1. Beyond the Standard Model
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 Startup Forum
Cosener’s House, April 12th, 2007
John Ellis, TH Division, PH Department, CERN

2. LHC Installation ~ Complete

3. LHC Cryogenic Operating Conditions
SC 1.9 K, 1.3 bar
Superfluid He II below  point
Low viscosity: permeates magnets
High thermal conductivity, large specific heat: stability

4. Cooldown of Sector 78

5. Magnet Temperatures in Sector 78

6. 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

7. Inner-Triplet Saga: II
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

8. 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 ?

9. 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?

10. Indications on the Higgs Mass
March 2007
Indications on the Higgs Mass
Sample observable:
W LEP & Tevatron
Combined information
on Higgs mass
mW, mt both reduced by ~ ½ σ

11. The LHC Physics Haystack(s)
Interesting cross sections
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
Susy
Higgs

12. 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 Total statistics collected
at previous machines by 2007
W e LEP / 107 Tevatron
Z ee LEP
Tevatron
– Belle/BaBar ?
H m=130 GeV ?
m= 1 TeV
Black holes
m > 3 TeV
(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

13. 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.

14. 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, …

15. Some Sample Higgs Signals
A la recherche du
Higgs perdu …
Some Sample Higgs Signals γγ γγ
ZZ* -> 4 leptons ττ

16. 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

17. 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 Higgs-particle couplings at the 10-20% level

18. The Big Open Questions LHC LHC LHC LHC 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

19. What is Supersymmetry (Susy)?
The last undiscovered symmetry?
Could unify matter and force particles
Links fermions and bosons
Relates particles of different spins
½ /
Higgs - Electron - Photon - Gravitino - Graviton
Helps fix masses, unify fundamental forces

20. Loop Corrections to Higgs Mass2
Consider generic fermion and boson loops:
Each is quadratically divergent: ∫Λd4k/k2
Leading divergence cancelled if
Supersymmetry! 2 ∙2

21. 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/

22. Astronomers say
that most of the
matter in the
Universe is
invisible
Dark Matter
‘Supersymmetric’ particles ?
We shall look for
them with the
LHC

23. 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 pairs
Heavier sparticles  lighter sparticles
Lightest supersymmetric particle (LSP) stable
Fayet

24. 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)

25. 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: < Ωχh2 < 0.124
3.3 σ
effect in
gμ – 2?

26. 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

27. Classic Supersymmetric Signature
Missing transverse energy
carried away by dark matter particles

28. Search for Supersymmetry
Light sparticles
@ low luminosity
Heavy sparticles

29. Initial LHC Reach for Supersymmetry
How soon will we know?
Initial LHC Reach for Supersymmetry

30. Implications of LHC Search for ILC
In CMSSM
LHC gluino
mass reach
Corresponding sparticle
ILC
LHC already sees
beyond ILC ‘at turn-on’
1032
1033
1 1033
1 1034
Blaising et al: 2006

31. Precision Observables in Susy
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

32. More Observables b → sγ gμ - 2 tan β = 10 tan β = 50
JE + Heinemeyer + Olive + Weber + Weiglein: 2007

33. Global Fit to all Observables
tan β = 10
tan β = 50
Likelihood
for m1/2
Likelihood
for Mh
JE + Heinemeyer + Olive + Weber + Weiglein: 2007

35. 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

36. Search for Hadronic W, Z Decays
Background-subtracted qW mass combinations in benchmark scenarios
Constrain sparticle mass spectra
Butterworth + JE + Raklev: 2007

37. 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!

38. 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

39. Triggering on GDM Events
Will be selected by many separate triggers
via combinations of μ, E energy, jets, τ
JE, Raklev, Øye: 2007

40. Efficiency for Detecting Metastable Staus
Good efficiency for reconstructing stau tracks
JE + Raklev + Oye

41. ATLAS Momentum resolution
Good momentum resolution
JE + Raklev + Oye

42. Reconstructing GDM Events
χ → stau τ
Squark → q χ
JE, Raklev, Øye: 2006

43. 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/

44. Extract Cores from Surrounding Rock?
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/

45. 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?

46. 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 colliders?

47. 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

48. Black Hole Production at LHC?
And if gravity becomes strong at the TeV scale …
Black Hole Production at LHC?
Multiple jets,
leptons from
Hawking
radiation

49. Black Hole Production @ LHC
Cambridge: al et Webber

50. Black Hole Decay Spectrum
Cambridge: al et Webber

51. Summary We do not know what the LHC will find:
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