Future Colliders:Opening Windows on the World

Young-Kee KimThe University of Chicago

ICFA SeminarSeptember 28 - October 1, 2005

Kyungpook National University, Daegu, Korea

Welcome to Korea

Calligraphy by my father

Accelerators are Powerful Microscopes.

They make high energy particle beams that allow us to see small things.

seen byhigh energy beam(better resolution)

seen bylow energy beam

(poorer resolution)

Accelerators are also Time Machines.

E = mc2

They make particles last seen in the earliest moments of the universe.

Energy

Particle and anti-particle annihilate.

particle beam

energy

anti-particle beam

energy

Accelerators powerful tools!

PEP-II, SLAC, Palo Alto, USA

HERA, DESY, Hamburg, Germany

KEKb, KEK, Tsukuba, Japan

Tevatron, Fermilab, Chicago, USA

1929

Ernest Lawrence(1901 - 1958)

3/4 of century later

Tevatron at Fermilabx104 bigger, x106 higher energy

Today

Many generations of Accelerators created with higher and higher energy given to the beam particle

CDF ~1500 Scientists D0

With advances in accelerators, we discovered many surprises.

Our field has been tremendously successful in creating and establishing

“Standard Model of Particle Physics” answering”what the universe is made of” and “how it works”

Energy

Lum

inos

ity(C

ollis

ion

Rat

e)

Time

~90 years ago

110,000

~60 years ago

110

~40 years ago

1100,000

Present

What is the universe made of?

electron

up quarkdown quark

atom

nucleus protonneutron

1100,000

of human hair

Rutherford

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?

top quark

anti-top quark

ZW+, W-

. . . .e e- u d s c b

gluons

Elementary Particles and Masses

e e+ u d s c b- - - - - - - -

(Mass proportional to area shown but all sizes still < 10-19 m)

Why are there so many? Where does mass come from?

Gravitational Force Electromagnetic Force

Issac Newton(1642 - 1727)

James Clerk Maxwell(1831 - 1879)

What holds the world together?Beginnings of Unification

Einstein tried to unify electromagnetism and gravity

but he failed.

Unification of Gravity and Electromagnetism?

radioactive decays

holding proton, nucleus

gluons

Weak Force

Strong Force

Enrico Fermi(1901 - 1954)

1 fm = 10-15 m

Dream of Unification continues!

We believe that there is an underlying simplicitybehind 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?

Particle Physics & Cosmology Questions from Astrophysical Observations

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?

Everything that we can see

particlesanti-particles

particles

Accelerators

Where did all antimatter go?

BigBang

Inflation

Create particles & antiparticles that existed ~0.001 ns after Big Bang

E = mc2

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.

Belle BaBar

Not only is the Universe expanding, it is

Accelerating!!

Where does energy come from?Dark Energy

What is the world made of?What holds the world together?

Where did we come from?

Primitive Thinker

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”

Answering the Questionswith Next Generation of Accelerators (Colliders)

e+e-

e-proton

proton-proton

today1970 1980 1990 2000 2010 2020 2030

LHC

ILC

TEVATRON

HERA

LEP,SLC

PEP-II, KEKB

VEPP, CLEO-c, BEPC

DANE

FNAL, CERN, J-PARC

Energy Frontier Colliders:

Flavor Specific Accelerators:

e+e- (b factory)

e+e- (c factory)

e+e- (s factory)

CLIC

Collider

LHCb

xx

x

xxx

x

xx xxx

x

Electron

Z,W Boson

Top Quark

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

Higgs Particles:Higgs Particles:

Coupling strength to HiggsCoupling strength to Higgsis proportional to massis proportional to mass

Mtop (GeV)

W

Z

W, Z

top

bottom

top

top

Higgs

Tevatron: Improve Higgs Mass Pred. via Quantum Corrections

Tevatron Run II

Current precision measurementsfavor light Higgs: < ~200 GeV.

MW

(GeV

)

Tevatron: Improve Higgs Mass Pred. via Quantum Corrections

Mtop (GeV)

MW

(GeV

)

LHC: Designed to discover Higgs with Mhiggs = 100 ~ 800 GeV

M (GeV)

130 GeV HiggsL = 100 fb-1

# of

eve

nts

/ 0.

5 G

eV

Tevatron: Improve Higgs Mass Pred. via Quantum CorrectionsLHC: Designed to discover Higgs with Mhiggs = 100 ~ 800 GeV

MHiggs (GeV)5

Dis

cove

ry L

umin

osity

(fb

-1)

Mtop (GeV)

MW

(GeV

)

Tevatron: Improve Higgs Mass Pred. via Quantum CorrectionsLHC: Designed to discover Higgs with Mhiggs = 100 ~ 800 GeV

Will the Tevatron’s prediction agree with what LHC sees?

5 D

isco

very

/ L

umin

osity

(fb

-1)

MHiggs (GeV)5

Dis

cove

ry L

umin

osity

(fb

-1)

easy

hard

Mtop (GeV)

MW

(GeV

)

115 GeV Higgs is an interesting case!LEP Saw a 2hint

Tevatron 2007

(2.5 fb-1 / expt)95% CL Limit

Tevatron 2009

(8 fb-1 / expt)

WH Wbb

ZH Zbb

75% chance for 3 evidence

10% chance for 5 discovery

LHC

H

ttH ttbb

qqH qq (forward qq jets)

But, Higgs sector may be very complex. New physics models expect multiple Higgs particles.

Higgs

WZ

WZ

d

u

e+

e-

Higgs

Z

Z

LEP

Tevatron

LHC

Supersymmetric Extension of Standard Model (SUSY)

e+ e-

superparticle

e e~

e

spin 1/2 spin 0 Me ≠ Me

Symmetry betweenfermions (matter) and bosons (forces)

“Undiscovered new symmetry”

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 < ~1 TeV,fermion and boson loops cancel and Higgs mass becomes stable.

particle super particleHiggs Mass:

~

Higgs in Minimal Supersymmetric Extension of Standard Model

tan

MA (GeV)Mtop (GeV)

MSSM

MW

(GeV

)

TevatronLHCILC

LHC

LHC will be the best place to discover Higgs particles!

If we discover a “Higgs-like” particle,is it alone responsible for giving mass to W, Z, fermions?

Experimenters must precisely measurethe properties of the Higgs particle

without invoking theoretical assumptions.

proton proton (anti-proton!)

e- e+

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

LHC:

ILC:

ILC can observe Higgs no matter how it decays!

100 120 140 160Recoil Mass (GeV)

MHiggs = 120 GeV

Num

ber

of E

vent

s /

1.5

GeV

Only possible at the ILC

ILC simulation for e+e- Z + Higgswith Z 2 b’s, and Higgs invisible

Cou

plin

g S

tren

gth

to H

iggs

Par

ticle

Mass (GeV)

Standard Model Coupling∞ particle mass

ILC experiments will have the unique ability to make model-independent tests of Higgs couplings

to other particles, at the percent level of accuracy

Standard Model Coupling∞ particle mass

LEP e+e- collider

Coupling Strength to Z boson

e : 0.1%: 0.1%: 0.1% : 0.2%q : 0.1%

(PDG values)

This sensitivity is sufficient to discover extra dimensions, SUSY, sources of CP violation, or other novel phenomena.

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.

HIGGS

If 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.

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.

1TeV = 103GeV(1016K)10-11 s

1016GeV(1029 K)10-38 s

1019GeV(1032K)10-41 s

2.3 x 10-13 GeV(2.7K)

12x109 y

EnergyTempTime

Unification of electromagnetic & weak forces

(electroweak theory)

Long term goal since 60’sWe are getting there.

Beautifully demonstratedat HERA ep Collider at DESY

The main missing link is Higgs boson

HERA

Q2 [GeV2]

Electromagnetic ForceWeak Force

f

HERA:H1 +ZEUS

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Higher energy, Shorter distance

Str

onge

r fo

rce

-1

-1

-1

104 108 1012 1016 1020

Q [GeV]

60

40

20

0

-1

13 orders of magnitude higher energy

The Standard Model fails to unify the strong and electroweak forces.

Adding super-partners

104 108 1012 1016 1020

Q [GeV]

60

40

20

0

-1

-1

-1

-1

With SUSY

But details count!Precision measurements are crucial.

Energy (GeV)

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 Unificationin Supersymmetry

Energy (TeV)

Mas

s S

quar

ed

With SUSYUnifying gravity to the other 3 is accomplished by String theory.

String theory predicts extra hidden dimensions in spacebeyond 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.

Large Extra Dimensions of Space

LHC can discover partner towers up to a given energy scale. ILC can identify the size, shape and # of extra dimensions.

qq,gg GN e+e-,+-

Mee, [GeV]

LHC

Mee [GeV]

DZero

Tevatron

GNq

q

e+

e-

Tevatron Sensitivity2.4 TeV @95% CL

Collision Energy [GeV]

Graviton disappears into the ED

Pro

duc

tion

Rat

e

ILC

GN

e+

e-

Mee [GeV]

Eve

nts

/ 50

GeV

/ 1

00 f

b-1

102

10

1

10-1

10-2

LHC

New forces of nature new gauge boson

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.

Mee [GeV] M [GeV]

Vec

tor

Cou

plin

g

Axial Coupling

Related to originof masses

Related toorigin of Higgs

Related toExtra dimensions

Tevatron LHC ILC104

103

102

10

1

10-1

Events/2GeV

qq Z’ e+e-

Tevatron sensitivity~1 TeV

CDF Preliminary

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.

Dark Matter in the LabUnderground experiments (CDMS) may detect Dark Matter candidates

(WIMPS) from the galactic halo via impact on colliding DM particle on nuclei.

Dark Matter Mass [GeV]

10-4

4

104

3

10-2

4

10 100 1000

Inte

ract

ion

Str

engh

[cm

2 ]

LHC may find DM particles (a SUSY particle) through missing energy analyses.(LHC is the best place to discover many of SUSY particles)

The ILC can determine its properties with extreme detail,allowing to compute

which fraction of the total DM density of the universe it makes.

Dark Matter Mass from Supersymmetry (GeV)F

ract

ion

of D

ark

Mat

ter

Den

sity

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.

Discovering a new particle is Exciting!Top quark event recorded early 90’s

We are listening to the story that top quarks are telling us:Story is consistent with our understanding

of the standard model so far. But why is the mass so large?We are now searching for a story we have not heard before.

Mtopworld = 172.7 ± 2.9 GeV

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.

Discovering “laws of nature” is even more Exciting!!

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 it’s story!

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.