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Beyond the Standard Model

This update covers the status of the LHC installation, including the cryogenic operating conditions and the challenges faced in Sector 78. It also discusses the latest findings related to the Standard Model, Higgs boson mass indications, and the potential for discovering new particles at the LHC. The description provides insights into the physics haystacks, event rates, and upcoming milestones. Additionally, it delves into the search for the Higgs boson, Supersymmetry, and other intriguing aspects of particle physics that the LHC aims to explore.

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Beyond the Standard Model

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  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 magnets @ 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

  9. Status of the Standard Model • Perfect agreement with all confirmedaccelerator 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. March 2007 Indications on the Higgs Mass Combined information on Higgs mass Sample observable: W mass @ LEP & Tevatron mW, mt both reduced by ~ ½ σ

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

  12. Process Events/sEvents per year Total statistics collected at previous machines by 2007 W e 15 108 104 LEP / 107 Tevatron Z ee 1.5107107 LEP 1107104 Tevatron 1061012–1013109 Belle/BaBar ? H m=130 GeV 0.02105 ? m= 1 TeV 0.001104--- Black holes 0.0001103--- m > 3 TeV (MD=3 TeV, n=4) Huge Statistics thanks to High Energy and Luminosity Event rates in ATLAS or CMS at L = 1033 cm-2 s-1 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. 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 • The origin of particle masses? Higgsboson? + 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 0 - ½ - 1 - 3/2 - 2 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/0509331

  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. 3.3 σ effect in gμ – 2? 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

  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. 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 thresholds @ ILC LHC already sees beyond ILC ‘at turn-on’ ‘month’ @ 1032 1 ‘year’ @ 1033 ‘month’ @ 1033 1 ‘year’ @ 1034 Blaising et al: 2006

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

  33. Global Fitto allObservables tan β = 10 tan β = 50 Likelihood for m1/2 Likelihood for Mh JE + Heinemeyer +Olive + Weber +Weiglein: 2007

  34. 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

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

  36. 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!

  37. 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

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

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

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

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

  42. 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

  43. 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

  44. 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?

  45. 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?

  46. Shape of dilepton spectrum Spin Effects in Decay Chains 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

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

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

  49. Black Hole Decay Spectrum Cambridge: al et Webber

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