Higgs 입자 사냥과 초대칭 현상의 발견

1. Higgs 입자 사냥과 초대칭 현상의 발견 최수용 성균관 대학교

2. 표준 모형의 Precision tests 양자고리 효과 표준 모형에서의 Higgs Higgs입자의 역할 Higgs입자의 성질 Higgs 입자 사냥 초대칭 초대칭이란? Higgs 및 초대칭 입자들 Outline

3. Higgs and Mass Generation

4. 표준 모형의 입자들 Spin ½ Spin 1

5. Particles with electric charge Classical EM QED Force mediated by “Gauge” particle Virtual photon Q1 Q2 Electromagnetic Interaction Q1 Q2

6. Quantum Mechanics • Energy and momentum conservation can be violated over short times and distances

7. Quarks and Leptons Beta decay Neutron decay Weak Interactions and W/Z R L

8. Particles and Interactions

9. Particle Decays • Heavy particle can decay into lighter particles • Leptons • Lepton number conserved • Quarks • d → uW • c → sW • t → bW

10. Symmetry • There is symmetry when there is a feature of a system that does not change when an operation is done

11. Electroweak Symmetry • Unify EM and Weak Interaction • EM interaction – U(1) • Weak interaction – SU(2) • Symmetric w.r.t. SU(2)xU(1) • All spin-1 bosons must be massless • But, weak bosons are massive • electroweak symmetry breaking • Massless fermion • Mass term: L and R should transform the same way • Left and right components transform differently • How to generate mass? Weak Interaction ne eL eR EM Interaction family

12. Peter Higgs Born 1929 Still alive Higgs field Weak charge Fills vacuum Excitation - massive Higgs particle Higgs Mechanism Physical vacuum Symmetry is broken

13. Self Interacting Scalar Field m2<0 and l >0 m2>0 and l >0 “Mexican hat”

14. EWSB and Superconductivity • U(1) local gauge symmetry is broken in superconductors • Higgs field – “Cooper” pair • Photons become screened by the condensate • Photons effectively become massive and the interaction becomes very short

15. 1 Higgs doublet 4 real degrees of freedom After symmetry breaking 1 degree of freedom 3 degrees of freedom → longitudinal component of W+,W-,Z Higgs Mechanism in SM

16. Vacuum Expectation Value • What is it? • Muon life time

17. Particle Masses • Vacuum Expectation Value • Weak gauge bosons • Fermion masses

18. Effective Mass • Motion of solid in liquid • Liquid has to be displaced • Effective mass of the object interacting with the liquid

19. The Higgs Field

20. The Higgs Field

21. The Higgs Field Large coupling to Higgs field ~ Large mass

22. Before SB After SB H H n H H H High Tc Superconductor Tc~1015K Weak Interaction n Weak gauge field

23. Particle Masses W,Z

25. Classical Mechanics – F=ma Theory of Relativity – E=mc2 Particle physics – microphysical origin of mass Mass of universe Ordinary matter is a small portion “Ordinary” matter Most of the mass from kinetic+binding energy of quarks Mass

26. Precision Tests of SM and Higgs Searches

27. Particle interaction Dynamic vacuum Particle creation e e * e e Relativistic QM t

28. Electron in dielectric medium Electron in vacuum Vacuum polarization e- e- e+ e+ e- e+ e+ e- e-

29. Electromagnetic Strong coupling constant Running

30. Tests at 0.1% accuracy Precision tests of the Standard Model

31. Test effects of quantum loop High statistics Well understood detector Theoretically safe procedure Example – W mass Precision Tests Mass of muon+neutrino

32. Precision Tests – MW from theory • Prediction using • SM parameters require measurement • Muon decay It’s really a test of consistency!

33. Indirect Higgs mass

34. Direct Higgs Searches at LEP • L3 had a couple of events

35. Direct Search Limit at LEP Indirect limit Low mass Higgs searches Possible at the Tevatron Ensured at the LHC Standard Model Higgs

36. So, what if there’s no EWSB? • Massless electrons • Chemistry is impossible • Massless quarks • mp>mn • Proton can decay to neutrons – no hydrogen • Rapid collapse to neutron star • Again no chemistry

37. Property of the Standard Model Higgs • Spin 0 • Mass ? • Width ? • Higgs decays: Mass of particle  friendly with Higgs

38. Higgs Branching Ratio

39. Production Not all channels are accessible QCD production ~106 more copius SM Higgs Production @ 1.96 TeV pp Collider (pb)

40. Higgs Searches at the Tevatron • Decay • Higgs coupling proportional to m • Decay preferably to massive particles kinematically allowed gg→H (MH>140 GeV) • H→W+W-→l+l-nn • Background: WW W/Z+H (MH<140 GeV) • WH→lnbb • ZH→l+l-bb, nnbb • Background: W/Z+jets, W+bb, Z+bb, top

41. Signature electron + MET + 2 b-jets Electrons in |h|<1.1 Background Physics – tt, single top (tb), W+jets and W+bb Instrumental – QCD multijet Associated production WHenbb

42. Associated production WHnbb • Compare number of observed events with expectation within 1.5 around the hypothesis Higgs mass • For 115 GeV Higgs • 9.31.8 events expected, 8 observed (0.3 WH) • Total acceptance ~ 0.230.03%

43. HWW(*)l+l-nn • 2 oppositely charged leptons and missing ET • Look for excess in the leptonic decay mode • Explicit mass cannot be reconstructed • WW decays from a spin 0 particle • leptons prefer to decay in the same direction

44. H→WW(*) l+l-nn • Select on MET, Dilepton Mass, HT • Final selection on opening angle

45. Summary of Standard Model Higgs Searches

46. The Near Future • New tracker installed, 20 times more data until 2009! design 2009 2006 base 2009년까지 130 GeV 이하 Higgs 증거 찾을 수 있다

47. SM Higgs Production at LHC 14 TeV pp • x40~100 that at Tevatron for ggH and qqH • 10 times for VH • tt-bar pair production also 100 times • Most cross sections available at NNLO

48. MH 100~130 GeV Excellent energy resolution of PbWO4 calorimeter Beam test shows 3% sampling term for resolution 0.5% at 100 GeV To reach the ultimate resolution, careful calibration procedure and constant monitoring is crucial ~4% initial miscalibration after lab tests during manufacturing Need 5 fb-1 to get 0.5% intercalibration Issues jet fake rate into photons Material budget which can cause Only QCD diphoton background. multijet and photon+jets not considered Old tracker simulation H+ggg+g also studied Inclusive Hgg

49. MH 120~140, 180~ The golden channel Easy to trigger and identify Clean Discovery channel Background ZZ* tt-bar with fake isolated leptons Zbb-bar with fake isolated leptons HZZ* 4

50. 140 ~ 500 GeV 영역에서 2010~2012 까지 발견 CMS에서의 전망