Super-Kamiokande Detector

Mauro Mezzetto INFN – Sezione di Padova

XXV Giornate di Studio sui Rivelatori, Cogne, 23 febbraio 2016 Few initial remarks

• I’m not a member of SK collaboration. I’m a member of the T2K collaboration, which is a «user» of SK. • SK had been designed in the early 90’s, so it’s not at the leading edge of technology • However its performances are outstanding • … and the physics results are «more than outstanding» • I took material from published papers and from three lectures: – T. Kajita lessons at the Nufact ‘05 School, Capri, 2005 – Y. Koshio «Overview of the Calibration System in SK», 2012 – S. Yamada «Commissioning of the new electronics and online system for the Super-Kamiokande Experiment”, 2009

PremiNobel Nobel Prizes alla to Neutrinofisica dei Physicsneutrini

1995: for the detection of the neutrino Fred Reines

1988: for the neutrino beam method and the demonstration of the doublet structure of the leptons through the discovery of the muon neutrino Lederman Stainberger Schwartz

2002: for pioneering contributions to astrophysics, in particular for the detection of cosmic neutrinos Ray Davis Koshiba 2015: for the discovery of neutrino oscillations, which shows that neutrinos have mass

Kajita Mc Donald

To my knowledge: SK is the only hep experiment to be awarded twice Breakthrough Prize 2015

Atsuto Suzuki Yifang Wang Yoichiro Suzuki Kamland Daya Bay Super-Kamiokande Takaaki Kajita K. Nishikawa Art McDonald Kam-Biu Luk Super-Kamiokande K2K & T2K SNO Daya Bay The origins: KamiokaNDe

• Kamiokande had been designed (early 80’s) mainly to search for proton decay. • Proton decay is the main signature of Grand Unified Theories (GUT): barionic number conservation is an accidental low in the standard model (not ralated to any gauge symmetry) and should be violated in higher unification schemes 29 • At the time the estimated decay time was τp=10 years, needed order of 1kton material (1 kton of water contains 3 x 1032 protons), KamiokaNDe was 3 kt. • Atmospheric neutrinos came into game because they are a natural background for proton decay. • Soon after the commissioning (1985) the collaboration worked hard to decrease the detection threshold in order to be sensitive to solar neutrinos. • And few weeks after the low threshold run it detected neutrinos from the SN1987A supernova explosion • The great successes of KamiokaNDe and the need of more statistics to achieve the necessary sensitivity convinced the collaboration to propose a 10 times bigger detector: Super-Kamiokande, which started data taking on 01/04/1996 Super-Kamiokande

11,146×(50cm φ PMT) : Inner detector 40% photo-cathode coverage

Number of observed Ch. photons ～ 6 /MeV (excluding scattered or reflected photons)

1,885×(20cm φ PMT) : Outer detector (Less photo-cathode coverage: Only needed to identify muons)

2m active detector region + 0.6m layer (no photon detection) 50,000 ton water Cherenkov detector γ (and neutron) shield (Fid. Mass is 22,500 tons)

Physics in Super-Kamiokande

Solar neutrinos: energy spectrum down to 4 MeV. Requires extremely good energy scale, maximum PMT coverage with sensitivity to the single photoelectron, good timing. Atmospheric neutrinos: energy spectrum from 100 MeV to several GeV. Electron events are measured by calorimetry, muon events by range (but SK contains muons up to 1.4 GeV) Beam neutrinos: energy spectrum from 200 Mev to 3 GeV. Require good PID performances (e- vs π0 and e- vs µ-). Requires good direction reconstruction (see later) SuperNovae neutrinos: in a galactic SN explosion order of 105 events are expected in 10s. Strong constraint to electronics and DAQ. Proton decay: requires zero background. Extreme performances in PID and energy reconstruction. Relic SN Neutrinos Indirect Dark Matter searches. Achievements

Solar neutrinos: first experiment to detect energy spectrum and direction of solar ν. Nobel Prize 2002 and Breaktrhrough Prize 2015

Atmospheric neutrinos: discovery of neutrino oscillations: Nobel Prize 2015 and Breaktrhrough Prize 2015

SuperNovae neutrinos: detection of the neutrinos emitted by SN1987A. A crucial test of SN Models. Nobel Prize 2002 and Breaktrhrough Prize 2015

Beam neutrinos: First confirmation of atmospheric neutrinos with a long baseline experiment: K2K. First direct detection of oscillation appearance and first measurement of

θ13 by T2K. Both awarded with the Breaktrhrough Prize 2015

Proton Decay: the «GUT Killer»: all the simplest (and most elegant) GUT models killed by the SK limits. Susy severely matched.

Indirect DM searches: via DM annihilation in the Sun producing neutrinos. The best limit for spin dependent interaction models. A Sun picture taken from deep underground …

Detecting Cherenkov photons

Number of Ch. photons with λ=300- 600 nm emitted by a relativistic particle per cm = 340.

Need an efficient detection of the electron photons. Large PMTs Photomultiplier tube (PMT) 50cm φ ν (Super-K) 20cm φ 1 (SNO) cosθ = nβ n (refractive index)=1.34 in water θ=42deg. for β=1

T. Kajita lectures at Nufact 05 school, Capri. Detecting Cherenkov photons and event reconstruction

lectron PMT

ν Color: timing Size: pulse height Time: vertex position Multiple direction Coulomb scattering Pulse height (number of pe’s): energy T. Kajita lectures at Nufact 05 school, Capri. Photomultipliers (Hamamatsu R3600) NIM A329 (1993) 299-313, NIM A501 (2003) 418-462

HV system by CAEN

Quantum Efficiency Transit Time Single p.e.

SNO: the water Cherenkov exp that shared with SK the Nobel Prize 2015 Various types of atmospheric neutrino events (1)

・Both CC ν and νµ (+NC) FC (fully contained) e ・Need particle identification to separate νe and νµ ν ・12,000events Outer detector (no signal) Single Cherenkov Single ring electron-like Cherenkov event ring muon- like event

Color: timing Size: pulse height Various types of atmospheric neutrino events (2)

Signal in the PC (partially contained) outer detector

ν

・97% CC νµ ・900 events

T. Kajita lectures at Nufact 05 school, Capri. Various types of atmospheric neutrino events (3)

・ almost pure CC ν Upward going µ muon ・1800 throught muons ・400 stopping muons ν

Upward Upward stopping through- muon going muon Particle identification electron-like muon-like event event

e: electromagnetic shower, µ: propagate almost straightly, multiple Coulomb scattering loose energy by ionization loss

Difference in the event pattern 2  p.e.(obs'd) − p.e. (expected)  Particle ID χ 2 =  e or µ  ∑  σ  θ <70deg  p.e.  Particle ID results

Cosmic ray μ e from μ decay

ε=99% Beam Neutrino energy reconstruction Direction of neutrino = known Quasi-elastic - For quasi-elastic events: ν + n → µ + p µ µ (E , p ) θµ µ µ Eµ, θµ Eν ν p 2 mN Eµ − mµ 2 Eν = mN − Eµ + pµ cosθ µ Background (non-quasi-elastic int.)

- νµ + n → µ + p + π µ θ (Eµ, pµ) Quasi- µ ν Elastic π p Non-QE Below threshold

T. Kajita lectures at Nufact 05 school, Capri. Eν (reconstructed) – Eν (true) T2K experimet

Detect νµ−νe oscillations to measure θ13 and δCP

• Beam neutrino from the J- Parc 30 GeV syncrotron • SK at 295 km, off-axis with respect to the neutrino direction • A sophisticated close detectors system (280 m from the target) to measure the neutrino beam before oscillations

Data taking started in 2009 Long shutdown for the 2011 tsunami Taking data

First experiment to detect νµ−νe oscillations and measure θ13 Water purification system The key feature to detect solar and SN neutrinos

Air Purification

Calibration Nucl.Instrum.Meth. A737 (2014) 253-272 Requirements

• Number of photo-elections and arrival timing for each PMT • Understand water quality in detail • Systematic errors of reconstruction: energy, position, direction, efficiency • Long term monitoring of PMT gain, water condition, energy scale etc.

Pre - Calibration

Aim: have all the PMT’s tuned to the same overall gain (QE x HV gain)

• 400 PMT’s had been prepared with precise gain measurement before SK start • Installed uniformely in the detector • HV of the other PMT’s adjusted thanks to the Xenon flush lamp

Initial calibration Number of photo-electrons

Electronics calibration • Relation channel vs pC

HV adjustment • Used ~ p.e. light for each PMT • Adjusted QE x HV gain

Gain measurement QE measurement • At the single p.e. level • Absolute/Relative PMT gain

Charge with p.e. for data Charge with p.e. for MC

• Fine tuning for PMT correction efficiency HV adjustment

• Light source (Xenon lamp + Scintillator ball) at the center of the detector • Adjust number of photo-electorns in all PMTs to reference PMT (light non uniform in all the PMTs due the cylindrical shape of SK, light reflections and water transparency) • QE x HV gain is then equalized Gain adjustment

• Relative gain of each PMT measured by the ratio of low/high intensity of laser light (30 levels of intensity). Correction of observed photo-electons for each PMT • Absolute gain averaged for the whole detector determined by the single p.e. peal by Nickel calibration • Problem: electronics pedestal drift in time

Detector calibration by an electron LINAC Precise calibration of absolute energy scale, energy resolution, and angular resolution using electron LINAC.

ENDCAP

0.1mm thick Ti window

• Beam energy: 5 ~ 16 MeV/c • Beam energy spread: < 0.5 % Nucl.Instrum.Meth. A421 (1999) 113-129 16N calibration With a Deuterium-Tritium (DT) generator

Data taken at various positions in the detector. Uniform direction complementary to LINAC calibration. 16 16 DT generator D+T→He+n n+ O→p+ N(τ (14.2 MeV) 1/2 = 7.13 s) 16N decay (precisely known): 106 n/pulse 6.129MeVγ + 4.29MeVβ (66.2%), 10.419 MeV β(28.0%), etc. ~1% of n creates 16N Nucl.Instrum.Meth. A458 (2001) 638-649

Timing calibration

3, New Electronics IEEE Trans.Nucl.Sci. 57 (2010) 428-432 QTC-Based Electronics with Ethernet (QBEE)

Interface Card Network Ethernet Features Readout • 24channel input • QTC (custom ASIC)

• Charge measurement PMT • wide dynamic range 60MHz Clock signal (>2000pC) TDC Trigger • multi-hit TDC (AMT3) • Data is sent to Online system via Ethernet

• External 60MHz clock is used Calibration Pulser for synchronization with other Qbees • On-board pulsar for charge calibration QTC TDC FPGA • Low power consumption 42 ( < 1W/ch ) Data-readout via Ethernet QBEE throughput from analog pulsar Custom Network Interface Card Input to a readout PC

12 10 MAX : 8 11.8MB/s 6 (~95Mbps) 4 2 Requirement 0 throughput rate (MB/s) rate throughput 0 4 8 12 16 20 input data rate (MB/s)

• TCP/IP firmware (SiTCP) and interface  Required data transfer speed : logic are implemented on FPGA (PMT dark noise) 10kHz x 6byte x 24ch • IP address is set by dip switch • 32MB SDRAM = 1.5MB/sec/board  Fast enough. Reaches the theoretical limit of 100BASE-TX !!

43

4, New Online System Event builder 24PMTs 30QBees QBee Front Software Merger QBee End PC trigger Front Organizer QBee End PC Recorded Software Data: . QBee Front Merger trigger 9MB/s

. QBee End PC typical . Software . 1hit cell Ethernet Merger = 6bytel Sorting trigger Disk . (ch, T, Q) Data from 30Qbee 13,000. 550 20 10 PMTs QBees Front-end PCs Merger PCs Offline analysis

- LINUX Multi-threaded softwares are running on Online PCs equipped with 4 CPU cores. - From electronics to offline disk, data is transferred using TCP/IP protocol, with commercial Ethernet network equipments. 45 T2K (neutrino beam from Tokai to Kamioka) trigger  By using GPS data of SK and Tokai sites, PMT hits within ±500μs are recorded as T2K triggered event ( 1st priority in software trigger ) 2 3 Every hit Merger 1 nd HITSUM rd st st

+ Reduction Reduction data Triggered data Reduction Software Offline T2K triggered trigger T2K triggered Disk data SK-GPS data data

check

From Tokai Tokai-GPS - In Apr., 1st neutrino beam was produced at J-PARC in Tokai. Data - Still beam is in commissioning status, but in SK DAQ, T2K trigger and reduction are now applied to SK data and being checked. Online trigger monitor at SK

Spill information coming from J-PARC

46 M. Mezzetto, INFN Padova, TAUP 2015, 47 Torino Ice Cube

Un altro modo di guardare il cielo

Ice Cube, South Pole. For the first time detected galacting neutrinos, opening the field of neutrino astronomy. Km3Net

Capo Passero, Sicily. INFN collaboration with Fr, Nl, De, Gr Conclusions

• Super-Kamiokande experiment is a succesful story with unmatched performances in atmosferic, solar, beam, supernovae neutrinos, proton decay and indirect DM searches • After 20 years of operation it’s ready for a major upgrade