Christopher Lester Identifying New Physics at ATLAS and the Large Hadron Collider

1. Christopher LesterIdentifying New Physics at ATLAS and the Large Hadron Collider

2. Physics case What isthe LHC? My role My job today is to convince/remind you: #2 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 look for “new physics” over the next 10 to15 years #1 That I have a valuable role to play in the exploitation of this experiment … #3

3. Item #1Large 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 PART LATER

8. Item #2The Physics

9. 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.

10. 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 ? • ….

11. Each theory fixes one of more of the problems of The Standard Model • BUT THERE IS NO EXPERIMENTAL EVIDENCE FOR ANY OF THEM YET !! • Theorists have been working cut-off from reality for far too long! • Desperate need for experiment to generate real data to: • shoot down all bad theories • identify any good ones left over 2007: Experiment must lead theory!

12. What do most new ideas have in common? • One or more heavy invisible particles - sometimes produced in every event. • A large numbers of extra massive particles • Such a particle may or may not be a dark matter candidate • Dark matter may or may not exist!

13. Working out the physics which led to the observed data will be A GREATER CHALLENGE THAN EVER FACED BEFOREin high energy physics.

14. Why so? Must understand – it connects to my research Here Be Monsters What we can see What we can’t see. Moreover, we can’t assume much about it either! What we can see

15. Item #3This is where we connect to my own research.

16. In short:Understanding the physicshas become an inference problem(or a large number of them) • Note Cavendish Inference Group • very handy group to have around! • Progress has been based on: • importing and encouraging such techniques into my field • Watching for spin-offs! [ Non commercial! ] • Intend to continue this transfer!

17. Note: I have two hats #2 #1 Hat for INTERPRETINGTHE PHYSICS FROM DATA Hat for BUILDING THE EXPERIMENT You must take this side on trust!. Insufficient time to talk about both!

18. Talk at which many of you were present described data analysis in some detail – 18 slides:

19. Example: 18 slides in 1 slide • Choose a parameter space • Identify what you are prepared to consider as a potentially valid answer to the questions you are interested in. SM uncertainty matters. • Measure things • Identify salient and robust features in experimentally observable kinematic distributions • Find all interpretations • Determine all possible models and configurations of those models which could have lead to those observations • Careful posterior • Go to great lengths to calculate the posterior as accurately and impartially as possible. But approximate where necessary. • Sample efficiently • Use the most appropriate samplers to draw possible solutions from the parameter space of choice, and record posterior distributions on variable of choice • Sanity check all results! Both look the same to the detector

20. Can only outline some key points • Efficient parameter determination within a class of related models / Distinguishing models • New physics typically requires simultaneous determination of 5 to 100 parameters • Cavendish HEP has led the way exploring these spaces with Markov and non-Markov Chain Samplers • Now can explore SPACES not SLICES. • MT2 and its friends • Known internationally as “The Cambrdige MT2 Variable” • Measures slepton masses • Example payoff: Winning Entry in international competition: • “ATLAS Blind Data Challenge” – mock experimental data of unknown origin – followed up by NewScientist. Have brought techniques from cutting-edge inference theory to HEP for LHC physics analyses Better Kinemaitic Variables Raising the profile of the group internationally

21. Physics case What isthe LHC? My role Conclusions • I hope your attention span was > 10 mins! 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 look for “new physics” over the next 10 to15 years If I achieved any of these then I’m happy! That I have a valuable role to play in the exploitation of this experiment …

22. Still many things to work on … • Can’t distinguish many models: many more signals must be exploited • Taus • Gauge bosons • Higgses • Must understand jet fragmentation – SM jet BGs. • Sflavour physics? • Understand missing ET main signal ( TALK OVER )

23. SPARE SLIDES

24. N.B. There’s a “guarantee” of sorts … • 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 decision • Do not concentrate on Higgs • Aim to be expert in identifying anything “Beyond the Standard Model” • Not trivial to dismiss many good ideas …

25. 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.

26. Black Holes in Extra Dimensions at the LHC DECAY PRODUCTION Real Monsters!

27. Conclusions • Was asked to talk about: • “Your vision for your future research programme at Cambridge” • In context of the LHC we have • Predictable items • Make the detector work, plan and build a new one before the old one dies • Commissioning – understand MET resolution, jet energy scale, alignment, … graduate students galore • Unpredictable items • What new physics may nature hold? • What will we see of it? • How will we measure it? MANYUNKNOWNS ADAPTABILITY IS THE KEY

28. 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.

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

30. 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

31. 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

32. 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.

33. 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?

34. Large Hadron Collider (LHC)

35. Collider nearing completion

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

37. 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)

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

39. 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

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

41. Calorimetersand Central Solenoid

42. 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

43. 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

44. 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.

45. 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

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

47. 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)

48. 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.

49. 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.

50. 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)