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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