New Views in Particle Physics V emes Rencontres du Vietnam Conference Summary

1. New Views in Particle Physics Vemes Rencontres du Vietnam Conference Summary Stanley Wojcicki Stanford University Hanoi, Vietnam August 11, 2004

2. The Main Themes at the Meeting • Past and Future of Particle Physics • CP Violation • Electroweak Physics • Neutrino Physics • Heavy Flavor Physics • QCD • New Facilities • Physics in Vietnam • Astrophysics/Cosmology Connection

3. Plan of This Talk • Cannot possibly cover all the material that was presented • Will focus on few topics that represent the main activities in the field today • Because of time limitations had to exclude a number of important topics • Gave short shrift to theory, technology, astrophysics • Hopefully, the talk will be on the level understandable and of interest to both particle and astrophysics communities • Start with historical perspective, end with a look at the future

4. Particle Physics - The Past • Particle Physics was born a little over 60 years ago, a child of: • Cosmic Ray Physics (phenomena) • Nuclear Physics (methodology) • Its growth was aided by World War II related developments: • Acceptance of big science • Respect for physics as a “useful” science • Cold war • Its remarkable evolution was a result of successful interplay of: • Theory • Experiment • Technology (accelerators and detectors)

5. How Discoveries Happen? • Theory motivated (predicted): • positron, parity violation, neutrino, charm quark,W-, gluons, neutral currents • Unexpected experimental: • muon, strange particles, CP violation, third generation, neutrino masses, dark energy • Technology enabled: • antiproton, two neutrinos, nucleon substructure, W and Z bosons, top quark

6. Then and Now The first “Barkas and Rosenfeld wallet card ” from 1957, the forerunner of the current PDG summary. The latest, 2002 edition of PDG Review of Particle Properties, contains 974 pages.

7. Elementary Particles in1957

8. Our “Playground” • Quarks • Leptons • Force Carriers • “New” Phenomena • Via quantum loops • Through direct observations Will organize talk around these points

9. The Quark Sector • The quark mass states and flavor states are different • The are connected by a unitary transformation, VCKM • The sector can be characterizedby 10measurable parameters, 6 masses, 3 angles, and 1 phase

10. Quark Masses • Quark masses are very hierarchical • The knowledge of heavy quark masses is needed to extract CKM matrix elements with precision and to calculate loop corrections • The top quark mass is especially important: • it allows one to set limit on Higgs mass • its knowledge is needed for precision tests of EW theory • Top quark decays before it hadronizes • Its many decay modes call for several different analyses

11. Top mass - an example Multivariate Template Method, 33 Lepton+Jets Events with SVX b-tag Combined D0 and CDF measurement from Run 1: mtop = 178.0+-4.3GeV Run 2 goal is uncertainty of 1% (1.5 - 2.0 GeV)

12. CKM Matrix • Consider first absolute values of VCKM elements • Can be determined from inclusive and exclusive decay rates and loop diagrams • The matrix is almost diagonal

13. CKM Matrix (ctd) • For only 3 generations, CKM matrix has to be unitary • Unitarity is satisfied but not a stringent test because of diagonal nature of the matrix • There was a small deviation from unitarity (row 1) • Recent measurements move Vus upward, giving a better agreement with unitarity PDG: 0.2196 (15) Hyperons: 0.2250 (27) Unitarity: 0.2265 (23) K+->p0e+n: 0.2272 (22,7,18) K0L->pln: 0.2252 (8,21)

14. Vub - small element • Information comes from charmless B decays • Small branching ratios is one experimental problem • Difference between B’s and b quarks is another • Lattice gauge calculations • Better new data (CLEO) • Inclusive/exclusive difference (3.23 +- .62) x 10-3 (4.57 +-.61) x 10-3

15. Vtb -Better DirectMeasurement? • Today our information on Vtb comes from dominance of t->bl+nl over those without b and is quite poor = 0.94+0.31-0.24 • Single top production proportional to |Vtb|2 • Full Run2 Tevatron data might make observation possible

16. CKM Phase - CP Violation • CKM matrix unitarity implies that sum of products over elements of row and column must vanish - equivalent to a triangle • 1st and 3rd rows - all sides O(l3) -> large angles V*tbVud

17. CKM Triangle (ctd) • Closing of a triangle is an important check of validity of Standard Model • Different measurements place different constraints on the triangle with different levels of accuracy: • First class, uncertainties in 2nd order (B->J/ K0s) • Second class, uncertainties ~10% but constrained (eK) • Third class, accuracies are model dependent (B->Kp)

18. CP violation - History • 1964 - CP discovered through observation of decay K0L->p+p- ; measurement of e • 1974 - Kobayashi-Maskawa paper, three generations needed for CP violation in SM • ~2000 - Determination that e’is not zero, ie existence of direct CP violation • ~2000 - initiation of study of CP violation in B decays with asymmetric B factories at SLAC & KEK • ~2004 - very strong constraint on SM CKM phase as responsible for CP violation observed

19. Different CP violation mechanisms • CP violation occurs when different amplitudes, with a relative phase, contribute to the same final state • Unlike the K system, the B system has many channels with potential CP violation with varying level of quality of theoretical predictability. • The B->J/ K0S is the “golden”channel, A a sin(2b)sin(Dmt)

20.    fKs,’Ks, Ksp0… The Richness of B Physics The ability to investigate all these channels has been made possible by the excellent performance of the 2 colliders (285 and 244 fb-1 accumulated so far)

21. CP violation in the B system • One can observe time dependent asymmetries by tagging the other B • The asymmetries occur on a scale of fraction of a mm • The golden B decay channel, B->J/YK, gives sin2b=0.736+-.049

22. Global Unitary Triangle Fit Excellent agreement between different measurements, both CP violating and CP conserving More measurements to come in the future

23. Other CP Results • Other measurements in the B and K system - consistent with the Standard Model • Only potential anomaly in fKS final state: • BELLE -> A = -0.96+-.50 • BaBar -> A = +.47+-.34 • Expect similar A as in J/Y K0S decay (~0.74) • Direct CP violation; recent evidence from the rates for B->Kp decay channels: • BaBar: A = 0.133 +- .030 • BELLE: A = 0.088 +- .035 ,the B0->K+p- is higher

24. CKM Matrix Summary • The parameters are now measured quite well • The overall picture is consistent with the Standard Model expectations • Regarding CP: “We left the era of hoping for New Physics alternatives to CKM; we are in the era of seeking corrections from NP to CKM” (Y.Nir) • Now is “the time for theory of quark masses and CKM elements” (J.Rosner)

25. Leptons (mainly neutrinos) • The last decade has seen a revolution in neutrino physics • Contrary to Standard Model picture, there is good evidence that neutrinos have masses and do change flavor • Thus they have a great similarity to quarks: mass states and flavor states are related by a unitary matrix. • CKM matrix -> PMNS matrix

26. Neutrino Oscillations Fraction of I in a Fraction of b in 1 Change in phase Uai*, Ubi, mi2 are constants of nature; L,E experimental parameters

27. Dm2 and L/E scales • To obtain maximum oscillations, we want phase, ie. (L/E )Dm2, to be around p/2: • For atmospheric Dm2 (2-3 x 10-3 eV2) • Atmospheric - E~1 GeV, L~10-104 km • Accelerator - E~GeV’s -> L~few hundred km • Reactor - E~MeV’s -> L ~km, • For solar Dm2 (6-8 x 10-5 eV2) • Reactor - E~MeV’s -> L~100 km • Sun - E~MeV’s but mass eigenstate so L~108 km OK • LSND region - Dm2 (0.1 - 1 eV2) • Ignore in this summary; being addressed by MiniBooNE

28. Atmospheric neutrinos • Primary cosmic ray protons interact in the atmosphere to give hadronic showers • Large fraction of resulting p’s and m’s will decay giving nm’s and ne’s • At medium and high energies nm flux will be up/down symmetric • But upward going nm’s have longer pathlength

29. SuperK Results on nm Rates No oscillations Oscillations

30. (normalized by area) No Oscillation (KS prob: 0.11%) Best Fit (KS prob: 52%) K2K Experiment Experiment using SuperK and a nm beam from K2K with L=250km Best fit parameters: Maximum mixing Dm2 = 2.73 x 10-3 108 events observed 151+-11 expected (no osc)

31. K2K/SuperK Comparison

32. SNO Basic Idea • Use deuterons (heavy water) as target • This allows three separate measurements: • ne + d -> e- + p +p gives Fcc = Fe • nx + d -> nx + p + n gives Fnc = Fe +(Fm + Ft) • nx + e- -> nx + e- gives Fes = Fe +.154(Fm + Ft) • Each measurement gives a line in the space defined by Fe and(Fm + Ft)

33. SNO Results Summary BP04 nSSM = 5.8 (13)

34. KamLAND Experiment • A 1 kt underground liquid scintillator detector in Japan detecting ne’s from many reactors about 180 km away • In 766.3 ton-yr exposure, there are: • 258 observed events • 365 +- 24 expected if no oscillations • 7.5 +- 1.3 background events • Observed energy spectrum is distorted

35. Combined SNO/KamLAND Fit

36. Summary of Oscillation Results The Unknowns: Value of q13 Value of d (CP) Mass hierarchy Is q23 = 45o ? Nature of LSND anomaly Mass Differences: Dm12 ~ 8 meV Dm13 ~ 50 meV

37. Nature of neutrinos • Are neutrinos their own antiparticles, ie Majorana n’s? • No reason why not. No distinguishing quantum number if no lepton number conservation • If so, neutrinoless double beta decay possible • Probably only practical way to resolve the question

38. Experimental Status • Today a questionable claim to a signal in Germanium by a subset of Moscow Heidelberg group; meff=.39eV • Want to reach sensitivity of at least 20 meV • That would allow observable signal if masses degenerate (ie lowest mass >> 20 meV) or if inverted hierarchy • This will require: • About 1 ton of right isotope • Good resolution (2b2n suppression) • Low external background • Better knowledge of matrix elements

39. Summary of Double b Possibilities

40. Lepton number violation in l+- • Currently no lepton flavor violation observed in charged leptons • Best limit in m-->e- capture: 6 x 10-13 • There are good prospects for improving sensitivity in the future to 10-16 - 10-18 • That would give sensitivity to new physics: supersymmetry, heavy neutrinos, leptoquarks… • Flavor violation in n’s gives negligible effect

41. Forces and Force Carriers • The topics of interest in electroweak and strong forces are quite different • In the former we want to test SM predictions and/or make precise measurements • In the latter the interesting issues are either calculational or involve new phenomena

42. DELPHI enqq Direct W Mass Measurements • Tevatron, leptonic decay - 80.452 (059) • LEP2 - cross section evolution - 80.411 (044) • LEP2 - direct reconstruction - 80.420 (107) • Good agreement

43. Triple Gauge Couplings • Several Born level diagrams have to be combined to calculate W+W- pair production in e+e- collisions • The correct shape and agreement of W mass with direct masurements provides validation of theory

44. Radiative corrections • In comparing results of measurements with each other (or with theory) it is essential to include one loop corrections • Thus the MW, MZ relationship will be

45. Test of one-loop corrections • We can compare direct measurements of top quark and W masses with those optained from global electroweak fit • There is good agreement • Relatively light Higgs appears to be favored

46. Potential Problems • The decade old issue of conflict between ALR from SLD and AFB(b) from LEP has not gone away • Recent checks of LEP data found no systematic problems or independent evidence for anomalous b couplings • W->t coupling is somewhat high

47. QCD Topics • Heavy ions; new state of matter • New narrow states • Parton distribution functions • State of as • “From quarks to particles” issues • Interpretation of CP asymmetries • Calculation of CKM matrix elements • Understanding cross sections, lifetimes

48. Why do we need to understand QCD

49. Heavy Ion Collisions • 241 mb-1 of 200 GeV/nucleon data accumulated at RHIC at BNL • Unprecedented energy density in collision, many times the nuclear density • Allows one to search for and study a new state of matter - Quark Gluon Plasma, predicted to occur at T~175 MeV (1 GeV/fm3) • Is there evidence for such a state - deconfined quarks and gluons, as in early universe, t < 10-5 sec • “Little Big Bang” experiment

50. A sample of results • Energy density about 30 times nuclear density • Particle/antiparticle balance around y=0 • Transparency in collisions • Lack of low momenta • Still not enough data for J/Y detailed study • Jet quenching (high pT suppression) - gluon radiation in high color density environment (predicted by Bjorken in 1976)