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Beyond the Standard Model

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Presentation on theme: "Beyond the Standard Model"— Presentation transcript:

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

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