New Views in Particle Physics Vemes Rencontres du

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

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 in 1957

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 characterized by 10 measurable 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 D 0 and CDF measurement from Run 1: mtop = 178. 0+-4. 3 Ge. V Run 2 goal is uncertainty of 1% (1. 5 - 2. 0 Ge. V)

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) Unitarity: 0. 2265 (23) (8, 21) Hyperons: 0. 2250 (27) K+->p 0 e+n: 0. 2272 (22, 7, 18) K 0 L->pln: 0. 2252

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 Direct Measurement? • 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 Run 2 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 • 1 st and 3 rd rows - all sides O(l 3) -> large angles V*tb. Vud

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 2 nd order (B->J/ K 0 s) – Second class, uncertainties ~10% but constrained (e. K) – Third class, accuracies are model dependent (B->Kp)

18 CP violation - History • 1964 - CP discovered through observation of decay K 0 L ->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/ K 0 S is the “golden”channel, A a sin(2 b)sin(Dmt)

20 The Richness of B Physics f. Ks, ’Ks, Ksp 0… 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/ K, gives sin 2 b=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 f. KS final state: – BELLE -> A = -0. 96+-. 50 – Ba. Bar -> A = +. 47+-. 34 – Expect similar A as in J/ K 0 S decay (~0. 74) • Direct CP violation; recent evidence from the rates for B->Kp decay channels: – Ba. Bar: A = 0. 133 +-. 030 – BELLE: A = 0. 088 +-. 035 , the B 0 ->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, mi 2 are constants of nature; L, E experimental parameters

27 Dm 2 and L/E scales • To obtain maximum oscillations, we want phase, ie. (L/E )Dm 2, to be around p/2: • For atmospheric Dm 2 (2 -3 x 10 -3 e. V 2) – Atmospheric - E~1 Ge. V, L~10 -104 km – Accelerator - E~Ge. V’s -> L~few hundred km – Reactor - E~Me. V’s -> L ~km, • For solar Dm 2 (6 -8 x 10 -5 e. V 2) – Reactor - E~Me. V’s -> L~100 km – Sun - E~Me. V’s but mass eigenstate so L~108 km OK • LSND region - Dm 2 (0. 1 - 1 e. V 2) – Ignore in this summary; being addressed by Mini. Boo. NE

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 Super. K Results on nm Rates No oscillations Oscillations

30 K 2 K Experiment using Super. K and a nm beam from K 2 K with L=250 km (normalized by area) No Oscillation (KS prob: 0. 11%) Best Fit (KS prob: 52%) 108 events observed 151+-11 expected (no osc) Best fit parameters: Maximum mixing Dm 2 = 2. 73 x 10 -3

31 K 2 K/Super. K 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 BP 04 n. SSM = 5. 8 (13)

34 Kam. LAND 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/Kam. LAND Fit

36 Summary of Oscillation Results The Unknowns: a) Value of q 13 b) Value of d (CP) c) Mass hierarchy d) Is q 23 = 45 o ? e) Nature of LSND f) anomaly g) Mass Differences: Dm 12 ~ 8 me. V Dm 13 ~ 50 me. V

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=. 39 e. V Want to reach sensitivity of at least 20 me. V That would allow observable signal if masses degenerate (ie lowest mass >> 20 me. V) or if inverted hierarchy This will require: – – About 1 ton of right isotope Good resolution (2 b 2 n 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 Direct W Mass Measurements • • Tevatron, leptonic decay - 80. 452 (059) LEP 2 - cross section evolution - 80. 411 (044) LEP 2 - direct reconstruction - 80. 420 (107) Good agreement DELPHI enqq

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 Ge. V/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 Me. V (1 Ge. V/fm 3) • 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/ detailed study • Jet quenching (high p. T suppression) - gluon radiation in high color density environment (predicted by Bjorken in 1976)

51 Jet Quenching Evidence

52 Potential New Narrow States • According to the quark model, the observed states will be composed of either 2 (mesons) or 3 (baryons) quarks • That restriction limits quantum numbers of allowable states and the allowable SU(3) representations (1, 8, 10) • Observation of a state with “forbidden” quantum numbers will indicate more complex combinations (pentaquarks, quark molecules, etc)

53 Experimental Indications • Recently there has been several reports of new narrow states • There have been some confirmations but also some contradictory experimental results • The most interesting of these is a state with mass around 1540 Me. V, with quantum numbers of K+ n • Such state has been predicted in 1997 as S=1 member of an antidecuplet; it would be most likely a pentaquark Predicted state Diakonov, Petrov, Polyakov

54 Examples of Mass Distributions “Discovery” “Confirmation” g + n -> K+ K- n The Jury is still out Negative result Secondary K interactions in BELLE

55 Running of as The strong coupling constant, as will have q 2 dependence, known as running. This dependence can be obtained in a number of ways, eg by looking at gluon radiation as function of cm energy in e+e- collisions:

56 Summary of as measurements • • • LEPI - as(m. Z) = 0. 1199 LEPII - as(m. Z) = 0. 1202 R value in e+e- - as(m. Z) = 0. 1200 4 jet analysis - as(m. Z) = 0. 1170 Tau BR (hadrons/leptons) - as(m. Z) = 0. 1181 Hadronic collisions - experimental precision equally good; but large theoretical uncertainties at this time

57 Structure Functions • The range in x and q 2 greatly extended by HERA • One can make accurate gluon distribution measurements at high x at the Tevatron; currently interpretation limited by theoretical uncertainties • Knowledge of parton distribution functions important for future searches for new physics at LHC

58 Progress in understanding cross sections

59 CP violation and QCD • Relating experimental values from CP violation experiments to fundamental parameters will require better ability to calculate QCD effects • Some of the examples are e. K, e. K’, B->Kp asymmetry • Many of the CP violation effects in the B system involve interference effects with (or between) different penguin diagrams

60 Higgs Situation Current Situation 8. 5 fm-1 4. 4 fm-1 Potential Tevatron Sensitivity MHiggs < 237 Ge. V (95% CL)

61 The Road Ahead of Us • I will end by attempting to look into the future • First I want to say few words about physics possibilities • Then I want to make few general comments about some aspects of our field

62 Where are we today • A great deal of progress has been achieved over the last 60 years • The particle physics phenomena are well described by our Standard Model • Much work and very precise experiments have confirmed various features of the SM • Only neutrino physics has shown verified departures from Standard Model • We know that Standard Model is only an effective theory and deeper theory must exist • We look to the future to find the answers to what it is

Future (next 10 years) 63 Predictions are hard, especially if they are about future (Yogi Berra) • Electroweak Physics (Tevatron, LHC) – Existence of Higgs, its mass – Supersymmetry and its mass scale – Overall consistency of electroweak parameters • Neutrino Physics (Accelerator beams, reactors, nuclear physics expts) – Value of q 13 or a better limit – Resolution of LSND anomaly – Double beta decay with 100 kg detector • CP violation (B-factories, LHCb, BTe. V) – Better statistics, better calculations – Maaybe disagreements with Standard Model – K 0 L -> p 0 n n • New Phenomena (Muon and/or n factories) – mu-e capture – New surprises • Astrophysics (Ice. Cube, ANTARES, NESTOR, underground DM detectors) – Dark matter – Neutrino astronomy – High energy cosmic rays

64 Higgs at LHC

65 Other Physics Dark matter searches Optimistic SUSY models tested NOn. A and T 2 K q 13 sensitivities Double b decay sensitivity

66 Future (10 years after that) • Electroweak physics (Linear Collider, SLHC) – Detailed studies of Higgs, its couplings – Precision mass of SUSY particles – New phenomena (WLWL scattering) • New Neutrino Facilities (superbeams, n factories, beta beams) – Mass hierarchy – CP violation – New phenomena • Megaton Detector – Nucleon decay – Precision neutrino studies

67 Electroweak Physics at Linear Collider Higgs mass measurement Top mass measurement from energy scan (mt=175 Ge. V)

68 The Astrophysics Connection • The field started out looking up to the “heavens” and trying to understand its “gifts”, ie cosmic rays • We are once again looking to the heavens and now try to understand “it” from what we learn on earth • Astrophysics/cosmology/particle physics connection may well be one of the most exciting developments in the field in the last decade

69 Historical Comment • Particle Physics was in its infancy in the 1956 -1965 decade • Many key discovery were made then: parity violation, neutrino, V-A, 2 n’s, CP violation, SU(3), W • Astrophysics/cosmology are in the same phase today

70 Big Science, Long Time Scales • Over the last 50 years the field has grown very much in complexity • Single purpose experiments, tend now to give way to programmatic approach with large multipurpose detectors • One consequence of this is large collaborations: in my first publication there were 6 authors; there were 79 institutions in the most recent BABAR publication; 19 authors with last name of Zhang in last BES publication. • Another one is long time scales - in MINOS, 10 years from first collaboration meeting to the present (first accelerator n this December) • Needless to say, that presents problems for postdocs and graduate students.

71 The Quest for Higher Energies • The progress in particle physics has been made possible in the past by the availability of ever higher energies • All indications are that the progress in the future will also require new colliders with ever higher energies • LHC will open up a new, and hopefully very fruitful, domain for exploration • Further ahead, ever increasing size and hence cost of new facilities (accelerators and detector systems) will make this more and more difficult • The challenge in front of us is to make it nevertheless possible

72 Internationalization • The next big machine will have to be INTERNATIONAL in true meaning of the word • This will not be easy (look at ITER) but we must overcome the challenges if we want to maintain progress • Our record in bringing in new areas in the world into the community of particle physicists is quite good - this Conference is a good example • Somehow we have to learn from our very good record in building detectors, and extrapolate them to the accelerators • The reward will hopefully be not only progress in particle physics but also progress in mutual understanding

73 Final Words (from Judy Jackson)