1. Manfred Jeitler December 18, 2009 1 Particle Physics From an experiment-driven to a theory-driven field Manfred Jeitler Institute of High Energy Physics of the Austrian Academy of Sciences

2. Manfred Jeitler December 18, 2009 2 Particle Physics in a nutshell n elementary particles first postulated in antiquity –Democritus called them ἄ τομος (undividable = elementary), atoms –what we call atoms today is not at all undividable! –philosophical reasoning, no experimental evidence »maximally underdetermined n indirect evidence for atoms –elements react in ratios of small whole numbers »John Dalton 1803: “law of multiple proportions” –erratic movement of small objects »Brownian motion 1827 (Robert Brown)

3. Manfred Jeitler December 18, 2009 3 1897 the electron e-e- Thomson direct evidence for first elementary particle: the electron

4. Manfred Jeitler December 18, 2009 4 1897 the proton e-e- 1900-1924 1914 Rutherford p another constituent of matter: the proton

5. Manfred Jeitler December 18, 2009 5 1897 the photon 1900-1924  Planck Einstein Compton e-e- p the particle of light: the photon

6. Manfred Jeitler December 18, 2009 6 1897 the neutron e-e- 1900-1924  1914 n p 1932 Chadwick there is still something else in the nucleus: the neutron

7. Manfred Jeitler December 18, 2009 7 a particle theory of the world - all aspects nicely determined n a few particles nicely described our world –very simple: for a scientist, beautiful ! –Occam’s razor n each of them had been accurately determined by experiment n almost everything explained –except some details: for instance, what keeps the particles in a nucleus together? n but experimentalists continued their observations!

8. Manfred Jeitler December 18, 2009 8 1897 the muon e-e- 1900-1924  1914 µ p 1932 n 1937 Hess Anderson, Neddermeyer e+e+ Who ordered this ? more particles appearing

9. Manfred Jeitler December 18, 2009 9 1897 „I have heard it said that the finder of a new elementary particle used to be rewarded by a Nobel Prize, but that now such a discovery ought to be punished by a $10,000 fine.“ e-e- 1900-1924  1914 K p 1932 n 1937 µ 1947  e+e+ 1947-...   In his Nobel prize speech in 1955, Willis Lamb expressed nicely the general attitude at the time: Lamb too many particles?

10. Manfred Jeitler December 18, 2009 10 the theorists’ turn n get some order into this “particle zoo” n after some more work (details later) everything was again classified into a model: The Standard Model (~1970)

11. Manfred Jeitler December 18, 2009 11 fermions (spin ½) charge 0 +2/3 -1/3 d u u d u d leptonsquarks +1 0 proton neutron baryons interactions strong weak gravitation ? weak W, Z electromagnetic  strong g force carriers = bosons (spin 1) e e     uct dsb the Standard Model two extra generations

12. Manfred Jeitler December 18, 2009 12  ++ u u u  u d d u s  c d DD s u  b b  d u u d u d protonneutron mesons baryons... nucleus He nucleus (  -particle) atom matter The Standard Model explaining all the particles

13. Manfred Jeitler December 18, 2009 13 where did the “extra generations” come from? n “leptons” (like electron) and “quarks” (like in proton and neutron) have heavier, unstable partners n predicted by theory ? n found as a surprise by experiment ?

14. Manfred Jeitler December 18, 2009 14 the second generation n muon (μ) –2 nd generation of “leptons” (the electron’s partner) –observed by chance, not expected n “strange” quark (s-quark) –2 nd generation of “hadrons” (the up and down quarks’ partner) –observed by chance, not expected n puzzle observed: no “flavor-changing neutral currents” –particle decays described by strange quark (inside an unstable particle) decaying into up quark, but never into down quark –why ?!

15. Manfred Jeitler December 18, 2009 15 the GIM mechanism Glashow - Iliopoulos -Maiani

16. Manfred Jeitler December 18, 2009 16 discovery of the “charm” quark n predicted by theory (1970) n but experimentalists payed no attention ! n discovered accidentally (1974) –in the “J/ψ” particle –Sam Ting and Burt Richter

17. Manfred Jeitler December 18, 2009 17 decay of a “charmed” baryon (Σ c ++ )

18. Manfred Jeitler December 18, 2009 18 bubble chamber

19. Manfred Jeitler December 18, 2009 19 drift chamber

20. Manfred Jeitler December 18, 2009 20 another question: are particles completely symmetrical ?   e n imagine as little billiards balls n no room for any asymmetry (left - right)? n few people doubted symmetry n but this conviction was underdetermined –and turned out wrong

21. Manfred Jeitler December 18, 2009 21 parity violation n parity (= mirror-image) symmetry had not been proved for all interactions n C.N.Yang and T.D.Lee conjectured that parity symmetry might be broken in Weak interactions –based on experimental evidence n C.S.Wu proved this experimentally –in the same year (1956) n  the world’s mirror image differs from the world itself

22. Manfred Jeitler December 18, 2009 22 Chen Ning Yang and Tsung-Dao Lee (Nobel prize 1957) Chien-Shiung Wu parity violation

23. Manfred Jeitler December 18, 2009 23 save the symmetry! n parity violation came as a shock ! n physicists hoped to find the lost symmetry again on a higher level

24. Manfred Jeitler December 18, 2009 24 Charge-Parity symmetry Parity Charge charge conjugation: replace particles by anti-particles CP left-handed neutrino right-handed neutrino right-handed anti-neutrino X In “Weak Interactions”, P and C “maximally violated” but the combined CP symmetry is mostly conserved

25. Manfred Jeitler December 18, 2009 25 the next shock: CP symmetry is also broken! n but (rarely) K 0 L also decays into two π’s K0LK0L    K0SK0S   CP = -1 CP = +1 K0LK0L CP = -1   CP = +1

26. Manfred Jeitler December 18, 2009 26 1964 experiment the first signal: K 0 L   +  -

27. Manfred Jeitler December 18, 2009 27 CP-violation n people were unhappy and proposed other explanations for the experimental findings (1964) n but soon had to accept CP-violation as a fact n theories were developed to explain it n one theory predicted a further “generation” of quarks (1973)

28. Manfred Jeitler December 18, 2009 28  Makoto Kobayashi Toshihide Maskawa  Nobel prize 2008 (together with Yoichiro Nambu)

29. Manfred Jeitler December 18, 2009 29 the Cabibbo-Kobayashi-Maskawa matrix and the”unitarity triangle“ a 3 x 3 “quark mixing matrix” can explain CP-violation n so, there should be two more quarks (“b” and “t”) –“beauty”, or “bottom” –“truth”, or “top” n “c” (“charm”) had not yet been found in 1973 !

30. Manfred Jeitler December 18, 2009 30 mechanism of CP-violaiton n one theory (“Standard Model”) predicted: –3 generations of quarks –ε’ not equal 0 n another theory (“superweak model”) predicted: –nothing concerning a 3 rd generation of quarks –nothing concerning ε’ n question to philosophers: –what would the “realist” conclude ? –what would the “antirealist” conclude ?

31. Manfred Jeitler December 18, 2009 31 three generations - why so complex? n CP-violation, three generations... just a whim of nature? n no! n CP-violation is of fundamental importance for our universe –but nobody had thought of this before

32. Manfred Jeitler December 18, 2009 32 particle physics and cosmology: the big bang

33. Manfred Jeitler December 18, 2009 33 the Big Bang, antimatter, and us n according to present understanding, the Universe was created in the “Big Bang” n matter and antimatter were created in equal quantities –there is almost no antimatter in the Universe n both would have disappeared if no matter excess had developed n CP-violation is necessary condition! –Sakharov, 1965

34. Manfred Jeitler December 18, 2009 34

35. Manfred Jeitler December 18, 2009 35 n we wouldn’t be around without CP-violation –and lots of other facts –“fine tuning” of constants of nature n... and so we wouldn’t be able to ask these questions! n anthropic principle –don’t invoke it - it’s not politically correct! –physicists are supposed to understand everything - not just to show it can’t be otherwise –although we sometimes use it and don’t care »ever wondered why we live on Earth, and not on Venus or Jupiter? –people don’t like it - but it might still be the right answer! but why?

36. Manfred Jeitler December 18, 2009 36 welcome to the Multiverse ! n anthropic principle made socially acceptable n maybe our “Universe” is just a bubble –among uncountably infinitely many other bubbles in the Multiverse –in each bubble universe, one set of laws of physics and natural constants is realized –just “one point in the parameter landscape” n unless we manage to communicate with other universes: –how? –or find some indirect proof … –is this science or theology?

37. Manfred Jeitler December 18, 2009 37 completing the Standard Model: the W ± and Z 0 bosons (1983)

38. Manfred Jeitler December 18, 2009 38 completing the Standard Model: the top quark (1995)

39. Manfred Jeitler December 18, 2009 39 Standard Model: Complete and proved? No alternatives? n very good description of nature n many predictions but: n does not describe everything: –e.g., neutrino masses not predicted one important ingredient still not found in experiment: the HIGGS BOSON –predicted by the mechanism proposed to give mass to quarks

40. Manfred Jeitler December 18, 2009 40 to Higgs or not to Higgs... n very good evidence for Standard Model in all other respects n but the “allowed mass window” (masses not yet excluded by experiments or theory) is getting smaller n also, it’s taking so long... –merely psychological factor? n  “theoreticians are getting cold feet” –John Ellis (one of the chief theoreticians at CERN) n  lots of new theories (no Higgs after all, invisible Higgs, little Higgs,... you name it) –much time and little data - theoreticians leave no stone unturned (?)

41. Manfred Jeitler December 18, 2009 41 bosons SUSY SUSY particles. green: known particles of the Standard Model red: hypothetical new particles for each known elementary particle there should exist a supersymmetric partner fermions Supersymmetry

42. Manfred Jeitler December 18, 2009 42 massive astrophysical cosmic halo objects? weakly interacting massive particles? questions of cosmology to particle physics: Why is there more matter than anti-matter in the universe? What is the universe made of? What is dark matter? What is dark energy?  answers to these questions concerning the largest scales might come from the physics of the smallest scales - elementary particle physics dark matter: MACHOS vs WIMPS

43. Manfred Jeitler December 18, 2009 43... and much more n superstrings n extra dimensions

44. Manfred Jeitler December 18, 2009 44 data dearth n so many theories n so many explored alternatives n probably some unexplored alternatives (?) n give us data !!

45. Manfred Jeitler December 18, 2009 45 CMS just starting !

46. Manfred Jeitler December 18, 2009 46 how to observe particles Tracks of particles in a typical collider experiment (CMS, CERN) just starting !

47. Manfred Jeitler December 18, 2009 47 just starting !

48. Manfred Jeitler December 18, 2009 48 LIGO ( Laser Interferometer Gravitational Wave Observatory, USA) measurement of gravitational waves still waiting for signal!

49. Manfred Jeitler December 18, 2009 49 important questions of today’s particle physics (ongoing experiments) Where do particles get their mass from? (by interaction with the Higgs particle?) Why are these masses so different? Is there an overall (hidden) symmetry such as supersymmetry (SUSY)  “mirror world” of all known particles?. What is the nature of “dark matter” and “dark energy” in the universe? Why is there more matter than anti-matter? Why have neutrinos such small mass? Is there a Grand Unification which combines all interactions, including gravitation? Are there extra dimensions, D > 4 ? (  string theory, …)

50. Manfred Jeitler December 18, 2009 50 where are we now ? n many theories in particle physics are strongly underdetermined at present n numerous conceived alternatives –in violation of Latin grammar, and often also common sense n maybe nature has some unconceived alternatives in store for us? n finally, the Large Hadron Collider is online, and we may hope for some answers

51. Manfred Jeitler December 18, 2009 51 THANK YOU

52. Manfred Jeitler December 18, 2009 52 BACKUP

53. Manfred Jeitler December 18, 2009 53 parity violation n parity (= mirror-image) symmetry had not been proved, however, for all interactions n C.N.Yang and T.D.Lee conjectured that parity might not be conserved in Weak interactions (1956) –θ  2π (positive parity) and –τ  3π (negative parity) –“τ-θ puzzle” –K +  2π (positive parity) and –K +  3π (negative parity) n they convinced C.S.Wu to test parity conservation in experiment n β-decay of 60 Cobalt n  the world’s mirror image differs from the world itself

54. Manfred Jeitler December 18, 2009 54 CP-eigenvalue n particles can be attributed a “CP-eigenvalue” –like charge, mass, parity n this eigenvalue is multiplicative: –CP (  ) = -1 –CP (  ) = +1 n there are 2 kinds of “neutral K-mesons” –the (long-lived) K 0 L decays into 3  -mesons –the (short-lived) K 0 S decays into 2  -mesons n K 0 L and K 0 S differ by their CP-eigenvalue ! n CP(K 0 L ) = -1 CP(K 0 S ) = +1 K0LK0L    K0SK0S   CP = -1 CP = +1

55. Manfred Jeitler December 18, 2009 55 CP-violation K0LK0L    K0SK0S   K0LK0L   CP = -1 CP = +1 CP = -1 CP = +1 1964: sometimes (0.3 percent) also

56. Manfred Jeitler December 18, 2009 56 proton decay? n if baryon number conservation is violated (Sakharov condition #1), the proton could decay –for example, p  e + π 0 –no other conservation law forbids this n another argument for possible proton decay: there is no field that corresponds to baryon number conservation –in gauge theories, long-range fields give rise to absolutely conserved quantities n proton decay is definitely very slow –good for us: else, we would have problems with radiation damage! n experimental limits very low –half-life > 10 36 years (“Superkamiokande” detector, Japan) n spin-off: neutrino detectors

57. Manfred Jeitler December 18, 2009 57 the Standard Model works only with particles which are originally massless! mass is created through interaction with a (hypothetical) Higgs field due to spontaneous symmetry breaking this field is present everywhere in the universe “oscillations” in the Higgs field manifest themselves as Higgs particles, which should be observed at LHC / CERN over the next few years spontaneous symmetry breaking energy Higgs field hot universe (soon after big bang) cold universe (condensates in an asymmetric state with Higgs field) 0 v particles are massless particles acquire mass the Higgs boson