1. 1 Overview of Particle Physics -- the path to the Standard Model

2. 2 Topics l historical flashback over development of the field o “prehistory” 19 th century o electron, radioactivity, nucleus o cosmic rays o spectroscopy era o collider era l standard model of particle physics

3. 3 Electron – 1897 J.J Thomson Top quark 1995 A Century of Particle Physics

4. 4 Sizes and distance scales  visible light: wavelength ≈5∙10 -7 m  virus 10 -7 m  molecule 10 -9 m  atom 10 -10 m  nucleus 10 -14 m  nucleon 10 -15 m  quark <10 -18 m

5. 5 The Building Blocks of a Dew Drop  dew drop: 10 21 molecules of water.  Each molecule = one oxygen atom and two hydrogen atoms (H 2 O).  Atom: nucleus surrounded by electrons.  Electrons bound to the nucleus by photons  nucleus of a hydrogen atom = single proton.  Proton: three quarks, held together by gluons just as photons hold the electron to the nucleus in the atom

6. 6 Very early era (19 th century)  chemistry, electromagnetism  discharge tubes, “canal rays”, “cathode rays”  photoelectric effect (Hertz, 1887)  radioactivity (Becquerel, 1895)  X-rays (Röntgen, 1895) 

7. 7 Atoms, Nucleus  electron: first hint that atom not indivisible  natural radioactivity  understanding of composition of atom, nucleus  atom = nucleus surrounded by electrons (Geiger, Marsden, Rutherford, 1906 -1911)  hydrogen nucleus = proton, is component of all nuclei (1920)  neutron (Bothe, Becker, Joliot-Curie, Chadwick, 1930 – 1932)

8. 8

9. 9 Cosmic rays lDiscovered by Victor Hess (1912) lObservations on mountains and in balloon: intensity of cosmic radiation increases with height above surface of Earth – must come from “outer space” lMuch of cosmic radiation from sun (rather low energy protons) lVery high energy radiation from outside solar system, but probably from within galaxy

10. 10

11. 11 Cosmic rays -- “elementary” particles  new detectors (cloud chambers, emulsions) exposed to cosmic rays  discovery of many new particles lpositron (anti-electron) : predicted by Dirac (1928), discovered by Anderson 1932 l muon (μ): 1937 Nedermeyer l pion (π) predicted by Yukawa (1935), observed 1947 (Lattes, Occhialini, Powell) l strange particles (K, Λ, Σ,…..

12. 12 Particle Zoo  1940’s to 1960’s : lPlethora of new particles discovered (mainly in cosmic rays): l e-, p, n, ν, μ -, π ±, π 0, Λ 0, Σ +, Σ 0, Ξ,….  question: l Can nature be so messy? l are all these particles really intrinsically different? l or can we recognize patterns or symmetries in their nature (charge, mass, flavor) or the way they behave (decays)?

13. 13 The Particle Zoo!  ±,  0, e,  ±, K ±, K 0 S, K 0 L,  0, p, n,  +,  0, , , …

14. 14 Particle spectroscopy era  1950’s – 1960’s: accelerators, better detectors  even more new particles are found, many of them extremely short-lived (decay after 10 -21 sec)  1962: “eightfold way”, “flavor SU(3)” symmetry (Gell-Mann, Ne’eman) lallows classification of particles into “multiplets” lMass formula relating masses of particles in same multiplet l quark model – three different kinds of quarks (u, d, s) lAllows prediction of new particle Ω -, with all of its properties (mass, spin, expected decay modes,..) l subsequent observation of Ω - with expected properties at BNL (1964)

15. 15 Ω - BNL 1964  eight-fold way  quark model – particles made up of three different “quarks” – u, d, s  p = uud, n = udd,… Ω - = sss  refinement of these ideas, more quarks, “color”, gauge field theory  Standard Model http://www.bnl.gov/bnlweb/history/Omega-minus.asp

16. 16  A theoretical model of interactions of elementary particles, based on quantum field theory  Symmetry: lSU(3) x SU(2) x U(1)  “Matter particles” lQuarks: up, down, charm,strange, top, bottom lLeptons: electron, muon, tau, neutrinos  “Force particles” lGauge Bosons o  (electromagnetic force) oW , Z (weak, electromagnetic) og gluons (strong force)  Higgs boson lspontaneous symmetry breaking of SU(2) lmass Standard Model

17. 17 Contemporary Physics Education Project

18. 18 u uu d dde b bb  c cc s ss  gggg g ggg  ZW±W± e   QuarksLeptons +2/3-1/3 -1 0 I II III BosonsFermions Particles of Standard Model t t t

19. 19 “every-day” matter Proton d u d e Neutron e u d u ElectronElectron Neutrino  Photon

20. 20 q2q2 q1q1 Electron Proton Photon Electromagnetic interaction

21. 21 Weak interaction  Beta decay d u d Neutron Proton u d u e Electron e Anti-electron Neutrino W  Mean lifetime of a free neutron ~ 10.3 minutes Mean lifetime of a free proton > 10 31 years!

22. 22 The Strong Force u u d d g Strong force caused by the exchange of gluons

23. 23 Forces (interactions)  Strong interaction1 lBinds protons and neutrons to form nuclei  Electromagnetic interaction 10 -2 lBinds electrons and nuclei to form atoms lBinds atoms to form molecules etc.  Weak interaction  10 -10 lCauses radioactivity  Gravitational interaction  10 -39 lBinds matter on large scales

24. 24 What holds the world together? interaction participants relative strength field quantum (boson) strong quarks 1 g gluon electro- magnetic charged particles 10 -2  photon weak all particles  10 -10 W ± Z 0 gravity all particles  10 -39 G graviton

25. 25 The Discovery of Top Quark  1977 – 1992 lMany null results  1992 – 1993 lA few interesting events show up  1994, DØ lm t > 131 GeV/c 2  1994, CDF lFirst evidence lm t ~ 170 GeV/c 2  1995 – CDF, DØ lDiscovery!

26. 26 Creating Top Anti-Top Quark pairs

27. 27 Artist’s impression of a top event

28. 28 What do we actually “see” Jet-1 Jet-2 Muon Electron Missing energy

29. 29 “event display” of a DØ top event jets e  tt  -

30. 30 Ω b (http://www.fnal.gov/pub/presspass/images/DZero-Omega-discovery.html  2008 DØ experiment at Fermilab: l discover brother of Ω -, the Ω b l Ω - = sss, Ω b = ssb, l theory predicts properties, decay modes,.. l confirmed by experiment

31. 31 Summary  we’ve come a long way ……  Standard Model (theory of particle interactions) works embarrassingly well! lHas been tested by many hundreds of precision measurements over last three decades – very few measurements differ by more than 1 or 2 standard deviations lEven some amount of frustration – always hope to see experimental result in disagreement with theory  But there are some open questions …………………