A gigantic detector to explore elementary particle unification
theories and the mysteries of the Universe’s evolution

Peering into the Universe and its ele mentary particles from underground
The planned Hyper-Kamiokande detector will consist of anorder of magnitude larger tank than the predecessor, SuperKamiokande, and will be equipped with ultra high sensitivity
photosensors. The Hyper-Kamiokande detector is both a“microscope,” used to observe elementary particles, and a“telescope”, used to study the Sun and supernovas throughneutrinos. Hyper-Kamiokande aims to elucidate the Grand

Unified Theory and explain the evolution of the Universe
through the investigation of proton decay, CP violation (thedifference between neutrinos and antineutrinos), and theobservation of neutrinos from supernova explosions. The
Hyper-Kamiokande experiment is an international research
project aiming to become operational in 2027.

Large-aperture photosensors
The photosensor for Hyper-Kamiokande has
a 50-cm-diameter detection area with twice
improvements in sensitivity, resolutions andsafety as compared with Super-Kamiokande.
Under international collaboration, we aredeveloping a supplementary "compound eye"
unit using multiple photosensors to detect lightpatterns and timing precisely with the combined
use of these sensors.

↑The multi-photosensor
unit←World's largest
Courtesy of Hamamatsu Photonics K.K. photomultiplier tube

A megaton water tank
The huge Hyper-Kamiokande tank will be usedin order to obtain in only 10 years an amountof data corresponding to 100 years of datacollection time using Super-Kamiokande. This
allows the observation of previously unrevealedr a re p h e n o m e n a a n d s m a l l v a l u e s o f C P
violation.

Experimental Technique
The photosensors on the tank wall detect the very weak Cherenkov
light emitted along its direction of travel by a charged particle
ejected in the collision between neutrinos and water in the tank.
This Cherenkov light is emitted in the form of a cone shape or in mostcases a ring as the charged
Cherenkov lightparticle is eventually absorbed.
The energy, direction and typeof neutrinos are determined
neutrinousing the information obtained
Chargedfrom the photosensors, suchparticleas the quantity of light and thein waterring shape.
Photosensors

10 times
fiducial volume

50,000 tons

Super-Kamiokande

260,000 tons

Hyper-Kamiokande

Bringing Neutrino Research to the Next Level
The discover y of neutrino oscillations in the SuperKamiokande experiment in 1998, for which the 2015 Nobel
Prize in Physics was awarded, led to the investigation andmeasurement of the properties of the neutrino whichindicate the need for an update of the Standard Model. In
2001, the solar neutrino oscillation was discovered. In 2011,
the T2K experiment, which used a neutrino beam from thehigh intensity accelerator J-PARC and the Super-Kamiokande
detector, confirmed the third neutrino oscillation. Now that
all neutrino oscillation modes have been confirmed, the fieldof neutrino research has opened up for further investigations
and discoveries.
Based on the highly sensitive techniques for neutrino
observation developed by Super-Kamiokande over the years,
Hyper-Kamiokande represents a further improvement insensitivity. Hyper-Kamiokande consists of a cylindrical tank,with a height of 72m and a diameter of 68m. The fiducial
volume of the tank is approximately 10 times larger than thatof the Super-Kamiokande detector. On the tank wall, 40,000
ultra high sensitivity photosensors will be installed in order todetect the very weak Cherenkov light generated in the water.
Through the realization of the Hyper-Kamiokande experiment,
we will lead neutrino research into the future.

Kamioka Observatory, ICRR,The University of Tokyo
Mail : hk-public@km.icrr.u-tokyo.ac.jp
URL : http://www.hyper-k.org/

2021.07

The region that the present colliders can explore

The origin, evolution, and future ofThe region that nucleon decay and neutrino experiments can explore
the Universe and its particles
1610 GeV
102GeVAt the birth of the universe, itInflationis thought that the four forces thatgovern our world (the strong, weak,The Grandelectromagnetic, and gravitational
Unified Theoryforces) were unified in the form of asingle force. When temperatures fellwith the evolution of the universe,
10 -38 sec
this unified force separated to the fourforces.
The Grand Unified Theory, which governed the universe
until about 10 -38 seconds after the Big Bang (10 16 GeV, interms of the energy of the universe), deals with energies toohigh to inspect directly through collision experiments in anaccelerator. However, the Hyper-Kamiokande experiment candirectly investigate the Grand Unified Theory by exploring
proton decay. If protons decaying into more light particles
can be observed, it means that all matter, including humanbeings, in the universe has a finite lifetime and will decay inthe future.
Hyper-Kamiokande will elucidate neutrino properties such as
the CP violation and approach the mysteries surrounding theevolution of the universe and the birth of life, through theobservation of solar and supernova neutrinos.

Baryon numberproduction

Remaining
Dark Matter

Mixing of neutrinomass / the origin ofCP violation

Supersymmetry
theory1MeV

Synthesis of light elements

10-10

Energy emission
from fixed stars

Synthesis ofheavy elementsfrom supernova burst

Synthesis of heavy elements

10 -5 sec

100 sec

380,000
years

A gigantic detector to confront elementary particle unification theories andthe mysteries of the Universe’s evolution
Determining the Orderingof the Neutrino Masses

CP Violation Measurement
Hyper-Kamiokande will investigate CP violation (i.e the difference
between particles and anti-particles) by observation of oscillations
using neutrino/anti-neutrino beam from J-PARC accelerator.
The present universe is filled with "matter" such as stars andhuman beings, but "anti-matter" is not seen. This imbalance
between matter and antimatter might occur because of CP
violation in neutrinos. We will investigate this asymmetry.

The end ofthe Universe?
Humanbeings

The birth of human beings

Nucleon decay

Based on the observation of neutrinos oscillations, the differences
between the three neutrino masses have been measured. However,
it is not known whether the two masses that compose solar
neutrinos are heavier or lighter than the third mass. Determining
the ordering of the neutrino masses is an important line ofresearch not only because it increases the precision of CP violation
measurements, but also because it is an essential ingredient for
determining whether the neutrino is a Majorana fermion, a type ofparticle which is indistinguishable from its antiparticle.

1 billionyears

Age ofthe Universe

13.8 billion 35
10 years
years

Collaboration with the J-PARC Accelerator
In addition to natural neutrinos such as atmospheric andsolar neutrinos, a high intensity and high quality neutrino
beam from the J-PARC accelerator in Tokai, Ibaraki, may be
used for precisely studying the properties of neutrinos such
as CP violation.
Hyper-Kamiokande is expected to observe 30 times as manyneutrinos as the T2K experiment after the increase of theJ-PARC beam power.
©JAEA/KEK J-PARC Center

Kamioka-town, Hida-city, Gifu

Hyper-Kamiokande
Tokai-village, Naka-gun, Ibaraki

J-PARC accelerator

Uncover the mystery ofneutrino oscillation
Cosmic Neutrino Observation
Using cosmic neutrinos such as the neutrinos originatingin the Sun, our galactic center, or a supernova explosion,
we may study the stellar objects themselves. It is
expected that Hyper-Kamiokande will enable us toelucidate the history
the universe.

©NASAelectron neutrino

2×10-4eV

Energy©ESA and the Planck Collaboration

secmuon neutrino

tau neutrino

10-3eV

0.3eVElectromagnetic force
Weak force
Strong force
Gravity force

Neutrinos and Neutrino oscillations
The matter in the Universe consist of elementary particles
called quarks and leptons. For example, one proton, madeof three quarks, and one electron, which is a kind of lepton,
form a hydrogen atom. The neutrino is a kind of lepton
without electric charge and exists in types; electron neutrino,
mu neutrino and tau neutrino.
The three types of neutrinos mix with each other and canchange their type. This phenomenon is called “Neutrino
oscillation” and was discovered by Super-Kamiokande in
1998. The detailed study of neutrino oscillation enables us toreveal the properties of neutrinos.
The Standard Model, which describes the elementary
particle system, seemed to be completed by the discoveryof the Higgs boson particle. However, the information about
neutrino mass and its mixing rate obtained by previous
studies have a large difference from those of quarks. It isconsidered that a more fundamental framework is needed
beyond the Standard Model.
Neutrino oscillation experiments are expected to be a key
to address what the fundamental framework of elementary
particles is.

1keV

Revealing the mystery ofUniverse’s origin and evolutionProton Decay Searches
One of the important questions for the elementary
particle physics community is whether or not a proton
remains stable forever. The Grand Unified Theory, which
includes the Standard Model of particle physics, predicts
that protons decay
into lighter particles.
Hyper-Kamiokande willbe the most sensitive
detector in the world
for use in proton decay
searches. The aim ofHyper-Kamiokande
is to explore newhorizons beyond theStandard Model.

Verification of Grand Unified Theories

International Collaboration
The Hyper-Kamiokande is an international research project.
Many researchers from various countries are working
together to realize the experiment. As of April 2021, theHyper-Kamiokande collaboration consists of about 400
researches from 19 countries; Armenia, Brazil, Canada, Czech,France, Germany, India, Italy, Japan, Korea, Mexico, Poland,Russia, Spain, Sweden, Switzerland, UK, Ukraine, USA.