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Super-K upgrade and Hyper-Kamiokande

Shoei Nakayama , ICRR, University of Tokyo

for the Super-Kamiokande collaboration and the Hyper-Kamiokande proto-collaboration

The 9th International Workshop on Ring Imaging Cherenkov Detectors (RICH2016) September 5-9, 2016 @ Bled, Slovenia Super-Kamiokande

n World largest “ν & proton decay” detector n 4π acceptance, uniform response n Cherenkov ring pattern on detector wall n Excellent event reconstruction

Super-Kamiokande IV Run 999999 Sub 0 Event 686 11-11-23:19:16:48 Inner: 2222 hits, 4687 pe n µ/e mis-identification < 1% @~1 GeV Outer: 6 hits, 6 pe Trigger: 0x07 D_wall: 1270.2 cm e-like, p = 480.6 MeV/c

Charge(pe) >26.7

41.4 m 23.3-26.7 Super-Kamiokande20.2-23.3 IV 17.3-20.2 PID parameter Run14.7-17.3 999999 Sub 0 Event 97 11-11-21:09:15:4912.2-14.7 Inner:10.0-12.2 915 hits, 2461 pe 8.0-10.0 Outer: 2 hits, 0 pe 6.2- 8.0 e Trigger: 0x07 4.7- 6.2 (Atmospheric ν Data/MC) D_wall: 3.3- 1161.7 4.7 cm Super Kamiokande IV 1417.4 days : Monitoring mu-like, 2.2- p3.3 = 461.7 MeV/c 1.3- 2.2 0.7- 1.3 0.2- 0.7 Charge(pe) < 0.2 >26.7 e-like 3191 muon-like 3110 23.3-26.7 800 Super-Kamiokande20.2-23.3 IV 0 mu-e decays 250 e-like µ-like Run17.3-20.2 999999 Sub 0 Event 819 640 14.7-17.3 39.3 m 11-11-21:09:44:57 480 12.2-14.7 ©ScientificAmerican Inner:10.0-12.2 2413 hits, 5283 pe Outer: 8.0-10.0 6 hits, 5 pe 320 Trigger: 6.2- 0x078.0 µ D_wall: 4.7- 1463.9 6.2 cm 160 2 e-like 3.3- rings:4.7 mass = 134.9 MeV/c^2 200 2.2- 3.3 0 0 500 1000 1500 2000 1.3- 2.2 0.7- 1.3 Times (ns) Charge(pe) 0.2- 0.7 < 0.2 • 1000 m underground >26.7 CCQE electron CCQE muon 23.3-26.7 20.2-23.3 310 17.3-20.2 1 mu-e 150 decay 14.7-17.3 248 12.2-14.7 • 10.0-12.2 0 186 50 kton ultrapure water 8.0-10.0 6.2- 8.0 124 4.7- 6.2 π 3.3- 4.7 62 2.2- 3.3 100 1.3- 2.2 0 • 22.5 kton fiducial 0.7- 1.3 0 500 1000 1500 2000 0.2- 0.7 < 0.2 Times (ns)

1100 0 mu-e 50 • Inner volume viewed by decays 880

660

440

11,000 50-cm PMTs 220 0 0 -10 -8 -6 -4 -2 0 2 4 6 8 10 0 500 1000 1500 2000 PID likelihood sub-GeV 1ring (FC) Times (ns) 2 Super-K 20th anniversary !

96 97 98 99 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16

SK-I SK-II SK-III SK-IV Half PMTs Fully recovered Electronics upgraded

1996.4.1 2006.4.23 2008.9.6 1998 Discovery of atmospheric oscillation 2001 Discovery of solar 2004 Confirmation of atm. ν oscillation by K2K

2012 Discovery of νe appearance driven by non-zero θ13 by T2K 2015 Novel Prize to Kajita-san 20 years continuous hardware/software/analyses improvements 3 Super-K recent results (1)

Atmospheric Accelerator neutrinos (T2K)

Three flavor ν oscillation analysis 7.48 x 1020 pot ν-mode beam + SK-I,II,III,IV 5326 days livetime 7.47 x 1020 pot ν-mode beam

2 Preliminary 3 T2K Run1-7c preliminary Δχ 2

Normal ν mass hierarchy (radians) 68.27%CL CP

δ 1 90%CL Inverted ν mass hierarchy Best-fit RPDGeactor 2015 exp. 0 (PDG2015) Normal Hierarchy -1 Inverted Hierarchy Δχ2 -2 Fixed Mass Hierarchy -3 0 0.02 0.04 0.06 0.08 0.1 2 sin θ13

2 2 2 • Δχ = χ NH-χ IH = -4.3 (-3.1 expected) • T2K-only result consistent with 2 the reactor θ13 measurement • Probability for IH is 0.031 (sin θ23=0.6) 2 and 0.007 (sin θ23=0.4) • Favors δCP = -π/2 region 2 Probability for NH is 0.45 (sin θ23=0.6) à Hint of the neutrino CPV ? 4 Super-K recent results (2)

Solar neutrinos Proton decay search

(D-N) / ½ (D+N) ± ± = -3.3 1.0 0.5 % p à e+π0 No (~3σ non-zero significance) candidate

Preliminary

Solar + 0 Two events p à µ π consistent KamLAND w/ BG SK-I~IV + Solar 5200 days data KamLAND Preliminary • No evidence of proton decays in 0.3 Mt·yrs Super-K data • Direct indication of terrestrial matter • pàe+π0 lifetime > 1.6 x 1034 yrs effects (= Day/Night flux difference) and more results • 2σ tension between KamLAND and (ν appearance search, WIMP search, 2 τ solar ν results in Δm 12 various proton decay modes, ...) 5 SK-Gd project

Dissolve ~0.1% gadolinium into Super-K to tag neutrons [ Beacom and Vagins, PRL93:171101 (2004) ] • Diffuse neutrino background (νs from past SNe) search à 2-5σ detection expected (depending on flux models) • BG reduction in proton decay search Delayed coincidence • Better atm. ν energy reconstruction ΔT~30 μs, Vertices within 50 cm Better ν / ν discrimination and more …

Demonstration done with a 200-ton tank imitating Super-K (EGADS) • Gd-water purification system • Light attenuation in Gd-water • Neutron tagging performance à Confirmed the feasibility

6 SK-Gd status and plan

• Constructing the Gd-water purification system New hall in the mine for SK-Gd water system – Based on experiences in EGADS – Installation to be done in FY2016

• Developed the special elastomer for stopping water leaks from the Super-K tank – Low elution to ultrapure water and Gd-water, Low radon emanation, …

• In 2015, SK collaboration approved the SK-Gd project • T2K+SK joint statement made in January 2016 – SK refurbishment in 2018 is anticipated

7 Hyper-Kamiokande

Next decade’s flagship experiment for the study of 0.26 Mt • Neutrino oscillations • Nucleon decays • Astrophysical neutrinos 60 m 0.26 Mt An order of magnitude larger tank than SK’s + Ultrasensitive photosensors 74 m 2016.7.13 ( 3rd proto-collaboration meeting @ QMUL)

Proto-collaboration formed in January 2015 ~250 member and growing from 12 countries

8 χ χ à ν ν WIMP Hyper-K Physics annihilation

Nucleon decay 3σ “discovery” potential Supernovae ν Solar ν • 1 × 1035 years (90%CL) for p à e+ π0 • 3 × 1034 years (90%CL) for p à ν K+

Explores full picture of ν oscillations Beam ν Atmospheric ν • Discovers leptonic CPV [ J-PARC beam ν ]

78% coverage of δCP at 3σ o o o o δCP measurement precision (0 , 90 ) : 7 - 21

• Resolves ν mass hierarchy / θ23 octant [ Atmospheric ν (+Beam ν) ] Neutrino astrophysics • Solar ν : Day/Night asymmetry 6σ from KamLAND best fit • Supernova ν (> 100k events for a [email protected].), Diffuse supernova ν background, Indirect DM search, …

Proton decay [Letter of Intent] arXiv:1109.3262, [LBL studies] PTEP(2015)053C02 9 Hyper-K detector

Hyper-K Tank

0.26 Mt 60 m tall × 74 m diameter 260 kton mass 0.26 Mt 60 m (186 kton fiducial volume : ~10 × SK’s) Innermost main volume viewed by 40,000 of new 50cm photosensors à 40% photocathode coverage Two cylindrical tanks with staging Design was updated (original design: 2 horizontal egg-shaped tanks) Fiducial volume is 2/3 of original, and cost is significantly reduced Most of physics sensitivities maintained, thanks to new ultrasensitive PMTs

Staged construction of the tanks : second tank 6 years after first one

Possibility to put one of the two tanks in Korea is also being investigated 10 New 50 cm photodetectors Super-K PMT Hamamatsu R3600 Box&Line PMT Hybrid Photodetector (HPD) Established Hamamatsu R12860 Hamamatsu R12850 0V New 0V New +2kV +8kV QE QE - - Used ~20yrs High High 302 A . Suzuk i et a l . / Improuement of 20 i n PMTs

Venetian------Blind------dynode- - -

Box&Line dynode Avalanche diode 20mmφ, 2ch segmented x 1600 Bombardment • MF i g . 6ight. E l ect ron t ra j ector i es s imissmu l ated for the present 2 0 ai n . PM T dynodedynode . x 100 Avalanche • Various drift pass x preamp gain A 'B

I I I ' ~- v • à R&D ongoing aiming for D ' E Large acceptance High CE • Unique drift pass à High T/Q resolution further better performance , and lower cost G H I 1_ I l Almost completed. Baseline HK choice 11

F i g . 7. Si mu l ated s i ng l e-photoe l ect ron t rans i t t i me d i st r i but i ons for the present 20 i n . PMT(A) and the proposed dynode st ructures (B - I ) . One d i v i s i on i n the f i gure cor responds to 5 ns . x 1.4 ×2 Improvements QE [%] QE SK PMT R3600 High-QE photocathode Wavelength [nm] × High collection efficiency by × an improved dynode structure New PMT 2 = Photon detection efficiency ×2 higher than SK PMT’s Super-K PMT (relativeSK PMT’s) to

1 photon detection efficiency detection photon 1 Photon incident position (degree)

Glass bulb design improved for higher pressure tolerance • Smoother curvature • Thicker glass (especially in the neck part) à 50 tubes tested a 1.25 MPa (= 125m) with no failure Pressure tolerance ×2 higher than SK PMT’s 12 Single photoelectron resolutions

Single photoelectron charge Single photoelectron timing σ/mean FWHM Super-K 53 % Super-K 7.3 ns Box&Line 35 % Box&Line 4.1 ns Entries (a.u.) Entries (a.u.) HPD 16 % HPD 3.8 ns (2ch AD) (2ch AD)

-1 0 1 2 3 -10 -5 0 5 10 15 20 ChargePhotoelectrons [photoelectron] TimeTime [nsec](ns) Multi-PE Charge

1.2 1PE Charge and timing resolution much improved 1 Super-K Box&Line relative to Super-K PMT 0.8 2PEs HPD 0.6 (1ch AD) * HPD performances are currently limited by 0.4 preamplifier performances 0.2 à Fast / low-noise preamp is under development 0 0 1 2 3 4 5 13 Photoelectron Dark rate, After pulse, and Long term testing

Dark rates of new B&L PMT are typically 10kHz (@13oC, 0.5PE thr.) • Expected to be similar for the HPD à Trying to reduce by half (similar level to SK PMT’s) Higher after-pulse rates observed initially in B&L PMT à Reduced much by optimizing the dynode shape Long term testing of 50 cm Box&Line PMTs in EGADS tanks for 1.5 years so far à Showing reasonably stable gain & dark rate 50cm HPDs will also be installed when successfully developed 14 PMT cover Prototype design 11-15mm acrylic Every PMT in HK to be housed in a protective cover to prevent a chain reaction of the PMT implosion • Cover with small (~1 cmφ) holes limits the water flow into evacuated area if PMT implodes 3mm stainless steel à Avoid shockwave arising outside the cover

PMT implosion test carried out at 60m/80m water depths

Central PMT in 3×3 PMT array artificially imploded

Water-filled shaft Confirmed that pressure pulse in Kamisunagawa outside cover was very weak and JAPAN no chain implosion happened Sunk down to 60m/80m 15 Various Hyper-K R&Ds ongoing

Inner Outer Detector Detector KM3NeT inspired multi-PMT module option • Directional information from PMTs, finer granularity • Pressure tolerance • Natural housing for in-water electronics

New 11” HQE PMT Evaluation board New calibration sources and by ETEL/ADIT for new ASIC automated calibration system

and more … 16 Leptonic CPV sensitivity

Long baseline program using the upgraded J-PARC ν / ν beam

1.3 MW by 2026 T2K, T2K-II Hyper-K

o o 7 precision at δCP = 0 o o 21 precision at δCP = 90

Exclusion of sin(δCP) = 0

at 3σ for 78% of δCP values at 5σ for 62% of δCP values Great potential to discover ν CPV 17 Atmospheric neutrino studies

P( νµà νe ) P( νµà νe ) Mass hierarchy sensitivity à NH NH atmospheric + beam à à IH IH (Neutrino direction) zenith

θ 1 year à cos 0.1 1 10 100 0.1 1 10 100 Neutrino energy (GeV) n HK has sensitivity to mass hierarchy (NH or IH) through atmospheric νs n Sensitivity further improved in combination of beam+atmospheric νs Can determine the hierarchy at >3σ after 5 years, >5σ after 10 years 18 Nucleon decay search

1 order of magnitude sensitivity improvements Leading measurement in p à e+π0 mode Competitive with DUNE in kaon modes

Hyper-K With smaller tank & high density (40%) 35 ultra-sensitive PMT array, can achieve 10 same performance as larger tank LAr 40kt current limit by SK 34 • 10 Tag neutrons captured on H to reject p à e+π0 atmospheric ν BGs, thanks to the PMT discovery potential (3σ) efficiency improvement

19 Status/Timeline

Construction : 8 years

• Hyper-K Design Report has been written up – describes comprehensively the updated detector design, construction method, physics sensitivities, etc. • 1st round of the international review by Hyper-K Advisory Committee (HKAC) was done in February 2016 • Preparing for the budget request and quick startup 20 Summary

• 20 years have passed since Super-K data-taking started – Discovery of atmospheric/solar ν oscillations, ν appearance (T2K), …

• SK will be upgraded to SK-Gd, which will enhance various physics sensitivities by dissolving gadolinium in SK water – Aiming at the first observation of DSNB (SN relic νs)

• Hyper-Kamiokande is a natural continuation of successful Super-K, and has great potential to discover new physics – Leptonic CPV, proton decays, …

• Successful development of high efficiency 50cm PMT enabled the HK detector design update, reducing cost significantly without degrading physics sensitivities 21