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The Muon: A Laboratory for Particle Physics

The Muon: A Laboratory for Particle Physics. Everything you always wanted to know about the muon but were afraid to ask. B. Lee Roberts Department of Physics Boston University. roberts@bu.edu http://physics.bu.edu/roberts.html. Outline. Introduction to the muon

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The Muon: A Laboratory for Particle Physics

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  1. The Muon: A Laboratory for Particle Physics Everything you always wanted to know about the muon but were afraid to ask. B. Lee Roberts Department of Physics Boston University roberts@bu.edu http://physics.bu.edu/roberts.html B. Lee Roberts, Oxford University, 19 October 2004

  2. Outline • Introduction to the muon • Selected weak interaction parameters • Muonium • Lepton Flavor Violation • Magnetic and electric dipole moments • Summary and conclusions. B. Lee Roberts, Oxford University, 19 October 2004

  3. The Muon (“Who ordered that?”) • Lifetime ~2.2 ms, practically forever • 2nd generation lepton • mm/me = 206.768 277(24) • produced polarized For decay in flight, “forward” and “backward” muons are highly polarized. B. Lee Roberts, Oxford University, 19 October 2004

  4. The Muon – ctd. • Decay is self analyzing • It can be produced copiously in pion decay • PSI has 108m/s in a new beam B. Lee Roberts, Oxford University, 19 October 2004

  5. A precise measurement of tm+ leads to a precise determination of GF • Predictive power in weak sector of SM: • Top quark mass prediction: mt = 177  20 GeV • Input: GF(17 ppm),a(4 ppb at q2=0),MZ (23 ppm), • 2004 Update from D0 mt = 178  4.3 GeV B. Lee Roberts, Oxford University, 19 October 2004

  6. mLan @ PSI aims for a factor of 20 improvement B. Lee Roberts, Oxford University, 19 October 2004

  7. The Leptonic Currents • Lepton current is (V – A) There have been extensive studies at PSI by Gerber, Fetscher, et al. to look for other couplings in muon decay. B. Lee Roberts, Oxford University, 19 October 2004

  8. Leptonic and hadronic currents • For nuclear m- capture there are induced formfactors and the hadronic current contains 6 terms. • the induced pseudoscaler term is important further enhanced in radiative muon capture A new experiment at PSI MuCap hopes to resolve the present 3 s discrepancy with PCAC B. Lee Roberts, Oxford University, 19 October 2004

  9. Muonium Hydrogen (without the proton) Zeeman splitting mm/mp = 3.183 345 24(37) (120 ppb) where mp comes from proton NMR in the same B field B. Lee Roberts, Oxford University, 19 October 2004

  10. muonium and hydrogen hfs → proton structure B. Lee Roberts, Oxford University, 19 October 2004

  11. Lepton Flavor • We have found empirically that lepton number is conserved in muon decay and in beta decay. • e.g. • What about or B. Lee Roberts, Oxford University, 19 October 2004

  12. General Statements • We know that n oscillate • neutral lepton flavor violation • Expect charged lepton flavor violation at some level • enhanced if there is new dynamics at the TeV scale • in particular if there is SUSY • We expect CP in the lepton sector (EDMs as well as n oscillations) • possible connection with cosmology (leptogenesis) B. Lee Roberts, Oxford University, 19 October 2004

  13. Lepton Flavor Violation Muon MDM (g-2) chiral changing Muon EDM The Muon Trio: B. Lee Roberts, Oxford University, 19 October 2004

  14. Past and Future of LFV Limits MEGm → e g • 10-13 BR sensitivity • under construction at PSI, first data in 2006 MECOm++A→e++A • 10-17 BR sensitivity • approved at Brookhaven, not yet funded (Needs Congressional approval) m+e-→m-e+ Branching Ratio Limit B. Lee Roberts, Oxford University, 19 October 2004

  15. Magnetic Dipole Moments The field was started by Stern B. Lee Roberts, Oxford University, 19 October 2004

  16. Z. Phys. 7, 249 (1921) B. Lee Roberts, Oxford University, 19 October 2004

  17. 673 (1924) (in modern language) B. Lee Roberts, Oxford University, 19 October 2004

  18. Dirac + Pauli moment B. Lee Roberts, Oxford University, 19 October 2004

  19. Dirac Equation Predicts g=2 • radiative corrections change g B. Lee Roberts, Oxford University, 19 October 2004

  20. The CERN Muon (g-2) Experiments The muon was shown to be a point particle obeying QED The final CERN precision was 7.3 ppm B. Lee Roberts, Oxford University, 19 October 2004

  21. Standard Model Value for (g-2) relative contribution of heavier things B. Lee Roberts, Oxford University, 19 October 2004

  22. Two Hadronic Issues: • Lowest order hadronic contribution • Hadronic light-by-light B. Lee Roberts, Oxford University, 19 October 2004

  23. Lowest Order Hadronic from e+e- annihilation B. Lee Roberts, Oxford University, 19 October 2004

  24. a(had) from hadronic t decay? • Assume: CVC, no 2nd-class currents, isospin breaking corrections. • n.b. t decay has no isoscalar piece, while e+e- does • Many inconsistencies in comparison of e+e- and t decay: - Using CVC to predict t branching ratios gives 0.7 to 3.6 s discrepancies with reality. - Fpfrom t decayhas different shape from e+e-. B. Lee Roberts, Oxford University, 19 October 2004

  25. Pion Formfactor 45 45 CMD-2 KLOE 40 35 30 25 20 15 • Comparison with CMD-2 in the Energy Range 0.37 <sp<0.93 GeV2 10 (375.6  0.8stat  4.9syst+theo) 10-10 KLOE 1.3% Error (378.6  2.7stat  2.3syst+theo) 10-10 0.9% Error 5 CMD2 0 • At large values of sp (>mr2) KLOE is consistent with CMD and therefore • They confirm the deviation from t-data! • . sp [GeV2] 0.4 0.5 0.6 0.7 0.8 0.9 KLOE Data on R(s) 2pcontribution to amhadr • KLOE has evaluated theDispersions Integral for the 2-Pion-Channel in the Energy Range0.35 <sp<0.95 GeV2 ampp = (388.7  0.8stat  3.5syst  3.5theo) 10-10 Courtesy of G. Venanzone B. Lee Roberts, Oxford University, 19 October 2004

  26. A. Höcker at ICHEP04 B. Lee Roberts, Oxford University, 19 October 2004

  27. SM Theory from ICHEP04 (A. Höcker) Weak contribution aweak = +(15.4 ± 0.3) 10–10 Hadronic contribution from higher order : ahad [(/)3]= – (10.0 ± 0.6) 10–10 Hadronic contribution from LBL scattering: ahad [LBL]= + (12.0 ± 3.5) 10–10 BNL E821 (2004): aexp =(11 659 208.0  5.8) 1010 not yet published not yet published Observed Difference with Experiment: preliminary B. Lee Roberts, Oxford University, 19 October 2004

  28. Hadronic light-by-light • This contribution must be determined by calculation. • the knowledge of this contribution limits knowledge of theory value. B. Lee Roberts, Oxford University, 19 October 2004

  29. aμ is sensitive to a wide range of new physics • muon substructure • anomalous couplings • SUSY (with large tanβ ) • many other things (extra dimensions, etc.) B. Lee Roberts, Oxford University, 19 October 2004

  30. SUSY connection between am , Dμ , μ→ e B. Lee Roberts, Oxford University, 19 October 2004

  31. In CMSSM, am can be combined with b → sg, cosmological relic density Wh2, and LEP Higgs searches to constrain c mass With expected improvements in ahad + E969 the error on the difference Excluded by direct searches Allowed 2s band am(exp)– am(e+e- theory) Preferred Excluded for neutral dark matter same discrepancy no discrepancy Courtesy K.Olivebased on Ellis, Olive, Santoso, Spanos B. Lee Roberts, Oxford University, 19 October 2004

  32. Spin Precession Frequencies: m in B field 0 spin difference frequency = ws - wc The motional E - field, β X B, is much stronger than laboratory electric fields. The EDM causes the spin to precess out of plane. B. Lee Roberts, Oxford University, 19 October 2004

  33. Experimental Technique Spin Momentum Central orbit Kicker Modules R=711.2cm d=9cm Electric Quadrupoles polarized m Protons Pions Inflector (from AGS) p=3.1GeV/c Target (1.45T) Injection orbit • Muon polarization • Muon storage ring • injection & kicking • focus by Electric Quadrupoles • 24 electron calorimeters Storage ring B. Lee Roberts, Oxford University, 19 October 2004

  34. muon (g-2) storage ring B. Lee Roberts, Oxford University, 19 October 2004

  35. r = 7112 mm B0 = 1.45 T tcyc = 149 ns t(g-2) = 4.37 ms tm = 64.4 ms pm = 3.094 GeV/c The Storage Ring Magnet B. Lee Roberts, Oxford University, 19 October 2004

  36. 2001 B Field Measurement

  37. B. Lee Roberts, Oxford University, 19 October 2004

  38. Detectors and vacuum chamber Detector acceptance depends on radial position of the m when it decays. B. Lee Roberts, Oxford University, 19 October 2004

  39. B. Lee Roberts, Oxford University, 19 October 2004

  40. Fourier Transform: residuals to 5-parameter fit beam motion across a scintillating fiber – ~15 turn period B. Lee Roberts, Oxford University, 19 October 2004

  41. Where we came from: B. Lee Roberts, Oxford University, 19 October 2004

  42. Today with e+e- based theory: All E821 results were obtained with a “blind” analysis. B. Lee Roberts, Oxford University, 19 October 2004

  43. Life Beyond E821? • With a 2.7 s discrepancy, you’ve got to go further. • A new upgraded experiment was approved by the BNL PAC in September E969 • Goal: total error = 0.2 ppm • lower systematic errors • more beam B. Lee Roberts, Oxford University, 19 October 2004

  44. E969: Systematic Error Goal • Field improvements will involve better trolley calibrations, better tracking of the field with time, temperature stability of room, improvements in the hardware • Precession improvements will involve new scraping scheme, lower thresholds, more complete digitization periods, better energy calibration B. Lee Roberts, Oxford University, 19 October 2004

  45. Improved transmission into the ring Inflectoraperture Inflector Storage ring aperture E821 Closed End E821 Prototype Open End B. Lee Roberts, Oxford University, 19 October 2004

  46. Expect for both sides Near side Far side Pedestal vs. Time E969: backward decay beam E821: Pions @ 3.115 GeV/c Pions @ 5.32 GeV/c m momentum collimator Decay muons @ 3.094 GeV/c No hadron-induced prompt flash Approximately the same muon flux is realized x 1 more muons E821 B. Lee Roberts, Oxford University, 19 October 2004

  47. Electric and Magnetic Dipole Moments Transformation properties: An EDM implies both PandT are violated. An EDM at a measureable level would imply non-standard model CP. The baryon/antibaryon asymmetry in the universe, needs new sources of CP. B. Lee Roberts, Oxford University, 19 October 2004

  48. Present EDM Limits *projected B. Lee Roberts, Oxford University, 19 October 2004

  49. Model Calculations of m EDM μ EDM may be enhanced above mμ/me× e EDM Magnitude increases with magnitude of ν Yukawa couplings and tan β μ EDM greatly enhanced when heavy neutrinos non-degenerate B. Lee Roberts, Oxford University, 19 October 2004

  50. aμ implications for the muon EDM B. Lee Roberts, Oxford University, 19 October 2004

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