Quest for the Higgs Boson is our understanding of the universe about to change ?

1. Quest for the Higgs Bosonis our understanding of the universe about to change ? Bernd Stelzer on behalf of the ATLAS Group Simon Fraser University Organized by SFU’s Physics Department and VP Research Office

2. SFU ATLAS Group Faculty Dugan O'Neil, Bernd Stelzer and Mike Vetterli, postdoctoral fellows JiriKvita, Michele Petteni and Andres Tanasijczuk, and graduate students Michelle Boudreau, Noel Dawe, Jennifer Godfrey, Jamie Horton, David Shinkaruk, Michel Trottier-McDonald, and Koos van Nieuwkoop. Bernd Stelzer

3. Outline • Particle Physics and the Fundamental Building Blocks of Nature • The Large Hadron Collider • The ATLAS and CMS experiments • Particle Physics Successes and Mysteries • What is the Origin of Mass? • Latest results in the search for the Higgs Boson • Conclusions Bernd Stelzer

4. News Stories – What are they about? • Last December, media was covering stories about ‘hints’ for elusive Higgs boson at the Large Hadron Collider Bernd Stelzer

5. News Stories – What are they about? Dugan O’Neil Mike Vetterli • On July 4th, media was headlining stories about the Higgs boson • What is this all about…? Bernd Stelzer

6. Knowledge gained in the last Century 1 10 1 100,000 1 10,000 1 10 ~0 ~1910 ~1940 ~1970 LHC atom ? 10-17 cm nucleus 10-12 cm 10-13 cm 10-8 cm Bernd Stelzer

7. Standard Model Weak 7 Bernd Stelzer

8. The Large Hadron Collider (LHC) ATLAS Mont Blanc Lake Geneva p p LHC Bernd Stelzer

9. The Large Hadron Collider (LHC) LHC • protons go fast: 99.999999% of the speed of light • make a full turn 11254 times per second Bernd Stelzer

10. Large Hadron Collider 1eV = 1.6 x 10-19 J • More facts: • CERN’s LHC pp collider at 8 (7) TeV (design 14 TeV – increase in 2014) • Beams circulate ~10h travelling more than 10 billion km (to Neptune and back!) For the LHC Bernd Stelzer

11. Large Hadron Collider • Circumference: 26 659 m • 9593 superconducting magnets • Total of 1232 Dipole magnets: • 15m long, 35 tons, 8.4 T • Operated at 1.9K (colder than outer space) Bernd Stelzer

12. First Collision Events Bernd Stelzer

13. Producing Massive Particles R. Goscinny, U. Uderzo Asterix and the Big Fight Creating massive fundamental particles p p Energy particle beam energy particle beam energy Ea Eb mx mX mX Bernd Stelzer

14. What is a proton? • Can create particle X with mass mX< 2Ebeam GeV/c2 Bernd Stelzer

15. Collisions at ATLAS Bernd Stelzer

16. How to Discover new Particles The mass mZ of the parent particle can be determined from the kinematics of its decay products. E.g. for Z->μμ we can make use of: Relativistic kinematics From relativity: Bernd Stelzer

17. Units and Numbers We will mostly use the unit “GeV”=Giga electronVolt Bernd Stelzer • Mass is measured in electronVolt / c2where: c = speed of light: • 1 eV/c2 = 1.8 x 10-36 kg • melectron=0.5 MeV/c2 = 1 x10-30 kg • msun= 2 x 1030 kg

18. Discover new Particles J/ψ DiscoveryNobel Prize 1976 Neutral resonances havea long history of discovery Y Discovery 1977 +1 Z Boson DiscoveryNobel Prize 1983 A history of resonance discoveries Bernd Stelzer

19. Particle Identification • Collisions enclosed by layers of different detectors (like an onion): • separate particle types • measure their energies / momenta Bernd Stelzer

20. ATLAS and CMS Detectors Eiffel tower Eiffel tower 100 million electronic channels 3000 km of wires Bernd Stelzer

21. ATLAS Tracking Detector Bernd Stelzer

22. Calorimeters TRIUMF: assembly of one of the Canadian components, completed in 2004 e or  • Measure energy and position of electrically charged and neutral particles • Electrons and photons (electromagnetic calorimeter) • Hadrons: protons, pions, etc,… (hadronic calorimeter) Bernd Stelzer

23. Muon System Bernd Stelzer

24. ATLAS Collaboration 3000 Physicists from 38 countries and174 institutes (150 Canadians from 10 institutes ) Bernd Stelzer

25. The Standard Model …it’s the most precise theory there is! Bernd Stelzer “Feynman diagrams” allow us to calculate any processes with a production rate prediction better than 1-10% Tested and verified in many experiments

26. What we try to find at the LHC • What is the Origin of mass?Find the Higgs boson or rule it out. • Nature of Dark Matter?Weakly Interacting massive particle must have mass ~0.1-1 TeVto reproduce observed DM density. • Grand Unification:Do all forces become one at high energies? Higher gauge groups in GUT inspired models give rise to new particles possibly at the Terascale • Where did the anti-matter go?broken symmetries of nature in quark flavor and neutrino sector • Explore the unknownsurprises can happen at any time Bernd Stelzer

27. Physics Beyond the Standard Model Many theoretical models for physics Beyond the Standard Model Bernd Stelzer

28. Why is the Higgs called the God Particle? Bernd Stelzer

29. What is Mass? • Newton, definition #1 of Principia: • “the quantity of matter is the measure of the same, arising from its density and its bulk conjointly.”I think it means: (m = ρV) • Merriam-Webster dictionary: • “the property of a body that is a measure of its inertia and that is commonly taken as a measure of the amount of material it contains and causes it to have weight in a gravitational field” Bernd Stelzer

30. Generation of Mass in the Standard Model • According to the Standard Model of particle physics, particles acquired mass during a phase transition when the Universe was ~10-12 seconds old and cooling rapidly • During this phase transition, a scalar field (the Higgs field) turns on • Temperature (energy) of universe at transition: ~few 100 GeV Bernd Stelzer

31. The Higgs Mechanism 1964 Bernd Stelzer

32. The Higgs Mechanism Bernd Stelzer

33. The Higgs Mechanism Why do particles have mass? • Higgs field acts as “backgroundfield” (e.g. like a fluid) • Heaviest particles interact moststrongly with Higgs field • Field slows particles downgives them mass Bernd Stelzer

34. The Higgs Mechanism Arrival of celebrity: Guests cluster near celebrity Party: Guests are evenly spread D. Miller / UCL • Guests act like Higgs field slowing celebrity down • Celebrity moves slower <=> acquires mass Bernd Stelzer

35. Higgs Field and Higgs Boson particle • In particle physics fields are associated with particles, e.g. • electric field  photon • strong interaction field  gluon • In initial paper Peter Higgs did not identify field with particle • he added that a measurable consequence is the existence of a new bosons (particle) only after journal’s peer review Bernd Stelzer

36. Searching for the Higgs • Sounds good, but how do we know it's true? • Excite the Higgs field make Higgs particles !!! • Need to collide particles with enough energy • to create the Higgs boson: E=mc2 • Complementary approach taken: • Look for Higgs in quantum effects • Need to measure mass of W boson super precisely Bernd Stelzer

37. W Boson Mass Precision Constraints • Derive W mass from precisely measured electroweak measurements (Large Electron Positron Collider at CERN, Tevatron at Fermilab) • Radiative corrections dominated by top quark and Higgs quantum loops allows constraint on Higgs mass MHiggs=94+25-22 GeV Bernd Stelzer

38. The Large Hadron Collider (LHC) ATLAS Mont Blanc Lake Geneva p p LHC Bernd Stelzer

39. 2012 Data Taking 94% good quality data 2012: 6.6 fb-1 at 8 TeV 2011 5.6 fb-1 at 7 TeV 2010 0.05 fb-1 at 7 TeV ATLAS Control Room • Delivered ”luminosity” L= 5.6+6.6 fb-1 • Corresponds to 8x1020proton-proton interactions • Number of events = Luminosity x cross section • Corresponds to ~170 Higgs bosons (in diphoton decay) • But need to find them above all the background! • Data included in results that were taken less than 2 weeks before! Bernd Stelzer

40. Grid Computing In Canada: Tier-1 center: TRIUMF/SFU Tier-2 center: SFU, UVic, Alberta Toronto, McGill 260 sites >140,000 CPU cores >25 PB disk ≈39 PB tape 100 k Bernd Stelzer

41. Measuring the Standard Model Inner error: statistical Outer error: total Higgs • Important on their own and as foundation for Higgs searches • Most of these processes are backgrounds to Higgs • Reconstruction and measurement of challenging processes • are good training for Higgs final states Bernd Stelzer

42. Standard Model Higgs Searches at the LHC Most sensitive channels 120<mH<130 GeV: H WW(*) lνlν H γγ, H ZZ (4l) H ττ, W/ZH W/Z bb • √s=7  8 TeV: • Higgs cross-section increases by ~ 1.3 for mH ~ 125 GeV • Increase for backgrounds e.g. 1.3-1.4 for tt, Zbb •  Expected increase in Higgs sensitivity: 10 - 15% Bernd Stelzer

43. Yellow Band, Green Band Illustration Bernd Stelzer

44. 2011 Results Combination of 12 analyses: H γγ W/ZHW/Z bb H ττ H ZZ(*)  4l H WW(*)  lνlν H ZZ  llqq H ZZ  llνν H WW  lνqq Excluded at 95% CL 111.4 < mH< 122.1 GeV (except 116.6-119.4) 129.2 < mH< 541 GeV (expected 120-560 GeV) Bernd Stelzer

45. Direct Higgs Search • Higgs boson is unstable and decays very quickly • 0.2% decay into two photons • 0.014% decay into two Z bosons that furtherdecay into electrons or muons • High mass resolution and puritymakes them easy Higgs boson “discovery channels” Bernd Stelzer

46. A Higgs Boson Candidate or ? Bernd Stelzer

47. Finding the Higgs with Photons Higgs  • Higgs boson decays to two energetic photons (via W/top loop) • Higgs mass can be determined from decay kinematics • Background process looks identical • many times larger at any given mass background M() Bernd Stelzer

48. ATLAS DiPhoton Mass Spectrum Bernd Stelzer

49. ATLAS DiPhoton Mass Spectrum Interesting! A bump! Need to quantify significance, given background Bernd Stelzer

50. H γγ 2011 data Excluded (95% CL): 112-122.5 GeV, 132-143 GeV Expected: 110-139.5 GeV 2011+2012 data 2012 data Bernd Stelzer