Anticipating New Physics @ the LHC

• Why the Terascale?• Scenarios for Electroweak Symmetry

Breaking and the Gauge Hierarchy– LHC Signatures– Connection to Dark Matter

• Summary: Discoveries are only months away!

APS April Meeting, 2007 J. Hewett, Stanford Linear Accelerator Center

Why the Terascale?

• Electroweak Symmetry breaks at energies ~ 1 TeV (Higgs or ???)

• Gauge Hierarchy: Nature is fine-tuned or Higgs mass must be stabilized by

New Physics ~ 1 TeV

• Dark Matter: Weakly Interacting Massive Particle must have mass ~ 1 TeV to reproduce observed DM density

The LHC is turning on!

The anticipation has fueled many ideas!

A Cellar of New Ideas

’67 The Standard Model

’77 Vin de Technicolor

’70’s Supersymmetry: MSSM

’90’s-now SUSY Beyond MSSM

’90’s CP Violating Higgs

’98 Extra Dimensions

’02 Little Higgs

’03 Fat Higgs

’03 Higgsless’04 Split Supersymmetry’05 Twin Higgs

a classic!aged to perfection

better drink now

mature, balanced, welldeveloped - the Wino’s choice

complex structure

sleeper of the vintagewhat a surprise!

svinters blend

all upfront, no finishlacks symmetry

young, still tannicneeds to develop

bold, peppery, spicyuncertain terrior

J. Hewett

finely-tuned

double the taste

Discoveries at the LHC will find the vintage nature has bottled.

The Standard Model of Particle Physics

Symmetry:

SU(3)C x SU(2)L x U(1)Y

Building Blocks of Matter:

QCD Electroweak

Spontaneously Broken to QED

This structure is experimentally confirmed!

The Standard Model Higgs Boson

Economy: 1 scalar doublet

Higgs Potential:V() = 22/2 + 4/4

Spontaneous Symmetry BreakingChooses a vacuum v = 0||0and shifts the field = - v

V() = m22/2 + v3 + 4/4

gives 1 physical Higgs scalar with m = 2 v

Masses of electroweak gauge bosons proportional to v

We need to discover the Higgs and experimentally test this potential and the Higgs properties!

Higgs Mass Upper Bound: Gauge Boson Scattering

Higgs

Higgs

Bad violation of unitarity ~ E2

Restores unitarity

Expand cross section into partial wavesUnitarity bound (Optical theorem!) |Re a0| < ½Gives mH < 1 TeV

LHC is designed to explore this entire region!

Present Limits:

Direct Searches at LEP: mH > 114.4 GeV

Indirect Searches at LEP/SLC:mH < 150-200 GeV @ 95% CL

Z ZHiggs

Z

Higgs @ the LHC:

Production mechanisms & rates

Signal determined by final state versus background

Higgs Search StrategiesLow: MH < 140 GeV Medium: 130<MH<500 GeV High: MH > ~500 GeV

The Hierarchy ProblemEnergy (GeV)

1019

1016

103

10-18Solar SystemGravity

Weak

GUT

Planckd

ese

rt

Future Collider Energies

All of known physics

mH2 ~ ~

MPl2

Quantum Corrections:

Virtual Effects dragWeak Scale to MPl

The Hierarchy Problem: Supersymmetry

Energy (GeV)

1019

1016

103

10-18Solar SystemGravity

Weak

GUT

Planckd

ese

rt

Future Collider Energies

All of known physics

mH2 ~ ~

MPl2

Quantum Corrections:

Virtual Effects dragWeak Scale to MPl

mH2

~

~ - MPl2

boson

fermion

Large virtual effects cancel order by order in perturbation theory

Supersymmetry:

•Symmetry between fermions and bosons•Predicts that every particle has a superpartner of equal mass ( SUSY is broken: many competing models!)•Suppresses quantum effects•Can make quantum mechanics consistent with gravity (with other ingredients)

Supersymmetry at the LHC

SUSY discovery generally ‘easy’ at LHC

Cut: ETmiss > 300

GeV

LHC Supersymmetry Discovery Reach

Model where gravity mediates SUSY breaking – 5 free parameters at high energies

Squark and Gluino mass reach is2.5-3.0 TeV @ 300 fb-1

MSSM only viable for mh < 135 GeV

Carena, Haber hep-ph/0208209

MSSM: tension with fine-tuning

Competing factors:– Mass of lightest higgs mh < MZ at tree-level

large quantum corrections from top sector

If stop mass ~ 1 TeV

– Stability of Higgs mass stops cut-off top contribution to quadratic

divergence stops can’t be too heavy

– Z mass relationship

< (130 GeV)2

Resolve Fine-Tuning: Extend the MSSM

• NMSSM (Next-to Minimal SSM)– Add a Higgs Singlet- Evade LEP bounds – minimize fine-tuning!- Regions where Higgs discovery is difficult @ LHC

• MNMSSM (Minimally Non-minimal MSSM)– Lightest higgs < 145 GeV– Observable @ LHC

• Gauge Extensions of MSSM– Mh < 250 (350) GeV

• Split Supersymmetry

Dermisek, Gunion, …

Batra, Delgado, Kaplan, Tait

Panagiotakopoulos, Pilaftis

•A component of Dark Matter could be the Lightest Neutralino of Supersymmetry - stable and neutral with mass ~ 0.1 – 1 TeV•In this case, electroweak strength annihilation gives relic density of

m2

ΩCDM h2 ~ (1 TeV)2

Dark Matter in Supersymmetry

Mass of Dark Matter Particle from Supersymmetry (TeV)

Fra

cti

on

of

tota

l D

ark

Matt

er

den

sit

y

Determination of Dark Matter Density @ LHC

• Measure SUSY properties @ LHC

• Benchmark point SPS1a

• Dependence on Stau mass determination

Baltz, Battaglia, Peskin, Wizansky hep-ph/0602187

The Hierarchy Problem: Extra Dimensions

Energy (GeV)

1019

1016

103

10-18Solar SystemGravity

Weak – Quantum Gravity

GUT

Planckd

ese

rt

Future Collider Energies

All of known physics

Simplest Model: Large Extra Dimensions

= Fundamental scale in 4 + dimensions

MPl2 = (Volume) MD

2+

Gravity propagates in D = 3+1 + dimensions

Arkani-Hamed, Dimopoulis, Dvali

Kaluza-Klein Modes in a Detector

Mee [GeV]

Eve

nts

/ 50

GeV

/ 1

00 f

b-1

102

10

1

10-1

10-2

LHC

Indirect Signature

Missing Energy Signature

pp g + Gn

JLH Vacavant, Hinchliffe

Graviton Exchange Modified with Running Gravitational Coupling

Insert Form Factor in coupling to

parameterize running

M*D-2 [1+q2/t2M*

2 ]-1

Could reduce signal!D=3+4M* = 4 TeV

SM

t=

1

0.5

JLH, Rizzo, to appear

Black Hole Production @ LHC:

Black Holes produced when s > M*

Classical Approximation: [space curvature << E]

E/2

E/2b

b < Rs(E) BH forms

Geometric Considerations:

Naïve = Rs2(E), details show this holds up to a

factor of a few

Dimopoulos, LandsbergGiddings, Thomas

Production rate is enormous!

1 per sec at LHC!

JLH, Lillie, Rizzohep-ph/0503178

Determination of Number of Large Extra Dimensions

Black Hole event simulation @ LHC

The Hierarchy Problem: Extra Dimensions

Energy (GeV)

1019

1016

103

10-18Solar SystemGravity

Weak

GUT

Planckd

ese

rt

Future Collider Energies

All of known physics

Model II: Warped Extra Dimensions

wk = MPl e-kr

strong curvature

Randall, Sundrum

Number of Events in Drell-Yan

For this same model embedded in a string theory: AdS5 x S

Kaluza-Klein Modes in a Detector: SM on the brane

Davoudiasl, JLH, Rizzo

Kaluza-Klein Modes in a Detector: SM off the brane

Fermion wavefunctions in the bulk: decreased couplings to light fermions for gauge & graviton KK states

gg Gn ZZ

gg gn tt

Agashe, Davoudiasl, Perez, Soni hep-ph/0701186

-

Lillie, Randall, Wang, hep-ph/0701164

Issue: Top Collimation

Lillie, Randall, Wang, hep-ph/0701164

gg gn tt-

g1 = 2 TeV g1 = 4 TeV

The Hierarchy Problem: Little Higgs

Energy (GeV)

1019

1016

103

10-18Solar SystemGravity

Weak

GUT

Planckd

ese

rt

Future Collider Energies

All of known physics

Little Hierarchies!

104 New Physics!

Simplest Model: The Littlest Higgs with ~ 10 TeV

No UV completion

Arkani-Hamed, Cohen, Katz, Nelson

The Hierarchy Problem: Little Higgs

Energy (GeV)

1019

1016

103

10-18Solar SystemGravity

Weak

GUT

Planck

Future Collider Energies

All of known physics

Stacks of Little Hierarchies

104 New Physics!

Simplest Model: The Littlest Higgs with 1 ~ 10 TeV 2 ~ 100 TeV 3 ~ 1000 TeV …..

105

106

.

.

.

New Physics!

New Physics!

Little Higgs: The Basics

• The Higgs becomes a component of a larger multiplet of scalars,

transforms non-linearly under a new global symmetry

• New global symmetry undergoes SSB leaves Higgs as goldstone• Part of global symmetry is gauged Higgs is pseudo-goldstone

• Careful gauging removes Higgs 1-loop divergences

2

mh2 ~ , > 10 TeV, @ 2-loops!

(162)2

3-Scale Model

> 10 TeV: New Strong Dynamics

Global Symmetry

f ~ /4 ~ TeV: Symmetires Broken

Pseudo-Goldstone Scalars New Gauge Fields New Fermions

v ~ f/4 ~ 100 GeV: Light Higgs

SM vector bosons & fermions

Sample Spectrum

Little Higgs Gauge Production

Azuelos etal, hep-ph/0402037

Birkedal, Matchev, Perelstein, hep-ph/0412278

WZ WH WZ 2j + 3l +

The Hierarchy Problem: HiggslessEnergy (GeV)

1019

1016

103

10-18Solar SystemGravity

Weak

GUT

Planckd

ese

rt

Future Collider Energies

All of known physics

Warped Extra Dimensions

wk = MPl e-kr

With NO Higgs boson!

strong curvature

Csaki, Grojean,Murayama, Pilo, Terning

Framework: EW Symmetry Broken by Boundary Conditions

SU(2)L x SU(2)R x U(1)B-L in 5-d Warped bulk

Planckbrane TeV-brane

SU(2)R x U(1)B-L

U(1)Y

SU(2)L x SU(2)R

SU(2)D

SU(2) Custodial Symmetryis preserved!

WR, ZR get

Planckscale masses

W, Z get TeV scale masses left massless!

BC’s restricted by variation of the action at boundary

Exchange gauge KK towers:

Conditions on KK masses & couplings:

(g1111)2 = k (g11k)2

4(g1111)2 M12 = k (g11k)2 Mk

2

Necessary, but not sufficient, to guarantee perturbative unitarity!

Csaki etal, hep-ph/0305237

Unitarity in Gauge Boson Scattering: What do we do without a Higgs?

Production of Gauge KK States @ LHC

gg, qq g1 dijets-

Davoudiasl, JLH, Lilllie, Rizzo Balyaev, Christensen

Gauge Hierarchy Problem

Cosmological Constant Problem

Planck Scale

Weak Scale

CosmologicalScale

The Hierarchy Problem: Who Cares!!

We have much bigger Problems!

Split Supersymmetry:

Energy (GeV) MGUT ~ 1016 GeV

MS : SUSY broken at high scale ~ 109-13 GeV

Mweak

1 light Higgs + Fermionsprotected by chiral symmetry

Scalars receive mass @ high scale

Arkani-Hamed, Dimopoulis hep-ph/0405159Giudice, Romanino hep-ph/0406088

Collider Phenomenology: Gluinos

• Pair produced via strong interactions as usual• Gluinos are long-lived• No MET signature• Form R-hadrons

g~q~

q

q

10

Rate ~ 0, due to heavy squark masses!

Gluino pair + jet cross section

JLH, Lillie, Masip, Rizzo hep-ph/0408248

100 fb-1

Density of Stopped Gluinos in ATLAS

See also ATLAS study, Kraan etal hep-ph/0511014

Arvanitaki, etal hep-ph/0506242

This is a Special Time in Particle Physics

• Urgent QuestionsProvocative discoveries lead to urgent questions

• ConnectionsQuestions seem to be related in fundamental, yet

mysterious, ways

• ToolsWe have the experimental tools, technologies,

and strategies to tackle these questions

We are witnessing a Scientific Revolution in the Making!

The LHC is Turning On!!!!!!!!

And we are ready!

Higgs Coupling Determinations @ LHC

Observed Channels:– gg H ZZ, WW, – qqH qqZZ, qqWW, qq,

qq– WH WWW, W; ZH Z– ttH, with H WW, , bb

Duhrssen, Heinemeyer, Logan, Rainwater, Weiglein, Zeppenfeld

Employ Narrow Width Approx:

(H)SM p x

(H) B(Hxx) = p

SM totTheoretical Assumption: V VSM , V=W,Z