James Stirling

IPPP, University of Durham

with acknowledgements to R Barbieri, J Ellis, D Miller (ICHEP04), M Peskin (Victoria LCW), S. Dawson, R. Heuer

The International Linear Collider

– an overview of the physics motivation and theory

ECFA Workshop 2WJ Stirling

the most up-to-date reference…

The LHC-LC Study Group Report

Georg Weiglein et al.

www.ippp.dur.ac.uk/~georg/lhclc/

ECFA Workshop 3WJ Stirling

Particle Physics 2004

gauge sector

mass sector

EWSB sector

flavour sector

… and beyond?… and beyond?

ECFA Workshop 4WJ Stirling

Particle Physics 2004

gauge sector

mass sector

EWSB sector

flavour sector

… and beyond?… and beyond?

QCD 1

?pentaquarks

QCD 2

CKM

EWSB

mass

ECFA Workshop 5WJ Stirling

2.7

g-2

discrepancies?

NuTeV

LEPEWWG 2004

?

ECFA Workshop 6WJ Stirling

limits?

t

S Z

+ 69H - 4

2

5

H

m = 178.2 3.9 GeV

(M ) = 0.1186 0.0027

m = 114

= 15.8/13 df (prob = 2

GeV

m < 260 GeV (

6

95 )

%)

% cl

Higgs

SUSYdark matter

ECFA Workshop 7WJ Stirling

the key questions

1) What is the origin of mass? Is it the Higgs mechanism or …?

2) What is the origin of the matter-antimatter asymmetry in the universe?

3) What are the properties of neutrinos?

4) Is there unification of particles and forces including gravity?

5) What is the dark matter?

particle physics

2) present and future B Factories3) solar, atmospheric, reactor, (super)beam, 0,

…, NuFact experiments1), 4), 5) high-energy colliders: Tevatron, LHC, ILC

ECFA Workshop 8WJ Stirling

key issue: electroweak symmetry breaking

• Supersymmetry (MSSM and variants)

• Higgs as Pseudo Goldstone Boson

• Composite Higgs

• Technicolour

• Higgsless models

• Extra dimensions

• …

Note: in all scenarios, something (or some combination of things) has to mimic a light Higgs boson in the precision electroweak (EWPO) fits!

Scenarios include:

The Calculability Principle (Barbieri):

Restrict to models in which the Fermi scale (GF-1 or MZ) can be related to

some other physical scale (NP say) in a calculable manner, i.e. MZ = NP f(ai) where the ai are physical parameters. Then

CP consistency with data SUSY, Higgs as PGB

+ gauge unification+ dark matter candidate+ ‘naturally’ consistent with PEW data

but…• where is the Higgs?• where are the superpartners?• “little hierarchy” problem!

then…NMSSM with heavier h0 , more neutral

scalars etc.

Little Higgs Models

• embed SM in large gauge group• Higgs as PGB

• in mh2 cancel top loop with new heavy T quark

• new quarks, gauge bosons, Higgs bosons in the 1 – 10 TeV range

but…• too many such models?• too ad hoc?

nevertheless…at the very least, a useful “straw-man” alternative to SUSY!

ECFA Workshop 9WJ Stirling

what LHC can do: SM-like Higgs

fb-1

LHC: ATLAS

1 year @1033

1 year @1034

1 month @1033

ECFA Workshop 10WJ Stirling

what LHC can do: SUSY

Higgses sparticles

whole plane covered for at least one Higgs (but note large “only h” region!)

squark and gluino masses eventually up to ~2.5 TeV

ECFA Workshop 11WJ Stirling

however…• ‘hadro-philic’ bias in new physics searches (gg,qq X)

• large SM backgrounds always a problem (Higgs< total 10-9)

• EWPO: only modest improvement over Tevatron (mtop , mW )

• no longitudinal momentum balance; ‘missing pT’ for invisible particles is relatively crude tool; quark flavour tagging difficult

• strong model dependence of new physics analyses:

conventional SUSY

neutrino LSP (Murayama et al)

‘bosonic supersymmetry’ (Cheng, Matchev, Schmaltz)

multiple hypotheses, distinguished by different spin and energy flows, difficult to distinguish at LHC

Peskin (Victoria, 2004)

ECFA Workshop 12WJ Stirling

cross sections: LHC vs. ILC

ECFA Workshop 13WJ Stirling

ILC physics summarywhatever the scenario unveiled by Tevatron & LHC, ILC has an essential role to play

• continue with precision electroweak measurements (in particular, mtop )

• if a light Higgs exists, measure its properties (mass, couplings to fermions & gauge bosons, self-couplings, …)

• if LHC reveals other light ( e.g. SUSY) particles, measure the spectrum and properties

• if LHC reveals no light particles, explore the ~1 TeV region through precision measurements sensitive to virtual new physics

precision

current MW

Heinemeyer et al (LHCLC report)

mW (MeV) mtop

(GeV)sin2eff10

5

now 34 3.9 17

TeV Run 2 16 1.4 29

LHC 15 1-2 14-20

ILC-GigaZ 7 0.1 1.3

MW = cosw MZ [ 1 + α F(mt,MH,SUSY,..)+ …]

W

H

b

+

t

+ …

Heinemeyer, Weiglein 04

ECFA Workshop 15WJ Stirling

precision contd.

Heinemeyer et al 2003

precision EW measurements complement direct new physics measurements

ECFA Workshop 16WJ Stirling

Key questions• precise mass?• couplings to other particles – SM or not?• self-couplings?• other higgses?

Higgs physics at ILC

Key questions• precise mass?• couplings to other particles – SM or not?• self-couplings?• other higgses?

Higgs physics at ILC

compare with

)(

)(

hBR

bbhBRR

Example:

Guasch, Hollik, Penaranda 2003

also ttH coupling measurements – see LHCLC report

ECFA Workshop 18WJ Stirling

Key questions• precise mass?• couplings to other particles – SM or not?• self-couplings?• other Higgses?

Higgs physics at ILC

V() = ½ mh2 2 + 3 v 3 + ¼ 4

4

in SM: 3 = 4 = ½ mh

2 v-2

3 / 3 ~ 20%

h

h

Z*e

e

Z

ECFA Workshop 19WJ Stirling

supersymmetry at the ILCthe task:

• determination of kinematically accessible sparticle spectrum

• measure sparticle properties (masses, cross sections, JPC)

• use these (with complementary information from LHC) to constrain underlying SUSY model

• extrapolate to GUT scale using RGEs

the techniques:

• end point spectra

• threshold scans

• + e-e-, e, polarised beams

*

*+

++

+ **

- -

+

***

* Needs > 500 GeV. (Also < 500 study in LHC/LC)

+ e+e- threshold scan.- e-e- threshold scan (s-wave allowed)

David Miller, ICHEP04

example of a global MSSM spectrum fit

LSP

see e.g. LHCLC report for details, many more examples, and references

the LHC-LC synergy: using precisely measured LSP mass at ILC to constrain LHC measurements of slepton and squark masses

ECFA Workshop 22WJ Stirling

… then on to the GUT scale!

Allanach, Blair, Kraml, Martyn, Polesello, Porod,,Zerwas

ECFA Workshop 23WJ Stirling

… and if nothing below 500 GeV?W

h

b

+

t

+ ?

little Higgsheavy Higgsno Higgs…

a generic feature of such models is heavy s-channel resonances in the 1-3 TeV range

(new gauge bosons, technipions, KK resonances, …)

e

e

W

W

Z’e

e

f

f

Z’e

e

WL

WL

ECFA Workshop 24WJ Stirling

ILC (eeff)LHC (direct)

sensitivity to new heavy Z’sensitivity to new heavy

resonances in ee WW

M = 1.9 TeVSM couplings (a=1)LC: 500 GeV, 500 pb-1

LHC

LC

assume a1=1

Richard 2003

Barklow et al, LHCLC report

Summary of the case for the TeV ILC

1. Definite; mt<100MeV

2. If there is a light Higgs

3. and extra particles

4. If LHC sees nothing newbelow ~ 500 GeV mass

Vital constraint.Increasingly sure

it can be done.

LHC probably sees.ILC shows what it is.

LHC and ILC needed topin down model, identify DM(?),

extrapolate to GUT scale.

Then LHC + ILC point to CLIC, andmaybe superLHC

ILC looks beyondLHC’s direct reach

David MillerICHEP04