The Final Report of
the Subcommittee on Future Projects ofHigh Energy Physics in Japan

19 May 1997

Subcommittee members:
K. Hagiwara (KEK), K. Inoue (Kyushu Univ.), K. Kawagoe (Kobe Univ.),
S. Kim (Univ. of Tsukuba), S. Komamiya (Univ. of Tokyo, Subcommittee Chair),Y. Kuno (KEK), H. Kurashige (Kyoto Univ.), T. Matsui (KEK),
A. Suzuki (Tohoku Univ.), S. Suzuki (Nagoya Univ.),
N. Toge (KEK), K. Tokushuku (KEK), T. Yanagida (Univ. of Tokyo),
T. Yamanaka (Osaka Univ.), M. Yamauchi (KEK), Y. Yamazaki (KEK),
M. Yoshioka (KEK, Subcommittee Secretary)Preface
Development of High Energy Physics in Japan has reached a new stage following the construction of TRISTAN. Through landing at once at the energy frontier, our accelerator technology
has been advanced drastically and established a quality abreast with the leading technology of
the world. We believe that the era of pilgrimage for foreign frontier research bases is over, and
it is globally recognized that scientists in Japan have gained ability sucient to carry out topquality researches, even domestically. Although TRISTAN was not blessed with the discoveryof new particles, their testing of the gluon self-coupling, their contribution to the understandingof the photon structure function, and their rst verication of the short-range increase of theelectro-magnetic interaction, are amongst the many results respected internationally.
Here, by High Energy Physics we mean the experimental study of elementary particle physics
by means of high energy accelerators. From the post-war era of recovery, until very recently, we
cannot deny that our research in fundamental science, which includes the eld of high energy
physics, has relied to a considerable extent on the research done in the West. However, we have
now technology, industrial basis and economic power sucient to contribute internationallyeven in the eld of fundamental science. In order to achieve an international contribution basedon a long-term perspective, it is essential not only to fortify the collaborative links overseas,
but to develop world-class research facilities in Japan, to explore the frontier technology, andto substantiate the new creations in the culture of mankind.
Currently in high energy physics we are witnessing the completion of a paradigm so-called
the `Standard Model'. However, the fundamental questions such as that concerning the originof mass are still unsolved. We rmly believe that the experimental discoveries of the near
future will give answers to these questions, and open up a new horizon of science. Given thissituation, the scientists of the European nations have decided on the construction of the next
generation hadron collider LHC. On the other hand, we believe that experiments at an e+ e;
Linear Collider will be crucial in order to determine with condence the directions of Physics
beyond the Standard Model. Thus a consensus has been attained amongst the community ofparticle physicists in Japan that our next principal project in high energy physics should be
the construction of this e+ e; Linear Collider as its host country, and that it is an international
contribution which also prots our country.
Following major developments in the eld such as the starting of the KEKB project in Japanii

and the termination of the SSC project in the United States, the High Energy Physics Committee of Japan set up the second Subcommittee on Future Projects of High Energy Physics
in Japan in 1994. The mission of the subcommittee is to study the perspectives of the international academia, and to examine the future directions of Japanese high energy physics over the
next ten years. The Subcommittee began its activity in the August of 1994, and has examined
the future projects, concentrating in particular on the physics and the technology of the e+ e;
Linear Collider. In the meanwhile, there have been further academic developments such as theprecision measurements at LEP and SLC which indicate the presence of Physics beyond theStandard Model, and the discovery of the top quark at TEVATRON, which has strengthened
the physics case for the e+ e; Linear Collider. The Subcommittee, after one year of intensive
studies, therefore submitted an Interim Report in July 1995 to the High Energy Committee ofJapan, which recommended an early construction of the e+ e; Linear Collider. Since then, we
have continued assessing and debating on the Linear Collider and other future projects in highenergy physics, leading to the submission of this report.

iii

Executive Summary

Principal Recommendations

Preface

7

2

1

ii

Contents

1 The Value of Fundamental Science

9

The Status of Particle Physics and Perspectives . . . . . . . . . . . . . . . . . . . 9
The Challenges in the Energy Frontier . . . . . . . . . . . . . . . . . . . . . . . . 11
The Necessity of an Early Construction of an e+ e; Linear Collider . . . . . . . . 12
The First Phase and the Second Phase of the Linear Collider Project . . . . . . . 15

2 The Status of Particle Physics and the Challenges at the Energy Frontier
2.1
2.2
2.3
2.4

3 Directions of High Energy Physics in the World and Future Projects in Japan 17

23

3.1 The History of High Energy Physics in Europe and the United States . . . . . . 17
3.2 An Analysis of the Current Status of High Energy Physics in Overseas . . . . . 18
3.3 The History of High Energy Physics in Japan . . . . . . . . . . . . . . . . . . . . 19

4 The Principal Project

4.1 The Linear Collider Accelerator . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.1.1 The Principles of a Linear Collider . . . . . . . . . . . . . . . . . . . . . . 23
4.1.2 The First Challenge: High Power RF Technology . . . . . . . . . . . . . 24
4.1.3 The Second Challenge: Collisions . . . . . . . . . . . . . . . . . . . . . . . 24
4.1.4 The Third Challenge: The Optimization of Parameters . . . . . . . . . . 24
4.1.5 The Fourth Challenge: Reliability and Cost . . . . . . . . . . . . . . . . . 25
4.1.6 Approaching the Problems . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.2 The Basic Construction and Development of the Linear Collider . . . . . . . . . 26
4.2.1 The Electron and Positron Sources . . . . . . . . . . . . . . . . . . . . . . 27
4.2.2 The Damping Ring, the ATF . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.2.3 The Bunch Compressor . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.2.4 The Main Linear Accelerator . . . . . . . . . . . . . . . . . . . . . . . . . 28
iv

33

4.2.5 The Final Focus Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.2.6 Other Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.3 Organization for the Linear Collider Development and Construction . . . . . . . 29

5 Other Projects
5.1 An Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.2 Projects in Japan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
5.2.1 The KEKB Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
5.2.2 The Long-Baseline Neutrino-Oscillation Experiments . . . . . . . . . . . . 37
5.2.3 The Japan Hadron Facility (JHF) . . . . . . . . . . . . . . . . . . . . . . 37
5.2.4 Non-Accelerator Particle Physics Programs . . . . . . . . . . . . . . . . . 39
5.3 Projects in Overseas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
5.3.1 The LHC Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
5.3.2 The SLC/SLD Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . 40
5.3.3 LEP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
5.3.4 Fermilab TEVATRON . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
5.3.5 DESY HERA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
5.3.6 Fixed-Target Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
5.3.7 The Tau-Charm Factory . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

44

An Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
The Roles of KEK and the Universities . . . . . . . . . . . . . . . . . . . . . . . 45
Diversity of the Human Resources for the Principal Project . . . . . . . . . . . . 46
The Structuring of a Suitable Environment for an International Laboratory . . . 47

6 Human Resources Development and Organization
6.1
6.2
6.3
6.4

48

An Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
High Energy Physics as a Branch of Science and its Relationship to Other Fields 49
Other Fields of Accelerator Science . . . . . . . . . . . . . . . . . . . . . . . . . . 50
The Relationship between Accelerator Science and Other Fields . . . . . . . . . . 53

7 Interdisciplinary Aspects
7.1
7.2
7.3
7.4

v

Principal Recommendations
Concerning the future projects of high energy physics in Japan, we make the following recommendations.
1. The e+ e; Linear Collider project is the next principal project for research in high energy
physics in Japan.
The center-of-mass energy of the collision in its rst phase will be 250500 GeV.
Aiming at its concurrent operation with LHC, every eort has to be taken to start
its construction in the beginning of the 2000s. After the completion of the rst phase,>1 TeV will be made.
the second phase upgrade to the center-of-mass energy The e+ e; Linear Collider project should be open to the international research community, and Japan should play the leading role as its host country.
An organization to execute the project should be formed and its globalization shouldbe actively pursued.
2. It is essential to carry out the KEKB project, which is under construction, as planned. The
other domestic and international projects in accelerator and non-accelerator experiments
should also be promoted, in order to develop a broad academic basis.
3. The cultivation of human resources should be pursued in order to push forward the principal and the other projects.

1

Executive Summary
There is enough evidence for us to expect that the experiments in the near future will enable
us to discover new directions in high energy physics and thereby lead to its major development.
The `Standard Model' of the modern particle physics is based on a principle called the gauge
symmetry. Under this symmetry, it is natural for the fundamental particles to be massless. The
most important untested sector of the `Standard Model' is the `mechanism for giving masses
to the fundamental particles', or the mechanism that breaks the gauge symmetry. This is thesector whose experimental resolution will bring out the direction for a new paradigm beyond
the Standard Model.
This will be made possible by the discovery of the particle involved in the mechanism of
mass generation, the Higgs particle, and by analyzing its properties. The `SupersymmetricGrand Unied Theory', which is currently the most promising candidate for a theory beyondthe `Standard Model', predicts the presence of at least one Higgs particle with a mass below 150
GeV. The determination of the existence or absence of this light Higgs particle and the analysis
of its properties is the most important and urgent project of the current high energy physics.
The e+ e; Linear Collider is a unique facility capable of unambiguously determining whether
the light Higgs particle exists and, once the particle is found, its properties can be studied ingreat detail. For this reason the research and development (R&D) of the e+ e; Linear Collider
has been actively conducted throughout the world over the past ten years. Also in Japan, theR&D of the Linear Collider project has been actively pursued and the major achievements havebeen made in collaborations and competitions with physicists in other countries, by utilizing
the accelerator technology which is now abreast with the frontier in the world. And, at last, itsrealistic design is about to be made.
In general, proton{proton colliders such as the LHC can produce new particles of verylarge masses. However, the background level compared to the signals of the new particles isgenerally high, and hence only those produced in large numbers and with distinctive signatures
are detectable. In comparison, at an e+ e; Linear Collider, the signals of new particles are
generally at the same level as the background, and also the production processes are often
simple enough to facilitate accurate predictions of signals and backgrounds. Thus if the newparticles are within the energy range of the e+ e; collider, they will be readily detected andtheir properties can be analyzed in detail.
2

The e+ e; Linear Collider will have the greatest impact on the progress of particle physics
if it begins operation concurrently with the European proton{proton collider LHC, and at thecenter-of-mass energy of 250500 GeV. This is because the model-independent determinationof the presence or absence of the light Higgs particle at the Linear Collider is expected to help
improving signicantly the discovery capability of the LHC experiments. This Subcommittee
proposed the early construction of this e+ e; Linear Collider (LC1) in the Interim Report in 1995.
Reecting upon the substantial recent progress in the development of accelerator technologies,
the proposal was considered realistic by the community. Furthermore, as the second phase
Linear Collider project (LC2), we proposed that an upgrade to a center-of-mass energy ofabout 1 TeV or higher should be made after the completion of LC1. At LC2, extending upon theachievements of LC1, the search for the colorless supersymmetric particles and measurements
their properties, as well as the search for the heavy Higgs bosons, will be made. Also, even
if the light Higgs particle does not exist, the precision experiments on the pair productions of
W +W ; and tt, which will be done simultaneously with the LHC studies of WW scattering, will
provide clues for the determination of the origin of mass. Regarding this e+ e; Linear Collider
project as the next principal project of Japanese high energy physics, we have clearly stated in
the Interim Report that it is the consensus amongst us the high energy physicists of Japan toannounce our intention to host the project in order to make possible its early realization.
Construction of the Linear Collider must be based on technical design standards that meetthe international critical assessment. To this end it is essential to create an organizational anddevelopmental structure that is open to the international community. In order to realize thisprincipal project, the e+ e; Linear Collider project, it is essential for the entire high energy
physics community of Japan to contribute. In order to reect maximally the opinions of thecommunity onto the realization of the project, a committee made up of the leaders of the Linear
Collider project in the universities and KEK should be formed, where the global strategies should
be determined based upon a research into the various possibilities of its realization. KEK should
host the `LC project promotion oce' in order to execute the project with due responsibility.
The oce should operate as the executive center for the research and development and theconstruction of the collider and the preparations for experiments, in such a manner to respect
strategic recommendations given by the above committee.
If the European LHC and the Asian{Pacic e+ e; Linear Collider should harness research
activities in mutual inuence and cooperation, the global pursuit of particle physics research will
be accelerated. The construction of the e+ e; Linear Collider, while being hosted and principally
executed by Japan, should be done in collaboration with the whole world, in particular with
the Asian and Pacic countries that have been making marked economic developments. Thus
the Linear Collider project should be regarded as a part of Japan's international contribution
in the eld of fundamental science, and it is a project in accord with the spirit of the Basic Lawof Science and Technology which was passed in multi-partisan approval in the 1995 national
congress. For our country to continue having an active economy and lively culture into the3future in a society with more elderly people and higher cost for social services, such a project
capable of motivating the participants of the next generation is necessary. In this context, theinvestment into scientic technology, in particular the fundamental science, should be made,now.
The era of catching-up in technology and basic science with the western developed nations isover, and the international expectation for our contribution is high. It is the duty of our country
towards the 21st century to tackle the unexplored areas of fundamental science and, within theinternational cooperation and the sharing of responsibilities, to take a part in the birth of the
new human intellectual asset. For this reason also, projects capable of creating common humanacademic and cultural asset should be actively pursued. The merits of the e+ e; Linear Collider
project should be envisaged with such broad perspective.
High energy physics to this date has developed along with the accelerator experiments at
the energy frontier. Our principal project, the e+ e; Linear Collider, is also along this maincourse. However, history provides ample evidence that a major academic development can haveunanticipated starting points. Thus, with an emphasis still on the Linear Collider project,
the formation of a broad academic basis requires promotion of a variety of complementary
experimental projects. In particular, the low-energy high-luminosity e+ e; collider KEKB is
expected to continue producing valuable data for more than ten years after its commissioning.
Its on-schedule execution is essential in order to gain a handle onto the problem of CP-violation,
which is one of the central problems of particle physics.
Among other national projects, the Super-Kamiokande experiment has been brought into
operation by the leading contribution from Japanese physicists. Together with various othernon-accelerator experiments, it is expected to bring many new results on the nucleon decay, theneutrino oscillation, and the search for the dark matter, which will lead to breakthroughs bothin particle physics and astronomy.
Furthermore, at the `Japan Hadron Facility (JHF)', which is basically a nuclear physics
project, various particle physics experiments are anticipated, such as the measurements of rare
hadron decays and neutrino oscillations utilizing the high-intensity K , , neutron and othersecondary particle beams, which may bring insight into physics beyond the Standard Model.
It should be also pointed out that we have taken part in international collaborative experiments abroad and have achieved a number of remarkable results. In collider experiments wecontributed to the discovery of the top quark at the Fermilab TEVATRON experiments. Alsoin the US, at SLAC SLC we have been taking part in experiments using polarized electron
beams. In Europe, we have been participating in the CERN LEP collaborations, making the
precision tests of the `Standard Model' by studying the Z and W boson properties. At DESY
HERA we are taking part in the study of the proton structure using electron{proton collisions.
Besides the collider experiments, we have been conducting the CERN neutrino oscillation
experiments. Also at Fermilab and BNL, we are contributing to experiments on CP violation
and rare processes by utilizing K mesons. Our participation in these international collaborative4

experiments has not only helped achieve rst class research results but has contributed to thetraining of many physicists with global orientation capable of conducting fruitful collaborationsin the international environment, and to developing our experience and personal relationships
necessary for the large-scale international collaborations in the future.
The CERN LHC project, which has the utmost academic importance rivalling our principal
project, the e+ e; Linear Collider, has also seen our major contributions. The LHC project is
to start operation in 2005, and it has introduced a new scheme in which the European member
states of CERN lead the project jointly, while asking for monetary contributions from othernon-member nations participating in the project. In the case of DESY HERA, Germany is
its host country and part of its funding is made up by contributions from other countries.
These various forms of international collaborations will be respectable reference when we begin
the construction of the e+ e; Linear Collider as its host country. It is crucial to develop an
environment that promote active participation by overseas researchers in our country and in
this respect too, there are many points to learn from these projects.
However great may be the scope of the project, the prime driving force in research is thecreativity and enthusiasm of the individual scientists and engineers. A research organization
capable of drawing on their creativity is necessary, and the project must be executed by anorganization receiving just scientic reputation internationally. In order to execute major enterprises such as our principal project, the e+ e; Linear Collider, the nurturing of the scientistsof the younger generation is necessary. In this respect, the eective collaborative relationshipbetween the universities and the central laboratory (KEK) needs to be reinforced. We hope fordiscussions on this matter with broad perspectives and support the activity of the Subcommittee
for enhancing the activities of university high-energy-physics groups. In particular, although thecentralization of funding and personnel to the central laboratory may seem ecient, it may not
be the most eective approach in the light of the long-term collaboration between the central
laboratory and the universities. Improvements are needed in the funding to university groups
and their management in order to help the development of core facilities of universities which
will strengthen the baseline of the academia as a whole.
History has shown repeatedly that many of the fruits of fundamental science, although notof direct applicability to the economy and living of the era, can lead to technological revolutionsat later times. In addition, the spin-o technology from fundamental science can often leadto immediate developments in industrial technology. Concerning the inuence of high energy
physics, there are numerous applications of the accelerator technology. The analysis of thestructure of material using synchrotron radiation, the structural analysis of organic polymer
by neutron scattering, the medical applications of particle beams et cetera are innumerable
instances of these. The Linear Collider with its low-emittance e; source is the leading candidate
for the realization of the free electron laser, which is regarded as the dream light source of thenext generation. The free electron laser programs are close to be realized at several Linear
Collider test facilities. Some of the basic technologies such as fast computing with a large5memory capacity, fast electronic circuits and high precision machine crafting technology, havebeen sharpened by demands from the high energy experiments.
The essence of fundamental science, which includes high energy physics, is the pursuit of thetruth, and it is a creative cultural activity which stems from one of the basic human instincts,
namely, the curiosity towards the Nature. In the past, the origin of mass and the beginning of
the universe were questions whose very scientic meaning was doubtful. The establishment ofthe `Standard Model' in the 1970s and the 80s enabled us to describe the interactions between
particles almost completely, and we now recognize that the origin of the masses of fundamental
particles is the key to understand the next layer of Nature. The origin of mass will be probed andclaried by experiments at LHC and the e+ e; Linear Collider. Furthermore, the development ofparticle physics has brought insight into the particle interactions at high energies, allowing us todeduce the sequence of events in the high energy early universe. Together with the developmentof the big bang cosmology, this led to the advent of the modern cosmology. The understandingof the origin of mass, the understanding of the matter vs. anti-matter asymmetry of the universe,the discovery of the origin of the cosmic dark matter, are amongst the anticipated results inparticle physics which will profoundly aect our understanding of Nature and the universe.
Thus high energy physics is an active area of science whose major progress in the 21st century
is anticipated, and it should be strongly supported together with the other areas of progressing
sciences.

6

Chapter 1

The Value of Fundamental Science
For mankind to continue its progress in harmony with Nature, it is a necessity to develop a
deep understanding of Nature and to have a scientic view of Nature.
In its origin, the pursuit of the truth is the creative cultural activity of the self-enlightening
mankind with active intellectual curiosity, and the intellectual asset of mankind, which is theamalgamation of the record of this pursuit, has in itself a value in providing us with intellectual
wealth and further progress. Fundamental science has inuence over our thinking and the viewof the universe, the physical world and life. It can thus greatly inuence philosophy and thought,
as well as even literature and art.
Furthermore, fundamental science is strongly linked with the society via technology forindustry. The year 1997 has seen the centenary of the discovery of the electron. Only withthe discovery of the electron have the inventions of the electronic computer and the electron
microscopy become possible the development of the quantum mechanics and the theory of
relativity led to the progress of the present day sophistication of electronic technology, machinetechnology and material technology. The examples are innumerable.
Thus the progress in fundamental science has brought technological revolutions in later eras,
and has contributed to the human society through the dramatic development of industry. It isan undeniable fact of history that the apparently useless pursuit of the truth, which perseveres
to nd the essence of Nature and of matter, has brought about the technological revolutions
directly related to the society. It might even be regarded as an inevitable consequence of thehistory of mankind who has achieved the enrichment of living through the eectual utilizationof the knowledge of Nature.
In this light, the history of mankind in promoting fundamental science is of a just cause, andthis positive attitude towards fundamental science should to be relocated in the human society
in a more claried manner.
The striving of fundamental science has a facet which immediately motivates the progressof industrial technology. In particular, the experimental study of fundamental science is eversupported by the latest technology of the era and demands higher technological targets. One
7notable example is the progress in the capacity of electronic computers motivated by the demandfor instant analysis of huge amounts of data, which came hand in hand with the progress ofhigh energy physics. Thus fundamental science and engineering share a mutual supportive
development, and the promotion of the two as a whole is an essential necessity.
Today, the investigation of the origins of matter and the study of the fundamental lawsof Nature is a task of high energy physics which, through its role in challenging the mostfundamental questions of natural science, has been a leading branch of fundamental science.
And now high energy physics aspires to nd the essence of matter, the origin of mass and theunied picture of the forces.
In addition, the recent progress in high energy physics and the development of big bang
cosmology have brought to light the intimate connection between high energy physics andcosmology. It can be said that the future developments of high energy physics holds the key
to the mystery of the creation of the universe, the evolution of the matter universe, and themystery of the end of the universe. Thus high energy physics, in not only purposing to clarify thefundamental laws of Nature and of matter, but in purposing to nd the origins, the evolution,and the end of matter, is clearly a branch of science challenging the fundamental questions.
There is thus purpose in further promoting high energy physics, given the value of the pursuitof the truth in creating the new culture of mankind, and given that it enriches the knowledgeof the origin of the universe, which underlies the existence of mankind.
We cannot hope for progress in high energy physics without the progress in accelerator science which is its experimental methodology. As the object of research turns to the innitesimalregions, the accelerators searching the regions become larger and more sophisticated. This tendency to greater scales is beginning to appear in other branches of fundamental science, andin dealing with the sophistication and size, high energy physics is a leading model. As thetendency to sophistication and enormity develop further in many branches of science, a task
for the future is in creating a large-scale research organization capable of projecting creative
research activities scientically in an organized fashion, for fruitful achievements. Big sciences
should hence be promoted rigorously.
Today, with a high anticipation for global contribution, the role of Japan towards the 21st
century is in actively tackling the unexplored regions of fundamental science and to take part inthe creation of the intellectual asset of mankind in a global collaboration and sharing of roles.
In order for our country to establish a true scientic and technological national foundation,
it is clear that we need a capacity for developing new technology with a unique and longterm perspective. This developmental capacity can only be nurtured through a backbone offundamental science, and from this perspective too, eorts in fundamental science needs to be
encouraged further.

8

Chapter 2

The Status of Particle Physics andthe Challenges at the Energy
Frontier
2.1 The Status of Particle Physics and Perspectives
Particle Physics, having pursued the understanding of the ultimate structure of Nature, is facinga grand transition at the establishment of the Standard Model. With the discovery of the top
quark at the Fermilab TEVATRON in the US, the six quarks and leptons that represent thethree generations of basic constituents of matter have all been discovered. The particles thatmediate the interactions between them, the photon, the gluon, the W boson and the Z boson,
have also been discovered. The interactions among these elementary particles have been studied
experimentally with great accuracy to verify the predictions of the Standard Model. The successof the Standard Model, which is dictated by the Quantum Field Theory based on the principleof local gauge invariance, has established the gauge principle as the principle governing thefundamental dynamics of Nature. This has provided a framework for theoretical studies of theinnitesimal world beyond the Standard Model, and has led to numerous theoretical conjectures.
Most attractive of such conjectures include the grand unied theory which attempts to unify thestrong, weak, and electromagnetic interactions, the technicolor model and other models basedon strong-coupling gauge theories, the supersymmetric models, and, in seeking the unicationof all forces including gravity, the supergravity and superstring theories.
As well as further conrmation of the Standard Model and understanding of its entirety,
the current task of high energy physics lies in the construction of our view of Nature towards
the understanding of the physics of the innitesimal world beyond the Standard Model. In
particular, the immediate focus of attention is in the origin of the masses of the fundamental
particles, in other words, in the mechanism that breaks the electroweak gauge symmetry whichunies the electromagnetic interaction and the weak interaction. The Standard Model has
9born many great successes, but they are limited to the domain of gauge interactions that arecompletely described by the gauge principle. Our knowledge of the interactions of the Higgs
boson, which plays an essential role in the electroweak gauge symmetry breaking and the origin
of fundamental particle masses, is experimentally completely missing. The discovery of the
Higgs boson and the study of its properties, as well as the study of the origin of the Higgs
boson, has a role not only in the complete understanding of the Standard Model but is alsoessential in the pursuit of the `hidden principle' which governs the innitesimal world beyond
the Standard Model.
There are roughly two possible scenarios for the nature of the Higgs boson, which have been
proposed through theoretical attempts to understand the Standard Model more deeply.
First, according to the ideas as represented by the technicolor model, the spontaneous
breaking of the electroweak symmetry is realized as a consequence of a new strong-coupling
gauge theory. The Higgs boson has a composite structure constructed through its dynamics.
The energy region from a few TeV up to 10 TeV will be colorfully decorated by many newparticles which are consequences of this new dynamics. While there is no complete theory
which describes the origin of the quark and lepton masses based on this scenario, the possibilityof the dynamical breaking of the gauge symmetry needs to be continually assessed.
The other scenario, which has been increasingly considered more likely recently, is the solution of the problems associated with the Higgs boson in the framework of the supersymmetry
theory. According to this theory, all particles in Nature are accompanied by supersymmetricparticles, partners diering in spin. Interactions of these particles are constrained strongly bysupersymmetry. Supersymmetry is the only fundamental symmetry which can extend consistently the symmetry of the four-dimensional space-time. Based on the results amassed in the
study of the unied theories such as the supergravity and superstring theories, it is believedthat whatever the fundamental mechanics may be, supersymmetry will play an essential role in
Nature.
The Minimal Supersymmetric Standard Model, which is the supersymmetric extension of
the Standard Model, predicts new particles in the mass range of a few hundred GeV to 1 TeV
as supersymmetric partners of the Standard Model particles. In addition, it has a prediction
which is of utmost importance for the planning of future projects: The Higgs boson will havea mass below about 150 GeV. The phenomenological viability of this theory has been studied from many aspects, and it is gaining an increasingly solid support as the most promising
candidate for the next level of theory beyond the Standard Model. In particular, the recent
precision measurements in the gauge coupling constants strongly indicate that in the presenceof supersymmetry, the strong, the electro-magnetic and the weak interactions will be grandunied at the energy of the order of 1016 GeV. The discovery of supersymmetry, which is the
key to the understanding of the ultimate unied theory which includes the gravity, is the mostimportant task for high energy physics.
102.2 The Challenges in the Energy Frontier
As discussed in the preceding section, the progress in our understanding of Nature criticallyrequires the understanding of the mechanism for spontaneous gauge symmetry breaking in theStandard Model, that is, the origin of mass. In order for the current and future accelerator andnon-accelerator particle physics experiments to lead to the discovery of the `hidden principle'
underlying the innitesimal world beyond the gauge principle, it is necessary that the mechanismof mass generation is understood. For example, the B-factory challenges the origin of matter inthe universe by exploring the matter{anti-matter asymmetry in the quark-mass matrix, but forthis insight to lead to a more profound understanding of Nature, it is necessary to understand themechanism which leads to the quark-mass matrix. Similar statements can be made concerning
the Kamioka and other non-accelerator underground experiments exploring the neutrino masses
and the lepton mass matrix, and the cosmological observations aimed at studying the dark
matter which holds a principal part in the mass of the universe. The understanding of thegauge symmetry breaking mechanism, the origin of the particle masses, is the key leading us tothe nal understanding of Nature.
The mechanism for spontaneously breaking the gauge symmetry and giving masses to thegauge bosons, such as the W and Z bosons of the Standard Model, is generically called the
Higgs mechanism. It has a general consequence that there exists one or more electrically neutral
spin-zero particle (the Higgs boson). The exploration of the origin of mass thus resides in the
discovery and the analysis of the Higgs boson(s) and its (their) properties. This is the mostimportant task for experiments in the energy frontier.
Thus the pursuit of the Higgs boson is placed a spirited emphasis in the current experiments
at the energy frontier. The CERN e+ e; collider LEP has shown that the Higgs boson mass isabove 65 GeV, and the eort is channeled into searching for the Higgs boson of masses up to
90 GeV at the second phase project LEP2. The CERN pp collider LHC will greatly expand thediscovery potential for the Higgs boson. In this project which starts operation around 2006, theHiggs boson of all allowed mass range is expected to be discovered in the `Minimal Standard
Model' which assumes just one Higgs boson.
Figure 2.1 shows the allowed ranges of the Higgs boson and the top-quark masses in the
Minimal Standard Model, according to the energy scale  where new physics emerges. In the
Minimal Standard Model, the Higgs boson gives masses to the W and the Z bosons as well as
to all quarks and leptons. From TEVATRON experiments the top-quark mass is known to be
175  6 GeV (the oblong area). So, there are upper and lower limits to the Higgs boson mass.
If new physics beyond the `Minimal Standard Model' does not emerge below   1 TeV, thenthe Higgs boson mass must be less than about 500 GeV. If the Higgs boson is heavier, above
700 GeV, its mass exceeds the scale of `New Physics' and the Higgs boson must be taken as acomposite system made by new strong interactions rather than as a fundamental particle. On
the other hand, if new physics does not emerge up to   1016 GeV where the grand unication
11

600
500
400

3

Λ = 10 GeV

Λ = 10 GeV

6300

Λ = 10 GeV

16

200

100

LEP1

0

100
0

TEVATRON

200

mt (GeV)

12300

In the previous section we summarized the scenarios for Higgs boson searches according to the`Minimal Standard Model' where a single Higgs boson is responsible for the mass generation of
all fundamental particles. However, the latest results in particle physics theory strongly suggeststhat the `Minimal Standard Model' is not realistic. For example, on one hand, according to thetechnicolor model and other models where new strong interactions break the gauge symmetry,

2.3 The Necessity of an Early Construction of an e+e; Linear
Colliderof the electromagnetic, the weak and the strong interactions is anticipated, the Higgs bosonmust have a mass between 130 GeV and 190 GeV. Assuming this `Minimal Standard Model',the LHC experiments will be able to nd the Higgs boson at all allowable mass range.

Figure 2.1: The theoretically allowed range of the Higgs boson mass mH as a function of the
top quark mass mt in the Minimal Standard Model where a single Higgs boson is responsible
for the masses of all particles including the W and Z bosons and the top quark.  is the scaleat which new physics beyond the Standard Model emerges. The lower limit on mH from LEP1
experiments and the range of mt measured at the Fermilab TEVATRON experiments are also
shown.

mH (GeV)1/α1 (E)1/α2 (E)1/α3 (E)4

6

LEP1 & SLC
2

8

10

12

14

16

18

GUT

SM
MSSM

the Higgs boson may not be found clearly as a fundamental particle. On the other hand,according to the supersymmetric models there are at least four scalar (spin zero) Higgs bosons.
In these more attractive models the discovery of the Higgs boson is generically more dicult,and there is possibility that even the LHC experiments will not nd them.
60
50
40
30
20
10
0

10 10 10 10 10 10 10 10 10

E (GeV)13

In particular, due to the theoretical development of the 1980s and the precision experimentsin the early 1990s the supersymmetric Standard Model has become the leading candidate for
explaining the origin of the Higgs boson. According to this theory, the spontaneous gauge
symmetry breaking mechanism is understood naturally in connection with the breaking of supersymmetry. It also successfully explains the non-observation of proton decay at undergroundexperiments such as the Kamioka experiment. Furthermore, the grand unication predictions
on the electromagnetic, weak and the strong gauge couplings have agreed quantitatively withthe precision experimental measurements. In gure 2.2 we show the prediction on the three

Figure 2.2: The high-energy scale running of three gauge couplings 1 , 2 and 3 inferred fromthe precision measurements at 100 GeV. If only the Standard Model particles exist (dashedlines), the coupling do not unify. In the supersymmetric Standard Model (continuous lines), due
to the eect of many supersymmetric particles with masses below 1 TeV, the grand unicationof the three interactions is realized at an energy scale of about 1016 GeV.

1/αirunning gauge couplings at high energies according to the Minimal Standard Model, and its supersymmetric version, with the most precise inputs from measurements such as those at LEP1.
It can be seen that due to the eect of the many supersymmetric particles with masses below
about 1 TeV, which are expected in the supersymmetric theory, the three gauge couplings converge at the energy scale   1016 GeV. Because of this high grand unication energy scale, theproton lifetime becomes suciently long. Whether the decay will be observable at, for example,
the super-Kamiokande experiment depends on the details of this grand unication model. On
the other hand, if the supersymmetric particles do not exist (dashed lines), the grand unicationof the three gauge couplings is not realized.
One of the most important consequences of the supersymmetric Standard Model is that in
the general model which does not jeopardize the grand unication of the three gauge couplings,
there is at least one Higgs boson with a mass below 150 GeV. In the Minimal Supersymmetricmodel, the Higgs boson can be found at the LHC in some cases but there is a signicantpossibility that it is not detectable. According to the latest theoretical calculations and thesimulations, an e+ e; Linear Collider with a center-of-mass energy of 250  500 GeV candenitely nd the Higgs boson predicted by the supersymmetric grand unied theory, and candetermine its quantum numbers and its coupling to the Z boson. In this regard, the Linear
Collider is capable of determining whether this boldest and most attractive theory of modern
particle physics is related to our world. If the Higgs boson of mass below 150 GeV does notexist then, however theoretically attractive the supersymmetry theory is, the generation of massin this world is not directly related to it and we must nd a completely dierent mechanism
which involves a new strong interaction for the origin of mass. On the other hand, if the Higgs
boson is discovered in the anticipated mass range, we can immediately direct our attention to
the search for the supersymmetric particles and the testing of supersymmetric models involving
gravity as well. The Linear Collider will determine the direction of particle physics research.
Although the LHC has an enormous potential including the possible discoveries of supersymmetric particles, if the Higgs boson mass is less than about 150 GeV, it is dicult for the
LHC experiment to determine model independently the presence or the absence of the Higgs
boson. Indeed, for a Higgs boson of a mass less than 150 GeV such as the one predicted by
the supersymmetric grand unied theory, its discovery demands a very dicult analysis even if
its properties happen to favor its detection at the LHC. If the colored supersymmetric particles
are heavy and the signals are not distinct, there is a signicant possibility that after some timesince the beginning of its experimental operation, no decisive evidence of either the Higgs bosonor the supersymmetric particles is to be found. If, at this time, the results of Linear Collider
experiments are available, the great discovery potential of the LHC can be maximized. If the
Linear Collider discovers that there is no Higgs boson of any type below 150 GeV, the LHC
can devote its attention to the detection of a new strong interaction involving the W and theZ bosons at still higher luminosities. On the other hand, if the Higgs boson is found below
150 GeV, the LHC can aim at detecting the supersymmetric particles. It should be remem14

bered that in the past, when new particles were discovered in hadronic collisions, as in the caseof the J=, , the W and the Z bosons and the top quark, the masses and electronic chargesof their decay products such as the electron, the neutrino, the b-quark, the W -boson and soon, were already known. The colored supersymmetric particles to be produced at the LHC, thegluino and the scalar quarks, will generally decay into colorless supersymmetric particles suchas the gauginos and the scalar leptons. The masses and properties of these decay products will
not be determined without resorting to specic model assumptions. Therefore, the search forsupersymmetric particles at the LHC is associated with a new kind of diculty. If the Linear
Collider can discover these colorless supersymmetric particles and can determine their masses,
the discovery capacity of the LHC for the gluino and the scalar quarks will be dramatically
improved, and accurate measurements of their masses will become possible. Indeed, unless thenumerous signals of gluino and scalar quark production match the predictions of the existingmodels of supersymmetry breaking, the `discovery of supersymmetry' by the LHC alone may be
a dicult task. In addition, since the mass spectrum of the supersymmetric particles is considered to be the key in searching for the ultimate model of particle physics including gravity, theconcurrent operation of the Linear Collider and the LHC has an immeasurable value in order
to discover supersymmetry and search for the ultimate unied theory.

2.4 The First Phase and the Second Phase of the Linear Collider Project
As stated above, the Linear Collider will make the greatest contribution to the progress ofparticle physics if it operates concurrently with the LHC at the center-of-mass energy 250 
500 GeV. Reecting upon the recent dramatic progress in the accelerator technology, this isconsidered realizable. Therefore, we recommend as the rst phase of the Linear Collider project(LC1) an experiment concurrent with the LHC at 250  500 GeV. The aim of LC1 is todetermine the presence of a Higgs boson with a mass below 150 GeV and thereby determine therelevance of the currently most promising supersymmetric unied theory, and thus determine
the future direction of particle physics. In addition, through precision studies of the W +W ;production and the top-quark-pair production, model-independent information concerning theorigin of mass can be obtained. Together with the possibility of the detection of relatively lightsupersymmetric particles at LC1, these information obtained at LC1 will increase the physics
discovery potential of the LHC signicantly. In order to attain the physics goals above, LC1
must achieve an annual integrated luminosity of above 10 fb;1 .
In order to clarify the origin of the Higgs boson in addition to its discovery, other scalar
Higgs bosons and the supersymmetric particles, or if the Higgs boson is a composite state,
the eects of the new strong interaction, must be searched for. To this end, a center-of-massenergy of about 1 TeV is necessary, and this should be achieved in the second phase of the Linear
Collider project (LC2). At 1 TeV energies, LC2 experiments dramatically improve the discovery
15

potential of the colorless supersymmetric particles, which parallels the ability of the LHC tosearch for the colored supersymmetric particles. In addition, the precision measurements of
W + W ; production at around 1 TeV will provide complementary information to the strong
interaction studies of the W boson at the LHC which is considered dicult. Furthermore,
although no theoretical model which explains its origin is known, a Higgs boson with a mass
about 700 GeV or below can exist in principle, and LC2 can determine its properties and clarify
its origins. An integrated annual luminosity of a few 10 fb;1 is necessary in the LC2 project.
The Linear Collider project aims at the rst phase to determine the direction of particle
physics and at the second phase to clarify the picture of new physics beyond the Standard
Model. Through the entire project an eective collaboration and competition with the LHC
project should be pursued. Based on the capability for accelerator technology and particle
physics experiments developed in the TRISTAN project, and based on the rapidly developing
research on Linear Collider construction technology by international collaborations, it is themost important and pressing task for the high energy physicists of Japan to realize the Linear
Collider project with the support of international communities. With the numerous theoreticalevidence in mind, we are rmly convinced of the fruitfulness of the Linear Collide project as
our contribution to the world in fundamental science.

16

Chapter 3

Directions of High Energy Physics inthe World and Future Projects inJapan
3.1 The History of High Energy Physics in Europe and theUnited States
The advances of research in high energy physics was led by the United States during and afterWorld War II by making a number of discoveries through constructing accelerators one after
another. After the war, many European and Japanese high energy physicists moved to the
US and have joined research activities at laboratories such as the Fermi National Accelerator
Laboratory (Fermilab), the Brookhaven National Laboratory (BNL), and the Stanford Linear
Accelerator Center (SLAC). In Europe CERN (the European Laboratory for Particle Physics)
was established in 1953. CERN has not only promoted collaborations within the western Europe but also accepted researchers from the US and other areas. In Germany the Deutsches
Elektronen-Synchrotron (DESY) was established independently. Experiments at DESY has led
to many achievements through the international collaborations with CERN and with physicistsof countries outside the western Europe.
In the mid 1970s, a state of healthy competition began between the US and Europe, andmany accelerators of similar types have been constructed in the two regions at around thesame time. SPEAR (SLAC, 1972) and DORIS (DESY, 1973), PETRA (DESY, 1978) and PEP(SLAC, 1980), SppS (CERN, 1981) and TEVATRON (Fermilab, 1987), and SLC (SLAC, 1989)
and LEP (CERN, 1989) are examples of these. Regarding the electron{positron experiments at
SLC and LEP, the experiment at SLAC SLC accelerator began rst but the LEP experiments
at CERN swiftly caught up, and overtaken SLC in the statistical precision of the Z boson
samples. From Japan, an experimental group at rst joined LEP, and then other groups joined
SLC when the polarized electron beams became available, thus being actively involved in the17frontier electron{positron experiments.
Since the beginning of the 1980s, the well organized researchers in Europe have brought
fruits such as the discovery of the gluon at DESY and the discovery of the W and Z bosons
at CERN. A plan was then laid out at CERN for the construction of the LHC pp collider inthe LEP tunnel. Challenged by the European successes in the early 1980s, the US physicists
planned an unprecendented pp collider SSC as a huge national project. The SSC project wasaiming at the construction of a 40 TeV pp collider in a circular tunnel of 87 km circumference.
Although it was once approved by the U.S. Congress, its construction was halted when thefunding for the continued project was turned down by the 1993 Congress.
In the meantime, the Soviet Union built accelerators at several laboratories including thosein Dubna and Novosibirsk, and conducted researches in collaboration with the East European
nations, as well as having collaborative links with CERN. However, its research environmenthas been changing signicantly since the dissociation of the Soviet Union.

3.2 An Analysis of the Current Status of High Energy Physics
in Overseas
An analysis of the current future plans in North America and Europe is presented below:
After the termination of the SSC project in the United States, the U.S. future plans currently include (1) participation in the LHC project (including the support for the accelerator
construction), (2) the upgrade of the TEVATRON (the main injector), (3) the SLAC B-factory(PEP{II). The projects (2) and (3) have been approved. The participation in the LHC projectis a natural path to take after termination of the SSC project. Talks are under way with CERN
for the funding arrangements.1
It is possible in the US for an approved project to be overturned by the Congress as in
the case of SSC, a scheme should be found for ensuring the execution of the projects involving
international collaborations. Such a scheme should be examined carefully when collaboratingwith the United States in the future.
In addition to the existing plans above, SLAC has a plan of the NLC (Next Linear Collider)project centered around it. SLAC has made many achievements until now such as the construction of the Two-Mile Linac which is a central laboratory for linear accelerators, constructionof the world's rst Linear Collider SLC, and the R&D for the next generation Linear Collider.
However, the relative population of researchers who have historically been involved in hadroncollider experiments is large in the US, and there are those supporting a hadron collider of anenergy higher than the LHC, as well as those supporting the muon collider project.
In Europe, the future plans are currently converging on the LHC project. Capability for
1
Note added on the English translation (Jan/23/1998): After the present report was accepted by the HighEnergy Committee in May 1997, the agreement was reached by the end of the year 1997 between the US
government and CERN for the US participation in the LHC project.

18

extending the other projects are therefore limited, and this applies equally to the case of LEP2
which is currently running. There is a strict limit to the annual operation hours of LEP2, andeven if the LHC project will be delayed, the extension of the LEP2 project for a few years isdicult, unless there is a clear discovery of new physics or denite signs of it.
Plans other than the LHC includes Linear Collider projects (TESLA with a superconductor
linac, and SBLC with an normal-conductor linac) for which DESY has taken a central role.
The R&D for TESLA is made in collaboration with, for instance, the United States. DESY
has research carried out simultaneously, for example, on free electron lasers (FEL) together
with researchers in the elds of nuclear physics and synchrotron radiation, with the hope ofgaining supports from scientists of those elds for the TESLA project. This is in the same vein
as our Linear Collider project in Japan. However, since the European central project is the
LHC, Germany must collaborate with the LHC and make a signicant contribution to CERN
at the same time as the Linear Collider project. CERN has itself a plan for a two-beam Linear
Collider called CLIC, and there has been much active R&D work. However, this is considered
as a project next to the LHC. Therefore, if there is a possibility abroad, e.g. in Japan, for a
Linear Collider such as the rst phase project presented in this report, it is expected that CERN
will collaborate with us rather than making objections. However, they still hope to construct a
Linear Collider in the energy range above 1 TeV by themselves. Thus, both in Europe and in
North America, the importance of a Linear Collider is highly recognized.
In Asian countries other than Japan, an e+ e; collider with a center-of-mass energy of 3 GeV
was constructed in China in 1988 and began operation. In 1995, the Asian Committee for Future
Accelerators (ACFA) was established amongst Japan, China, South Korea, Taiwan, India andThailand. ACFA promotes organized collaboration in accelerator-related elds in Asia. In 1996,
Malaysia joined the ACFA. Here, too, the Linear Collider project has received strong interests,
and the ACFA regards the Linear Collider as a project for the Asian{Pacic region, hoping thatJapan will play the leading role in the establishment of an international organization for thispurpose.

3.3 The History of High Energy Physics in Japan
After the World War II, a 1.3 GeV electron synchrotron was built in the Institute for Nuclear
Study of University of Tokyo after overcoming many diculties, reviving the research in nuclear
physics and particle physics. This accelerator had its purpose as a trial machine for a morelarge-scale high energy accelerator, but it had also served as a training ground for scientists who
have later led the eld of high energy physics in Japan. At the same time, many scientists went
over mainly to the United States until the 1960s as an arena of frontier physics research, andduring the 1970s onwards we have participated in international collaborations in Europe as wellas in the US. Research activity overseas has, thus, taken an important part. However, there
arose a movement for the construction of a frontier research institution in Japan as well, and in19

April 1971, KEK (then National Laboratory for High Energy Physics, Japan) was founded. In
KEK the proton synchrotron and the synchrotron radiation facility (the Photon Factory) wereconstructed. In the Fall of 1986 the e+ e; collider TRISTAN started operation, which brought
KEK to the energy frontier. The fruit of the construction of TRISTAN is overwhelming, and it
signies the end of an era where Japanese scientists sought for major research bases abroad andwe have gained ability to carry out top-level researches also in Japan. In particular, throughthe construction of TRISTAN, the Japanese accelerator technology has dramatically improved,
becoming abreast with the top level technology in the world. Thus, our country, especiallyon the e+ e; collider, has achieved world class results. In 1994, we began construction of ahigh luminosity e+ e; collider B-factory, KEKB, as the extension of the then principal project
TRISTAN. It is expected to be completed in 1998. KEKB is expected to produce results which
can lead to a great progress in the research on the particle{anti-particle and space-inversion
asymmetry.
As stated in chapter 2, the most important and pressing task in high energy physics, namely
the understanding of the mechanism of the electroweak gauge symmetry breaking, or the originof particle masses, has led to huge hadron collider projects LHC and SSC. However, for the
discovery of the light Higgs boson, as expected, for instance, in supersymmetric theories, thee+ e; Linear Collider has more advantage. Thus, from mid 1980s the R&D on the Linear
Collider has taken place throughout the world. Japan has led the frontier together with theUnited States, Germany, France, Russia and CERN. The following is a history of the formationof the consensus that `the Linear Collider is the next principal project in Japan' in the Japanesehigh energy physics community.
The rst Subcommittee on Future Projects of High Energy Physics in Japan (chairman
Yorikiyo Nagashima) was formed in 1984. After two years of discussions it was concluded in 1986
that the key to a breakthrough for new physics beyond the Standard Model is in experiments at
the energy frontier, recommending two main objectives (1) to immediately begin R&D on the
TeV range Linear Collider to be built in Japan, and (2) to promote the participation in SSC.
Based on this report, the rst-term 5-year project for the Linear Collider research and development was carried out, and the summary was published in January 1993. In the meantime,
the analysis of LEP precision data and the theoretical research have sharpened the recognition
that an early construction of an e+ e; Linear Collider at center-of-mass energies in the range
300  500 GeV is essential for discovering the light Higgs boson predicted by the supersymmetric models. Active discussions and detailed analysis of the scientists throughout the country
were compiled into the report JLC{1 (KEK Report 92{16, JLC: Japan Linear Collider) whichsummarizes the possible accelerator design and physics at the Linear Collider. Reecting upon
the urgency of the construction of a Linear Collider at 300  500 GeV, the High Energy Physics
Committee of Japan proposed in April 1993 a plan for the second-term 3-year project. Here,the years 1993  1995 were set the second-term development planning period, aiming at thedevelopment of the prototype main equipment and the optimization of the parameters and de20

sign, leading to the completion of a conceptual design. In particular, the completion of the
ATF (Accelerator Test Facility), which is a miniature version of the JLC, was given a central
position, and at the same time participation in foreign research and development was made andthe participation of foreign countries in the R&D in Japan was invited.
As stated in the Preface, the High Energy Physics Committee of Japan set up this current
Subcommittee in 1994. The Subcommittee submitted an Interim Report in July 1995 on theurgent topic of an early construction of the e+ e; Linear Collider, thus consolidating the consensus of the academia. The basic statement in the report of the rst Subcommittee: \the key forthe breakthrough towards new physics is in the experiments at the energy frontier" has equally
been supported by the current Subcommittee. The backbone for the evolution of this current
report from the rst report lies in the following two factors rst, the demand of physics andtechnological capabilities leading to an increased desire for an early construction of a Linear
Collider, and second, the termination of the SSC project.
In Fall 1995, the Basic Law of Science and Technology was enacted by the Japanese parliament through multi-partisan support. This has a major impact on the future plan of highenergy physics in Japan. As stated in the Basic Law, our country should play a leading role in
the investment in fundamental science based on long-term perspective. However, if our contribution is centered on overseas research facilities, the foundation in basic science in Japan will
not be improved, leading to a poor research ground as compared to the economic power. Thatthe research funding for fundamental science should be doubled, as the Basic Law dictates, isreasonable since fundamental research in the past was based almost entirely in Europe and theUnited States. It is through the development of science and technology that our country canmaintain the active economy also in the future in a society with an increase of the higher age
population. The investment for the future should hence be given the highest priority even when
the national budget is limited. The investment into high energy physics, in particular, should
be seen in a long-term perspective as a part of the investment in fundamental science. It should
be stressed that high energy physics is an area of fundamental science where a great scienticprogress is expected in the near future, and that it is an area where the frontier research is
expected to give rise to numerous technological osprings which could contribute directly to theeconomy.
The development in high energy physics should be considered as one of the central themesof the frontier research areas, and now is the time for us high energy physicists to make theidea permeate into the academia, the political world and the industry. We believe that there
is an exceptionally strong case for hosting the Linear Collider in Japan as our international
contribution, since it is an academic project of fundamental importance, where our contribution
has been most wanted, and since it is certain to attract many frontier researchers from overseas.
Thus looking at every aspect, the scientic importance of experiments to be carried out
at the e+ e; Linear Collider, the high quality of Japan's accelerator technology, the presenceof a developed industrial basis for its realization, the consensus in the high energy physics
21

community, and the status of the high energy physics projects overseas, it is clear that there isa well-founded need for the construction of the e+ e; Linear Collider in Japan where Japanesescientists and industry play a leading role.

22

Chapter 4

The Principal Project
4.1 The Linear Collider Accelerator
4.1.1 The Principles of a Linear Collider
Electron{positron collider accelerator of the past have mainly been based on a storage ringsystem. The electrons and positrons are converged into bunches of particles with lengths ofa few millimeters and widths of a few hundred microns, and they orbit around at the speedof light under the control of magnetic elds produced by electromagnets. The electrons andpositrons emit synchrotron radiation in the forward direction and lose their energy, and inorder to compensate for it there are radio frequency (RF) cavities placed in the ring. Since thebunches pass the cavity at a great frequency, a small number of low accelerating gradient in thecavity allow to store and preserve the beams with energies up to a few tens of GeV. However,
the energy loss per unit time due to synchrotron radiation is proportional to the fourth powerof the beam energy and inversely proportional to the square of the orbital radius of curvature.
In order to keep the electric power supplied to the accelerating cavity constant and raise theenergy, the orbital radius of curvature must be increased as the second power of the beam energy.
The number of the various equipment comprising the accelerator is roughly proportional to thelength of the accelerator, and thus the construction cost increases as the second power of thetarget energy. This storage ring system has contributed to many glorious achievements forenergies up to that of the CERN LEP2 (center-of-mass energy 200 GeV maximum) which iscurrently in operation. However, the realization of energies greatly surpassing LEP2, which has
a circumference length of 27 km, by an increased ring size is not realistic. This has led to theinvention of the Linear Collider concept which utilizes the linear accelerator because it does
not suer from the synchrotron radiation loss. The Linear Collider accelerates electrons andpositrons separately by two opposing linear accelerators and collides them at the center. By thissystem the accelerator length is approximately proportional to the target energy. We list theproperties of the Linear Collider and the problems necessary to be resolved for its realization.
23

4.1.2 The First Challenge: High Power RF Technology
At the Linear Collider, the beams must be accelerated at once in a single cycle of the linear
accelerator from the generation of the electrons and positrons to a few hundred GeV. Thisrequires far more accelerating equipment than the storage ring system. Indeed, in order torealize the center-of-mass energy of 0:5  1 TeV, linear accelerators of total length 20  30
km is required even if a high acceleration electric eld of  50 MeV/m is utilized. The linear
accelerators are composed of as many as a few thousand RF sources and accelerating cavities.
The rst challenge for the design of a Linear Collider lies in operating these numerous andhigh-electric-eld accelerating cavities, as well as the high-electric-power RF sources driving
them, with a good power eciency and reliability.

4.1.3 The Second Challenge: Collisions
The frequency of the repeated collisions at the Linear Collider is determined by the repetition
frequency of the accelerating pulses of the Linear Collider. Due to the upper limit for electric
power and the technical issues in high electric power RF sources, this is limited to several
hundred times per second. This is less than a thousandth of the case of a typical storage ring.
On the other hand, the typical reaction cross sections in electron{positron collisions are inversely
proportional to the square of the center-of-mass energy, and so a luminosity a hundred times
greater than that of TRISTAN is required at a thousandth lower collision frequency. Due tothe limit on the electromagnetic energy which can be stored in the cavities, it is impossible toraise the number of particles beyond the storage ring system in order to raise the luminosity.
At the Linear Collider, the luminosity must be raised by powerfully focusing the colliding beam
size to a thousandth that of the ordinary storage rings, namely, to the order of nanometers.
The second challenge for the design of a Linear Collider is thus in realizing the emittanceconservation during the acceleration and in realizing the small beam size and a stable runningof collisions.

4.1.4 The Third Challenge: The Optimization of Parameters
When two bunches at the nanometer scale collide, in addition to the electron{positron particle
reactions, the Beamstrahlung radiation is emitted due to the strong electromagnetic eld createdby the powerfully focused bunches. A large number of low energy electron{positron pairs are
generated there. These will become the noise for the physical experiments. The number of theiroccurrence is proportional to the number of particles per bunch and inversely proportional to
the width of the bunch. In order to perform meaningful experiments the pair-production noisemust be kept below a certain level. Thus, the number of particles per bunch and the beam
size at the collision point create a boundary condition for the design of the Linear Collider.
In reality, these two parameters are also related to numerous parameters in the operation of
the Linear Collider such as the operation conditions for the linear accelerators and the beam
24

emittance. For this and many other reasons, numerous parameters are mutually interrelated,
and their optimization is the third challenge in the design of the Linear Collider.

4.1.5 The Fourth Challenge: Reliability and Cost
For an ecient running of the experiments, it is important to raise the yearly integrated luminosity. To this end the maximum luminosity of the accelerators needs to be improved andbe kept stable simultaneously. Therefore, in the designing of the accelerators, in addition to
the beam acceleration, the beam focusing and the parameter optimization listed above, considerations must be made towards the reliability, the operational rate, the maintenance and theconservation. In other words, the long-term stable operation of the equipment is a necessity
which requires a sucient design margins. Another important problem is in keeping the production cost low, while keeping the quality of the equipment high. Indeed, in the construction
stage of the Linear Collider, the manufacturing of the various and numerous equipment will beassigned to the industry. The viability of the production scheme to be taken up by the manufacturers, as well as the incorporation of the existing technology tested for reliability, should beconsidered carefully. This is the fourth challenge in the design of the Linear Collider.

4.1.6 Approaching the Problems
The development of the Linear Collider began throughout the world after the ICFA (International Committee for Future Accelerator) Workshop near the end of the 1980s. Various
explorations were made regarding: for instance, the assessment of the accelerator technology.
The First International Linear Collider Workshop in 1988 at SLAC marked the beginning of anorganized study of the next generation Linear Collider systems. The rst Linear Collider SLC
at SLAC (center-of-mass energy  92 GeV) began its operation in 1986 and the experiments
were started in 1989. The basic construction of a Linear Collider, apart from the capacityof each subsystem, can be found in SLC. The operational experience obtained there will be abasis of the next-generation Linear Collider. Due to the geographical limit, SLC accelerates
both electrons and positrons in the same linear accelerator. The acceleration of electrons andpositrons in two separate linear accelerators is a system which will be realized for the rst timein next-generation Linear Colliders. Next-generation Linear Colliders have been studied andproposed in various forms in Japan, the United States, Europe and Russia. The possibilities
contain, rst of all, the choice in whether the main accelerators are made of superconducting
or normal-conductors. For the case of the normal-conductors there is further choice in termsof the frequency and the bunch structure. There is also a proposal for the two-beam system,
where one accelerator creates and amplies RF power and supplies it to the other accelerator
which is placed parallel to it. The groups in countries mentioned above have each from theirown standpoint assessed the realistic possibilities regarding the various hardware in order toresolve the above four challenges, and have worked at wide-range constructional parameter op25

timization in the presence of friendly competition. In the 1990s, the laboratories KEK, SLAC,
CERN, DESY and Protovino have each proposed as Linear Collider systems including the JLC(Japan), NLC (SLAC), CLIC (CERN), TESLA (international collaboration based in DESY),
SBLC (DESY) and VLEPP (Protovino). The constructions of test accelerators such as ATF(JLC), NLCTA (NLC), CTF (CLIC), TTF (TESLA) also began at this time. In the rst half ofthe 1990s the SLC luminosity went up and the polarized electron beams have come into use. In
1994, the international collaboration FFTB at SLAC succeeded in realizing a 60 nm beam spot
size and its measurement. 1995 onwards has seen the outcomes of the test accelerators such as
ATF, which includes the generation of the multi-bunch beam at ATF, the development of theacceleration and measurement techniques, the steady progress of the SLAC X-band klystrontowards the realization of NLC, the development of the RF electron gun at CLIC and theprogress in high electric eld superconducting cavity. Thus the four problems described above
are gradually being resolved, and today we are entering the practical designing stage after theconceptual studies.

4.2 The Basic Construction and Development of the Linear Collider
As mentioned in the third chapter, the Linear Collider research and development in Japanbegan in 1986 following the report of the rst Subcommittee on Future Projects of High Energy
Physics in Japan. The results are described in detail in the report submitted to the HighEnergy Physics Committee of Japan. As described in that report, we have adopted for themain linear accelerator a system where the peak voltage is raised by the temporal compressionof the RF source from the pulse-operated klystron. This is supplied to the normal-conducting
accelerating structure, which accelerates the electron{positron multi-bunch beam. Given thisdirection, the theoretical study of the beam dynamics and the parameters was organized inparallel with the hardware development including the detector equipment. Here we describe
the conceptual design of the Linear Collider accelerator from the beam source to the collision
point according to the above choices (see gure 4.1). The Linear Collider accelerator consistsof: the electron/positron source generating a multi-bunch high-current beam, the damping
ring which produces ultra-low emittance beam, the bunch compressor which reduces the bunch
length, the main accelerator structure which accelerates electrons and positrons eectively while
keeping the low emittance of the beams, high-electric-power RF source, the nal collision unit
which focuses and collides the nanometer scale beams, and the monitor system which operates
and adjusts the system steadily and eciently.

26

4.2.1 The Electron and Positron Sources
Although the electrons are usually generated by the thermionic-cathode electron gun, systematic
study of the supersymmetric grand unied theory requires polarized electron beams. An electron
source combining GaAs strained layer super-lattice photo-cathode and circularly polarized laser
beam is the most promising for this purpose.
Positrons do not exist by themselves in Nature, and for their generation we shoot electron
beams at energies of the order several up to ten GeV onto a heavy metal target such as tungsten
alloy, and choose positrons out of the electromagnetic shower of particles generated. In orderto improve the positron yield, a powerful focusing unit and improved acceptance will need
to be developed. While the experience at SLC provides the data on the endurance of themetallic target against the heating by the incoming electron beam, there is much still requiring
development, such as the radiation safety measures in an high beam current environment,
and construction of the target with improved maintainability. More research and development
should be strongly promoted.

4.2.2 The Damping Ring, the ATF
A beam generated at the electron and positron sources is accelerated up to a few GeV, andis injected into a small storage ring called the damping ring. By allowing the beam to emit
synchrotron light for a few tens of milliseconds, the emittance is reduced. Here, great care must
be taken over the precision in the location of the equipment such as the electromagnets and in
the electric properties of the vacuum chamber and the accelerating cavities, in order to achieve
the low emittance. The beam injection and extraction units and the feedback technology arealso important. The lower limit for the emittance is governed by the beam optics of the ring.
It is necessary to examine this limit early on and reect this in the overall design. This was
the motivation for the ATF project. The ATF is a development project which is important
not only for simulating the damping rings but also in simulating parameters as closely with theactual Linear Collider as possible. The ATF can thus be said to be the miniature version of theaccelerator equipment necessary for the Linear Collider.

4.2.3 The Bunch Compressor
The bunch length of the low emittance beam provided by the damping rings is a few millimeters,
and this is too long for the focal depth which is about 0.1 mm. Also, the conservation of theemittance through the main linear accelerator would require the bunch length to be short inorder for the RF acceleration to uniformly accelerate the particles within a bunch. The bunch
length of a few millimeters is too long and this is compressed by a special beam line which
comprises of beam optical units and accelerating equipment. There are several methods in thebunch compression, but all methods require a few hundred meters of equipment. It is necessary
to experimentally assess the resolution of problems associated with the bunch compressor, and27

the prototype testing of the connections between the damping ring, the bunch compressor andthe main linear accelerator with or without using beams needs to be analyzed.

4.2.4 The Main Linear Accelerator
The main linear accelerator is the largest part of the accelerator facility. A few thousand units of
the radio frequency (RF) source, the RF power compression unit and the accelerating structure
set with a unit length of about 10 m, are aligned through a tunnel of a total length 20  30 km,
and the units are operated at 50  150 Hz. The peak output of the RF source is 50 MW or more,
and after the pulse compression this becomes a few hundred MW. The electric eld strength
in the accelerating structure will be  50 MV/m. In order to accelerate the multi-bunch beam
without emittance degradation, the unprecedented development of a new type of accelerating
structure which does not cause beam instability is necessary, as well as the precision locationand the beam control technology. As mentioned above, it is important to develop a practicalconstruction plan based on considerations of the reliability, operation rate, lifetime and the costof the few thousand accelerator units.
Currently in Japan, as a central technology in the development of the main accelerator,
we are studying the X-band linac. As a back-up technology, we have also begun investigating
the C-band linac. The development of the X-band linac is carried out in close collaboration
with SLAC and the Protovino laboratory. SLAC has succeeded in extracting 60 Hz output of
75 MW peak output power and 1.1-microsecond pulse width in 1996. SLAC has also succeededin focusing the beams using permanent magnets for the sake of saving the operating power of the
klystron. These provide a milestone for Linear Collider development alongside the experiments
at FFTB. At the Linear Collider it will be necessary to install at least 5000 such klystronsand operate them stably. The methodology in mass-production and the improvement of thereliability are amongst the most important issues in the next step. The modulator power
supplier for supplying pulsed power to the klystron has a large number of components and is an
important item governing the reliability and the cost of the accelerator, and this requires moredevelopment too. The development of the C-band linac, including the hardware technology, hasbeen started. As a back-up technology, evaluation of its reliability and cost is urgently needed.
The possibility of the energy upgrade is another important factor.
There are currently multiple methods studied for the temporal compression and divisionof the klystron output, which eectively raises the peak electric power, and feeds it to theaccelerating structure. The decision on the technology choice will have to be based on a broad
range of factors including the results of the low and high RF power tests, and the stability andreliability of the entire systems.
There are various types of accelerating structures which have been developed. Generally,
the mechanical precision of the individual accelerator cell can be achieved within the current
industrial standard. In addition to the development of the component technology, the next28

outstanding tasks will include the further experimental studies, the mass production of highprecision accelerating structures, the reduction of cost, and the development of the technology
for installation of these components in the accelerator tunnel.
We are also developing the L-band superconducting cavity in Japan. Here we are establishing
the cavity production and processing technology for a stable output of 40 MV=m high electriceld based on the superb experience with superconducting cavity gained at TRISTAN.

4.2.5 The Final Focus Unit
The electron and positron beams which have been accelerated by the main linear accelerator
to a high energy, while keeping the emittance low, are focused at the nal focus unit to thenanometer scale and are collided at the interaction point. The considerations of the issues
associated with the strong focusing, and the technological development of the precision controlof the collisions and the measurements are essential in order to achieve and preserve a highluminosity. The collimators and the masks near the collision point, which will reduce thebackground to the experiments, will require special considerations, distinct from those in theconventional ring-type accelerators. The SLAC FFTB experiments which started in 1992 havestudied the beam focusing and the control near the collision point. This is an experimental
project pursued by an international collaboration. A Japanese group has also participated init, leading to important achievements in beam optics design, the focusing magnet and the beam
monitor instrumentation. As a result, the beam optics design, required for the nal focus unit of
the Linear Collider is in principle already demonstrated, and the monitoring technology for thenanometer-scale beam cross-section size appearing at the collision point has almost completely
been established.

4.2.6 Other Factors
Design considerations on the accelerator control and beam diagnostic tools, autonomous feedback systems etc have much to learn from the experience from the operation and developmentof SLC. However, the beam control technology at the Linear Collider needs to be much moreadvanced than that at SLC in many respects, and concrete studies based on the specic designof the Linear Collider is urgently required.

4.3 Organization for the Linear Collider Development and Construction
The rst Subcommittee on Future Projects of High Energy Physics in Japan pointed out in1986 that research at the energy frontier is the most important task. As a national project,
the development of the Linear Collider was proposed, and participation in international collaborative SSC project was supported. The current Subcommittee recommended that the Linear29Collider should be hosted by Japan, and while the construction will be realized by international
collaboration with Japan playing a key role, the experiments will be done on an internationaland open collaborative basis. The eld of high energy physics in Japan has so far reached thecurrent stage by learning from Europe and the US, but this Subcommittee believes that throughthis construction of the Linear Collider and through its role in providing research opportunity toscientists throughout the world, Japan will make an international contribution aecting many
facets in the future of Japan.
In the Linear Collider research and development, the various international collaborationsof the past have functioned well. The early construction of the Linear Collider from now onwill have to motivate such collaborations further and aggregate the wisdom both within the
country and overseas. The determination of the technological methodology adapted for eachpart of the accelerator, and the detailed selection of the parameters, will need to be organizedscientically on the basis of the technological and practical merits, judged by the developmentgroups centered on the laboratories in charge. The Linear Collider needs to be constructedaccording to the technological design which will stand up to international reviews, and forthis reason an open environment for the research and development is essential. In realizingthese activities, the Subcommittee truly realizes that Japan, in being the host country for theconstruction of the Linear Collider, is undertaking a great task and responsibility. To be thehost country of the Linear Collider means that this could be the rst Japanese opportunity tobuild a large-scale international center in fundamental science. This will be a long-term basewhich will be handed over from the current generation to the next generation. This will be anational and international contribution not only in the area of high energy physics but also inraising and keeping the level of particle beam accelerator science and other related elds. Thisnaturally brings out the necessity for high energy physicists and accelerator scientists of Japanto pursue further their respective studies in accord with the status thus acquired. At the sametime, this will be an extremely good opportunity in forming a model for the future of big sciencein Japan.
We must also actively promote the collaborative structure with the national and overseas
industry. Our primary anticipation for the industry is in their combining of the industrial
high-level technology with the knowledge of accelerator amassed so far, leading to a improved
reliability of the various hardware for the Linear Collider and optimized mass production. Since
the technology in demand are often of a standard unprecedented in the conventional accelerators,
the research institutions and the industry should both analyze the technological problems andtheir solutions, and sharing the results as a team. For many cases the collaborative involvementof researchers both in the industry and in the academia is called for from the initial stages ofdevelopment. This Subcommittee recommends the leaders of high energy physics communityand of KEK to keep promoting this collaborative research and development structure.
In order to clarify the structure of international technological collaborations, the technological necessities in the development and construction of the Linear Collider must be found out
30

in their entirety, and this information must be made a common realization of the researchers
involved. Furthermore, the presence of the facility, equipment and human resources in the
countries involved which are available for the Linear Collider project should be claried throughstraight communication, and the utilization of these resources in the early realization of the Linear Collider should be sought. The strategy necessary in the construction of the new facilities
and the development of the human resources should be actively discussed. In the past, various test facilities throughout the world and the KEK ATF have been utilized for collaborative
development, and will continue to be utilized internationally. Given the progress in researchand development, a structured analysis of the new facility required for the experimental studies
should be made rapidly. In addition, the analysis of the tunnel facility for the Linear Collider
accelerator as well as the site evaluation work need to be made.
For the smooth execution of the principal project, the e+ e; Linear Collider, it is important
for the high energy physics community as a whole to support the project, and the opinionsof the community should be reected suciently in it. To this end, a committee comprisingof the leaders of the Linear Collider project in the universities and KEK should be created,which will take in the opinions of the community and discuss the strategies to be adopted. Inorder to respect these strategies and to execute the project with due responsibility, KEK should
host the `LC promotion oce', which will be the center for the promotion of the researchand development, construction and experimental preparation. The strategies in executing the
project and the debates leading to the decisions should be made public, and eorts must be madefor improved communication, for which the LC promotion oce and the committee describedabove are responsible. In addition, it is of course necessary to form an international assessment
committee which continuously assesses the progress of the project. These organizations for thepromotion of the project need to become internationalized as the project itself will become
international.

31Electron-Positron Linear Collider

32

Figure 4.1: The conceptual design of the e+ e; Linear Collider.

JLC

500 GeV JLC-I → 1.5 TeV JLC

0.5 km

11 km

Main Linac

BC2

11 km

IP

Main Linac
FFS, Collimator

Collimator, FFS

8GeV Pre-linac BC1

BC2Spin Rotator BC1

8GeV Pre-linac

Detector

1.98 GeV Damping Ring
Pre-damping Ring

0.5 km

6 km

1.98 GeV Damping Ring
Spin Rotator

10 GeV Linac

1.98GeV Linac e+ Target

E-Gun

E-Gun
1.98GeV Linac

30 km

1.0 TeV Configuration~1.0 x101085 bunches x 150 Hz

Positron

85 bunches x 150 Hz
1.4 nsec

Electron

SeishiTakeda/96115/JLC-I/xdiag/E_colorXL
T.Okugi (Tokyo Metropolitan Univ) 12/2/96
Updated for MCPAC97 by N.Toge 1/22/97

Chapter 5

Other Projects
5.1 An Overview
A large part of progress in high energy physics has so far been brought about from accelerator
experiments which are directed at the energy frontier. This is because the purpose of particle
physics is in the exploration of the innitesimal world, and the measurements of reactions at
higher energies are the most direct method for studying material structure at smaller scales. The
experimental research at large accelerators has successfully conrmed predictions of the uniedelectroweak theory, contributing greatly to the establishment of the Standard Model. Now, thecurrent theoretical research focuses on the grand unied theory which unies the strong, theelectromagnetic and the weak interactions, the supersymmetric grand unied theories which
are based on supersymmetry, the supergravity and superstring theories which unify all forces
including gravity. Phenomenological predictions of these new models are calculable for various
measurable and observable processes, and the methodology in particle physics have become
numerous and diverse. Given this diversication in the particle physics methodology, we believethat unique focus of individual research group should be valued, and that research plans otherthan the Linear Collider project should also be promoted.
For example, diversication of the research projects in the energy frontier is shown by the
TRISTAN experiment in Japan, the international collaborative experiments at LEP and SLC
studying Z 0 physics at electron{positron colliders, the discovery of the top quark in proton{anti-proton collision experiments at the Fermilab TEVATRON, the ep collision experiments at
HERA and so on. The Japanese experimental groups have chosen the suitable projects fromprograms at these various types of accelerators, and have made impressive achievements. In
particular, the university research teams have actively taken part in the overseas large-scalecollaborative projects through for instance the US/Japan Cooperation in High Energy Physics,
advancing further on their research achievements. Japanese researchers are also playing anactive role in the participation in the 10 TeV energy range large proton{proton collider project
LHC.
Complementary with the energy frontier experiments, projects in Japan such as the low en33

ergy high-luminosity electron{positron colliding beam accelerator KEKB and the high-intensity
proton accelerator JHF are making a steady progress. These projects aim at studying CPviolation and other problems in the fundamental symmetries and at studying physics at highenergy scales through the study of the rare decays. In terms of non-accelerator experiments suchas the proton decay and the neutrino experiments, Japanese physicists have produced top-class
results superlative in the world.
The Japanese high energy physics researchers have made achievements merited internationally in various research projects. The environment supporting the diverse research topics should
hence be maintained in the future.
Such diversication of research in particle physics is important not only in promoting research achievements, but also in nurturing researchers possessing long-term perspective. In
recent years, the future plans in high energy physics experiments have become large-scale intheir scope, requiring a considerable number of years towards their realization. In this era,continuous generation of young talented people requires the continual experimental activities,
especially at universities, which are provided by experimental projects other than the Linear
Collider project. The steady build-up of young generation of researchers, with the experienceand knowledge obtained through the various large and small experiments both inside and outside
the country, is essential for the future success of the Japanese high energy physics.
In other words, the execution of the diverse projects promotes the national personnel development, while the acquisition of depth and variety in research leads to long-term success of the
Linear Collider project. Thus, while emphasizing the importance of the Linear Collider project,
we believe that the other projects also need to be promoted steadily at the same time.
The projects other than the Linear Collider project can be categorized roughly into theprojects in Japan and the international collaborative experiments. They range from researches
as extensions of the currently operating research projects, to the energy frontier projects suchas the LHC project. They also vary in scope, from the large-scale domestic projects such as
KEKB and JHF, down to university level international collaborations. Furthermore, there willneed to be exibility enough to accept programs based on new ideas which are not in the list
below. We summarize below the goal, the current status and future perspective for each of the
projects in Japan and overseas.

5.2 Projects in JapanAs for the projects in Japan, the three `branches' of the rst Subcommittee on Future Projectsof High Energy Physics in Japan of 1986 have developed into three pillars at the core of the
projects in Japan. The rst pillar, the low-energy high-intensity electron collider project, iscurrently in progress in the form of the high-intensity electron{positron collider KEKB built
on the success of the TRISTAN project. The preparations are under way at KEK and at othernational and foreign research institutes. The KEKB project aims to study the origin of the34

violation of the CP symmetry. The second pillar, the high-intensity proton accelerator, is being
developed in the form of the 50 GeV 10 A high-intensity proton accelerator project JHF. Thistakes the form of an extension of the present 12 GeV proton synchrotron at KEK. As for thethird pillar, non-accelerator particle physics experiments, there are various experimental planssuch as the Superkamiokande which has already begun operation. As a completely new formof particle physics experiments, there is the long-baseline neutrino-oscillation experiment whichis to begin operation in the Japanese Fiscal Year 1998, where neutrino beams, created at the
KEK 12 GeV proton synchrotron, are projected towards the aforementioned Superkamiokande
detector which is located 250 km away. These projects are all complementary with the Linear
Collider project in the energy frontier, and are pursued as extensions of previous or current
projects. We describe the physics and the perspective for each of the projects in the following.

5.2.1 The KEKB Project
The violation of the CP symmetry is one of the most important subjects in particle physics,
since it is related to the origin of the matter universe. However, there has been no denite
experimental evidence for CP symmetry violation other than in the K 0 K 0 system where it was
discovered in 1964. In 1972, Kobayashi and Maskawa investigated possible sources of violationof the CP symmetry in the unied theory of the weak and the electromagnetic interactions
based on the gauge principle. They concluded as follows: the observed violation of the CP
symmetry requires the presence of either six or more quarks or several new particles such as
scalar bosons and new interactions. This rst possibility is attractive for not requiring any new
interactions, but was too revolutionary to be immediately accepted at the time, when only threequarks u d s were known. However, the subsequent progress in high energy physics led to thediscovery of the c (charm) quark in 1974, the b (bottom) quark in 1976 and the t (top) quarkin 1994, leading to a wide acceptance of the Kobayashi-Maskawa model as the standard theory
for CP violation.
As pointed out in the original paper of Kobayashi and Maskawa, there are several other possibilities for the origin of the CP violation, and experiments capable of distinguishing between
these have become desired. In particular, the Kobayashi-Maskawa model predicts the CP violation eect, whose strength is only one part in a thousand in the neutral K -meson system, tobe as great as one tenth in the neutral B meson system. This should be veried experimentally.
From this perspective, the KEKB project has been launched as an electron{positron collider experiment which aims to deepen the understanding of CP violation through the detailed
investigation of the decay processes of the B mesons. KEKB adopts a scheme where B mesons
are created in high-luminosity collisions of electron and positron beams of asymmetric energies. In addition to the potential discovery of CP violation at systems other than the neutral
K mesons, this project is capable of measuring the complex phase of the Kobayashi-Maskawa
matrix elements, and can provide a clear resolution to the choice between the two possibilities
35

proposed in the 1972 Kobayashi-Maskawa paper for the origin of the CP violation.
The construction project of the KEKB accelerator began in 1994 reusing the old TRISTAN MR tunnel. The KEKB has beam energies of 8 GeV on 3.5 GeV and design luminosity
goal of 1034 cm;2 s;1 . Its design is based on the technology developed further upon experiences
cultivated at the TRISTAN project, such as the RF-cavity technology, is adopted. KEK also
possesses medium scale electron accelerators which are currently operational, such as the accumulation ring (AR) and the Photon Factory ring. One advantage at KEK is that KEKB canbe constructed, while tests are being made at these accelerators.
There is only one beam collision point at KEKB, where the BELLE experiment is to beinstalled. The detector is a spectrometer comprising the silicon strip detector, the drift chamber
and the CsI calorimeter. A special attention is paid in providing high-precision measurementsof low energy particles. The detailed design for the detector is already complete, and theconstruction is in steady progress.
There are several other projects at institutes throughout the world which aim to study
CP violation in B meson systems. At SLAC, the construction of an asymmetric electron{
positron collider (PEP{II), similar to KEKB, is under way. Its experiments are due to begin
simultaneously with KEKB. At Fermilab, experiments utilizing B mesons from TEVATRON
are planned. At DESY, the HERA{B project is planned, which utilizes B mesons created incollisions of the HERA proton beam with a xed target. CERN is planning on the LHC{B
project, where similar measurements will be made using B mesons produced at LHC.
Numerous simulation studies have been made on the physics potential of the KEKB project.
The following scenario is being considered. Firstly, according to the Kobayashi-Maskawa model,
CP violation in the decay mode B ! J=Ks0 should be observed within one or two years of
initial experiments at an accumulated integrated luminosity of between 20 and 60 fb;1 . If
the signal is detected, not only will this be the rst discovery of CP violation outside of theK meson system, but it will be a verication of the mechanism of CP violation based on the
mixing of six quarks, which was the principle behind Kobayashi and Maskawa's prediction on
the existence of six quarks in 1972. If the CP violation is not observed during this period, it
will strongly indicate that the CP violation in K mesons cannot be explained in the frameworkof the Kobayashi-Maskawa model.
In the second stage of the project, the maximum luminosity of the KEKB accelerator willreach the target value 1034 cm;2 s;1 , and an integrated luminosity of 200 fb;1 will be accumulated. The measurement of all parameters of the unitarity triangle will become possible then,and all matrix elements of the Kobayashi-Maskawa matrix, including their complex phases, will
be made, except for Vts . This will allow the conrmation of the consistency of the unitarity
triangle, the comparisons with the decays of the K and the D mesons, and tests of all otherprocesses involving the Kobayashi-Maskawa matrix. Later on, the measurement precision canbe improved, and if any contradictions are discovered in any of these, they will be a basis forstudying Physics beyond the Standard Model. Furthermore, by raising the KEKB energy by 5
36

%, the CP violation in Bs decays can be discovered and the decay modes can be studied.
In any case, KEKB is expected to continue producing important results for more than ten
years after its starting operation, and the pursuit of the KEKB project will be an integral partof the progress of high energy physics in Japan.

5.2.2 The Long-Baseline Neutrino-Oscillation Experiments
While neutrinos are assumed to be mass-less in the Standard Model, the possibility that they
may possess small masses and induce the quantum mixing of the three generations of leptons,
is an important subject of particle physics. It is contrasted with the quark mixing throughthe Kobayashi-Maskawa matrix. It has been discovered recently that the number of solar
neutrinos observed at Kamiokande and other underground experiments is considerably smaller
than predictions of the standard solar model. It is conjectures that this is likely due to neutrino
oscillations. Furthermore, Kamiokande and other experiments have observed an anomaly in theratio between the muon neutrino and the electron neutrino in the atmospheric neutrino ux,
and this indicates that the muon neutrinos created in collisions of cosmic rays in the upper
atmosphere turn into other neutrinos before reaching the underground detectors.
Whether the anomaly in the atmospheric neutrinos is due to neutrino oscillations can beveried in terrestrial experiments. The long-baseline neutrino-oscillation experiment whichconnects KEK and Superkamiokande, was planned in this vein. Its preparations are under way
ahead of other similar experiments in the world. This experiment uses muon neutrinos createdby the 12 GeV proton synchrotron at KEK and measures their ux at Kamioka, 250 km awayfrom KEK, using the Superkamiokande detector which is the largest water Cerenkov device inthe world.
If the muon neutrinos turn into electron neutrinos, Superkamiokande will detect electron
neutrinos, and if the muon neutrinos turn into other particles, Superkamiokande will detect
a reduction in the number of muon neutrinos. In order to detect the conversion into the tau
neutrinos directly, a higher energy for the neutrino beam is necessary. An upgrade to theneutrino source which utilizes the 50 GeV proton synchrotron of the Japan Hadron Facility(JHF) is currently planned, and is described in the next subsection.

5.2.3 The Japan Hadron Facility (JHF)
The Japan Hadron Facility (JHF) is a project for constructing a high intensity proton accelerator
complex, comprising the 50 GeV 10 A proton main ring (50 GeV PS) and the 3 GeV 200 Aproton booster ring. This project is being promoted mainly by researchers in the eld of nuclear
physics, but it is also an inter-disciplinary project which can serve high energy physics and solidstate physics through the use of its secondary neutron and meson beams.
The 50 GeV proton synchrotron of the JHF project will exceed the AGS accelerator of the
Brookhaven National Laboratory (BNL) in the United States both in beam energy and intensity,37

making it the most powerful machine in the world in this energy range. The high energy physics
experiments to be carried out at JHF can be considered as extensions of the particle physics
experiments which are currently carried out at the 12 GeV KEK proton synchrotron accelerator(KEK{PS).
The research in particle physics studied at the JHF project can be characterized as pursuitof the `Intensity Frontier' with high-intensity proton beams, as opposed to experiments at theenergy frontier. In particular, the precision measurements of the K meson rare decays, such as
the K !  , will allow tests of the Standard Model and the determination of the KobayashiMaskawa quark mixing matrix elements. The search for the decay modes forbidden in theStandard Model will allow the study of new physics beyond the Standard Model. Anotherimportant topic will be the search for the hints of new physics through the investigation of
new modes of CP symmetry violation and time-reversal symmetry violation, and through thestudies of fundamental symmetries in the K meson system.
Another important application is the upgrade of the long-baseline neutrino-oscillation experiment, mentioned in the previous section, using the JHF 50 GeV proton synchrotron. By using
neutrino beams with higher energies, direct measurement of lepton appearance in the nalstate through neutrino oscillation will become possible at Super-Kamiokande, besides higher
precision and statistics are expected in studies of neutrino oscillations in general. Furthermore,
if oscillations are seen, it will also be possible to investigate the CP violation in lepton mixing, analogous to the Kobayashi-Maskawa mechanism in quark mixing. It is hoped that thelong-baseline neutrino-oscillation experiment will provide a key to the understanding of the still
mysterious properties of the neutrinos.
By using the high intensity muon beams generated from a proton beam, it will be possible
to investigate lepton-avor violating processes such as + ! e+ and ; ; e; conversion in
nuclei with an unparalleled sensitivity. Many models, which are extended from the Standard
Model, such as the Supersymmetric Grand Unied Theory, predicts lepton-avor violation at
the order of a tenth or a hundredth of the current experimental lower bound. They will become
within the reach of experiments at JHF. The rare muon processes, along with the proton decay,
are considered to be the most appropriate experimental measurement in the testing of theSupersymmetric Grand Unied Theory.
Considering the fact that hadron accelerators capable of xed target experiments have become scarce throughout the world, it is hoped that the JHF project will attract international
interest as a facility open to the world. The Japanese experimental groups which have taken
part in the xed target international collaborative experiments in the United States and Europe
will gain a ground for research activities based in Japan. We consider it necessary from now on
for Japan to take up a leadership in international research collaborations and to promote thecollaborative experiments at JHF.

38

5.2.4 Non-Accelerator Particle Physics Programs
The current directions in particle physics capitalize on the success of the electroweak uniedtheory and formation of the Grand Unied Theory which involves also the strong force, andtheories which also unify the fourth force, gravity. The experimental verication of these uniedtheories have become essential for the progress of particle physics. Non-accelerator particle
physics programs aims at nding the proton decay, events induced by nite neutrino masses,
and magnetic monopoles and so on, which are predicted by Grand Unied Theories. Since
most of these are dicult to study in the accelerator environment, non-accelerator particle
physics programs are complementary to accelerator particle physics programs. The simultaneous
execution of both types of experiments is hoped to bring further progress in particle physics.
Particle physics deals with fundamental laws of nature that governs the creation, the evolution and the end of the universe. The detection of the signals from particle interactions which
took place during the creation of the universe, the creation of the elements and the formationof galaxies, holds the key to clarifying the picture of the universe. Another important topic in
non-accelerator particle physics is detection of particles originating from the Earth, the Sun andthe active galactic objects, and the detection of the particles which have been produced throughthe evolution of the universe. Discoveries in such studies can bring revolutions to cosmology
and particle physics, and this eld has attracted much attention recently.
Non-accelerator particle physics research in Japan has been playing the leading role in theworld. Particularly outstanding research achievements have been accomplished at experiments,
such as, the Superkamiokande experiment which chiey aims to detect the proton decay, thesolar neutrinos and the atmospheric neutrinos, the search for the double beta decay and thecosmic dark matter at Osaka University, the search for the cosmic anti-matter and the cosmic
dark matter at University of Tokyo, and the search for the axion at Kyoto University havecultivated important results. They deserve continued support in the future.
As described above, Nature and the Universe are themselves a great laboratory for particle
physics. Non-accelerator particle physics, which explores a new aspect in particle physics andcosmology, deals with much that is still unexplored, and it is important to promote uniqueoriginal research activities which cultivate this eld. The development of devices for detecting
ultra-weak particle interactions, based on high capacity liquid scintillator planned at Tohoku
University, and various experiments involving ultra-cold neutrons planned by the physicist groupsupported by Grant-in-Aid for Scientic Research on Priority Areas are amongst the mostpromising future projects.
For the sake of progress in particle physics, while the advancement of accelerator particle
physics at the energy frontier is the most pressing topic, smaller-scale and original research in
non-accelerator particle physics will also be important. Such research activities lead not only tothe progress in particle physics, but also to the training of researchers and to the advancementof the experimental technology, which lead to improved general research capability.
39

5.3 Projects in Overseas
The prime motivation for participating in international collaborative projects is in allowing the
researchers to take part in large scale projects whose execution is impractical for one country
alone, and in contributing to ingenious experiments which are not carried out in Japan. At
the same time, the participation will also bring about positive inuence towards the cultivation of the human resources. For instance, by providing young people, such as the graduate
students and the assistants, with opportunities of participating in experiments overseas, evenat smaller scale ones, personnel can be nurtured with a global orientation who are capable ofcarrying out research in collaboration in an international environment, and their personal relationships with overseas researchers and experience will be essential for promoting future large
scale collaborative projects.
We examine below the current status and the future perspective of the international collaborative experiments where Japanese high energy physicists are participating.

5.3.1 The LHC Project
LHC (Large Hadron Collider) is a 14 TeV next-generation proton{proton colliding beam accelerator at CERN, which will be constructed inside the LEP tunnel after the termination of the
LEP2 program. LHC will begin the proton-proton collision experiments in 2005, and its nal
target luminosity will be 1034 cm;2 s;1 . The Japanese contribution will consist of participationof researchers from KEK and the universities in the proton{proton collision experiment ATLAS,
as well as in the construction of the accelerator.
As discussed in chapter 2, the biggest objective of the LHC project is the discovery of the
Higgs particle. The collider is capable of nding not only the Standard Model Higgs particle but
also the Higgs particles in a wide mass range predicted by the supersymmetric theories. It will
also search for colored supersymmetric particles, explore new phenomena which are predictedby the technicolor model, and look for other unknown phenomena beyond the Standard Modelat the energy frontier. In addition to the search for new particles, it will also allow us to study
a rich set of phenomena such as the precision measurements of the top quark properties and themeasurements of CP violation in B mesons decays. The LHC project can also support various
options such as the LHC-B project which focuses on the measurement of CP violation, and thecollisions of heavy ions such as lead ions.

5.3.2 The SLC/SLD Experiments
SLC, which began its high energy physics program in 1989, is the rst Linear Collider in theworld which accelerates electrons and positrons to 50 GeV, splits them via arcs and collides
them. High energy physicists from Nagoya and Tohoku Universities have been participating in
the SLD detector experiment as a part of the US/Japan Cooperation in High Energy Physics.
The acceleration of polarized electrons became possible in 1992, and the measurement of the40

electron polarization asymmetry in Z boson production cross section led to the measurement of
the Weinberg angle of the electroweak interaction at an accuracy comparable to the LEP data.
The SLD group has been considering an option where the nal focus unit will be modied andthe experiments continued in order to observe about three million polarized Z boson events.
The experience gained at SLC and SLD is hoped to play an essential role in the developmentof the accelerator and the detector at the future Linear Collider project.

5.3.3 LEPThe European Laboratory for Particle Physics (CERN) constructed the Large Electron{Positron
Collider (LEP), which is the largest and the highest energy electron{positron colliding beam
accelerator in the world, and began experiments in 1989. Out of the four detectors, the OPAL
experiment has a group of Japanese researchers mainly from the University of Tokyo, which hastaken a central role in the project since the design stage of the detector.
LEP began experiments with the center-of-mass energies near the Z boson mass (LEP1). In
addition to carrying out precise verication of the Standard Model such as the determination of
the quark and lepton generation numbers, LEP experiments searched for new particles such as
the Higgs boson and supersymmetric particles and new phenomena. In the second stage (LEP2),
the beam energy was upgraded and in 1996 the center-of-mass energy exceeded the W boson
pair production threshold, reaching 172 GeV. LEP will continue upgrading the beam energy
and will carry out precision tests of the electroweak interaction using W boson pair production.
In addition, the Higgs boson of mass up to about the Z boson mass can be discovered. Thereis also much hope towards the discovery of the supersymmetric particles.
Ever since the initial experimental program, LEP has been at the energy frontier, and thephysics studied at LEP is of the same nature, albeit at smaller energies, as the physics of thenext generation energy frontier at the Linear Collider. Thus, it is hoped that the physics results
gained at LEP2 will provide crucial information for the Linear Collider project.

5.3.4 Fermilab TEVATRONTEVATRON is a proton{antiproton colliding beam accelerator of the highest center-of-massenergy in the world (1.8 TeV) built at the Fermi National Accelerator Laboratory (Fermilab) in
the United States. Its operation began in 1987. The characteristic feature of a hadron collider
at the energy frontier is that it is capable of discovering new phenomena at energy ranges
which are out of the reach of the contemporary electron{positron colliders. A Japanese groupof researchers from University of Tsukuba and other institutes has participated in the CDF
experiment, which is one of the two collider experiments at TEVATRON, since the preparatory
stage. An integrated luminosity of 0.11 fb;1 has been acquired by the February of 1996, which
led to the evidence for top-quark production in 1994.
In 1999, the main injector ring, currently under construction, will be completed, and it will41

allow the data accumulation of 2 fb;1 per year. This will enable precision measurements ofthe top-quark and W -boson masses, as well as precision measurements of the parameters in the
Kobayashi-Maskawa matrix involving B mesons. As for future programs, the TeV33 projectwill involve construction of a recycler ring around 2004, which will be used as the storage ringfor antiprotons. It will enable improvement of the luminosity to 1033 cm;2 s;1 . It is anticipatedthat the discovery of the Higgs boson up to the mass of 120 GeV will then be possible.

5.3.5 DESY HERAThe Deutsches Elektronen-Synchrotron (DESY) operates the only existing electron{proton colliding beam accelerator (HERA) in the world, which began its operation in 1992. There are
two international collaborative experimental groups organized for the collision experiments, andmembers of the Institute of Nuclear Study at University of Tokyo (currently a part of KEK)
and Tokyo Metropolitan University have been participating in the ZEUS collaboration.
Electron{proton scattering experiments at high energy is eectively a huge electron microscope which utilizes the electrons as the probe for studying the quarks inside the proton. The
center-of-mass collision energy is about 300 GeV, and is more than ten times higher than thecorresponding xed target experiments in the past. Using the data obtained up to 1995, precision measurements were made on the distribution of quarks and gluons inside the proton. The
results provided a good test of Quantum Chromo-Dynamics (QCD) which constitutes a core of
the Standard Model.
After 1998, scattering experiments using a polarized electron beam will become possible, andan upgrade towards a higher luminosity will be made in 2000. It is hoped that this will enablevarious precision studies of the electroweak interactions such as the search for the right-handed
W -boson and right-handed neutrinos.
In addition to the collision experiments described above, there is the HERMES experiment
which studies the scattering of a polarized electron beam o a stationary nuclear target. The
experiment has been in operation at HERA simultaneously with the collision experiments since1995. Members of Tokyo Institute of Technology have participated in this experiment. Furthermore, an approval has been given to the HERA-B project, which produces B -mesons using
the HERA proton beam on a stationary nuclear target. The detector for the HERA-B projectis currently under construction.

5.3.6 Fixed-Target Experiments
There are several noteworthy xed-target experiments carried out abroad as international collaborative projects. Examples include the KTeV experiment carried out at the Fermi National
Accelerator Laboratory (Fermilab) and the E787 experiment at the Brookhaven National Laboratory (BNL), which study the weak interaction through the precision measurements of the K
meson decays. The Osaka University group has participated in the KTeV experiment, carrying
42

out the measurement (E832) of a direct CP violation parameter Re( 0 = ) and the search (E799)
for the rare decay modes such as KL ! 0 e+ e; and KL ! 0 + ;. Physicists from KEK and
Osaka University have participated in BNL E787 and have searched for K + ! +  . 1
After the year 2000, there are plans under way for experiments involving the decays of
the K mesons using the Fermilab main injector ring and the BNL AGS. One of the principal
topics in the study of the K meson decays will be the detection of the direct CP violation in
KL ! 0  to determine the parameter in the Kobayashi-Maskawa matrix. This experimentwill be carried out concurrently with the B-factories and will play a complementary role in the
search for the origin of CP violation.
At the CERN Super Proton Synchrotron (SPS), there are two neutrino experiments currently
in progress which aim to detect the neutrino oscillation  !  . A Japanese group based
mainly in Nagoya University has participated in the CHORUS experiment, being responsible
for the emulsion target which is the essential part of the experimental setup. We await theexperimental results. The Nagoya group is also running an experiment (E872) which searchesfor  at Fermilab by using the emulsion target technique.
As for the next-generation neutrino experiments, CERN and Fermilab have plans for longbaseline neutrino-oscillation experiments, which are due to start operation at the beginning of
the 21st century. These long-baseline experiments will allow the detection of neutrino oscillations  ! e and  !  for a broad parameter range which has not been covered before,
thus leading to clarication of the nature of the neutrinos.
In addition, there is the COMPASS experiment that has been proposed through a consolidation of research programs on glueball and other hadron spectroscopy. Japanese groups are
participating in this and also in the study of the nucleon spin structure functions at SPS byusing the proton and muon beams.

5.3.7 The Tau-Charm Factory

Note added on the English translation (Jan/23/1998):

The rst candidate event was observed in the summer

At the Institute of High Energy Physics (IHEP) in China, the Beijing Tau-Charm Factory(BTCF) is currently under construction. This is an electron{positron two-ring accelerator
collider with a beam energy of 1.53 GeV and the target luminosity of 1033 cm;2 s;1 . BTCF aims
at studying the scalar glueball, the particle{antiparticle mixing in the D-mesons, and the CP
violation in the decay of the tau. KEK has announced its support for the BTCF accelerator anddetector development, and the Asian Committee for Future Accelerator (ACFA) also supports
the pursuit of the R&D. This project is the only accelerator project for high energy physics
programs in Asia outside Japan, and may become an important corner stone in the ChinaJapan collaboration in the future.

1of 1997.

43

Chapter 6

Human Resources Development andOrganization
6.1 An Overview
High energy physics is a eld which utilizes a variety of frontier scientic technology. In orderto achieve progress in the research of particle physics through acclerator and non-accelerator
experiments, it is desirable to raise a broad interest and to aggregate a wide range of personel.
High energy physics is a eld based on large-scale projects with long term perspective. For
the success of the principal project, the e+ e; Linear Collider, it is essential to clearly dene thedirection of the project and to exploit fully the collective capability of the community. At thesame time, it is very important to have a research system which encourages the creativity andthe enthusiasm of the frontier researches. The successful execution of such projects requires thenurturing of the younger generation researchers.
However large the project might be, the driving force of research lies in the creativity andenthusiasm of the individual researchers, and the key in pushing ahead the project resides inextracting such indivusual capability. The role of the leaders of the organization is not only
to show the direction of the project in general, but also to provide a creative environment, inwhich unique ideas can be introduced to the system after a scientically fair evaluation.
The next principal project e+ e; Linear Collider is a project of the Asia{Pacic region which
is open to the rest of the world. Eorts should be made toward the build-up of an environment
which is suitable for promoting an adequate international set-up. This is required for aspects ofboth the project organization and encouragement for personnel, from the R&D and construction
phase of the project.

44

6.2 The Roles of KEK and the Universities
As a result of discussions on the interrelationship between the universities and inter-university
research institutes, the High Energy Committee of Japan founded the Subcommittee for enhancing the activities of university high-energy-physics groups in 1996. The Subcommittee on Future
Projects of High Energy Physics in Japan expresses its support for the important activities to be
carried out by the Subcommittee for enhancing the activities of university high-energy-physics
groups, and hopes that discussions from broad perspectives there will be reected for the benetof the next-generation researchers who would be responsible for future developments of highenergy physics.
Japanese high energy physics experiments so far have been carried out mainly in the formof collaborative work in constructing experimental facilities and conducting experiments which
utilize the infrastructure of central laboratories, most typically KEK. Many research projects
have been conducted in the framework of such collaborations between universities and central
laboratories. Training of the next-generation researchers has also been taking place in suchan environment. It should be noted that a superb work environment, where top-class research
activities are conducted, is indispensable for educating competent scientists who would carryon the research leadership of tomorrow. The TRISTAN project has played a great positive rolein this respect. Namely, the Japanese high energy physics community has seen a vast growth inits population and competitiveness, and an increasing number of universities, previously withno high energy physics groups, have come to join TRISTAN experiments. Naturally, this trend
should be maintained and encouraged through the B-factory project, eventually passing on to
the Linear Collider project.
At present, more than a half of the entire Japanese high energy physics researchers atuniversities belong to a group with approximately 10 or more members each, where graduate
students are included in the count. However, the rest of the high energy physicist population is
distributed in much smaller groups with only one or two sta members each, and they are facingdiculty participating in large collaborations. On the other hand, the researchers at universities
have an advantage of having a greater access to undergraduate students, and are in a position to
give more positive impacts on them towards high energy physics. It is imperative that the eortsof researchers under varying conditions be coherently consolidated for promoting the principal
project. The importance of building up structured collaborative links among universities, andbetween KEK and universities, must be underlined.
While promoting the Linear Collider project, the university groups have a specic responsibility for raising the next-generation researchers, as well as for spearheading the work in new,advanced research topics. In this context, an important aspect of their task lies in R&D eorts
on accelerator and detector technologies, which are driven by exible thinking and long-term
perspectives. For this purpose, suitable research infrastructure needs to be steadily accumulated
in universities so that they have their own R&D capabilities for developing pioneering exper45

imental technologies for the future. This denitely allows universities to have more eective
collaboration with KEK.
Due to the government policy for ecient execution of the budget, the funding and humanresources for those research programs which utilize the KEK facilities have so far been preferentially allocated to KEK. Although the current system is in a way ecient, it is recognizedthat there are rooms for improvement. A point to be noted here is that the system has to be
operated in a way that individual university groups are encouraged to exercise their researchcapability to its full extent, with a sucient degree of self discipline and long-term perspective
and commitment. This is particularly important for creating an even more solid collaborative
relationship between universities and KEK. For these reasons, this subcommittee considers it
important to explore the possibility of a revised system that allocates budgets to universities
based on claried responsibilities and commitment in high energy physics projects.

6.3 Diversity of the Human Resources for the Principal Project
The realization of the Linear Collider requires the aggregation of the frontier technologies. In
addition to technologies specic to high energy physics, those from various other frontier areas
related to materials and manufacturing need to be collectively used. Therefore the project
should attract the attention of researchers from a broad range of communities, and the personnel
cultivation and the formation of the experimental organization need to be made more broadly,
while extending the bounds of the high energy physics community. The progress in the eld ofaccelerator science has generated a variety of users, for example in solid state physics throughthe use of synchrotron radiation and neutron beams, in radiation therapy through exploiting
various particle beams, and in the study of future energy source problems. It is desirable toactivate communication among scientists in these elds, especially with the young researchers
who are interested in accelerator technology and high energy experiments.
The number of engineering and technical stas at universities and research laboratories has
been small as compared to those in the US and in Europe, and it is decreasing further as a resultof the general reduction of civil servants in Japan. It is necessary for the entire high energy
physics community to keep trying to obtain the support of the public and the bureaucratic
sectors for stopping this trend and also for making the salary structure more attractive to theengineering and technical stas.
Concerning the development and the construction of accelerators and detectors, Japan has
created a unique scheme of collaborating with many industrial engineers and researchers. Thissystem of collaboration with industry which possesses a large number of technical sta has
the benet of mutually raising the ability in accelerator science and frontier technology, and ofeectively securing the personnel. This should be encouraged further in the future. In doing
so, a collaborative research basis which allows for the accumulation of technology regardless ofthe personnel movement should be developed. The universities and KEK should also organize46

a system for inviting these industrial engineers and researchers as visiting researchers, graduate
students or research students. CERN, in constructing LHC, also is organizing the research anddevelopment in collaboration with the industry, and utilize the capability of the industry in the
manufacturing of components such as the superconducting magnets. When the project scale
exceeds a certain limit, this system is advantageous for securing a broad range of personnel, forthe large scale production system and for the quality control of a large number of components,and should be further promoted.

6.4 The Structuring of a Suitable Environment for an International Laboratory
At an international laboratory there should be no national, racial and other discriminations in
the personnel management and membership of executive committees.
For Japan to function eectively as the host country for the Linear Collider, it is essential
to prepare an environment suitable for inviting researchers from throughout the world. In
particular, the housings, the medical care, the education of children, the language educationand the employment of the spouses are amongst the very basic needs which should be provided
to the foreign researchers. At the same time sincere care should be made concerning the culturalenvironment for the long-term visitors. Not only amongst the researchers but also the relevant
departments of the government and the local communities should welcome the presence ofdierent cultures and to help resolve various diculty faced by the foreign researchers and thestudents who will participate in the project. There should be a permanent section at the central
institute created specically for helping foreign researchers and their family members.
In order to promote collaborative research nationally and internationally as an international
laboratory, international personnel exchange programs are essential, and they should be morestrongly encouraged. In particular, the mobility of temporary and sta scientists into and fromJapan with respect to overseas institutes is still low, and its promotion will be essential forthe creation of a truly international research institute. Furthermore, for the sake of an active
promotion of the research internationalization, eorts should be urgently made such that both
short-term and long-term visitors can utilize KEK as a base for their research.

47

Chapter 7

Interdisciplinary Aspects
7.1 An Overview
What is science? This question, concerning both natural and social sciences, have been discussed for years from various standpoints, including, philosophical, religious and ideological andother perspectives. However, it would be safe to characterize one aspect of scientic endeavors
as organization and categorization of the total knowledge of human being. While the progress ofscience induces development of deeper and more specialized branches of research, it also createsanother stream of eorts whereby attempts are made to understand Nature from a more consolidated and unied standpoint. Such trends are naturally expected from the nature of science
itself. There are quite a few cases where a progress in one eld of science, while contributing toaccumulate the intellectual asset of its own eld, ignited a revolutionary transition of methodology or paradigm in other elds. Interdisciplinary eorts made by researchers of multiple elds
have opened a number of new branches of science, and helped enrich science as a whole. Thishistory indicates that the most desirable form of progress in science should be found in active
and balanced interactions among many research elds, including applied sciences.
High energy physics, while rapidly absorbing the fruits of other elds and applying them,
directly or indirectly, to its advancement of accelerator and experimental technologies, is in
an excellent position to promote development of a new interdisciplinary eld, as well as tocontribute to the progress of other branches of science. The general observations on the scienticresearch above strongly corroborates such an expectation. Moreover, it is felt that this trend
will be more evident in the near future. This chapter attempts to examine the mission of highenergy physics in such a global scientic context.

48

7.2 High Energy Physics as a Branch of Science and its Relationship to Other Fields
When one examines Science as the systematic aggregation of accumulated human knowledge,
each eld of natural sciences is found to have two facets. One facet is characterized by theobjects or phenomena that the eld of science specically deals with. They are characteristics
which are distinct to each eld. The other facet is represented by abstract principles or a generalparadigm which dictate the methodology and the laws that the eld deals with. Interdisciplinaryinteractions of dierent branches of science, including high energy physics, takes place throughthe link that is provided by this second facet.
In terms of the rst facet, according to the analysis above, particle physics is a eld of naturalsciences which attempts to disclose the fundamental particles and their interactions. The highenergy experiments at the LHC and at the Linear Collider are hoped to bring answers to thequestion of the origin of mass. This, in turn, is expected to bring hints to more fundamental
questions, such as, why the specic particles exist in the specic pattern and how the spacetime structure of our universe allows these particles to exist. For instance, the supersymmetrictheories, which are considered to be the most promising candidates for new physics, indicatethat our space-time is not in fact 4-dimensional (i.e., one time dimension and three spacialdimensions). Rather, they suggest that our space possesses extra dimensions which is related
to the existence of particles with dierent spins, super-partners. Some of the more ambitious
attempts to build a truly unied theory, which includes the gravity and all particles, have led tothe superstring theory. There, the very question as to why the present space-time is apparently
four-dimensional is considered to be one of the major research topics.
The research topics of particle physics have always been our most fundamental questions
concerning Nature, the fruits of which have inuenced our views of Nature and the universe
profoundly, and will continue doing so in the future. On the other hand, because the scales ofenergy and space-time distances in particle physics research is so much dierent from the restof the objects in natural sciences, it is dicult to imagine that the new laws of particle physics
that will be discovered in the future will aect research in the other elds directly. The only
exception may lie in the relation between particle physics and cosmology, because the originof the universe through big bang cosmology is thought to be an ultra-high-energy phenomenon
relevant to particle physics. Thus cosmology and particle physics are now beginning to fuse intoone eld of science. Through this fusion of the innitesimal and the innite, particle physics
and cosmology will continue having great inuences on our view of Nature.
The other facet of particle physics is that the laws of Nature found in the world of particles
may be abstracted and applied to other elds of natural sciences. Conversely, the laws of Nature
discovered in the macroscopic world may be rediscovered as laws governing the interactions
between fundamental particles.
Through this second facet, the research in particle physics will develop jointly with the re49

search in other elds. This is the facet which allows particle physicists to actively participate
in the interdisciplinary approaches which are beyond the conventional classication of scienticelds. There are numerous examples of such interdisciplinary developments. Some well-known
examples include the application of a theoretical framework developed in electric engineering
onto the quantum mechanical world, and a well-known concept in the theory of superconductivity which plays a fundamental role in the understanding of the origin of the mass of thefundamental particles. The study of complex systems, and research areas described with keywords such as chaos, catastrophe and non-linearity, which have recently met strong interests,
have large overlap with particle physics research when faced with such fundamental questions
as the origin of the universe and the space-time.
There are numerous other examples, but in more abstract terms, the entire cultural background, including art, can promote the introduction of new concepts in science. The modern
days are said to be an era of scientic technology. This is not only because the technologicaldevelopment has been a driving force behind the entire era but also because the DNA and othergenetics research as well as other branches of biology including the study of the brain, havecreated a profound inuence on the spirit of the era. The origin of mass and the creation of
the universe, as described in chapters 1 and 2, were questions whose scientic value was under
scepticism in the past. The great transitions in particle physics such as the understanding of theorigin of mass, is about to be triggered by the Linear Collider experiments. Since the conceptof mass is so fundamental to matter, our understanding of its origin will lead to the revolution
in the human view of matter, the universe and Nature, as well as science. Since such greattransition can be expected now, it is crucial further promoting particle physics research and theLinear Collider project.

7.3 Other Fields of Accelerator Science
The eld currently known as High Energy Physics can be dened historically as the researchconcerning the fundamental units of matter and the fundamental particles, and the interactions
governing them. It has been called particle physics for this reason. At the beginning of the20th century, the smallest units of matter were the atoms, and then they became the nucleus of
the hydrogen atom, that is, the proton, and now the constituents of the proton, the quarks, areconsidered the fundamental particles (the constituents of quarks are also speculated by sometheorists). Starting from the discovery of the atomic structure where the positive electric charge
is condensed at the center of the atom, the study of particle physics in the 20th century has taken
as its central methodology the utilization of higher and higher energy particles collided withmatter for studying their structure and interactions. In particular, the study of the elementary
particles as the constituents of the nucleus obtained the name High Energy (Nuclear) Physics
since higher and higher energy accelerators have led to the discoveries of particles of higher andhigher masses. Thus the naming came from the study of the properties of nuclei at high energies,
50

but more generally, it is the experimental science utilizing high energy accelerators. Whileparticle physics in the traditional sense has developed by high energy accelerator experiments,
the study of the nuclear properties at `low' energies using low-energy accelerator is now called thelow-energy nuclear physics and it is also a developing eld. As high energy physics continuallyshifts its attention to higher energies, there is now a new eld at an intermediate energy, called
the medium-energy nuclear physics.
The historical circumstance that the invention of the particle accelerator had its purposein the study of particle physics has its natural consequence that high energy physics has been
the driving force behind the progress in accelerator technology. Since high energy physics now
demands yet higher energy accelerators and demands more sophisticated accelerator technology,
this role as the driving force is becoming ever more important. On the other hand, the particle
accelerator, which have been developed along with the progress of high energy physics not
only nds applications in particle physics in the broad sense described above, but also has
provided revolutionary research methodology in many other elds. There are now developmentsin accelerator technology specic to the research of each corresponding research eld. As a result,
there are now cases where developments in accelerator technology with objectives outside highenergy physics have been applied to high energy physics research. Thus accelerator-based
research has spread over a broad range of science and engineering, and it has found broad
industrial applications. We are observing the advent of the common scientic interdisciplinaryeld of Accelerator Science.
As for the industrialized applications of the accelerator, there is the radiative isotope production for medical and manufacturing purposes. The use of the proton and heavy ion accelerators
for the treatment of cancer is currently becoming a practical method after the experimental
preparatory stage. The industrial application in material processing using primary beams is
expected to become more abundant.
The research and development, and the construction and operation of particle acceleratorsfor high energy physics have contributed to other elds of accelerator science. One example isthe synchrotron radiation. The synchrotron radiation, for its brightness and other properties,
have attracted much attention from various other scientic and engineering elds as soon as thehigh energy electron{positron accelerator rings were constructed. As a result, many synchrotron
radiation rings have been built, and currently, the so-called third generation rings are built andbeing operated. On one hand it is already regarded as an everyday research methodology
in science, and on the other hand there is much anticipation towards its industrial applicationsuch as the semiconductor manufacturing. The improvement of synchrotron radiation brightness
requires the improvement in the beam characteristics. These are precisely the characteristics
required by the B-factory and the Linear Collider damping rings. The progress in synchrotron
radiation rings has gone hand-in-hand with high energy electron accelerators.
In addition, the most promising electron beam source of the free electron laser, which is
expected to become the dream light source of the future, is the high-luminosity Linear Collider.
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There are several test facilities of Linear Collider which are about to realize X-ray free electron
lasers with high coherence.
On the other hand, the high energy proton accelerators have attracted attention as thepulse neutron source, and KEK has the history of constructing KENS ahead of the world
which utilizes the proton beams from the 500 MeV booster. As a result of the recognitionof its usefulness, ISIS was constructed in Britain which has a hundred times greater power,
and LANSCE was constructed in the United States. These proton beam accelerators havealso become an important technique for a broad range of sciences. In particular, neutrons
are sensitive to the presence of hydrogen, and it has been regarded as a powerful tool in the
structural analysis of biological polymers. Since a neutron has roughly the same mass as ahydrogen nucleus, and since it is possible to explore various properties of materials which cannot
be explored by light, it is the most promising probe in the study of material structure. The
high-intensity high-energy proton accelerator can also create muons, which can be considered
as heavy electrons, in large quantities. The muons are also attracting attention in the studyof materials utilizing its unique characteristics, similarly to the pulse neutron source. Becauseof such wide and diverse interests, the JHF project in Japan, the ESS project in Europe, andthe ORNS project in the US are about to be constructed as the third generation neutron andmuon source. The construction of these high-intensity high-energy proton accelerators requires
the development of the high electric-power RF accelerator equipment, the minimization of thebeam loss and the beam instability, and other sophisticated accelerator technology. These are
precisely the extension of the accelerator technology which has been developed so far for thehigh energy physics accelerators.
In particular, at KEK, the 12 GeV proton synchrotron (including the 500 MeV booster), theaccelerator PF (photon factory) for the synchrotron radiation, and TRISTAN were constructed
and operated. Currently KEKB is under construction, and in the near future JHF will be
constructed. Furthermore ATF has been built and has just begun operation. These accelerators
at KEK show precisely the history of the development of the accelerator technology driven by thedevelopment, research, construction and operation of the preceding accelerators. They clearly
demonstrate the necessity of progress in high energy physics accelerators for the progress ofaccelerator science. On the other hand, there are recently applications of technology developed
for the sake of other accelerators in high-energy-physics accelerators.
Considering the energy and environmental problems of the 21st century, it is beyond question that a clean and safe energy source is necessary to minimize environmental pollution. The
potential of the super-high-intensity high-energy proton accelerator for processing radioactive
waste from nuclear-power plants, and also in the nuclear-power generation based on a new concept, has recently obtained much attention. This will play a central role in the neutron science
research project planned at the Japan Atomic Energy Research Institute. For its realization,
the superconducting accelerating system which was developed for the rst time at TRISTAN
is a necessary element. Furthermore, the high-power RF system developed at KEKB, ATF
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and for JHF to accelerate high-current beams, and other aspects of the accelerator science as awhole, including the accelerator theory, will be needed. For the nuclear fusion reactor, which is
expected to be a dream energy source of the future and whose development is under competitions throughout the world, the super-high-current deuteron source will be an essential element
to be used in the materials research for the reactor. It is planned to be built on a collaborativebasis (IFMIF).
Reecting upon these historical circumstances, and from the viewpoint of accelerator science,the progress in high energy physics will be essential as a driving force in exploring the technologyof the 21st century.

7.4 The Relationship between Accelerator Science and Other
FieldsAs described above, Accelerator Science is an interdisciplinary science by itself and it has
deep connections with many other advanced technologies. The success of accelerator sciencein Japan, including high energy physics, is based not only on its economic power but in its
high technological capability. On the other hand, high energy physics has promoted progressin frontier advanced technology through the research, development, construction and operationof advanced accelerators. High energy physics accelerators should be designed and constructedby utilizing the highest standard of advanced technology available and exploring the limitsof the achievable characteristics, and should hence be called the energy frontier for that reason. Thus its research, development, construction and operation require the continual eort
to nd even one small step for the advancement of frontier technology. The fruits of such efforts will naturally contribute to further improving the technological standards. For example,
the super-high-precision machine processing, the superconducting technology, and the surface
processing technology necessary for the RF accelerator technology, as well as the high-precisioncomputer network, the high-speed electronic circuits and the high-speed measuring technology
are amongst the innumerable examples of the technology promoted by accelerator science.
(End)
This English language version of the HEPSC Final Report is a translation, prepared by the HEPSC members, of an original, authentic document produced in Japanese. Any questions that may arise about theinterpretation of the report should be resolved with regard to the original
Japanese document.

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