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**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

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**LHC Installation ~ Complete**

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**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

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Cooldown of Sector 78

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**Magnet Temperatures in Sector 78**

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**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

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**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

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**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 ?

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**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?

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**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

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**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

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**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

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**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.

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**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, …

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**Some Sample Higgs Signals**

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

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**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

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**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

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**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

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**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

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**Loop Corrections to Higgs Mass2**

Consider generic fermion and boson loops: Each is quadratically divergent: ∫Λd4k/k2 Leading divergence cancelled if Supersymmetry! 2 ∙2

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**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/

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

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**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

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**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)

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**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?

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**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

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**Classic Supersymmetric Signature**

Missing transverse energy carried away by dark matter particles

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**Search for Supersymmetry**

Light sparticles @ low luminosity Heavy sparticles

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**Initial LHC Reach for Supersymmetry**

How soon will we know? Initial LHC Reach for Supersymmetry

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**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

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**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

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**More Observables b → sγ gμ - 2 tan β = 10 tan β = 50**

JE + Heinemeyer + Olive + Weber + Weiglein: 2007

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**Global Fit to all Observables**

tan β = 10 tan β = 50 Likelihood for m1/2 Likelihood for Mh JE + Heinemeyer + Olive + Weber + Weiglein: 2007

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**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

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**Search for Hadronic W, Z Decays**

Background-subtracted qW mass combinations in benchmark scenarios Constrain sparticle mass spectra Butterworth + JE + Raklev: 2007

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**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!

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**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

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**Triggering on GDM Events**

Will be selected by many separate triggers via combinations of μ, E energy, jets, τ JE, Raklev, Øye: 2007

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**Efficiency for Detecting Metastable Staus**

Good efficiency for reconstructing stau tracks JE + Raklev + Oye

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**ATLAS Momentum resolution**

Good momentum resolution JE + Raklev + Oye

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**Reconstructing GDM Events**

χ → stau τ Squark → q χ JE, Raklev, Øye: 2006

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**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/

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**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/

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**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?

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**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?

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**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

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**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

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**Black Hole Production @ LHC**

Cambridge: al et Webber

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**Black Hole Decay Spectrum**

Cambridge: al et Webber

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**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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