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Beyond the Standard Model
• Commissioning update
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Status of the Standard Model
Search for ‘the’ Higgs boson
Look for supersymmetry/extra dimensions, …
Find something the theorists did not expect
LHC Startup Forum
Cosener’s House, April 12th, 2007
John Ellis, TH Division, PH Department, CERN
LHC Installation ~ Complete
LHC Cryogenic Operating Conditions
• SC magnets @ 1.9 K, 1.3 bar
• Superfluid He II below  point
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
• Low viscosity: permeates magnets
• High thermal conductivity, large specific heat: stability
Cooldown of Sector 78
Magnet Temperatures in Sector 78
Inner-Triplet Saga: I
• Failure of heat
exchanger at 9 bar
• Thin copper
‘accordion’
weakened by
brazing
• Engineering
solution found
• Remove and
replace in situ
Inner-Triplet Saga: II
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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
Remaining LHC Milestones
Last magnet delivered
October 2006
Last magnet tested
December 2006
Last magnet installed
March 2007
Machine closed
August 2007
First collisions
November 2007 ?
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?
March 2007
Indications on the Higgs Mass
Sample observable:
W mass @ LEP & Tevatron
mW, mt both reduced by ~ ½ σ
Combined information
on Higgs mass
The LHC Physics Haystack(s)
Interesting cross sections
Susy
Higgs
• 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
Huge Statistics thanks to High Energy and Luminosity
Event rates in ATLAS or CMS at L = 1033 cm-2 s-1
Process
Events/s
Events per year
W e
15
108
Z ee
1.5
107
107 LEP
tt
1
107
104 Tevatron
bb
106
1012 – 1013
H m=130 GeV
0.02
105
?
~g
~ m= 1 TeV
g
0.001
104
---
Black holes
m > 3 TeV
0.0001
103
Total statistics collected
at previous machines by 2007
104 LEP / 107 Tevatron
109 Belle/BaBar ?
---
(MD=3 TeV, n=4)
LHC is a factory for anything: top, W/Z, Higgs, SUSY, etc….
mass reach for discovery of new particles up to m ~ 5 TeV
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, …
A la recherche
du
Higgs perdu …
Some Sample Higgs Signals
γγ
γγ
ZZ* -> 4 leptons
ττ
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
Subsequent
LHC Running
• 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 Higgsparticle couplings at the
10-20% level
The Big Open Questions
• The origin of particle masses?
Higgs boson? + extra physics?
solution at energy < 1 TeV (1000 GeV)
LHC
• Why so many types of particles?
and the small matter-antimatter difference?
LHC
• 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
What is Supersymmetry (Susy)?
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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:
Λ 4
∫ d k/k2
2
• Leading divergence cancelled if
∙2
Supersymmetry!
Other Reasons to like Susy
It enables the gauge couplings to unify
It predicts mH < 150 GeV
As suggested
by EW data
Erler: 2007
JE, Nanopoulos, Olive + Santoso: hep-ph/0509331
Dark Matter in the Universe
Astronomers say
that
most of tell
the
Astronomers
us that most
matter
in theof the
matter in the
Universe
is
universe is
invisible
invisible
Dark Matter
‘Supersymmetric’ particles ?
We will look for it
We shall look for
with the
LHC
them
with
the
LHC
Lightest Supersymmetric Particle
• Stable in many models because of
conservation of R parity:
Fayet
R = (-1) 2S –L + 3B
where S = spin, L = lepton #, B = baryon #
• Particles have R = +1, sparticles R = -1:
Sparticles produced in pairs
Heavier sparticles  lighter sparticles
• Lightest supersymmetric particle (LSP) stable
Possible Nature of LSP
• No strong or electromagnetic interactions
Otherwise would bind to matter
Detectable as anomalous heavy nucleus
• Possible weakly-interacting scandidates
Sneutrino
(Excluded by LEP, direct searches)
Lightest neutralino χ
Gravitino
(nightmare for astrophysical detection)
Constraints on Supersymmetry
• Absence of sparticles at LEP, Tevatron
selectron, chargino > 100 GeV
squarks, gluino > 250 GeV
• Indirect constraints
Higgs > 114 GeV, b → s γ
• Density of dark matter
lightest sparticle χ:
WMAP: 0.094 < Ωχh2 < 0.124
3.3 σ
effect in
gμ – 2?
Current Constraints on CMSSM
Assuming the
lightest sparticle
is a neutralino
Excluded because stau LSP
Excluded by b  s gamma
WMAP constraint on relic density
Excluded (?) by latest g - 2
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
How soon will we know?
Initial LHC Reach for Supersymmetry
Implications of LHC Search for ILC
In CMSSM
LHC gluino
mass reach
Corresponding sparticle
thresholds @ ILC
LHC already sees
beyond ILC ‘at turn-on’
‘month’ @ 1032 ‘month’ @ 1033
1 ‘year’ @ 1033 1 ‘year’ @ 1034
Blaising et al: 2006
Can one estimate the scale of supersymmetry?
Precision Observables in Susy
Sensitivity to m1/2
in CMSSM
along WMAP lines
for different A
mW
tan β = 10
tan β = 50
sin2θW
Present & possible
future errors
JE + Heinemeyer + Olive + Weber + Weiglein: 2007
More
Observables
tan β = 10
tan β = 50
b → sγ
gμ - 2
JE + Heinemeyer + Olive + Weber + Weiglein: 2007
Global Fit
to all
Observables
tan β = 10
tan β = 50
Likelihood
for m1/2
Likelihood
for Mh
JE + Heinemeyer + Olive + Weber + Weiglein: 2007
m () spectrum
end-point : 109 GeV
precision ~ 0.3%
Reconstruction of `Typical’
Sparticle Decay Chain
~
q
m (j)max spectrum
threshold: 272 GeV
exp. precision ~2 %
Erice. Sept. 2, 2003
L
 q 02~

R
m (j)min spectrum
end-point: 552 GeV
precision ~1 %

 01
Msquark = 690
Mχ’ = 232
Mslepton = 157
Mχ = 121
(GeV)
L. Maiani: LHC Status
ATLAS
m (j) spectrum
end-point: 479 GeV
exp. precision ~1 %
14
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
Search for Hadronic W, Z Decays
• Backgroundsubtracted qW
mass combinations
in benchmark
scenarios
• Constrain sparticle
mass spectra
Butterworth + JE + Raklev: 2007
Possible Nature of SUSY Dark Matter
• No strong or electromagnetic interactions
Otherwise would bind to matter
Detectable as anomalous heavy nucleus
• Possible weakly-interacting scandidates
Sneutrino
(Excluded by LEP, direct searches)
Lightest neutralino χ
Gravitino
(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 χ
lightest slepton, probably lighter stau
• Constrained by astrophysics/cosmology
Triggering on GDM Events
Will be selected by many separate triggers
JE, Raklev, Øye: 2007
via combinations of μ, E energy, jets, τ
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
Very little room for water tank in LHC caverns,
only in forward directions where few staus
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?
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
Shape of dilepton spectrum
Chain DCBA:
Scalar/Fermion/Vector
Distinguish supersymmetry
from extra-D scenarios
Angular asymmetry
in q-lepton spectrum
Shape of q-lepton spectrum
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