Future Colliders:

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Future Colliders Opening Windows on the World
Young-Kee Kim The University of Chicago ICFA
Seminar September 28 - October 1, 2005 Kyungpook
National University, Daegu, Korea
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Welcome to Korea
Calligraphy by my father
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Accelerators are Powerful Microscopes.
They make high energy particle beams that allow
us to see small things.
seen by high energy beam (better resolution)
seen by low energy beam (poorer resolution)
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Accelerators are also Time Machines.
They make particles last seen in the earliest
moments of the universe.
Energy
anti-particle beam energy
particle beam energy
Particle and anti-particle annihilate.
E mc2

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Accelerators powerful tools!
KEKb, KEK, Tsukuba, Japan
PEP-II, SLAC, Palo Alto, USA
HERA, DESY, Hamburg, Germany
Tevatron, Fermilab, Chicago, USA
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1929
Ernest Lawrence (1901 - 1958)
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With advances in accelerators, we discovered many
surprises.
Our field has been tremendously successful in
creating and establishing Standard Model of
Particle Physics answeringwhat the universe is
made of and how it works
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What is the universe made of?
90 years ago
Rutherford
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Everything is made of electrons, up quarks and
down quarks.
Are electrons, up and down quarks the smallest
things? Are they made of even smaller things?
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Elementary Particles and Masses
top quark anti-top quark
ne nm ?nt e- m????t?? ???u d s c b
. . . .
- - - - - - -
-
ne nm ?nt e m????t?? ???u d s c b
Z
W, W-
? gluons
(Mass proportional to area shown but all sizes
still lt 10-19 m)
Why are there so many? Where does mass come from?
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What holds the world together? Beginnings of
Unification
Gravitational Force
Electromagnetic Force
Issac Newton (1642 - 1727)
James Clerk Maxwell (1831 - 1879)
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Unification of Gravity and Electromagnetism?
Einstein tried to unify electromagnetism and
gravity but he failed.
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radioactive decays
Enrico Fermi (1901 - 1954)
Weak Force
holding proton, nucleus
1 fm 10-15 m
Strong Force
gluons
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Dream of Unification continues! We believe that
there is an underlying simplicity behind vast
phenomena in nature. Do all the forces become
one? At high energy, do forces start to behave
the same as if there is just one force, not
several forces? Extra hidden dimensions in
space?
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Particle Physics Cosmology Questions from
Astrophysical Observations
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Everything is made of electrons, up quarks and
down quarks.
Galaxies are held together
by mass far
bigger (x5) than all stars combined. Dark Matter
- What is it?
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Accelerators
Inflation
Big Bang
particles anti-particles
Where did all antimatter go?
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Matter and Anti-Matter Asymmetry (CP
Violation)Belle at KEK in Japan and BaBar
at SLAC in USdiscovered CP violation in the B
system.From their subsequent precision
measurements of CP violation we know now that
there must be new physics with CP violation in
order to explain matter and anti-matter asymmetry
in the universe.
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Not only is the Universe expanding, it
is Accelerating!! Where does energy come
from? Dark Energy
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Primitive Thinker
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• 1. Are there undiscovered principles of nature
• New symmetries, new physical laws?
• 2. How can we solve the mystery of dark energy?
• 3. Are there extra dimensions of space?
• 4. Do all the forces become one?
• 5. Why are there so many kinds of particles?
• 6. What is dark matter?
• How can we make it in the laboratory?
• 7. What are neutrinos telling us?
• 8. How did the universe come to be?
• 9. What happened to the antimatter?

Evolved Thinker
From Quantum Universe
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Answering the Questionswith Next Generation of
Accelerators (Colliders)
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today
1970 1980 1990
2000 2010 2020
2030
Energy Frontier Colliders
ILC
LEP,SLC
CLIC ?? Collider
ee- e-proton proton-proton
HERA
LHC
TEVATRON
Flavor Specific Accelerators
LHCb
ee- (b factory) ee- (c factory) ee- (s
factory) ?
PEP-II, KEKB
VEPP, CLEO-c, BEPC
DA?NE FNAL, CERN,
J-PARC
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Origin of Mass There might be something (new
particle?!) in the universe that gives mass to
particles
Nothing in the universe
Something in the universe
Electron Z,W Boson Top Quark
Higgs Particles
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Tevatron Improve Higgs Mass Pred. via Quantum
Corrections
MW (GeV)
Mtop (GeV)
Current precision measurements favor light Higgs
lt 200 GeV.
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Tevatron Improve Higgs Mass Pred. via Quantum
Corrections
LHC Designed to discover Higgs with Mhiggs 100
800 GeV
130 GeV Higgs L 100 fb-1
of events / 0.5 GeV
MW (GeV)
M?? (GeV)
Mtop (GeV)
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Tevatron Improve Higgs Mass Pred. via Quantum
Corrections
LHC Designed to discover Higgs with Mhiggs 100
800 GeV
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Tevatron Improve Higgs Mass Pred. via Quantum
Corrections
LHC Designed to discover Higgs with Mhiggs 100
800 GeV
5? Discovery / Luminosity (fb-1)
Will the Tevatrons prediction agree with what
LHC sees?
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115 GeV Higgs is an interesting case!
LEP
Tevatron
LHC
But, Higgs sector may be very complex.
New physics models expect
multiple Higgs particles.
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Supersymmetric Extension of Standard Model (SUSY)

SUSY solves SM problems e.g. divergence of Higgs
mass, unification. SUSY provides a candidate
particle for Dark Matter, solution to
matter-antimatter asymmetry, possible connection
to Dark Energy?
If msuper particle lt 1 TeV, fermion and boson
loops cancel and Higgs mass becomes stable.
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Higgs in Minimal Supersymmetric Extension of
Standard Model
LHC
tan ?
MA (GeV)
LHC will be the best place to discover Higgs
particles!
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If we discover a Higgs-like particle, is it
alone responsible for giving mass to W, Z,
fermions? Experimenters must precisely
measure the properties of the Higgs
particle without invoking theoretical assumptions.
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LHC ILC

• elementary particles
• well-defined energy and angular momentum
• uses its full energy
• can capture nearly full information

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ILC can observe Higgs no matter how it decays!
ILC simulation for ee- ? Z Higgs with Z ? 2
bs, and Higgs ? invisible
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Coupling Strength to Higgs Particle
Mass (GeV)
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The Higgs is Different! All the matter particles
are spin-1/2 fermions. All the force carriers are
spin-1 bosons. Higgs particles are spin-0
bosons. The Higgs is neither matter nor
force The Higgs is just different. This would be
the first fundamental scalar ever
discovered. The Higgs field is thought to fill
the entire universe. Could give some handle of
dark energy(scalar field)? Many modern theories
predict other scalar particles like the
Higgs. Why, after all, should the Higgs be the
only one of its kind? Once nature learns how to
do something, she does it again! ILC can search
for new scalars with precision.
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HIGGSIf discovered,the Higgs is a very
powerful probe of new physics.Hadron
collider(s) will discover the Higgs.ILC will
use the Higgsas a window viewing the unknown.
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Unification
We want to believe that there was just one force
after the Big Bang. As the universe cooled down,
the single force split into the four that we
know today.
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Unification of electromagnetic weak
forces (electroweak theory) Long term goal since
60s We are getting there.
HERA H1 ZEUS
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But details count! Precision measurements are
crucial.
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Masses also evolve with energy and matter unifies
at high energies. ILC ability in measuring SUSY
parameters accurately is crucial to extract mass
evolution.
Discovering Matter Unification in Supersymmetry
Mass Squared
Energy (TeV)
Energy (GeV)
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Unifying gravity to the other 3 is accomplished
by String theory. String theory predicts extra
hidden dimensions in space beyond the three we
sense daily. Can we observe or feel them? too
small? Other models predict large extra
dimensions large enough to observe up to multi
TeV scale.
With SUSY
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Large Extra Dimensions of Space
LHC
qq,gg ??GN ??ee-,??-
Mee,?? GeV
LHC can discover partner towers up to a given
energy scale. ILC can identify the size, shape
and of extra dimensions.
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New forces of nature ? new gauge boson
Tevatron LHC
ILC
Events/2GeV
104 103 102 10 1 10-1
qq ??Z ??ee-
Related to origin of ??masses
Tevatron sensitivity 1 TeV CDF Preliminary
Related to origin of Higgs
Vector Coupling
Related to Extra dimensions
Axial Coupling
Mee GeV
M?? GeV
LHC has great discovery potential for multi TeV
Z. Using polarized e, e- beams, and measuring
angular distribution of leptons, ILC can measure
Z couplings to leptons and discriminate the
origins of the new force.
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Dark Matter (What is the role of Dark Matter in
galaxy formation and shapes?) a common bond
between astronomers, astrophysicists, and
particle physicists Astronomers
astrophysicists over the next two decades using
powerful new telescopes will tell us how dark
matter has shaped the stars and galaxies we see
in the night sky. Only particle accelerators can
produce dark matter in the laboratory and
understand exactly what it is. The ILC may be a
perfect machine to study dark matter.
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Dark Matter in the Lab
Underground experiments (CDMS) may detect Dark
Matter candidates (WIMPS) from the galactic halo
via impact on colliding DM particle on nuclei.
LHC may find DM particles (a SUSY particle)
through missing energy analyses. (LHC is the best
place to discover many of SUSY particles)
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The ILC can determine its properties with extreme
detail, allowing to compute which fraction of
the total DM density of the universe it makes.
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Particles Tell Stories! The discovery of a new
particle is often the opening chapter revealing
unexpected features of our universe. Particles
are messengers telling a profound story about
nature and laws of nature in microscopic
world. The role of physicists is to find the
particles and to listen to their stories.
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Discovering a new particle is Exciting!
Top quark event recorded early 90s
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Discovering laws of nature is even more
Exciting!!
We are hoping in the next 5 years LHC will
discover Higgs. ILC will allow us to listen
very carefully to Higgs.
This will open windows for discovering new laws
of nature.
This saga continues.
There might be
supersymmetric partners, dark matter,
another force carrier, large extra dimensions,
for other new
laws of nature.
Whatever is out there,
this is our best
opportunity to find its story!
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Now I want to speak as an experimentalist.I
think this is not only the best opportunitybut
also this is a unique opportunity.If we wait
too long, the window of opportunity may close and
we will never hear the end of the story.