Beyond the Standard Model • Commissioning update • • Status of the Standard Model Search for ‘the’ Higgs boson Look for supersymmetry/extra dimensions, … Find something theorists did not expect LHC Startup Forum Cosener’s House, April 12 th, 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 • 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 • • 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 Ge. V • Raises many unanswered questions: mass? flavour? unification?
March 2007 Indications on the Higgs Mass Sample observable: W mass @ LEP & Tevatron m. W, 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 Te. V)2 • Most have small couplings ~ α 2 • Compare with total cross section ~ 1/(100 Me. V)2 • Fraction ~ 1/1, 000, 000 • Need ~ 1, 000 events for signal • Compare needle ~ 1/100, 000 m 3 • Haystack ~ 100 m 3 • 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 Total statistics collected at previous machines by 2007 W e 15 108 Z ee 1. 5 107 LEP 1 107 104 Tevatron 104 LEP / 107 Tevatron 106 H m=130 Ge. V m= 1 Te. V Black holes m > 3 Te. V 1012 – 1013 0. 02 105 ? 0. 001 104 --- 0. 0001 103 109 Belle/Ba. Bar ? --- (MD=3 Te. V, 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 Te. V
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 5 fb-1, 1 fb-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 Te. V (1000 Ge. V) • 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
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 Mass 2 • Consider generic fermion and boson loops: • Each is quadratically divergent: Λ 4 ∫ d k/k 2 2 • Leading divergence cancelled if ∙ 2 Supersymmetry!
Other Reasons to like Susy It enables the gauge couplings to unify It predicts m. H < 150 Ge. V As suggested by EW data Erler: 2007 JE, Nanopoulos, Olive + Santoso: hep-ph/0509331
Astronomers say that most of the matter in the Universe is invisible 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: Fayet R = (-1) 2 S –L + 3 B 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 Ge. V squarks, gluino > 250 Ge. V • Indirect constraints Higgs > 114 Ge. V, b → s γ • Density of dark matter lightest sparticle χ: WMAP: 0. 094 < Ωχh 2 < 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’ @ 1034 Blaising et al: 2006
Can one estimate the scale of supersymmetry? Precision Observables in Susy Sensitivity to m 1/2 in CMSSM along WMAP lines for different A m. W tan β = 10 tan β = 50 sin 2θW 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 m 1/2 Likelihood for Mh JE + Heinemeyer + Olive + Weber + Weiglein: 2007
Search for Squark W Hadron Decays • Use k. T 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 q. W 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 10 m • 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 < 1 cm • Fix impact angle with accuracy 10 -3 • Bore into cavern wall and remove core of size 1 cm × 10 m = 10 -3 m 3 ~ 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 ~104 s, possible if ~106 s? 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/m. P? • Or larger?
How large could extra Dimensions be? • 1/Te. V? 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 Te. V 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 Te. V 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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