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2. Physics case Why Me? My job today is to convince/remind you: That this physics is important, and the search for itdeserves our full attention That there is likely to be physics “Beyond the Standard Model” That the Large Hadron Collider is likely to be the best place to do this work over the next 10 to15 years That I have a valuable role to play in the process of discovering the truth

3. Large Hadron Collider and ATLAS in 1 minute

4. Simple experimental aim: Collide protons and see what happens.

5. Large Hadron Collider (LHC)

6. Collider (LHC) nearing completion in CERN, Geneva

7. LHC protons 7 TeV protons 7 TeV The Semiconductor Tracker “ATLAS Experiment” to look at the collisions MORE ON THIS LATER

8. Note about “the brief” • Talk about: • “Your vision for your future research programme at Cambridge” • In context of the LHC we have • predictable items • Make the detector work • Commissioning – understand MET resolution, jet energy scale, alignment • unpredictable items • What new physics may nature hold? • What will we see of it? • How will we measure it? MANYUNKNOWNS ADAPTABILITY IS THE KEY

9. Physics Case • Why Physics beyond the Standard Model?

10. The Standard Model “The Standard Model” – not the final story • Higgs not yet found • Top-quark charge undetermined! • Quark masses poorly measured • Fine-tuning / “hierarchy problem” (technical) – Why are particles light? • Does not explain Dark Matter • No gauge coupling unification • Why three generations? None of these criticisms need necessarily be cause for alarm But new Physics, e.g. Supersymmetry, can help.

11. Possibilities for new physics … • Supersymmetry? • Minimal • Non-minimal • R-parity violating or conserving • Gauge mediated • Gravity mediated • Extra Dimensional Models • Large (particles trapped on “brane”) • Universal (particles everywhere) • With/without small black holes • “Littlest” Higgs ? • ….

13. There’s a strange “guarantee” … • Something newwill be found at the LHC • If the Higgs Boson exists • It will be found! • If the Higgs Boson doesn’t exist • Cross-section for W-boson scattering will be observed to deviate from Standard Model • Strategic “gamble” • Anticipate large • Look for everything • Do not concentrate on Higgs

14. What I Contribute Ana

15. High Energy Physics forthe 21st Century Step one: into the unknown Christopher Lester

16. Higgs not yet found Quark mixing not over-constrained yet Quark masses poorly measured Top-quark charge undetermined! No conflict with experiment (yet) Parts (QED) in extremely good agreement with experiment – even with atomic physics! (Lamb Shift, magnetic moments) Elementary particle content “reasonably” small … Standard Model Good Standard Model Bad

17. What is the charge of the top-quark? Based on 17 events. [Markus Klute] Preliminarily excludes exotic top-quark charge of -4/3 at 94% confidence. (365 pb-1) Spring 2006. Dark corners of the Standard Model

18. Higgs not yet found Quark mixing not over-constrained yet Top-quark charge undetermined! Quark masses poorly measured Fine-tuning / “hierarchy problem” (technical) – Why are particles light? Does not explain Dark Matter No gauge coupling unification No conflict with experiment (yet) Parts (QED) in extremely good agreement with experiment – even with atomic physics! (Lamb Shift, magnetic moments) Elementary particle content “reasonably” small … Standard Model Good Standard Model Bad New Physics, e.g. Supersymmetry, can help.

19. Four Questions: • What might the new physics be? (2) What sort of experiment will help us? (3) How will we go about extracting answers from the data? (4) Can we trust the answers? Will describe some later. Coming next! Very much the work of people in The Cavendish. Are they robust?

20. Large Hadron Collider (LHC)

21. Collider nearing completion

22. LHC protons 7 TeV protons 7 TeV The Semiconductor Tracker “ATLAS” Experiment

23. Note concerning units eV = electron-volt = 1.6 x 10-19 J GeV = 10 9 eV = 1.6 x 10-10 J TeV = 1012 eV = 1.6 x 10-7 J (= K.E. of 1.3mg mosquito at 0.5 m/s) Express most particle energies and masses in GeV … … but LHC proton beams are 7 TeV each (14 mosquitos in total)

24. Anatomy of the detector Layered like Onion Different layers for different types of particles Neutrino Muon

25. So main things we can do Average direction of things which were invisible • Distinguish the following from each other • Hadronic Jets, • B-jets (sometimes) • Electrons, Positrons, Muons, Anti-Muons • Tau leptons (sometimes) • Photons • Measure Directions and Momenta of the above. • Infer total transverse momentum of invisible particles. (eg neutrinos) electron Here Be Monsters Hadronic Jet photon

26. Muon Detector MAGNETIC FIELD MAGNETIC FIELD Muons bend away from us. Anti-muons bend toward us. Man for scale

27. Calorimetersand Central Solenoid

28. Right Honourable and Most Reverend Dr Rowan Douglas Williams, the 104th Lord Archbishop of Canterbury and Primate of All England Transition Radiation Tracker (TRT) – tracks charged particles and distinguishes electrons from pions

29. The SemiConductor Tracker (SCT) Records tracks of charged particles Most of the data-acquisition and calibration/monitoring software designed and written in Cambridge Many components designed and built in The Cavendish

30. 10cm SCT contains 4088 “Modules” 768 sensitive-strip diodes per side. (200 V) 3 infra-red communication channels. Collisions recorded @ 40MHz (every 25 ns) Neutron bombardment will degrade silicon over time. Individual strips will need recalibration. Optical properties need adjustment. May need to use redundant links.

31. SCT Data Acquisition Software • Present size: • 350,000 lines of code • ~6 developers • Much still to be done: • Have managed to control 500 modules at once • only 1/8th of final number • “multi-crate” development - parallelisation • Needs to become usable by non-experts • Needs to recover from anomalies automatically

32. Evidence that it will work: First cosmic rays seen in SCT and TRT! PRELIMINARY Data from morning of 18th May 2006

33. Back to the new physics • Fine-tuning / “hierarchy problem” (technical) – Why are particles light? • Does not explain Dark Matter • No gauge coupling unification Remember the aim was to fix some of these problems with the Standard Model Possibilities: • Supersymmetry • Minimal • Non-minimal • R-parity violating or conserving • Extra Dimensional Models • Large (SM trapped on brane) • Universal (SM everywhere) • With/without small black holes • “Littlest” Higgs ? • …. We will look at supersymmetry (SUSY)

34. Supersymmetry!CAUTION! • It may exist • It may not • First look for deviations from Standard Model! Experiment must lead theory. Gamble: IF DEVIATIONS ARE SEEN: • Old techniques won’t work • New physics not simple • Can new techniques in SUSY but can apply them elsewhere.

35. Electron Higgs Anti-Electron Higgs Selectron Higgsino Anti-selectron Higgsino What is Supersymmetry? Reverse the charges, retain the spins. Matter Antimatter Retain the charges,reverse the spins.(exchange boson with fermions). Supersymmetric Matter For technical reasons each sparticle can be heavier than its partner by no more than a TeV or so.

36. Neutralinos : The collective name of the supersymmetric partners of the photon, the Z-boson and the higgs boson. LSP : Lightest Supersymetric Particle. Often the lightest neutralino. Great! • Fix Hierarchy Problem • The Lightest Neutralino (LSP) is a prime candidate for neutral stable cold Dark Matter • Can have gauge coupling unification ΩCDMh2 = 0.103 ± 0.009(WMAP 3-year data)

37. Unfortunately • Doubling of particle content • Conservation of “R-parity” • LSPs generated in pairs • LSPs invisible to ATLAS • Large number of tuneable parameters • Assume just five of them exist for the moment – unification arguments

38. What might events look like? What we can see Here Be Monsters! (again) What we can see This is the high energy physics of the 21st Century!

39. (What they really look like) b soft gluon radiation? An example of an event where a higgs boson decayed to a pair of b-quarks/ b

40. So main EASY signatures are: • Lots of missing energy • Lots of leptons • Lots of jets • ATLAS Trigger: ETmiss > 70 GeV, 1 jet>80 GeV. (or 4 lower energy jets). Gives 20Hz at low luminosity. Just Count Events! Indicates deviation from The Standard Model.

41. Papers for RAE ? • Multidimensional likelihood maps • String inspired susy models • MT2 and friends • Courses • No need to revise: • Mathematics (all) • Computational Physics

42. events Signal S.M. Background Squark/gluon mass scale What you measure: Peak of Meff distribution correlates well with SUSY scale “as defined above” for mSUGRA and GMSB models. (Tovey)

43. The real test comes when you want to measure individual masses etc.

44. Technique 1: Kinematic Edges Plot distributions of the invariant masses of what you can see

45. ll llq ll llq S5 lq high lq low lq high lq low O1 llq Xq llq Xq Technique 1: Kinematic Edges

46. Technique 1: Kinematic Edges Account for all ambiguities: Both look the same to the detector

47. Technique 1: Kinematic Edges Use custom Markov-Chain algorithms to sample efficiently from the high dimensional parameter spaces of the model according to the Bayesian posterior probability. Shape of typical set is often something quite horrible.

48. Determine how edge positions depend on sparticle masses

49. Technique 1: Kinematic Endpoints Finally, project onto space of interest: Correlation between slepton mass measurement and neutralino mass measurement. Slepton mass

50. Other Techniques: • Look at the shapes of the distributions • Systematic errors harder to control • Create new variables • “Cambridge MT2 Variable”now international used methodfor sparticle mass measurementin pair production • Incorporate cross sections and branching ratio measurements • again, Cambridge “leading the way” as home to the most developed samplers for H.E.P.