The Final Report of
the Subcommittee on Future Projects ofHigh Energy Physics1

11 February 2012

Subcommittee members:
S. Asai (Univ. of Tokyo), M. Hazumi (KEK), K. Hanagaki (Osaka Univ., Secretary),
J. Hisano (Nagoya Univ.), T. Iijima (Nagoya Univ.), K. Inoue (Tohoku Univ.), K. Ishii (KEK),
T. Kobayashi (KEK), M. Kuriki (Hiroshima Univ.), T. Mori (Univ. of Tokyo, Chair),T. Moroi (Univ. of Tokyo), H. Murayama (Univ. of Tokyo/U.C. Berkeley),
T. Nakaya (Kyoto Univ.), M. Nojiri (KEK), T. Nomura (KEK, Secretary), Y. Ohnishi (KEK),
Y. Tabuchi (KEK), Y. Ushiroda (KEK), S. Yamashita (Univ. of Tokyo)

1 This is an English translation from the original Japanese Report.

Preface
The charge of the subcommittee is to examine future high energy physics projects in Japan
within the time scale of more than 10 years into the future and, most importantly, to report on future
large-scale projects which should follow those currently operational or under construction.
While the realization of large-scale projects requires an enormous amount of long-term
preparation, expectations are rising that important discoveries may be made at LHC or in theneutrino and other experimental sectors within the coming years. It appears that future strategies
based on an LHC upgrade and high intensity hadron accelerators are also being developed inEurope and in the United States. Considering these circumstances, Japan should take a leading rolein the world by indicating the direction of the future of high energy physics research, from thephysics point of view, should these new discoveries be made. It is expected that decisions on,
proposals for and the taking of the leadership of such future large-scale projects as ILC will bemade in a flexible way, in accordance with the new discoveries.
Another important issue to be resolved is how to advance particle physics research continuouslyon the various fronts, for example, at SuperKEKB, which is currently under construction or at themedium/small scale experiments at J-PARC and other facilities. Realization of future large-scale
projects may depend on the results obtained from these medium/small scale projects. In addition, a
coherent strategy for cosmological observations and underground particle physics experiments
needs to be adopted since these fields are becoming more and more important. The committee has
therefore also surveyed and examined these issues.

2

Contents
Recommendations!

4

1 Current Situation and Future Perspectives!

6

1.1 Current Situation of Particle Physics!

6

1.2 Future Perspectives of Particle Physics!

7

2 Energy Frontier!

10

2.1 Overview!

10

2.2 International Linear Collider !

10

2.3 LHC Upgrade!

13

2.4 Other Projects!

14

3 Neutrino Oscillation!

16

3.1 Neutrino Oscillation and Proton Decay!

16

3.2 Current Status !

16

3.3 Future Planning!

16

4 Flavour Physics!

21

4.1 Super B-factories !

21

4.2 Muon Physics!

22

4.3 Kaon Experiments!

23

4.4 Neutrons!

23

5 Non-Accelerator Particle Physics Experiments!

24

5.1 Underground Astroparticle Physics Experiments!

24

5.2 Cosmological Observations !

26

6 Human Resources and Development of Technology!

328

Recommendations
The committee makes the following recommendations concerning large-scale projects, which
comprise the core of future high energy physics research in Japan.
• Should a new particle such as a Higgs boson with a mass below approximately 1 TeV
be confirmed at LHC, Japan should take the leadership role in an early realization ofan e+e- linear collider. In particular, if the particle is light, experiments at low collisionenergy should be started at the earliest possible time. In parallel, continuous studies on newphysics should be pursued for both LHC and the upgraded LHC version. Should the energy
scale of new particles/physics be higher, accelerator R&D should be strengthened in orderto realize the necessary collision energy.
• Should the neutrino mixing angle θ13 be confirmed as large, Japan should aim torealize a large-scale neutrino detector through international cooperation, accompaniedby the necessary reinforcement of accelerator intensity, so allowing studies on CP
symmetry through neutrino oscillations. This new large-scale neutrino detector shouldhave sufficient sensitivity to allow the search for proton decays, which would be direct
evidence of Grand Unified Theories.
It is expected that the Committee on Future Projects, which includes the High Energy Physics
Committee members as its core, should be able to swiftly and flexibly update the strategies for thesekey, large-scale projects according to newly obtained knowledge from LHC and other sources.
It is important to complete and start the SuperKEKB including the detector, as scheduled. Someof the medium/small scale projects currently under consideration have the implicit potential todevelop into important research fields in the future, such as neutrino physics and as such, should bepromoted in parallel to pursue new physics in various directions. Flavour physics experiments suchas muon experiments at J-PARC, searches for dark matter and neutrinoless double beta decays orobservations of CMB B-mode polarization and dark energy are considered as projects that havesuch potential.

45

SuMIReCMB satellite

CMB B mode

Dark Matter

0νββ

nEDM

KOTO

Muon g-2

μ→e conversion

MEG

νCP

T2K

J-PARC

SuperKEKB

ILC
Site

BR〜10-9

imagingr~O(0.1)

degenerated

10-45cm2

~0.04

~0.02

O(0.01)

10-46cm2

Construction

Construction

Construction

Tech.Decision

O(10-13)sin22θ13
~0.1

10-27

spectroscopy

Construction

inverted hierarchy

10-11

Physics Run

10-47cm2

10-28

Observation

50ab-1

Construction

2020

Physics Run

O(10-14)

Construction

FX 750kW

Physics Run

SUSY <2.5TeV

2015

Timelines of Current/Future Projects

FX 300kW
SX 100kW

Construction

TDR & Review

SM Higgs

LHC SUSY <1TeV

2012

Physics Run>1MW

Physics Run

HL-LHC2025

1 Current Situation and Future Perspectives
1.1 Current Situation of Particle Physics
Particle physics has developed in order to clarify fundamental principles of interactions between
matter and to understand the underlying laws. One of the successes in this field is the standard
model of elementary particles based on the SU(3)C×SU(2)L×U(1)Y gauge theory, which describes
well phenomena below the electroweak scale (approximately 100GeV).
One of the most important questions in establishing a particle physics model at the electroweak
scale is to understand the mechanism of electroweak symmetry breaking, which must be
spontaneous to be a consistent theory. In the standard model and many other extended models,symmetry breaking is spontaneously induced by the condensation of the Higgs field, with the Higgs
boson appearing in the physical spectrum. Although it is the most important target of high energy
accelerator experiments such as LHC, the Higgs boson has not yet been discovered. Therefore,
there are many unresolved issues in the mechanism of spontaneous electroweak symmetry breaking,which is at the basis of the standard model. Understanding the details of this mechanism is thecurrent primary task of elementary particle physics and with it to clarify the existence of the Higgs
boson, and if it exists, to deeply investigate its nature.
The stability of the electroweak scale against radiative corrections is considered as an important
key to understanding the mechanism of electroweak symmetry breaking. In general, it is difficult tocontrol radiative corrections to mass terms for scalar fields, and hence the Higgs boson creates
tension within the context of the standard model. This is called the hierarchy problem. It implies
that a new particle physics model beyond that of the standard model and which is free from thehierarchy problem, may become relevant at the electroweak energy scale. New candidate physics
models include supersymmetric models and models with extra dimensions. New particles thatappear in these models are important targets for high energy accelerator experiments, as they could
lead to important findings in flavour physics and cosmology/astrophysics. Hence the possible
impact of these particles should be investigated in fields other than high energy accelerator
experiments.
The standard model Higgs boson, if it exists, is expected to be discovered at LHC. High
expectations have been raised for the 2012 LHC run, as possible signals of a light Higgs boson thatseem consistent with the precision electroweak measurements by LEP etc. were reported in 2011.
New coloured particles predicted by various new particle physics models such as supersymmetry or
extra dimensions would be copiously produced at LHC. Stringent bounds on the squarks andgluinos with masses below 1 TeV have already been set by the LHC experiments, while significant
progress is further expected in the next five years concerning the direct search for these new,beyond the standard model particles. In order to resolve the hierarchy problem in the Higgs sector,
interactions both in the top and the gauge sectors need to be extended and new particles will
necessarily appear in these sectors. The LHC experiments are currently leading particle physics
research in the search for these new particles, and the upcoming results from these experiments,
must therefore, be incorporated into any future plan for particle physics research.
In contrast, research into the flavour and CP structure of quarks and neutrinos, an important partof which is carried out in Japan, explores a different frontier to study the origin of matter in theuniverse and the origin of quark mixing, which is not accessible to the LHC experiments.
It is suggested that quark and charged lepton masses are also generated by Yukawa interactions
6with the Higgs field. This is specifically supported by the high precision tests of the KobayashiMaskawa mechanism at the B-factory experiments, in searches for lepton flavour violatingprocesses, and measurements of the electric dipole moments of the electron and neutron. While newphysics at the electroweak scale, if it exists, would create a new flavour structure and new sourcesof CP violation, there has as yet not been any significant experimental signal. This implies that the
new physics may involve a non-trivial mechanism to suppress flavour and CP violation, and thatsearches with higher precision may be necessary. In particular, efforts to achieve a higher precision
measurement, as well as a better theoretical prediction, of the anomalous magnetic moment of muon
are being made after an apparent inconsistency was reported as a possible hint of physics beyond
the standard model.
The discovery of neutrino oscillations suggests that the neutrinos have tiny masses. This infers
the existence of some new physics beyond the standard model to explain their tiny masses. In
addition, the pattern of the flavour mixing in the neutrino sector is quite different from that in thequark sector. This suggests that the origin of the neutrino masses is completely different from that of
the quark masses. Specifically, if the neutrinos are Majorana fermions, as predicted by the seesaw
mechanism, the neutrino masses would then be related to physics at an extremely high energy scale.
While neutrino experiments such as the T2K are currently measuring the neutrino mixing angle θ13,
there still remain open important questions in neutrino physics: CP violation, Dirac or Majorana
type neutrino masses, determination of absolute neutrino masses, and the neutrino mass hierarchy(normal or inverted).
It is of particular relevance that connections between particle physics and cosmology are
becoming more and more important. With recent astrophysical and cosmological observations, suchas those of WMAP, the cosmological parameters have been more precisely determined. In
particular, the energy densities of dark energy and dark matter are known to be approximately 73%
and 23% of the total energy density of the universe, respectively, while baryonic matter accounts fora mere 4% to 5%. In addition to this, cosmic density fluctuations are observed to be nearly scaleinvariant, strongly suggesting an inflationary origin of the primary density fluctuations. These
results pose new problems for particle physics, in addition to providing the basis for constructing
the standard model of cosmology. Furthermore, it is impossible to understand the mechanism togenerate a matter-antimatter asymmetry, the origin of dark matter, the mechanism of inflation, thenature of dark energy, etc. within the framework of the standard model of particle physics, andclearly some new physics beyond the standard model must have played an important role in theevolution of the universe. New knowledge of physics beyond the standard model, which bothpresent and future high energy experiments such as LHC and ILC are expected to provide, isindispensable in solving these cosmological problems.
1.2 Future Perspectives of Particle Physics
The energy frontier experiments at LHC and its upgrades will lead particle physics through direct
searches for the Higgs boson and new particles such as those predicted by supersymmetry.
Determination of the mass scales of the Higgs boson and the new particles through these direct
searches will be especially important in planning future particle physics projects.
For an understanding of the mechanism of electroweak symmetry breaking and also the origin ofquark and lepton masses, we need to know the quantum numbers and interactions of the Higgs
boson in addition to its mass. An excess of a Higgs-like signal has been reported at a mass ofaround 125 GeV; in this mass region there is a rich decay pattern. Some of the decay processes
induced by loop diagrams are sensitive to new physics, so if one finds a deviation from the standard
7

model prediction of the branching ratios of the Higgs boson, it will help to determine and optimize
the centre of mass energy of future colliders. A light Higgs boson is within the reach of ILC, andmore detailed studies compared to LHC can be performed.
New particles may be found in due course with the increase of the energy and luminosity of
LHC. The interactions and quantum numbers must be determined in order to reveal the symmetry
behind these new particles such as supersymmetry. In turn, these symmetries may lead to further
particle searches. This may also provide a clue to the hierarchy problem in electroweak symmetry
breaking. If the masses of these new particles are within the reach of the lepton colliders such as
ILC, the nature of the particles can be studied under relatively low background conditions. LHC
therefore has a high potential for discovering new coloured particles, while the ability to discoverparticles without colour charge is rather limited. Therefore, when a new particle is found at
LHC, lepton colliders would also be necessary to understand the nature of such particles.
In addition to the energy frontier experiments, precision measurements of hadronic and leptonic
flavour changing processes and electric dipole moments have also been useful tools in constructing
and establishing the standard model. They are expected to play important roles in the future study of
new physics beyond the standard model, which is expected to exist at the electroweak energy scale.
Since the heavier quarks couple more strongly with the origin of electroweak symmetry
breaking, they might be more sensitive to new physics. On the other hand, since the quark mixings
are well described by the Cabibbo-Kobayashi-Maskawa matrix, contributions from new physics toflavour-changing processes in B-meson decays are smaller than 10~20%. Thus, various B-meson
decays should be studied with higher precision in order to understand the details of flavourchanging processes and CP violation in these processes. The LHCb and the SuperKEKB
experiments both have high sensitivities to possible new physics signals in differing decay modes,
and hence are expected to play a complementary role for each other. Such indirect searches for new
physics in the form of flavour physics are important, independently of the direct searches at LHC,
and will help to gain knowledge of new physics beyond the electroweak energy scale together withthe results from LHC.
Although lepton flavour and CP symmetry are not strict symmetries of nature, the branchingratios for the charged lepton flavour violating processes and the electric dipole moments of leptons
and hadrons are strongly suppressed in the standard model. However, there is no reason to supposethat such symmetry breaking is insignificant also within the framework of new physics at theelectroweak energy scale; hence studies on charged lepton flavour violation and electric dipole
moments might show high sensitivity to such new physics at the electroweak energy scale. By
searching for the breaking of flavour and CP symmetries in flavour physics experiments such as
those at J-PARC and the MEG experiment, clues to new physics could be discovered. As for thebaryon- and lepton-numbers, which might be violated in physics at a very high-energy scale (e.g.,
Grand Unified Theories), searches for proton decays may provide important implications.
Observation of the neutrino oscillation strongly suggests physics beyond the standard model. To
understand this in detail, further intensive studies of the properties of the neutrinos are necessary. If
the neutrino oscillation experiments, such as the T2K experiment, find a sizable neutrino-mixing
angle θ13, this may also provide the opportunity to discover CP violation in the neutrino sector. All
the CP violation so far observed originates uniquely from the complex phase in the CabibboKobayashi-Maskawa matrix. Discovery of CP violation in neutrino oscillations would indicate a
new source, other than that in the quark sector. In addition, searches for neutrinoless double βdecays (0νββ) by, for example, KamLAND-Zen are important in settling the issue of whether the8neutrino mass is of a Majorana- or Dirac-type. If the neutrino mass is of a Majorana-type, itstrongly supports the notion that the tiny neutrino masses are a natural consequence of the seesaw
mechanism, and that the baryon-anti-baryon asymmetry in the universe is generated in a
leptogenesis scenario. It is considered as one of the most important goals of future particle physics
to reach a unified understanding of the origin of the flavour structure and the CP violation by
combining the knowledge of the lepton mass matrix with that of the quark sector.
Significant progress is also expected in gaining knowledge of the properties of dark matter.
There are various candidates for dark matter: weakly interacting massive particles (WIMPs),
coherent oscillation of scalar condensation, etc. Among them, there is also a scenario that thermally
produced WIMPs freeze-out from the thermal bath at a temperature slightly below its mass, tobecome dark matter. In order for such thermally produced WIMPs to be the main component ofdark matter, the pair annihilation cross section of the WIMPs should be at about 1 pb, whichcorresponds to the cross section obtained by exchanging a particle with a mass of order 100 GeV to
1 TeV. Thus, the dark matter particle may be embedded in a particle physics model that resolves thehierarchy problem. In fact, the cross section of supersymmetric dark matter particles scattering off
nuclei may be large enough to be detected by current and future direct dark-matter detection
experiments. Hence confirmation of dark matter particles by direct detection experiments such as
the XENON and XMASS is therefore anticipated.
At LHC, the dark-matter particle may be found by using the missing transverse momentum
information. With the discovery of such a candidate particle, detailed studies of its properties arenecessary to confirm whether it is really consistent with the dark matter in the universe. For thedetailed study of the properties of a dark matter candidate, ILC can also play an important role.
With such studies, important information in understanding the thermal history of the universe will
be provided.
Progress is also expected in the understanding of the evolution of the universe through inflation.
In particular, if the tensor-to-scalar ratio is larger than about 0.1, the Planck satellite would beconsidered able to detect the B-mode polarization of cosmic microwave background, whichstrongly supports the inflationary scenario of the universes evolution. The amplitude of the B-mode
provides information on the energy scale of inflation. If the tensor-to-scalar ratio is larger than about
0.01, various successive experiments such as POLARBEAR would be able to observe the B-mode
polarization.

9

2 Energy Frontier
2.1 Overview
Research at the energy frontier aims at discovering new particles and phenomena, as well as
determining their properties and the laws of nature governing them. The numerous
accomplishments in this area include the discovery of quarks, leptons, and gauge bosons, themeasurement of their quantum numbers and coupling strengths, and the determination of thesymmetries of the interactions and the number of particle generations. Precision measurements
performed at LEP and SLC provided firm ground for the gauge sector that forms the basis of theStandard Model. The Higgs and Yukawa sectors remain as yet, uncharted territory. It is expected
that, through the discovery of the Higgs boson and its properties, new interactions different from thegauge interactions will be studied, leading to the search for new physics beyond the Standard
Model. At the highest energies, the search for new physics involves the direct production of newparticles and phenomena.
In order to study higher energy reactions at hadron colliders such as LHC, either beam energy orluminosity can be increased, the latter increasing the reaction rates of high-energy partons. Since thebeams at hadron colliders consist of protons and/or antiprotons, which are composite particles, only
a fraction of their energy participates in the reaction, while the rest undergoes fragmentation andbecomes background. The Higgs boson can therefore be discovered through reconstructing its massfrom the photons and leptons, which are emitted when it decays. New particles accompanied by
missing transverse momentum, such as supersymmetric particles, may be detected in a wide energy
range when they are copiously produced via the strong interaction.
In contrast, to reach even higher energies with a lepton collider, candidates such as a linear
collider, which does not suffer from losses due synchrotron radiation of electrons and positrons
causing inefficiencies in their acceleration, or a muon collider employing the heavy lepton must be
used. Since all the energy is converted into the reaction in lepton colliders, the final states can bemeasured precisely. In addition, the beam energy and the polarization can be adjusted to separate
the intermediate and final states of the interactions, enabling the determination of the symmetry in
the reaction as well as the mass and quantum numbers of the new particles. New particles produced
from both electroweak and strong interactions can be searched for; after their discoveries, theirproperties can be studied in detail in a low background environment.
2.2 International Linear Collider
The ideal machine to study the Higgs boson, whose discovery is anticipated at LHC, isconsidered to be the International Linear Collider (ILC). At ILC, linear accelerators will be installed
in an underground tunnel to accelerate the electrons and positrons in opposite directions for head-on
collisions. Initially, the experiment can start with a shorter accelerator providing the minimum
energy required for the target of the physics study, subsequently extending its length to increase theenergy. At ILC, the targeted collision energy in the first stage is between 200 to 500 GeV(corresponding to a 30 km straight section) with a future option to upgrade it to 1 TeV within scope.
The first priority is to study the Higgs boson; the main objects of study include the following: (1)mass, (2) spin and parity, (3) coupling to gauge bosons, (4) decay branching ratios, (5) total decay
width, (6) Yukawa coupling to the top quark, and (7) self-coupling. The main production process ofthe Higgs boson at ILC is one accompanied by a Z boson. If the mass of the Higgs boson is around
120 GeV, the tasks (1)-(5) above can be optimally performed at a centre-of-mass energy of around10

250 GeV. Tasks (6) and (7) involve the production of top quarks or multiple Higgs bosons and sorequire a centre-of-mass energy of close to 500 GeV. The number of Higgs bosons produced will
exceed 105, studied in an environment with a good signal-to-noise ratio. Thus its mass can be
determined to a precision of within a few tens of MeV, while the gauge couplings can be determined
to within 1 percent. From the branching ratio measurements, the Yukawa couplings to the bottom
and charm quarks and to the tau lepton can also be determined to within a few percent. Even if the
Higgs boson decays to invisible particles such as dark matter, the measurements can be performed
in a model-independent manner through the analysis of the recoiling Z-boson. Given the massprecision to within a few tens of MeV, the Standard Model predicts the value of other observables tobe within 1 percent. By comparing them to the observed values, the Higgs and Yukawa sectors of
the Standard Model can be tested to high precision. A single measurement differing from thepredicted values would signal the discovery of new physics beyond the Standard Model.
New particles such as dark matter that may escape detection at LHC could be discovered at ILC
through their direct production. If the collision energy exceeds the production energy threshold,their discovery would be certain. For new particles that do not create a mass peak, such as
supersymmetric particles and those that do not possess a colour charge, such as a light dark matterparticle, it would be considered hopeless to discover them at LHC. At a lepton collider however,these new particles without a colour charge can be discovered via their decay products or throughinitial state radiation, so enabling the properties of dark matter particles and others to be determinedthrough detailed measurements. New particles or phenomena that are currently not predicted may
also be discovered. Furthermore, ILC possesses a sensitivity to new physics through comparison
with precise theoretical calculations, such as the Z’ bosons up to and exceeding 10 TeV. Schemes
are currently being developed to experimentally test the Grand Unified Theories, which areimportant for the very early universe, by combining measurements from the hadron collider
experiments.
Overall Plan, Framework, Budget and Schedule
ILC will be able to make significant progress, not only in the understanding of elementary
particle physics and cosmology, but also in advanced technologies such as super-conducting
accelerators. Furthermore, by forming a new international research centre integrating academic,
educational, and technological activities, ILC would facilitate these discoveries.
From 2000 to 2002, the world-wide high energy physics community, mainly represented by Asia,
U.S. and Europe, established a consensus with the aim to jointly construct an electron-positronlinear collider as a priority for its next main project. According to the agreement, the physics studiesof the design of the accelerator and detectors for ILC have been performed as world-wide
international activities. Notably, after GDE (Global Design Effort) was established in 2005 by major
particle physics laboratories operating high energy accelerators (KEK, DESY, Fermilab), global
activities have been promoted intensively to further the detailed technical design of ILC. More than
1000 researchers and engineers, and more than 300 laboratories, universities (over 40 in Japan), andmany private companies have participated in an R&D effort. In this process the Asian research
centre, the Japanese ILC team including KEK play a leading role. A synchrotron light facility, basedon superconducting accelerator technology developed by the ILC project, is now under constructionin Germany. In the U.S., a large project has been promoted to develop the super-conducting
accelerator for ILC, and concurrently for a high power proton accelerator. For detector R&D, twolarge international collaborations, corresponding to two experimental proposals have work inprogress. In addition, FALC (Funding Agency for Large Colliders) which is an informationexchange forum for administrative agencies has been setup and various issues for the realization of
11

ILC have been actively discussed.
Following the reference design in 2007 by GDE, GDE is now concentrating on the design
optimization and industrialization of the accelerator technology. Taking into account also initial
results from LHC physics, a TDR (Technical Design Report) will be published in 2012. If theconstruction site is determined with international consensus among those countries within 3 years of
the TDR publication, the ILC detector and accelerator construction could start in 2015. After a 7 to
10 year construction period, ILC operation and experimentation will be able to start from 2025
onwards. In the reference design, the construction costs and the annual operation costs were
estimated to be approximately 6.7 billion USD and 200 million USD, respectively for a 500 GeV
ILC version. Some cost reduction is expected as a consequence of technological innovations,
technical design optimizations, and collision energy justification based on the LHC results.
ILC Detector Technology R&D
ILC detector technology R&D is concurrently undertaken by two design teams, ILD and SiD, as
key international collaborations. To improve the hadron jet reconstruction scheme (Particle Flow
Algorithm) invented in LEP experiments, a pixel vertex detector, a large solid angle tracking
detector and a fine segmented calorimeter which is able to separate each shower particle, are being
developed. In Japan a version with a vertex detector surrounding the interaction point, a calorimeter,
and a large TPC tracking detector are being developed. In close collaboration with the theory group,
physics studies and optimization of the detector concept are being advanced. Japanese physicists are
participating mainly in the ILD conceptual design and will lead the ILC physics and detector studyin Asia and also organize an international collaboration with European and U.S. counterparts.
Experience of detector operation in Belle II, ATLAS and the T2K near detector have provided
useful information for important components of ILC detectors such as sensors.
ILC Accelerator R&D
In terms of ILC accelerator R&D, important technologies such as polarized electron sources,
positron beams, flat super-low emittance beams, high gradient super-conducting accelerators andnano-beam focusing are being developed. In ILC, a 1.2m, 9 cell super-conducting accelerator
module, made of Nb and cooled down to 2K is operated at 31.5 MV/m. ILC consists of 1,700
cryomodules and 15,000 cavities. In order to fabricate such a large number of cavities within areasonable time period and at a reasonable cost, while satisfying the required performance, themanufacturing process has to be stringently controlled. One of the goals in 2012 is to achieve amore than 90% cavity production yield, satisfying the 35 MV/m gradient requirement, which has
almost now been met. The current main issue is further cost reduction; industrial production of ILC
construction has been intensively furthered by designing and optimizing the production lines ofcavities and cryomodules, and constructing a pilot plant for the production systems engineering.
KEK operates key test facilities for ILC: The Accelerator Test Facility (ATF) and the Superconducting Test Facility (STF). The Aim of STF is to demonstrate the performance of the ILC main
linac cryomodule (a cryogenic chamber containing the super-conducting accelerator part). Twocavities from Europe, two cavities from the U.S. and four cavities from Japan were assembled into
one cryomodule and the operational test was carried out at STF from 2010 to 2011 with an average
gradient of 26 MV/m being achieved. An optical camera was specially designed and developed toinvestigate the properties of the inner surface of the ILC cavity. By observing the irregularities on
the cavity inner surface with this camera, some difficulties that caused cavity performancedegradation were identified.
12

The aim of ATF is to generate a flat super-low emittance beam by radiation damping, anddevelop and demonstrate the beam diagnostic technology and the final focus system with the beam.
ATF has already achieved a 0.015 mm･mrad vertically normalized emittance, which surpasses the
ILC requirement. The current issues under study are to realize and control a 35 nm beam size andestablish beam diagnostic technology at the prototype ILC final focus system (ATF2).
A polarized electron source has been developed by SLAC and Nagoya University with a 90%
polarization already having been achieved. The issues here are generating a 1ms long pulse anddeveloping a driver laser system. Further related activities to the positron generation are the R&D of
a super-conducting helical undulator and a prototype test of a positron generating target all of which
are in progress. An alternative positron source using the electron beam has been proposed in Japan.
2.3 LHC Upgrade
At present, there are two experimental groups, ATLAS and CMS, which are studying theelectroweak energy scale physics at LHC, CERN. Their primary goal is to search for new
phenomena beyond the Standard Model. Sixteen institutes in Japan are participating in ATLAS andhave worked on construction of the beam focusing magnets in the interaction region, the solenoid
magnet used for the charged particle spectrometer, the silicon strip detector, the muon trigger
chambers and have been playing important roles in the various stages from installation to operation.
Also significant contributions are being made on the data processing side, as a Tier-2 centre of the
GRID computing.
One important goal of LHC is to explore new physics and new phenomena at the electroweakenergy scale by making the best use of the high collision energy. It is therefore important to extend
the exploration region to a higher energy by increasing the luminosity. An increase in the integrated
luminosity from 100 fb-1 to 1000 fb-1 would allow an improvement in sensitivity for a search for
new physics, for example, in the mass reach of the squarks from 2.5 TeV to 3 TeV, or in the massscale in the case of Extra Dimensions from 9 TeV to 12 TeV. Once new particles or phenomena
have been discovered, LHC will be the only machine which can provide an opportunity to study the
new findings, that is until ILC is built and starts up.
In the long term plans for LHC, approximately 300 fb-1 of data are expected to be collected at thecentre of mass energy of 14 TeV by 2022. The high luminosity project (HL-LHC) will then start up
to shorten the luminosity doubling time and also to compensate for the aging accelerator
components near to the interaction region due to radiation. The aim is to accumulate an integrated
luminosity of 3000 fb-1 by 2030. To achieve this goal, luminosity levelling, that is to keep the beam
for longer at a lower instantaneous luminosity (5×1034cm-2s-1), rather than running at the maximum
instantaneous luminosity with a much shorter beam life time, may be adopted to gain in integrated
luminosity. This scheme is likely to require crab cavities.
The key elements of the luminosity upgrade are the development of the strong focusing magnets,
the injector upgrade to increase the number of protons, and the introduction of the crab crossing.
The current focusing magnets near the interaction region were developed and built by thecollaboration of KEK and Fermilab. Those magnets included, as well as all the magnets around theinteraction region will be replaced. However, the conventionally used material does not meet the
specifications of the magnetic field strength (which is 13 to 15 Tesla), and new materials are being
developed in Japan, US, and Europe. In addition to the design of the optics which has already been
started, the task sharing in the international collaboration is also underway. In the new materials
development for the magnets, attention will be paid to the wide range of applications, such as the13

LHC energy upgrade. Only KEKB to date has succeeded the crab crossing in the world, andtherefore Japan’s large contributions in this area as well as in the development of thesuperconducting magnets are expected.
For the HL-LHC, the whole inner tracker of ATLAS will be replaced. There are two main issues
here, radiation hardness, and a finer granularity necessary to cope with the high occupancy due tothe higher luminosity. In order to be more rate tolerant, all the trackers will be composed of silicondetectors. The innermost layers will be of silicon pixels while the outer layers will be comprised ofsilicon strip detectors. Since there is a strong vendor of silicon sensors in Japan, a strong
commitment to the development of the silicon detectors is expected. In fact, Japanese groups havealready started to develop radiation hardened sensors. Apart from the inner tracker, also an upgradeof the readout electronics for the calorimeter and muon detector, the improvement of the muon
trigger, and the rebuilding of the forward shield are planned. Japanese groups are heavily involvedin the development of the inner tracker, the trigger improvement using the inner tracker, and themuon trigger and its readout electronics.
The developments in the above technology for HL-LHC could also be useful for the LHC energy
upgrade. There is an idea in place to increase the centre of mass energy of LHC to 33 TeV, called
the High Energy LHC (HE-LHC). In order to achieve such a high energy, the present magnets
composed of NbTi cables must be replaced by ones made of new superconducting materials.
Workshops to develop such materials have been held since 2011. In 2013, prototype HTS magnets
will be developed under the EuCARD2 programme run by EC-FP7. It is important to promote basic
R&D in Japan on new superconducting materials such as Nb3Al and their application in accelerator
magnets, also with a view to a wider field of application.
2.4 Other Projects
The Compact Linear Collider (CLIC) and a muon collider are under investigation for the energy
frontier physics surpassing the ILC energy region. The CLIC study will be continued amounting tomore than 20 years while it is expected that the muon collider will take 30 years for full realizationof the project. As a further long term future project, laser-plasma acceleration is also under study.
Currently, there is no completed accelerator system with this technology and basic proof-ofprinciple tests of self-injection and plasma “afterburner” are being considered. Recently, a new laser
technology has been making rapid progress with possible laser-plasma acceleration being realized ifsome breakthroughs are made in a multi-stage acceleration scheme.
CLIC
CLIC is an electron-positron linear collider for the particle physics research up to a multi-TeV
centre of mass energy exceeding that of ILC. The maximum centre of mass energy goal is 3 TeV
for the nominal value that is determined by a technology limit rather than a physics motivation.
CLIC is being studied within the framework of a world-wide collaboration consisting of CERN and
42 institutes in 21 countries. Although the CLIC project is conceived as a future electron-positron
collider post ILC, a more urgent need by particle physics research at the multi-TeV energy mightarise depending on the results of the LHC experiments.
Just as for ILC, the main components of CLIC are electron and positron sources, a damping ring,
accelerating structures, RF power sources, and an interaction region. CLIC, however, adopts a twobeam acceleration concept to use microwaves generated by decelerating a low energy, high current
electron beam, as an RF power source, instead of klystrons, to accelerate low current beams to highenergy. In the two-beam acceleration scheme, the driver beam of 101 A is accelerated up to 2.38
14

GeV by 1 GHz klystrons and a delay loop and a two-stage combiner ring compresses the duration
between the beam pulses in order to make an appropriate pulse structure for the main beam. The
compressed driver beam is decelerated to 240 MeV, conversely, the main beam of 1 A is accelerated
from 9 GeV to 1.5 TeV. The frequency of the accelerating structures is 12 GHz (X band).
Difficulties anticipated in the CLIC technology are the pulse compression technique with combiner
rings, the transfer of the RF power from the drive beam to the main beam, and the development ofaccelerating structures for the very high gradients of 80-100 MV/m.
Power consumption is about 240 MW for a centre of mass energy of 500 GeV (luminosity of
1.4×1034cm-2s-1) and 560 MW for 3 TeV (luminosity of 2×1034cm-2s-1) version. The two-beamacceleration scheme at 12 GHz frequency may not be advantageous in comparison with ILC and thepower consumption in the current design which is equal to or larger than that of ILC. The key issue
in the CLIC two-beam acceleration scheme is an efficient transfer of beam power to reduce thepower consumption while trying to avoid the technical difficulty of using X-band klystrons.
Muon Collider
The muon is a lepton similar in nature to the electron. Since the associated synchrotron radiation
can be reduced due to the heavier mass of muon, a compact circular accelerator for muons can berealized up to a multi-TeV centre of mass energy. Another advantage of such a muon collider
compared to electron-positron colliders is the possibility to observe an s-channel resonanceproduction of a Higgs. The difficulties of the muon collider are in the production of high intensity
muons and accelerating them within the muon lifetime of 2 µsec, while colliding them with similar
luminosity to ILC. The nominal centre of mass energy is 4 TeV (2 TeV + 2 TeV) in the current plan.
Muons are obtained from decays of pions that are produced by bombarding a 16 GeV proton beam
onto a production target. A new technique called ionization cooling proposed by Skrinsky,
Parkhomchuk, and Neuffer is utilized to make the hot muon gas into a cold beam with low
emittance for luminosity. Muons of ~100 MeV thus produced are quickly accelerated in multi-stage
accelerators to 2 TeV in order to increase their lifetime in the laboratory frame. The primary issue inthe realization of a muon collider is to establish practical technologies to produce and cool downhigh intensity muons sufficiently, although many other problems such as radiation shielding againsthigh energy muon decays also needs to be resolved.

15

3 Neutrino Oscillation
3.1 Neutrino Oscillation and Proton Decay
One goal of neutrino physics is to understand “the origin of neutrino mass and the mixing” andto find a hint of new physics at ultra-high energies, such as that predicted by Grand Unified
Theories, beyond the standard model of particle physics. A next-generation neutrino experiment
aims to determine the mixing matrix of neutrinos with high accuracy including a test of CP
symmetry by measuring neutrino oscillations precisely. At this moment in the study of neutrino
oscillations, an important issue is the determination of the size of the neutrino mixing angle θ13
since its size limits the possibility of neutrino CP-violation experiments. In addition, it is possible tostudy Grand Unified Theories by searching for proton decay using a large-scale detector forneutrino experiments. The next-generation neutrino detector will be required to have a sensitivity
to a proton lifetime as long as 1035 years, a requirement consistent with the predictions from manymodels of Grand Unified Theories.
3.2 Current Status
Flavour Mixing
Understanding of the properties of neutrinos has been dramatically advanced in the last 14 years
since Super-Kamiokande discovered neutrino oscillation in 1998. Today it is an established fact thatneutrinos have finite masses and mix. Past experiments have constrained the neutrino oscillation
parameters; |Δm232|≒2.35×10-3eV2, θ23≒45°, θ12≒33°, Δm122≒7.6×10-5eV2. The mixing angle θ13
has not had a major development after an upper limit was given by the reactor-neutrino experiment
Chooz in 1999. In 2011 the T2K experiment found an indication of non-zero θ13 at 2.5σ
significance with 0.03 < sin22θ13 < 0.28 (90% C.L. for δ=0), which was supported by the results
reported by the MINOS and Double Chooz experiments. It is expected that the measurement of θ13
will further be improved in two to three years by the neutrino experiments such as T2K and Double
Chooz.
Proton Decay
Super-Kamiokande, the largest neutrino detector in the world, has taken the lead in the search for
proton decay. As for the proton lifetime, lower limits on individual decay modes are as follows;
p→e+π0 : 1.3×1034 years, p→µ+π0 : 1.1×1034 years, and p→νK+ : 4.0×1033 years. A major decay
mode in a typical Grand Unified Theory is p→e+π0, while p→νK+ is typical of a supersymmetricGrand Unified Theory. In many theories, similar lifetimes ranging from 1034 through 1035 years are
predicted.
3.3 Future Planning
The possibility that θ13 may be determined within a few years by the ongoing neutrino
experiments such as T2K and Double Chooz have raised high expectations. If a large neutrino
mixing angle θ13 is established, the aim should be to realize a large-scale neutrino detector throughinternational cooperation, together with a reinforcement of the J-PARC accelerator, toward studies
on CP symmetry through neutrino oscillations. The J-PARC accelerator is expected to achieve its
design power of 750 kW in approximately five years, and a feasibility study to further increase
beam power will be continued. As for the detector, the experimental plan should be clearlyprioritized by studying the feasibility of the plan in detail, including budget and construction period,
16

after evaluation of the sensitivity reach of the next-generation long baseline neutrino oscillation
experiment and its physics potential. Also the detector should have sufficient sensitivity to proton
decays which would be direct evidence of Grand Unified Theories.
CP Violation Measurement
The most suitable channel for a CP violation search is νµ→νe appearance. This is due to the factthat it needs to be an appearance channel, since CP violation effects are not present in thedisappearance channel. In addition, the CP conserving term is small due to the small θ13 in theνµ→νe channel while the CP violation effect is relatively large. There are basically two experimental
methods: (1) measuring the asymmetry of νe appearance probabilities between neutrinos and antineutrinos, and extracting the CP violating terms which are proportional to sinδ; and 2) measuring
the energy spectrum of νe appearance precisely by using the fact that the energy dependence of the δterm is different from the θ13 leading term. In either method the sensitivity needs to be 10 to 100
times higher than that of the T2K experiment for νe appearance, since the CP violation effectappears as a second order effect of small νe appearance probability. In order to have a reasonably
high discovery potential for a wide range of δ, a MW-class high power accelerator and an extremely
large detector with high sensitivity are needed. In Japan the following two plans are under study;(a) a megaton-class water Cherenkov detector, Hyper-Kamiokande, placed in Kamioka, 295 km
from J-PARC to employ mainly method (1); (b) a 100 kilo-ton liquid argon TPC placed in
Okinoshima, 658 km from J-PARC to employ mainly method (2).
J-PARC Accelerator and Neutrino Beam
J-PARC is a high intensity proton accelerator facility in Tokai, in the Ibaraki Prefecture,
constructed jointly by JAEA and KEK. It consists of a set of accelerators: LINAC, 3GeV Rapid
Cycle Synchrotron (RCS), and Main Ring (MR). For a long baseline neutrino oscillation
experiment, a neutrino beam is produced by using protons accelerated up to 30 GeV in MR, with adesign power of 750 kW. In 2009, the J-PARC construction was completed including the neutrino
beam facilities enabling the start of beam operation. A stable beam was provided for the T2K
experiment from January 2010, and a beam power of 145 kW was achieved in March 2011.
Although the facilities were damaged by the Great East Japan Earthquake, the operation was
resumed again in December 2011.
It is the main aim that the design beam power of 750 kW should be achieved in approximately
five years by realizing a high current and high repetition rate as described below. The higher currentof MR (increasing protons per bunch) is to be realized by upgrading the ion source and RFQ of
LINAC, by upgrading the LINAC energy to 400 MeV, by decreasing the space-charge effects andby enhancing the power of RCS. Furthermore, the RF upgrade of MR and the upgrade of magnet
power supplies will lead to the realization of a high repetition rate of MR. The present repetition
period of about 3 seconds will be shortened to 1 second. R&D and the production of components
are currently in progress.
The study to realize a beam power in excess of 1MW is also underway. Various ideas such as thepossibility of building a new booster ring to raise the injection energy to MR are underconsideration. In order to realize the power above 1MW, it is necessary to advance necessary R&D
by incorporating the experiences of high intensity operation and optimizing methods and designs.
Hyper-Kamiokande
Hyper-Kamiokande is a supersized next-generation water Cherenkov detector, which utilizes key
technologies established in Super-Kamiokande and has a total mass expanded to 1 Mton. Hyper17

Kamiokande has a wide-range of physics goals: a measurement of neutrino CP violation by using
neutrino beams from J-PARC, search for proton decay, determination of the neutrino mass hierarchy
and a measurement of neutrino CP violation by atmospheric neutrino observation, and theobservation of cosmic origin neutrinos.
Hyper-Kamiokande is comprised of two column-shaped detectors each 48 m wide, 54 m high,and 250 m long, located at 650 m underground of Nijuugo-yama mountain (1750 m waterequivalent), 8 km south of Super-Kamiokande. The distance from J-PARC is also 295 km just as
for Super-Kamiokande. 99,000 20-inch photomultiplier tubes are used with a total photon-sensitive
area coverage of 20% of the inner water tank. The expected detector performance is as follows;
misidentification probability for 500 MeV electrons and muons less than 1%; the momentum
resolutions of 5.6% for electrons and 3.6% for muons; the detection efficiency for electronneutrinos from the J-PARC neutrino beam 64%; rejection power of more than 95% for π0 producedby the neutrino beam.
Hyper-Kamiokande has a 25 times larger fiducial volume than Super-Kamiokande. It measuresneutrino oscillations with high statistics and accuracy by using the J-PARC neutrino beam with anextremely high sensitivity to CP violation in the neutrino sector. Assuming the J-PARC neutrino
beam data of 8 MW×year 2 (corresponding to approximately ten years at 750 kW of beam power),
the CP violation parameter δ can be determined to an accuracy of better than 18 degrees. CP
violation could be observed at a 3σ significance for 74% of the parameter region of δ if the neutrinomass hierarchy is known and sin22θ13 > 0.03. If the neutrino mass hierarchy is not known, the CP
sensitivity is reduced to 46% of the parameter region of δ for sin22θ13 ~ 0.1. However, in this casethe neutrino mass hierarchy can be determined at a 3σ significance for 10 years of atmospheric
neutrino observation for sin2θ23 > 0.4.
Hyper-Kamiokande has also a high sensitivity to proton decays: longer than 1×1035 years for p→ eπ0; longer than 2×1034 years for p → νΚ+. To date, Hyper-Kamiokande is the only detector thatexhibits a design with a sensitivity exceeding 1035 years for proton decays. Hyper-Kamiokande,
thanks to its huge fiducial volume, is also able to make other observations and measurements suchas precise solar neutrino observations, high-sensitive supernova neutrino observations, dark mattersearches and solar flare neutrino searches.
Although the key technologies for realizing Hyper-Kamiokande have been established at SuperKamiokande, a more realistic estimation of costs remains necessary. It is also necessary to develop
low-cost, large-size photo sensors, carry out long-term stability tests of the prototype, develop
technology for excavating a large volume at a low cost, and design the large-size tank andmechanical structure of the detector. The total number of readout channels of the photo-detectors
exceeds 100,000, and it is essential to develop front-end electronics that can process electric signals
in water. In parallel with these developments, systematic errors which limit the experimental
sensitivity need to be studied by T2K, including one option of using an anti-neutrino beam.
Liquid Argon TPC
In this plan, CP violation is sought by using a 100 kton liquid argon detector located on
Okinoshima island at an off-axis angle of 0.78 degree, 658 km from J-PARC.
The greatest advantage of the liquid argon detector is the capability it has to detect tracks fromall charged particles at an extremely low threshold. This enables the reconstruction of the neutrinoenergy precisely for a wider range of the neutrino spectrum. It also helps to suppress the2 Here we assume 1 year = 107 seconds.

18

background events in the measurement of electron neutrino appearance. In particular, the neutral
current π0 events, one of the main backgrounds for a water Cherenkov detector, are expected to be
removed efficiently by detecting the activity in the vicinity of the vertex and the different behaviourof the dE/dX at the front of the electromagnetic shower originating from electrons and photons.
CP violation is detected by accurately measuring the energy spectrum of the oscillation frommuon-neutrinos to electron-neutrinos. The first oscillation peak is located at 1.2 to 1.4 GeV and thesecond at 0.4 GeV. While the effect of CP violation and the matter effect compete at the first peakenergy, the effect of CP violation dominates at the second peak. Thus the sensitivity to CP violation
can be increased by measuring the first and second peaks simultaneously using a wide band energy
spectrum neutrino beam. With 8 MW×year (ten years at 750 kW) of data, CP violation can beobserved at more than a 3σ significance if δ is larger than 30 degrees.
In proton decay search, high sensitivity is expected in p→νK+ mode since the charged kaon canbe directly detected. It is therefore possible to obtain a lower limit of 6×1034 years for p→νK+ by
operating the 100 kton detector for 10 years.
Necessary conditions for realization of a 100 kton liquid argon detector are as follows: 1)“demonstration of physics performances” by confirming performances for charged particle
identification, energy reconstruction, and then reconstruction of neutrino interactions; 2)“demonstration of technologies” by establishing technologies for a large-size liquid argon tank, highvoltage (~MV), and a purification system to realize a long drift length. Tests with a small liquidargon detector have been carried out to demonstrate the physics performance by using a beam ofcharged particles. Beam tests of a 400 kg liquid argon TPC detector were already performed at JPARC using charged K, π, proton, and positron beams, and the expected performances are being
verified. Key technologies necessary for realizing the detector include a large-size cryogenic
container, ultra-pure liquid argon, a high-voltage generator and signal readouts. In order to establish
these technologies, it is necessary to accumulate techniques by starting with a small detector andproducing larger detectors step by step. While a 400-kg liquid argon TPC detector has been realizedin Japan, the world’s largest detector is currently 600 tons. It is planned that prototypes be produced
ranging from 100 tons to 1,000 tons and to use them to measure neutrino interaction cross sectionsin the liquid argon to study the physics potential. The physics performance and technologies forconstructing the detector should be established in the final prototype; thereafter a 100 kton detector
could be constructed.
Comparison of the Two Plans
The advantage of the experiment using Hyper-Kamiokande is that the beam flux is high at thecloser distance and that the CP asymmetry can be measured with high statistics. In addition, in theenergy range of about 1 GeV where neutrino oscillations occur and matter effects which can cause afake CP violation signature are small, a water Cherenkov detector displays a greater ability in
identifying particles with a high detection efficiency. Meanwhile, the disadvantage is that an antineutrino beam with a smaller cross-section is required and that it is necessary to keep systematic
errors below 5% in order to measure the CP asymmetry effect to O(10%). The advantage of theexperiment using a liquid argon TPC is that background rejection is high for π0 events and that highdetection efficiency and excellent particle identification are achieved over a wide energy range, sothat the CP parameter δ can be determined by an energy spectrum measurement. Meanwhile, thedisadvantage is that energy of the second oscillation peak is low with a small interaction crosssection and that the detector will be smaller than Hyper-Kamiokande therefore the statistics will bedecreased. Furthermore, the technologies for constructing a 100,000-ton liquid argon TPC need to19

be developed.
Other Domestic and Overseas Projects
In order to discover neutrino CP violation and determine the neutrino mass hierarchy throughneutrino oscillations, a neutrino oscillation experiment using an accelerator neutrino beam is ofprime importance. Therefore, various projects are also being studied in Europe and America. In the
United States, the NOvA experiment, which has a similar sensitivity to the T2K experiment, isunder construction. Further, the Long Baseline Neutrino Experiment (LBNE) project is underconsideration. In LBNE, a neutrino beam is generated by a beam with a power in excess of 700
kW at Fermilab and the far detector is located at the Sanford underground laboratory in theHomestake Mine 1,300 km away. The 33 kton liquid argon TPC is the first choice for the neutrino
detector, and it has excellent background rejection power over a wide energy range, excellent
particle identification and high detection efficiency. A water Cherenkov detector, with a fiducial
mass of 200 ktons, is the second choice, since this technology is well established even though thedetection efficiency is low.
In Europe, a scenario using a conventional neutrino beam from π decays produced at CERN andobserved at a distant underground laboratory is currently under consideration as the LAGUNA
project. In the LAGUNA project, the following is to be considered: 1) Seven undergroundlaboratories in Europe (the closest detector location is 130 km away from CERN, and the farthest is
2,300 km away); 2) Three detector options (water Cherenkov detector, liquid argon, and liquid
scintillator). Recently a middle-sized liquid argon TPC has been proposed at 2,300 km distance andan experiment specialized in measuring the matter effect is under consideration. As a concept forthe distant future, a β-beam and a neutrino factory are also being considered as an entirely new
method of generating neutrino beams. In the β-beam, unstable nuclei are accelerated and circulated
in a storage ring, producing the neutrino beam by beta decays of the nucleus. The Q-value of βdecay is so small (MeV level) that a low-emittance neutrino beam can be produced. A neutrino
factory is another idea that neutrinos from muon decays can be utilized as a beam, this method can
produce a neutrino beam with a well-known energy spectrum. Currently, it is not clear whether bothβ beam and neutrino factory can be realized or not. An experiment for testing these principles isunder way.
In parallel with the accelerator neutrino experiments, the measurements of θ13 by reactor antineutrino experiments provide important information for the CP measurement of neutrinos. By
gaining precise information on the size of θ13 from reactor experiments the effect of CP violation
can be cleanly extracted in the accelerator experiments. Especially, if θ13 is large (~10°), it isexpected that its size can be accurately measured in reactor experiments. The Double Chooz
experiment, RENO experiment, and DayaBay experiment are underway as the main reactor antineutrino experiments. Furthermore, the KASKA experiment is considered as a future experiment inJapan. Clearly it is important to consider a global neutrino programme of both accelerator
experiments together with upgrades of the reactor anti-neutrino experiments.

20

4 Flavour Physics
While aiming to completely understand the physics of the electroweak energy scale as the next
large milestone of elementary particle physics, the indirect search in flavour physics plays acomplementary role to the direct searches for new physics at LHC. The primary goal of flavour
physics is to identify tiny discrepancies in the measured observables from the standard model
predictions due to quantum mechanical contributions from off-shell high mass particles; therefore,
observables with small theoretical errors must be measured precisely with large statistics and wellcontrolled systematic uncertainties. In order to obtain high statistics, either collision luminosity or
beam intensity must be improved to an extreme; hence these are the experiments that explore theintensity frontier. Although the typical size of these projects is smaller, as the beam energy is lower
than that of energy frontier experiments for direct searches, there are nevertheless also technicalchallenges associated with high intensity. Japan has been one of the leading countries in flavour
physics experiments in recent years, as represented in the success of KEK B-factory. It is importantthat this role is preserved in the future.
There are at present some hints of new physics – namely the phenomena still consistent with thestandard model within theoretical or experimental errors, which could however be concluded to be
the new physics contribution in future developments – in terms of experimental results ranging fromthe muon g−2, B-factories and LHCb. The MEG experiment also recently drew significant interest
in its search for µ→eγ, however, no statistically significant signal has been found to date. Also, inthe case of a supersymmetry search at LHC no signatures have been found as yet. The situation will
become clearer in the coming few years. Should the next energy scale be higher than expected, thenthe indirect search will be even more important. On the other hand, once new physics phenomena
start to be observed by experiments, flavour physics will be required to identify the model of new
physics by finding which observables in the new physics effect are enhanced or suppressed, andalso determine the couplings of new physics. Therefore, in either case, it is advisable that the basic
approach be to keep a diversity of projects and to carry out various experiments in the future. In thefollowing subsections, individual targets of experiments (B meson, D meson, K meson, neutron, tau
lepton and muon) are described.
4.1 Super B-factories
SuperKEKB/Belle II project, which succeeds KEKB/Belle, is one of the largest class ofexperiments of flavour physics, and covers a wide variety of targets to measure such as bottom,
charm, and tau. As the largest player of the new physics search network at the intensity frontier, thismust be constructed and made operational without delay.
There are several independent measurements which draw attention, all of which could show
sensitivity to new physics within a few to ten years of data: understanding the difference in direct
CP violation in B→Kπ for charged and neutral modes, the search for charged Higgs by measuring
the branching fractions of B→τν, B→D(*)τν and b→sγ, the search for new complex phases bymeasurement of time-dependent CP asymmetry in b→sqq, the search for right handed currents bymeasuring time-dependent CP asymmetry in B→KSπ0γ, the search for lepton flavour violation in
tau decays such as τ→µγ and τ→µµµ, and the understanding of the large mixing in the D0 meson
system. Detection and measurement of neutral particles (KS, π0, γ, ν) are especially important for
those measurements, where the clean environment of a lepton collider is the key feature. The
statistical uncertainty dominates the precision of most of these measurements, and therefore theexpected large statistics is fairly promising. On the other hand, the precision of parameters such as
21

the meson form factors owe much to lattice QCD calculation, for which contribution from thetheory side is required. It is also important to understand the direct CP asymmetry in the D0 meson
system as reported by LHCb. Therefore, development of a theoretical calculation method for the D0
meson system is highly desirable.
In other countries, INFN Italy has taken the lead in advancing the SuperB project. Both
SuperKEKB and SuperB target high instantaneous luminosity (8×1035cm-2s-1 and >1036cm-2s-1,
respectively) by maximally squeezing the beam size. SuperB will realize this by digging a brandnew tunnel and SuperKEKB by reusing existing facilities. Just as in the era of KEKB and PEP-II,sound development in this field is foreseen with two projects competing for the accomplishments.
SuperKEKB will reach a milestone, namely to accumulate 50 ab−1 of integrated luminosity byaround 2021, provided everything proceeds well. By that time, observation of various new physics
phenomena or limitations on new physics are expected, however, in the case that the coupling of
new physics is too small, depending on how the research develops, there may be a case for a further
luminosity increase by more than a factor 10. In such an event, the feasibility of a further luminosity
upgrade must be considered based on the actual experience at SuperKEKB and INFN SuperB;
presently however there is no concrete idea.
There may also be the case that the centre-of-mass energy and beam energy asymmetry arealtered to being more optimal for the study of tau lepton and charmed meson decays. In fact, themachine operation at the tau/charm pair creation threshold with the target luminosity of 1035cm−2s−1
is already included in the programme of INFN SuperB and the Super charm-tau factory at BINP. As
an example, electron-positron collision with >1036cm−2s−1 at √s~4.2GeV (symmetric energy)
enables a search for τ→µγ with much higher sensitivity by suppressing initial state radiation
background.
4.2 Muon Physics
Discovery of the neutrino oscillation has stimulated interest in the search for lepton flavour
violation also in the charged lepton sector. In the standard model with the neutrino oscillation taken
into account, a charged lepton flavour violation process is highly suppressed to the level of 10-40 to
10-50. On the other hand, if new physics exists, charged lepton flavour violation processes can beenhanced to a measurable level. Thus discovery of charged lepton flavour violation processes would
be very clear evidence of new physics and experimental search for such processes should bestrongly promoted.
Lepton flavour violation in tau decays probes flavour mixing between the 3rd and 2nd or 1st
generations, whereas lepton flavour violation in muon decays probes the mixing between the 2nd
and the 1st generations. The MEG experiment at PSI has provided the upper limit of µ → e γ at 2.4
×10-12, and will continue to search with a sensitivity at O(10-13). Furthermore, there is a plan to
upgrade the MEG experiment to further improve the sensitivity. The atomic µ→e conversion
process is more comprehensive, and is also sensitive to non-photonic processes. In typical SUSY
models, the branching fraction for µ→e conversion is about two orders of magnitude less than thatof the µ → e γ decay. Therefore, both the COMET experiment at J-PARC and the mu2e experiment
at Fermilab, aim at a sensitivity of O(10-16) and have good potential for either discovering or
severely constraining new physics. In order to resolve technically challenging issues, it is desirable
to strengthen the organization of R&D through international cooperation and competition. As for
the COMET experiment at J-PARC, the design of a new beam line and muon production target is inprogress. If realized, this could become the flagship experiment of particle physics at J-PARC.
22

As for the muon anomalous magnetic moment, the BNL-E821 experiment measured to a 0.7
ppm precision, and claims a 3.4 σ deviation from the standard model. It is, therefore, important toverify this in new experiments with improved precision. It is also necessary to improve the accuracy
for the estimation of the hadronic contribution to the vacuum polarization. At Fermilab, a newexperiment using the same muon storage ring shipped from BNL is planned, aiming at a 0.1 ppm
precision. At J-PARC, an experiment, based on a new technology using an ultra-cold muon beam,
has been proposed, targeting a similar precision. It is therefore important to carry out an
independent experiment with different systematics from the existing measurement. Further, theR&D to establish the technical feasibility should be speedily advanced.
4.3 Kaon Experiments
Since the first observation of CP violation was reported in K meson decays, Kaon experiments
have made significant contributions to flavour physics for a long time. The next important target isthe search for new physics through the measurements of branching fractions of KL→π0νν and K+→π+νν. Abroad, NA62 is being prepared at CERN, which intends to observe O(100) events of K+→π+νν and determine the branching fraction; a similar experiment is also proposed in the US.
Simultaneously in Japan, the KOTO experiment that will measure the KL→π0νν is underconstruction, this plans to make maximum use of the high power (100kW) beam intensity of JPARC. Coupled with the charged mode, this measurement is expected to play a role in the search
for new physics. It begins by updating the current upper limit (2.6×10−8) obtained by the previous
experiment at the KEK-PS, then proceeds by exceeding the Grossman-Nir limit (1.5×10−9) andenters the sensitivity region where the new physics search is possible. In the late 2010s, KOTO willreach the branching fraction predicted by the standard model (2.4×10−11). In order to go beyond the
KOTO goal and search for a 10% level of deviation of new physics effects from the standard model,
a new beam line must be built by extending the experimental hall, and the detector must also be
significantly upgraded. The extension of the experimental hall should be studied in co-operation
with the nuclear physics community.
4.4 Neutrons
For the measurement of the neutron electric dipole moment (EDM) using ultra cold neutrons(UCN), the sensitivity of a single experiment has started to reach the region of new physics
predictions (current upper limit: 2.9×10−26 ecm, supersymmetry: 10−27-10−28 ecm). Hence,
expectations have risen for future developments. Most of the experiments being currently plannedor constructed utilize accelerator-based nuclear spallation sources, and aim for sensitivities of 10−27
to 10−28 ecm. At PSI, the operation starts this year and is aiming for 5×10−27 ecm. At TRIUMF, anexperiment which utilizes an extremely low temperature UCN source developed by KEK/RCNP isunder construction. An experiment at J-PARC proposes to extract a few % of the beam from the
LINAC to then be transferred to a special small extraction target. Use of an intense pulsed beam not
only provides high statistics and low systematic uncertainty but also enables one to reach 10−27 to10−28 ecm. Creating as many neutrons as possible in a short time, guiding them to the storage vessel
via a newly designed magnetic convergence unit, and other such ideas show there are many
innovations required and existing in key technologies. In order to gain international
competitiveness, it is important that practical R&D should be promptly started and advanced fromthe proof-of-principle stage. Construction of facilities and beam allocation should be coordinated ina close cooperation of JAEA and KEK.

23

5 Non-Accelerator Particle Physics Experiments
5.1 Underground Astroparticle Physics Experiments
Introduction
Various searches for rare phenomena are pursued underground utilizing the low radioactive
environment due to less cosmic ray flux and stable observational conditions. Especially, direct
searches for dark matter and searches for neutrinoless double beta decays (0νββ) are vigorously
pursued in international competition. In Japan, most underground projects are located at the
Kamioka site initially developed for neutrino observations and now hosting a growing undergroundastroparticle physics community. In spite of the disadvantage of being shallower than the sites
abroad, nevertheless, cooperation and effective sharing of existing research environments andresources enable the proposal of projects that achieve world class or leading sensitivity goals bothcost-effectively and quickly. Continuous support is indispensable to maintaining the world’s key
research centre for underground astroparticle physics.
Currently, the sizes of individual projects are not huge and a variety of key methods coexist. It is
important to keep the diversity for the moment, but at the same time it is also important to sharescientific directions in the field so that a large-scale cooperative project can be quickly andefficiently launched upon a new discovery. Researchers of underground experiments either belong
to the high energy, cosmic ray or nuclear physics communities and in order to cover large important
areas of research, these communities need to cooperate to achieve the appropriate evaluation,
promotion and support for projects.
Dark Matter Search
Recent developments in cosmological observations have definitely established the existence ofdark matter beyond the known matter particles. Hypothetically argued, mass and interaction crosssections of the dark matter particle range over tens of orders of magnitude among the various
hypotheses. Among possible candidates for dark matter particles are, weakly interacting massive
particles (WIMPs) predicted by supersymmetric models and which have attracted considerable
attention and been the goal of vigorous international research, aiming at a direct observation of
WIMPs.
While the DAMA/LIBRA experiments using NaI crystal reported an 8.9 sigma significant
seasonal variation in their signal rate, in correlation with the Earth’s orbital eccentricity, as evidenceof dark matter, other observations using different experimental techniques are providing
inconsistent results, so making the matter still very controversial. The experiments refuting the
DAMA/LIBRA results have much better sensitivities for WIMPs with masses of around 50GeV.
However, in these measurements of very low energy nuclear recoil, ionization in the media andquenching effects of scintillation light may still cause ambiguity. Moreover, several reports ofpossible indications of low mass WIMPs around 10GeV have further complicated the situation.
For discovery of SUSY WIMPs, it is important to improve the sensitivity to the cross section ataround 50GeV from the current 10-44cm2 level to 10-46cm2 level. To achieve this sensitivity,
realization of a large detector with about 1 ton effective mass is necessary. Since discovery is theprimary target, it is advisable to advance a scalable project such as XMASS1.5. If a signal isdetected, the next step would be to gain further confirmation and to explore the physics behind it. In
addition to high statistics measurements of the recoil spectrum and seasonal variation measured
with a large-scale detector such as XMASS2 with a 10 ton effective mass, measurements with24

different nuclei and different techniques, measurements of the direction of dark matter motion with
TPCs (NEWAGE) or emulsion techniques, and measurements of spin dependence and inelastic
scatterings will become important. These diverse investigations should be advanced in parallel. On
the other hand, verification of the controversial 8.9 sigma signal of DAMA/LIBRA by using thesame detector technology (NaI) is necessary. Under the existing circumstances where no signal ofsupersymmetry has been observed by LHC, searches over a wider parameter region of theories andfor other types of dark matter particles, such as axions should also be pursued without theoreticalprejudice.
Search for 0νββ
Searches for 0νββ decay are currently the only realistic way to investigate the Majorana nature ofneutrinos. Discovery of 0νββ would be clear evidence of Majorana neutrinos and lepton number
violation, irrespective of what kind of physics causes it. Since the decay rate is proportional to thesquare of the effective Majorana mass, absolute neutrino masses may be determined. While anaccuracy of approximately 200 meV is aimed for by a project to measure the absolute neutrino massfrom a beta decay spectra, cosmological measurements are expected to reach a sensitivity of 50
meV or ultimately 20 meV. The effective Majorana neutrino mass has been evaluated by the studiesof neutrino oscillations to be more than 60 meV for the case of degenerate neutrino masses, 20 to 60
meV for an inverted mass hierarchy, and less than 20 meV for the normal mass hierarchy case.
These mass regions set the milestones for future searches. A 6 sigma signal of 0νββ decay at theeffective mass of about 320 meV has been claimed by a high resolution measurement using 76Ge
(KKDC claim) and awaits further verification, since multiple background candidates are alreadyknown.
Current ongoing projects initially target a sensitivity of approximately 60meV to verify the
KKDC claim and the degenerated mass region, and also consider future extendability to 10~20
meV to explore the inverted mass hierarchy. Thus 0νββ searches are expected to lead the way in the
pursuit of absolute neutrino masses measurements in the future. If the absolute neutrino mass isdetermined by beta decay spectra measurements or by cosmological observations, or if theneutrino mass hierarchy is determined by the neutrino oscillation measurements, comparisons withmeasurements of 0νββ decay could enable the determination of the Majorana CP phases, to refutethe Majorana nature, and to possibly identify physics models behind the neutrino masses.
In order to cover the inverted mass hierarchy, about 1 ton of double beta decay nuclei would benecessary, and realization of such a huge detector with low radioactive background is the main
issue. This issue is shared by neutrino detectors and thus applying an existing neutrino detector to0νββ searches would be effective, just as KamLAND-Zen is based on the neutrino detector
KamLAND with a 136Xe source, also from the point of view of extendability. These detectors havethe merit of having more general purposes other than only 0νββ searches even if no signal of 0νββ
is found. If however, 0νββ decay is discovered, verification using different nuclei and different
methods would be necessary to resolve the uncertainties of nuclear matrix elements and the
difficulty of eliminating unidentified backgrounds, and also to identify the new physics behind 0νββdecay. Diverse R&D on particle identification techniques for rejection of unexpected backgrounds,
or detectors capable of measuring angular distributions and general devices applicable to various
nuclei are indispensable.
In Japan, several groups are advancing independent projects employing technologies of theirown originality and/or expertise. The CANDLES experiment using 48Ca has a good tolerance tobackground thanks to its highest Q-value but an isotopic enrichment is an important remaining issue25

in overcoming its low natural abundance of 0.2%. Also developments of drift chambers andemulsions which are capable of measuring angular distributions and multiple nuclei are underway
but need to be speeded up to become internationally competitive.
Although it is difficult to foresee science more than 5 years into the future, it is apparent that
future projects need to be large-scale and advance planning is important. If a new large-scale
neutrino detector is realized, Super-Kamiokande, for example, can be effectively converted into a
detector for dark matter or for 0νββ. There is a proposal for Super-KamLAND-Zen which combines
Super-Kamiokande and liquid scintillator to reach a 0νββ sensitivity of the normal mass hierarchy.
5.2 Cosmological Observations
Introduction
Recently, cosmological observations have become ever more important to elementary particle
physics. It is expected that experimental projects in cosmology will become more actively promoted
while keeping in good balance with accelerator-based projects as well as cooperating with closely
related research fields. In particular, the quests for understanding cosmic inflation and dark energy
are two important topics that require cosmological observations as their main tools; observations of
CMB polarization for testing inflation and studies of dark energy with the Subaru telescope are in
progress. Both of these observations are also very sensitive to the sum of neutrino masses. It is
expected that each method alone will eventually reach a sensitivity below 100 meV. This would be asignificant milestone as a sensitivity at this level corresponds to the lower limit for the inverted
mass hierarchy.
Verification of Cosmic Inflation with Cosmic Microwave Background (CMB)
Discovery of the B-mode polarization of the Cosmic Microwave Background (CMB) would bedirect evidence for cosmic inflation. It would also provide information about the energy scale ofcosmic inflation. The search for the B-mode polarization caused by inflationary gravitational waves
is also important as it provides a unique window on super high energy physics that cannot bedirectly accessed with accelerator based research.
The Japanese CMB group plays a key role in the international collaborations QUIET and
POLAREAR. QUIET has already published its initial result one that is one of the most precise
measurements of the CMB polarization to date. POLARBEAR was deployed in the Chilean
Atacama desert and started observations in 2012. An advantage of POLARBEAR is its large
primary mirror and ability to observe a large fraction of the sky. Projects that compete with
POLARBEAR include BICEP2/KECK, which are deployed at the South Pole. The experimental
sensitivities of these projects will exceed the sensitivity of the Planck satellite. One key discovery is
expected in 5 years if the tensor-to-scalar ratio is around 0.01 or larger. POLARBEAR plans to
deploy more telescopes in the future and measurements with these multiple telescopes will becomplementary to the observations of the satellite described below.
There are several studies on future satellite observations which aim to achieve even higher
sensitivities. The mission of such satellite projects will be to search for the tensor-to-scalar ratio
down to around 0.001 by observing the whole sky without atmospheric fluctuations. This would
allow us to test representative inflationary models in more detail. Even if a discovery is made by
POLARBEAR or any other competing project before such a satellite is launched, the high precision
B-mode measurements with a satellite would be important in narrowing down cosmologicalmodels. In Japan a feasibility study for the satellite named LiteBIRD, which is planned for launch26around 2020, is in progress. Major future satellite projects in Europe and the US propose thelaunching of relatively large satellites which may take a long time. The LiteBIRD satellite, incontrast, is small but sufficiently sensitive and able to focus on the tensor-to-scalar ratio
measurement and hence earlier observations and discoveries might be possible. Collaborative
studies of an international working group formed at JAXA have been in progress with participants
including high energy physicists, astronomers, superconducting device engineers, and cosmologists.
We expect that this activity will develop creating a good balance between independence andinternational cooperation.
Investigation of Dark Energy
A surprising discovery was made at the end of 20th century namely that of an accelerating
expansion of the universe as indicated by supernova data. The Physical model behind theaccelerating expansion is not yet known, and the unknown source that is responsible for theacceleration is called dark energy. In order to understand the essence of dark energy, it is importantat this stage to improve the precision of observations to see if the equation of state evolves as afunction of the cosmological scale. To this end, we should improve our understanding of the cosmic
composition (what existed in the universe, as well as when, where, and how). Type-Ia supernovae,
galaxy distributions, weak lensing and baryon acoustic oscillations are to be studied in future darkenergy observation projects.
SuMIRe is the next-generation dark energy project in Japan, which is an upgrade of the Subaru
telescope for imaging and spectroscopy. The Hyper Suprime Cam (HSC), which has been
constructed for weak lensing surveys with imaging, is scheduled to be deployed in 2012. With 900
million CCD pixels in the focal plane, the HSC will perform large-area surveys to detect billions ofgalaxies, investigate 2D distributions of dark matter from weak lensing analyses and obtain
improved knowledge about the history of the cosmic expansion and dark energy. Another
instrument is the Prime Focus Spectrograph (PFS), which is a new spectrometer to be installedaround 2016. The PFS will cover 2000 deg2 and measure redshifts of more than a million galaxies.
We expect that the spatial information from the HSC and the redshift (i.e. time) information fromthe PFS will show large synergies. SuMIRe will also allow the testing of cosmic inflation frommeasurements of non-Gaussianity, test general relativity on a long distance scale, and determine the
3D distribution of dark matter.
The SuMIRe project will be more sensitive than any other ground-based proposal and thus bequite competitive. Its goal is to reveal new and decisive knowledge on the nature of dark energy
before the observation with a new satellite (such as Euclid) starts around 2020.

27

6 Human Resources and Development of Technology
In high energy physics experiments physicists aim to achieve the world’s best results bycombining various cutting-edge technologies. The high energy physics experiments areconsequently full of forefront technologies and are thus a fascinating research field for young
researchers especially from the viewpoint of technology. Continuous development of technology
and the training of young researchers who support it are essential for this field of research tocontinue developing. Several problems concerning human resources and technologicaldevelopments have arisen recently.
• Length of cycles of experiments: high energy physics experiments become larger and take alonger time. It is difficult for even a competent student or young researcher to experience
the whole process of the experiment from project design, R&D and construction of
detectors, commissioning and operation, to data collection and physics analysis. More andmore young researchers miss opportunities to work on technological developments and it
could prevent smooth inheritance of technology.
• Specialization and subdivision of technology: there are many driving force technologies inhigh energy physics, such as accelerator technology, detector technology, electronics,
superconducting technology, mechanical engineering, etc. These cutting-edge technologies
have become more and more specialized and subdivided in recent years, and it is difficultfor individuals to obtain a broad experience of the various technologies used in the presenthigh energy physics experiments. This also causes difficulties in exchange of humanresources among subdivided fields of expertise.
• Lack of resources: because of the decline of the economy and the pressure for short term
outcomes, the budget for basic research is suffering from a significant reduction. This leads
to the closure of electronics workshops at universities, a decrease of technical support staff
at universities and laboratories, etc., resulting in the deterioration of the research
environment for developing cutting-edge technologies and causes difficulty in technologicalinheritance also due to the mass retirement of the baby-boom generation.
Active exchanges of human resources at various levels are important in order to mitigate theabove problems. Further efforts to increase the interchanges of personnel between projects andinstitutes will be necessary. Providing young researchers with opportunities to work on small/medium size experiments at the beginning of their careers as researchers, and employment of young
researchers inclined toward challenging cutting-edge technologies may be effective here. Also
necessary measures should be seriously considered and undertaken to help to continuously develop
forefront technologies and train young researchers who will support the technologies in the future.
Future large-scale projects cannot be realized without the technological development and theexistence of sufficient human resources.

28