5 inch HPD prototype

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APD 3mmφ, GNDbias voltage 150V

photo-cathode –8kV

100% coll. efficiency cathode 80mmφ -------- 3mmcathode 120mmφ -------- >10mm

• need higher voltage• larger AD• spherical cathode

electron bombarded gain 1000 ×avalanche gain 50 = 50,000

Jan.-2002 @CERN

5 inch HPD prototype (2)

measured quantum efficiency time response

Jan.-2002 @CERN

5 inch HPD prototype (3)

pulse height distribution (dark current)

• good single p.e. peak• dark rate is 24kHz

Jan.-2002 @CERN

5 inch HPD prototype (4)

(a) cathode uniformity

(b) anode uniformity

geomagnetic effect is seen

need higher voltageand/or larger AD

Jan.-2002 @CERN

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

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

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→ν K+) ～ 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