Physics at the International Linear Colliderchep.knu.ac.kr/KILCWS/KILCWS2/PlenarySession2/2.sychoi... · 2004-12-28 · ILC Physics Why ILC? 1 of 27 Physics at the International Linear

ILC Physics Why ILC? 1 of 27

Physics at the International Linear Collider

[Apology for no proper quotation]

Why ILC?

In recent years, all of the highest–energy particle accelerators have been collidingbeam facilities

e+e− SLC 90GeV 1989 − 1998e+e− LEP 90 − 210GeV 1989 − 2000pp Tevatron 1.8 − 2TeV 1988−pp LHC 14TeV 2007−

The ILC would be a successor to LEP and SLC at higher energy. What is it about

the results from these colliders that calls for a successor?

2nd KILC @ Dec/28, 2004 in Pohang S.Y. Choi (Chonbuk)


Their aim was to make precision tests of the Standard Model of electroweak/stronginteractions. This is a Yang–Mills gauge theory with the following ingredients:

Local gauge symmetry: SU(3)×SU(2)×U(1)

Unification of weak and EM interactions

Maximal parity violation

Spontaneous symmetry breaking

g2s /4π = 1/9, g2/4π = 1/30, g′2/4π = 1/99, 〈φ〉 = v = 246GeV

mW = gv/2, mZ = (g2 + g′2)1/2v/2, mγ,g = 0; mf = yfv/√

2

Z = cWW − sWB, γ = sWW + cWB with sW/cW = g′/g

Q = I3 + Y , QZ = I3 − Q sin2 θW



0

0.1

0.2

0.3

1 10 102

µ GeV

αs(µ

)

0

10

20

30

160 180 200

√s (GeV)

σW

W (

pb

)

YFSWW/RacoonWWno ZWW vertex (Gentle)only νe exchange (Gentle)

LEPPRELIMINARY

02/08/2004Measurement Fit |Omeas−Ofit|/σmeas

0 1 2 3

0 1 2 3

∆αhad(mZ)∆α(5) 0.02761 ± 0.00036 0.02768

mZ [GeV]mZ [GeV] 91.1875 ± 0.0021 91.1873

ΓZ [GeV]ΓZ [GeV] 2.4952 ± 0.0023 2.4965

σhad [nb]σ0 41.540 ± 0.037 41.481

RlRl 20.767 ± 0.025 20.739

AfbA0,l 0.01714 ± 0.00095 0.01642

Al(Pτ)Al(Pτ) 0.1465 ± 0.0032 0.1480

RbRb 0.21638 ± 0.00066 0.21566

RcRc 0.1720 ± 0.0030 0.1723

AfbA0,b 0.0997 ± 0.0016 0.1037

AfbA0,c 0.0706 ± 0.0035 0.0742

AbAb 0.925 ± 0.020 0.935

AcAc 0.670 ± 0.026 0.668

Al(SLD)Al(SLD) 0.1513 ± 0.0021 0.1480

sin2θeffsin2θlept(Qfb) 0.2324 ± 0.0012 0.2314

mW [GeV]mW [GeV] 80.425 ± 0.034 80.398

ΓW [GeV]ΓW [GeV] 2.133 ± 0.069 2.094

mt [GeV]mt [GeV] 178.0 ± 4.3 178.1

Winter 2004



Ecm [GeV]

σ had

[nb

]

σ from fitQED unfolded

measurements, error barsincreased by factor 10

ALEPHDELPHIL3OPAL

σ0

ΓZ

MZ

10

20

30

40

86 88 90 92 94

The theory of the Z reso-nance line shape is some-what sophisticated. The EWand strong radiative correc-tions must be included.

The final result agrees with

experiment at the parts–per–

mill level.

The beautiful experiments leave little room for doubt that EW interactions have abasic gauge symmetry SU(2)×U(1). This brings into focus the next question:

What is the agent that breaks this holy symmetry?



The Standard Model contains no dynamical mechanism for EWSB. It can onlybe explained by a new fundamental interaction operating at an energy scale of afew hundred GeV. Being ignorant of what the interaction is, physicists propose adescriptive theory by adding a SU(2) scalar doublet, yielding the Higgs boson.

The Higgs boson influences the structure of the W and Z, through the vertex

that gives these particles mass. Fitting the electroweak data, we can look for a

systematic shift due to a heavy Higgs boson. mhSM< 260 GeV (95% c.l.)

80.2

80.3

80.4

80.5

80.6

130 150 170 190 210

mH [GeV]114 300 1000

mt [GeV]

mW

[G

eV]

Preliminary

68% CL

∆α

LEP1, SLD Data

LEP2, pp− Data

0

1

2

3

4

5

6

10020 400

mH [GeV]

∆χ2

Excluded Preliminary

∆αhad =∆α(5)

0.02761±0.00036

0.02747±0.00012

incl. low Q2 data

Theory uncertainty



The Higgs boson(s) should be discovered at the LHC, if not before. From the LHC,we will also understand whether there are other new particles of comparable masswhich produce the physics of electroweak symmetry breaking.

Whatever the outcome of these experiments, the next step is to understand thephysics of electroweak symmetry breaking in detail.

To do this, we should apply the powerful experimental methods learned from LEP

and SLC to the Higgs boson and the new particles at a few hundred GeV energies.

International Linear Collider

e+e− with Ec ≥ 0.5 TeV and high luminosityEnergy scan ⊕ Beam polarization

Sensitive detectors ⊕ Precise theoretical predictions

LHC gives us a new global (mixed) picture.

ILC gives us new dynamic multi–dimensional total views.


ILC Physics References 7 of 27

Many materials for ILC physics

• ACFA LC report (2001)

• TESLA TDR (2001)

• LC resource book for Snowmass (2001)

• GLC project (2003)

• LC report from WWS (2003)

• LHC/LC note (2004)

• Response to ITRP questions (2004)

• Many LHC/LC related workshops

• · · ·


ILC Physics Higgs 8 of 27

Once a Higgs–like particle is found, ILC can make precision measurements of itsbasic properties.

If the Higgs boson is the one to give masses to all the SM particles, we need toobserve proportionality between mass and coupling.

We need to measure Higgs self couplings as well to determine the shape of the

Higgs pot and to understand what makes the Higgs boson condense in the vacuum.

τ τ-

-+

+

(GeV)

10

10

1

-3

-2

10-1

SM

Hig

gs B

ra

nch

ing

Ra

tio

bb

ggcc

γγ

MH

W W

100 110 120 130 140 150 160 [GeV]Hm

110 120 130 140 150 160 170 180 190

(H,X

)2 g

(H,X

)2

g∆

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1(H,Z)2g

(H,W)2g

)τ(H,2g

(H,b)2g

(H,t)2g

HΓ

without Syst. uncertainty

2 Experiments-1

L dt=2*300 fb∫-1WBF: 2*100 fb

101 100

Mass (GeV)

0.01

0.1

1

Co

up

lin

g c

on

sta

nt to

Hig

gs b

oso

n (κι)

Coupling-Mass Relation

c τ

b

W Z

Ht


ILC Physics Higgs 9 of 27

Spin and Self–couplings

s, GeV

cross

sec

tion, fb

0

5

10

15

210 220 230 240 250

s = 2

s = 0

s = 1

M* (GeV)

No. of

Even

ts

SM

H → Z*Z → (f1f–

1)(f2f–

2)MH = 150 GeV

Spin 1Spin 2

0

5

10

15

20

25

30

30 35 40 45 50 55 1.0 2.0 3.0

10

20Int (L) = 1 ab

−1

100% efficiency

sqrt(s) [TeV]

Mh = 120 GeV

Mh = 150 GeV

hhh−coupling sensitivityδλ/λ[%]

0.5 1.5 2.5

Pol−beam (eL)

At present, almost NOTHING is known about Higgs sector.

The profile depends on the new physics scenario at the TeV scale.


ILC Physics Too Many BSM Scenarios 10 of 27

TOO many new physics scenarios with extra dimensions and symmetries

• In the case of high cut–off scale

z SUSY (fermionic dimensions): the most well–motivated and studied

– ???

• In the case of low cut–off scale

z Large extra dimension (bosonic dimensions)

– Extra symmetries

∗ Techni–color

∗ Little Higgs

∗ Higgsless

∗ ???

• Hybrids or much wilder thoughts??


ILC Physics Too Many BSM Scenarios 11 of 27

Decisive principles and/or experiments DESPERATELY needed


ILC Physics Precision matters. 12 of 27

Precision matters!!

• Single Higgs? Two Higgs doublets? Additional singlets or triplets?

• SUSY or/and extra–dimension? Composite?

• Type–I or II or III Yukawa couplings and flavor mixings?

• Why top is heavy? Special for the 3rd generation?

• CP violation in Higgs sector? ⇒ γγ mode

gtop/gtop(SM)

gW

/gW

(SM

)

MSSM prediction:

100 GeV < mA < 200 GeV

200 GeV < mA < 300 GeV

300 GeV < mA < 1000 GeV

LHC 1σ

LC 1σLC 95% CL

mH = 120 GeV

0.8

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2

0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.2

gtop/gtop(SM)

gW

/gW

(SM

)

MSSM prediction:

100 GeV < mA < 200 GeV

200 GeV < mA < 300 GeV

300 GeV < mA < 1000 GeV

LHC 1σ

LC 1σLC 95% CL

mH = 120 GeV

0.8

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2

0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.2 80.30 80.35 80.40 80.45MW [GeV]

0.2312

0.2314

0.2316

0.2318

sin2 θ ef

f

predictions for MW and sin2θeff

δmtexp

= 2.0 GeV

δmtexp

= 0.1 GeV

mh = 115 GeV, δ∆αhad = 7 10 5

MSSM(SPS1b)

SM

prospective exp. errors 68% CL:

LHC/LC

GigaZ

150 200 250 300 350 400 450 500MA [GeV]

115

120

125

130

135

mh [G

eV]

∆mhexp

mt = 175 GeV, tanβ = 5

theory prediction for mh

δmtexp

= 2.0 GeV

δmtexp

= 1.0 GeV

δmtexp

= 0.1 GeV


ILC Physics Precision matters. 13 of 27

Precision mattered in the Universe as well!!


ILC Physics Heavy Higgs Bosons 14 of 27

Model–independent searches!!!


ILC Physics SUSY 15 of 27

Supersymmetry at the ILC

SSB SUSY + World =

S-parameters

Masses and Mixings of S-particles

d σ (Production and Decay)

Planck or ?? SUSY Physics

(m , M , µ , tan β ) ?? 0 2 S-particles ∃

Couplings

= Experiments

= Theories

Model–independent methods

• End–point spectra• Beam polarizations• e−e− ⊕ γe ⊕ γγ modes

What can be achieved?

• SUSY breaking mechanism• Grand extrapolation



LHC would discover SUSY phenomena quickly by 2009. However, the measure-ments at the LHC involve

Complicated cascade chainsLarge SM and other SUSY backgrounds

Model dependence of new physics analyses

Multiple hypotheses, distin-guished by different spins andenergy flows, DIFFICULT todistinguish at the LHC due tomissing/unfixed energies.

⇓

Model–independent analyses!!



)10χm(

60 70 80 90 100 110 120 130 140 150

)Rl~

m(

110

120

130

140

150

160

170

180

190

200

⇑

An LHC/LC synergy

The precisely measured LSPmass at the ILC constrains theLHC measurements of sfermionmasses.



Beam polarization Spinless?


ILC Physics SUSY and GUT 19 of 27

Masses

Couplings

Chirality

Mixing


ILC Physics Grand extrapolation 20 of 27

1015 1016

Q [GeV]

24

25

Now &LC/GigaZ


ILC Physics Cosmological connection 21 of 27

Dark Matter = LSP?

WMAP: 0.094 < Ωh2 < 0.128 (2σ)

WMAP: 7%

LHC: 15%

Planck: 2%

ILC: 3%


ILC Physics Extra dimensions 22 of 27

Extra dimensions at the ILC

z How to tell LED signals from others?

• How to decide nature of extra dimensions?

z Size and shape (topology)?

– Non–commutative geometry?

• Possible probes

z Quantum gravity effects (KK modes)?

– Brane excitation (KK modes of SM par-ticles)?

– Classical gravity effects (Black holes)?



Impossible in SM

Cleanest way to test J=2




ILC Physics Conclusions 25 of 27

Conclusions



c© The test of the 2nd (right) pillar of the SM - symmetry breaking and massgeneration - is the most important and urgent problem to solve.

c© The sub–TeV ILC will be crucial to carry out this mission and hence we needit regardless of the BSM scenarios.

c© To what extent the ILC will be able to explore the BSM depends on its scaleand thus luck.

c© If its scale is not too high, ILC [along with LHC ⊕ · · ·] can do a lot:

– Precision super–spectroscopy to test SSB mechanism

– Measurement of size and shape of LED

– Cosmological ⊕ low–high ⊕ CP–Baryon connections

z Certainly, unexpected phenomena are highly expected as history has taught us!




Documents

Physics at the International Linear Colliderchep.knu.ac.kr/KILCWS/KILCWS2/PlenarySession2/2.sychoi... · 2004-12-28 · ILC Physics Why ILC? 1 of 27 Physics at the International Linear