Development of the Hyper-Kamiokande detector
Y. Nishimura, for the Hyper-Kamiokande working groupResearch Center for Cosmic Neutrinos, Institute for Cosmic Ray Research, Kashiwa, Chiba,277-8582, Japan
E-mail ynisi@icrr.u-tokyo.ac.jp
Hyper-Kamiokande (Hyper-K) is a next
generation water Cherenkov detector planned in
Kamioka, Japan [1]. It is an upgrade plan ofSuper-Kamiokande (Super-K), currently running
to research various physics topics of neutrinos
and nuclear decays. Fig. 1 illustrates the designof Hyper-K consisting of two tanks withdimensions 48 (W)  54 (H)  250 (L) m3for each tank. Its total (fiducial) volume is 1.0(0.56) million metric tons, which is 20 (25) times Fig. 1 Hyper-Kamiokande
larger than that of Super-K [2]. In the base line
design, Hyper-K is equipped with 99,000 photo-detectors with a 50-cm diameter, and 25,000
photo-detectors with a 20-cm diameter for an outer veto layer to reject cosmic-ray muons. A
research to construct the water tank underground and development to improve the detector
performance are in progress for the actual detector construction in the very near future.
The Hyper-K working group, consisted of more than 200 members, started a study todetermine a concrete design of the cavity and tank construction, water circulation system,
photo-detector, data acquisition system, software of the detector simulation, calibration,
accelerator and a near detector in J-PARC for the neutrino long baseline experiment. Basedon a geological survey at the candidate site in Kamioka, the cavern shape and tank structure
are being optimized with considering a photo-detector supporter in water. The water
circulation system to keep an ultra-pure water in Hyper-K is also designed with calculating awater flow and cycle.
One of the important studies to improve the Hyper-K performance is the photo-detector
development, which could also improve the physics sensitivity not only by enlarging volume
but also by a good resolution. Two types of new large-aperture photo-detectors with a highefficiency are currently under development. One is the photomultiplier tube (PMT) with abox-and-line dynode to acquire a good charge and time resolution, whereas Super-K uses thePMT with a venetian-blind dynode. Other candidate, a hybrid photo-detector (HPD) with anarge-Aperture Photodetectors
or Hyper-Kamiokande

avalanche diode, would bring an excellent resolution on charge and time with a low

Hayato, Seikoproduction
Hirota, cost
Isaoexpected.
Kametani, Masayuki Nakahata, Tsuyoshi Nakaya,wa, Yusuke Suda,TheHidekazu
Tanaka, Keisuke Tateishi, and Masashi Yokoyama
prototypes of 50-cm diameter photo-detectors showed an improved resolution

compared with the Super-K PMT. Fig. 2 shows a single photoelectron peak, where a blackline shows the Super-K PMT, the box-and-line PMT in a blue line and the HPD in red. A time
resolution
ctors are currently
being of these photo-detectors at single photoelectron is shown in Fig. 3. The gooduse in the large
water of box-and-line PMT (blue) or HPD (red) implies an improved performance inresolution
e planned in Japan[1]:Hyper-K.
ch diameter size with anltiplier Tube (PMT)1.4with
1
1.2
ype. These are expected
ut timing and collection
0.8
1
T with a venetian 0.8blind
0.6
o there is a possibility to0.6
ese photodetectors from0.4
alkali technique. A0.4proof
0.2
or is planned in advance0.2
the best candidate0 for0-101

20-inch high-QE HPD(5mm dia. AD) w/ preamp.

20-inch high-QE HPD (5mm dia. AD) w/ preamp.

20-inch high-QE box&line PMT

20-inch high-QE box&line PMT

20-inch normal-QE Super-K PMT

20-inch normal-QE Super-K PMT

23Photoelectron-20-15-10-505101520 25
Time (ns)tors have already been Fig. 1. Schematic view of Hyper-Kamiokande.
PD, and a 20-inch PMTFig. 2 Single photoelectron peakFig. 3 Time resolution at single photoelectron
22% of the 20-inch PMT
odetectors were installed
13 for a proof of using (Evaluating Gadolinium’s Action on Detector Systems) expereport the specificationof iment
A usabilityof theseadvanceusing new
240 photo-detectors
photodetectors should(Fig. 2 be(a))confirmed[3]. Our inaim
is to so that theof the development and select the best photodetector for Hyper-K, based on this test,
Hyper-K detector runs over ten years to achieve the target sensitivity without any trouble. Aby 2016.
proof test started
using a 200-ton water tank in Kamioka, Japan, to ensure a long-term
The first proof test using eight 8-inch HPDs and five 20operation and performance. Currently the HPD with a 20-cm diameter and the Super-K PMTinch high-QE PMTs starts in 2013 (Fig. 2 (b)). It compareswith the high quantum efficiency improved from 22% to 30% are tested with the Super-KON
the relative performance of the HPD and the high-QE PMT toPMTs. The twotypes of new 50-cm photo-detectors will be also evaluated in the tank soon. InK) is a next generation the 227 20-inch PMT (R3600 by Hamamatsu Photonics K.K.)
future, structuresof the photo-detector
supporter
frame,
electronics will bewhich are also
installed
in reflector
the sameand
200-tond in Kamioka,nearJapan.
It used in Super-K,
tank.
in a small
prototype detector of Hyper-K.
de (Super-K),tested
currently

f neutrino physics andurrent design of Hypersions 48 (W) × 54 (H)al (fiducial) volume isis 20 (25) times larger
equipped with 99,000
etectors in the base line

f the newly developed
proof test is performed
epared for the EGADS

Research Center for Cosmic, The University of Tokyo,u-tokyo.ac.jp).
Shiozawa and H. Tanaka are
Ray Research, The University

h Department of Physics, The ~ (a) Outside view(b) Inside view from top

Fig. 2. The 200-ton water tank (EGADS) in Kamioka mine. New photodeFig. 4indicated
The 200-tontankwere
in installed
Kamioka,constructed
for thetectors
by dashedwaterbox lines
for thefirst proof test.

EGADS experiment. The 20-cm HPDs were installed in red boxes
and the PMT with high quantum efficiency in green boxes.

II. D EVELOPMENT OF NEW PHOTODETECTORS
A. 20-inch high-QE photomultiplier tube

The Hyper-K working group had a good progress of the detector R&D in a recent fewyears. Details of the Hyper-K detector design and recent activities such as the photo-detector
development will be presented.
References[1] K. Abe et al., arXiv:1109.3262 [hep-ex] (2011).
[2] The Super-Kamiokande Collaboration, Nucl. Instrum. Meth. A 501, 418-462 (2003).