Beyond the Standard Model

LHC Startup ForumCosener’s House, April 12th, 2007

John Ellis, TH Division, PH Department, CERN

• Commissioning update• Status of the Standard Model

• Search for ‘the’ Higgs boson

• Look for supersymmetry/extra dimensions, …

• Find something the theorists did not expect

LHC Installation ~ Complete

LHC Cryogenic Operating Conditions

• SC magnets @ 1.9 K, 1.3 bar• Superfluid He II below point

• Low viscosity: permeates magnets• High thermal conductivity, large specific heat: stability

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Cooldown of Sector 78

Magnet Temperatures in Sector 78

• Failure of heat exchanger at 9 bar

• Thin copper ‘accordion’ weakened by brazing

• Engineering solution found

• Remove and replace in situ

Inner-Triplet Saga: I

• Failure of cold-mass support at 20 bar

• Broke apart + damage to feed box?

• Due to asymmetric force on quadrupole

• Damaged assembly must be replaced

• Others may be reinforced in situ

• Insert tie rods in cryostat

• ‘Cock-up’

dixit UK

ambassador

Inner-Triplet Saga: II

Last magnet delivered October 2006

Last magnet tested December 2006

Last magnet installed March 2007

Machine closed August 2007

First collisions November 2007 ?

Remaining LHC MilestonesRemaining LHC Milestones

Status of the Standard Model

• Perfect agreement with all confirmed accelerator data

• Consistency with precision electroweak data (LEP et al) only if there is a Higgs boson

• Agreement seems to require a relatively light Higgs boson weighing < ~ 150 GeV

• Raises many unanswered questions:

mass? flavour? unification?

Indications on the Higgs Mass

Sample observable:W mass @ LEP & Tevatron

Combined informationon Higgs mass

March 2007

mW, mt both reduced by ~ ½ σ

The LHC Physics Haystack(s)

Interesting cross sections

Higgs

Susy

• Cross sections for heavy particles

~ 1 /(1 TeV)2

• Most have small couplings ~ α2

• Compare with total cross section

~ 1/(100 MeV)2

• Fraction ~ 1/1,000,000,000,000

• Need ~ 1,000 events for signal

• Compare needle

~ 1/100,000,000 m3

• Haystack ~ 100 m3

• Must look in ~ 100,000 haystacks

Event rates in ATLAS or CMS at L = 1033 cm-2 s-1

Huge Statistics thanks to High Energy and Luminosity

LHC is a factory for anything: top, W/Z, Higgs, SUSY, etc…. mass reach for discovery of new particles up to m ~ 5 TeV

Process Events/s Events per year Total statistics collected at previous machines by 2007

W e 15 108 104 LEP / 107 Tevatron

Z ee 1.5 107 107 LEP

1 107 104 Tevatron

106 1012 – 1013 109 Belle/BaBar ?

gg~~

tt

bb

H m=130 GeV 0.02 105 ?

m= 1 TeV 0.001 104 ---

Black holes 0.0001 103 ---m > 3 TeV (MD=3 TeV, n=4)

Start-up Physics

• Measure and understand minimum bias• Measure jets, start energy calibration• Measure W/Z, calibrate lepton energies• Measure top, calibrate jet energies &

missing ET

• First searches for Higgs:– Combine many signatures– need to understand detector very well

• First searches for SUSY, etc.

Looking for New Physics @ LHC

• Need to understand SM first:– calibration, alignment, systematics

• Searches for specific scenarios, e.g., SUSY, vs signature-based searches, e.g., monojets?

• False dichotomy!• How to discriminate between models?

– different Z’ models?– missing energy: SUSY vs UED?

• higher excitations, spin correlations, spectra, …

ττ

γγγγ

ZZ* -> 4 leptons

A la recherche du Higgs perdu …

Some Sample Higgs Signals

Potential of Initial LHC running

• A Standard Model Higgs boson could be discovered with 5-σ significance with 5fb-1, 1fb-1 would be sufficient to exclude a Standard Model Higgs boson at the 95% confidence level

• Signal would include ττ, γγ, bb, WW and ZZ

• Will need to understand detectors very well

• Will be possible to determine spin of Higgs decaying to γγ or ZZ

• Can measure invisible Higgs decays at 15-30% level

• Will be possible to determine many Higgs-particle couplings at the 10-20% level

Subsequent LHC Running

The Big Open Questions

• The origin of particle masses? Higgs boson? + extra physics?solution at energy < 1 TeV (1000 GeV)

• Why so many types of particles?and the small matter-antimatter difference?

• Unification of the fundamental forces?at very high energy?explore indirectly via particle masses, couplings

• Quantum theory of gravity?string theory: extra dimension?

LHC

LHC

LHC

LHC

What is Supersymmetry (Susy)?

• The last undiscovered symmetry?

• Could unify matter and force particles

• Links fermions and bosons

• Relates particles of different spins

0 - ½ - 1 - 3/2 - 2 Higgs - Electron - Photon - Gravitino - Graviton

• Helps fix masses, unify fundamental forces

Loop Corrections to Higgs Mass2

• Consider generic fermion and boson loops:

• Each is quadratically divergent: ∫Λd4k/k2

• Leading divergence cancelled if

Supersymmetry!

2

∙2

Other Reasons to like Susy

It enables the gauge couplings to unify

It predicts mH < 150 GeV

JE, Nanopoulos, Olive + Santoso: hep-ph/0509331

As suggestedby EW data

Erler: 2007

Astronomers tell us that most of the matter in the universe is invisible

We will look for it

with the LHC

Dark Matter in the Universe

Astronomers saythat most of thematter in theUniverse isinvisible Dark Matter

‘Supersymmetric’ particles ?

We shall look for them with the

LHC

Lightest Supersymmetric Particle

• Stable in many models because of conservation of R parity:

R = (-1) 2S –L + 3B

where S = spin, L = lepton #, B = baryon #

• Particles have R = +1, sparticles R = -1:Sparticles produced in pairsHeavier sparticles lighter sparticles

• Lightest supersymmetric particle (LSP) stable

Fayet

Possible Nature of LSP

• No strong or electromagnetic interactionsOtherwise would bind to matterDetectable as anomalous heavy nucleus

• Possible weakly-interacting scandidatesSneutrino

(Excluded by LEP, direct searches)Lightest neutralino χGravitino

(nightmare for astrophysical detection)

Constraints on Supersymmetry

• Absence of sparticles at LEP, Tevatronselectron, chargino > 100 GeV

squarks, gluino > 250 GeV

• Indirect constraintsHiggs > 114 GeV, b → s γ

• Density of dark matterlightest sparticle χ:

WMAP: 0.094 < Ωχh2 < 0.124

3.3 σeffect ingμ – 2?

Current Constraints on CMSSM

WMAP constraint on relic density

Excluded because stau LSP

Excluded by b s gamma

Excluded (?) by latest g - 2

Assuming the lightest sparticleis a neutralino

JE + Olive + Santoso + Spanos

Classic Supersymmetric Signature

Missing transverse energy

carried away by dark matter particles

Search for Supersymmetry

Light sparticles

@ low luminosity

Heavy sparticles

Initial LHC Reach for SupersymmetryHow soon will we know?

Implications of LHC Search for ILC

In CMSSM

LHC already sees beyond ILC ‘at turn-on’

1 ‘year’ @ 10341 ‘year’ @ 1033‘month’ @ 1033‘month’ @ 1032

LHC gluinomass reach

Corresponding sparticle thresholds @ ILC

Blaising et al: 2006

Precision Observables in Susy

mW

sin2θW

Present & possiblefuture errors

Sensitivity to m1/2 in CMSSM along WMAP linesfor different A

Can one estimate the scale of supersymmetry?

tan β = 50tan β = 10

JE + Heinemeyer + Olive + Weber + Weiglein: 2007

MoreObservables

b → sγ

tan β = 10 tan β = 50

gμ - 2

JE + Heinemeyer + Olive + Weber + Weiglein: 2007

Likelihoodfor m1/2

Global Fitto all

Observables

tan β = 10 tan β = 50

JE + Heinemeyer + Olive + Weber + Weiglein: 2007

Likelihoodfor Mh

Erice. Sept. 2, 2003 L. Maiani: LHC Status 14

m (l l ) spectrumend-point : 109 GeVprecision~ 0.3%

m (l l j)min spectrumend-point: 552 GeVprecision ~1 %

m (l±j) spectrumed-poit: 479 GeVexp. precisio ~1 %

m (j)max spectrumthreshod: 272 GeVexp. precisio ~2 %

Reconstruction of ̀Typical’Sparticle Decay Chain

Msquark = 690M÷ ’ = 232

Msepto = 157M÷ = 121(GeV)

ATLAS

Lq~ → q χ02

R

~l

l χ01

l

Search for Squark W Hadron Decays

• Use kT algorithm to define jets

• Cut on W mass

• W and QCD jets have different subjet splitting scales

• Corresponding to y cut

Butterworth + JE + Raklev: 2007

• Background-subtracted qW mass combinations in benchmark scenarios

• Constrain sparticle mass spectra

Search for Hadronic W, Z Decays

Butterworth + JE + Raklev: 2007

Possible Nature of SUSY Dark Matter

• No strong or electromagnetic interactionsOtherwise would bind to matterDetectable as anomalous heavy nucleus

• Possible weakly-interacting scandidatesSneutrino

(Excluded by LEP, direct searches)Lightest neutralino χGravitino

(nightmare for astrophysical detection)GDM: a bonanza for the LHC!

Possible Nature of NLSP if GDM

• NLSP = next-to-lightest sparticle• Very long lifetime due to gravitational

decay, e.g.:

• Could be hours, days, weeks, months or years!

• Generic possibilities:lightest neutralino χlightest slepton, probably lighter stau

• Constrained by astrophysics/cosmology

Triggering on GDM Events

Will be selected by many separate triggers

via combinations of μ, E energy, jets, τJE, Raklev, Øye: 2007

Efficiency for Detecting Metastable Staus

Good efficiency for reconstructing stau tracks

JE + Raklev + Oye

ATLAS Momentum resolution

Good momentum resolution

JE + Raklev + Oye

Reconstructing GDM Events

χ → stau τ

JE, Raklev, Øye: 2006

Squark → q χ

Stau Momentum Spectra• βγ typically peaked ~ 2

• Staus with βγ < 1 leave central tracker

after next beam crossing

• Staus with βγ < ¼ trapped inside calorimeter

• Staus with βγ < ½ stopped within 10m

• Can they be dug out of cavern wall?

De Roeck, JE, Gianotti, Moortgat, Olive + Pape: hep-ph/0508198

Extract Cores from Surrounding Rock?• Use muon system to locate impact point on

cavern wall with uncertainty < 1cm

• Fix impact angle with accuracy 10-3

• Bore into cavern wall and remove core of size 1cm × 1cm × 10m = 10-3m3 ~ 100 times/year

• Can this be done before staus decay?

Caveat radioactivity induced by collisions!

2-day technical stop ~ 1/month

• Not possible if lifetime ~104s, possible if ~106s?

Very little room for water tank in LHC caverns,only in forward directions where few staus

De Roeck, JE, Gianotti, Moortgat, Olive + Pape: hep-ph/0508198

String Theory

• Candidate for reconciling gravity with quantum mechanics

• Point-like particles → extended objects• Simplest possibility: lengths of string• Quantum consistency fixes # dimensions:• Bosonic string: 26, superstring: 10• Must compactify extra dimensions, scale ~ 1/mP?• Or larger?

How large could extra Dimensions be?

• 1/TeV?could break supersymmetry, electroweak

• micron?can rewrite hierarchy problem

• Infinite?warped compactifications

• Look for black holes, Kaluza-Klein excitations @ colliders?

Spin Effects in Decay Chains

Chain DCBA:

Scalar/Fermion/Vector

Shape of dilepton spectrum

Shape of q-lepton spectrum

Angular asymmetry

in q-lepton spectrum

Distinguish supersymmetry

from extra-D scenarios

Athanasiou+Lester+Smillie+Webber

And if gravity becomes strong at the TeV scale …

Black Hole Production at LHC?

Multiple jets,

leptons from

Hawking

radiation

Black Hole Production @ LHC

Cambridge: al et Webber

Black Hole Decay Spectrum

Cambridge: al et Webber

Summary• The origin of mass is the most pressing in particle

physics• Needs a solution at energy < 1 TeV

Higgs? Supersymmetry?

LHC will tell!• Lots of speculative ideas for other physics beyond the

Standard Model

Grand unification, strings, extra dimensions? …

LHC may also probe these speculations

We do not know what the LHC will find:

its discoveries will set agenda for future projects