(Lifetime and) Dipole Moments

Size: px

Start display at page:

Download "(Lifetime and) Dipole Moments"

Rudolph Simon
6 years ago
Views:

1 Precision Measurements with the Muon: (Lifetime and) Dipole Moments B.L. Roberts Department of Physics Boston University B. Lee Roberts, APPEAL07, CAST, 19 February p. 1/34

2 Outline Introduction to the muon Magnetic and electric dipole moments Summary and conclusions. B. Lee Roberts, APPEAL07, CAST, 19 February p. 2/34

3 The Muon: Discovered in 1936 Discovered in cosmic rays by Seth Neddermeyer and Carl Anderson B. Lee Roberts, APPEAL07, CAST, 19 February p. 3/34

4 Confirmed by: Street & Stevenson, Nishina, Tekeuchi & Ichimiya B. Lee Roberts, APPEAL07, CAST, 19 February p. 4/34

5 The Muon Lifetime A precise measurement of τ + leads to a precise determination of the Fermi constantg F B. Lee Roberts, APPEAL07, CAST, 19 February p. 5/34

6 Muon decay gives us unique access to the electroweak scale The V-A theory factorizes into a pure weak contribution, plus radiative corrections (including hadronic). The muon decays only via the weak interaction G F is one of the inputs to the standardmodel electroweak fits.

7 MuLan (PSI) has a new 11 ppm τ measurement (±10.9 ppm) from 2004 run. goal: 1 ppm, decays on tape in 2006 NEW RESULT B. Lee Roberts, APPEAL07, CAST, 19 February p. 7/34

8 Magnetic and Electric Dipole Moments B. Lee Roberts, APPEAL07, CAST, 19 February p. 8/34

9 Magnetic and Electric Dipole Moments B. Lee Roberts, APPEAL07, CAST, 19 February p. 9/34

10 Electric and Magnetic Dipole Moments: ie Γ = ef ψ γψ + F ψσ q ψ 2m ν 1 R R 2 R ν L Muon Magnetic Dipole Momoment a chiral changing Muon EDM B. Lee Roberts, APPEAL07, CAST, 19 February p. 10/34

11 Muon Magnetic Dipole Moment B. Lee Roberts, APPEAL07, CAST, 19 February p. 11/34

Kusch Schwinger and Foley, Schwinger, Kusch-Foley 1947 c 2( α ) 2 + +.. π γ e γ e + γ e vrs.

12 It s convenient to write the magnetic moment as a sum of two pieces: Dirac + Pauli moment Radiative corrections contribute to a for leptons γ Dirac Dirac Stern-Gerlach γ g = 2 + α π γ Kusch Schwinger and Foley, Schwinger, Kusch-Foley 1947 c 2( α ) π γ e γ e + γ e vrs. : relative contribution of heavier things B. Lee Roberts, APPEAL07, CAST, 19 February p. 12/34

13 The SM Value for the muon anomaly (10-10 ) *Hagiwara, et al., hep-ph , plus Davier et al., hep-ph B. Lee Roberts, APPEAL07, CAST, 19 February p. 13/34

14 Lowest Order Hadronic from e + e - annihilation B. Lee Roberts, APPEAL07, CAST, 19 February p. 14/34

15 Since a represents a sum over all physics, it is sensitive to a wide range of potential new physics B. L. Roberts, Workshop on Precision Measurements at Low Energy- PSI - 19 January p. 15/56

16 Since a represents a sum over all physics, it is sensitive to a wide range of potential new physics muon substructure anomalous couplings γ Triple Gauge Vertex W W g = 2? W ν W boson substructure? B. L. Roberts, Workshop on Precision Measurements at Low Energy- PSI - 19 January p. 16/56

17 Since a represents a sum over all physics, it is sensitive to a wide range of potential new physics muon substructure anomalous couplings SUSY (with large tanβ ) ν χ χ + γ χ 0 γ many other things (extra dimensions, etc.) B. L. Roberts, Workshop on Precision Measurements at Low Energy- PSI - 19 January p. 17/56

Since a represents a sum over all physics, it is sensitive to a wide range of potential new physics muon substructure anomalous couplings SUSY (with

18 Since a represents a sum over all physics, it is sensitive to a wide range of potential new physics muon substructure anomalous couplings SUSY (with large tanβ ) many other things (extra dimensions, etc.) B. L. Roberts, Workshop on Precision Measurements at Low Energy- PSI - 19 January p. 18/56

19 We measure the difference frequency between the spin and momentum precession With an electric quadrupole field for vertical focusing 0 B. Lee Roberts, APPEAL07, CAST, 19 February p. 19/34

20 Experimental Technique (from AGS) Protons Target Pions p=3.1gev/c Muon polarization Muon storage ring injection & kicking focus by Electric Quadrupoles 24 electron calorimeters π ν Inflector B v Injection orbit Central orbit Storage Kicker ring Modules R=711.2cm d=9cm (1.45T) x ~ c = 77 mm β ~ = 10 mrad B dl ~ = 0.1 Tm β R R Electric Quadrupoles B. Lee Roberts, APPEAL07, CAST, 19 February p. 20/34 x c

21 muon (g-2) storage ring Muon lifetime t = 64.4 s (g-2) period t a = 4.37 s Cyclotron period t C = 149 ns B. Lee Roberts, APPEAL07, CAST, 19 February p. 21/34

22 muon (g-2) storage ring Muon lifetime t = 64.4 s (g-2) period t a = 4.37 s Cyclotron period t C = 149 ns B. Lee Roberts, APPEAL07, CAST, 19 February p. 22/34

23 We count high-energy electrons as a function of time. B. Lee Roberts, APPEAL07, CAST, 19 February p. 23/34

24 E821 achieved 0.5 ppm and the e + e - based theory is also at the 0.5 ppm level. Both can be improved. (9.4 ppm) CERN (10 ppm) CERN (13 ppm) E821 (97) + (5 ppm) E821 (98) + (1.3 ppm) E821 (99) + (0.7 ppm) E821 (00) + (0.7 ppm) E821 (01) World Average + HMNT = Hagiwara, et. al., hep-ph HNMT 2006 e + e a X B. Lee Roberts, APPEAL07, CAST, 19 February p. 24/34

25 If the electroweak contribution is left out of the standard-model value, we get a 5.3 σ difference. Even if you believe that there is no discrepancy between E821 and the standard model, without the EW contribution there is a significant difference. Now if you will permit me to speculate... B. Lee Roberts, APPEAL07, CAST, 19 February p. 25/34

26 It s amusing to note that if we assume that SUSY is the source of the (g-2) difference, it forms a consistent picture with other constraints on the SUSY LSP (lightest supersymmetric partner) being the dark matter candidate. Present Δ 800 tan β = 10, > 0 m 0 (GeV) scalar mass m h = 114 GeV m χ ± = 104 GeV 1σ g 2 2σ gaugino mass m 1/2 (GeV) 2 Ω h = (WMAP) excluded for neutral dark matter Historically muon (g-2) has played an important role in restricting models of new physics. CMSSM calculation Following Ellis, Olive, Santoso, Spanos, provided by K. Olive B. Lee Roberts, APPEAL07, CAST, 19 February p. 26/34

27 If SUSY exists, the sleptons will mix, and there is a connection between a, D, e ~ e ~ e ~ e B B ~ ~ MDM, EDM ~ ~ B. Lee Roberts, APPEAL07, CAST, 19 February p. 27/34

28 Electric Dipole Moments E.M. Purcell and N.F. Ramsey, Phys. Rev. 78 (1950) B. Lee Roberts, APPEAL07, CAST, 19 February p. 28/34

29 Electric Dipole Moments E.M. Purcell and N.F. Ramsey, Phys. Rev. 78 (1950) The argument against electric dipole moments, in another form, raises directly the question of parity. B. Lee Roberts, APPEAL07, CAST, 19 February p. 29/34

30 Transformation Properties of Electric and Magnetic Dipole Moments An EDM implies both P and T are violated. Assuming CPT symmetry, an EDM at a measureable level would imply non-standard model CP. B. Lee Roberts, APPEAL07, CAST, 19 February p. 30/34

31 B. Lee Roberts, APPEAL07, CAST, 19 February p. 31/34

32 e EDM (e.cm) Hg n Multi Higgs Left - Right MSSM φ ~ 1 MSSM φ ~ α/π Excluded region (Tl atomic beam) Commins (2002) d e < 1.6 x e.cm E. Hinds e-edm experiment at Imperial College with YbF molecules is starting to explore this region Standard Model with thanks to Ed Hinds B. Lee Roberts, APPEAL07, CAST, 19 February p. 32/34

33 Muon EDM Limits: CERN3 and BNL B. Lee Roberts, APPEAL07, CAST, 19 February p. 33/34

34 Spin Frequencies: in B field with MDM & EDM 0 spin difference frequency = ω s - ω c B. Lee Roberts, APPEAL07, CAST, 19 February p. 34/34

35 Spin Frequencies: in B field with MDM & EDM 0 spin difference frequency = ω s - ω c B. Lee Roberts, APPEAL07, CAST, 19 February p. 35/34

36 Spin Frequencies: in B field with MDM & EDM 0 The motional E - field, β X B, is much stronger than laboratory electric fields (~GV/m). (not ω a B ω η B. Lee Roberts, APPEAL07, CAST, 19 February p. 36/34 ω β x B

37 Dedicated EDM Experiment 0 Use a radial E-field to turn off the ω a precession With ω a = 0, the EDM causes the spin to steadily precess out of the plane. ω η B. Lee Roberts, APPEAL07, CAST, 19 February p. 37/34

38 since ω 2 = ω a2 + ω η2, the Δ SM could be an EDM what value EDM would this correspond to? obviously this would be exciting. See: Feng, et al., Nucl. Phys. B 613 (2001) 366 The present limits are: SM value < *preliminary B. Lee Roberts, APPEAL07, CAST, 19 February p. 38/34

39 Frozen spin technique to measure EDM Turn off the (g-2) precession with radial E Up-Down detectors measure EDM asymmetry Look for an up-down asymmetry building up with time Side detectors measure (g-2) precession To prove the spin is frozen E v E + + θ + 2θ B B 0 (a) 1 Time [arb.] 2 B. Lee Roberts, APPEAL07, CAST, 19 February p. 39/34

40 To progress beyond 5 x e cm Need an even more intense source of muons, e.g. J-PARC Goal for a dedicated J-PARC experiment: e cm B. Lee Roberts, APPEAL07, CAST, 19 February p. 40/34

41 Summary and Outlook The muon has provided us with much knowledge on how nature works, and there is plenty of room for future surprises. Muon (g-2), with a precision of 0.5 ppm, has a 3.3 σ discrepancy with the standard model using e + e - data for the hadronic contribution. This new physics would show up in an EDM and perhaps LFV as well. An exciting and unique program of muon physics can be carried out here in Japan. The search for LFV and a muon EDM addresses important fundamental questions, no matter what is found at LHC. B. Lee Roberts, APPEAL07, CAST, 19 February p. 41/34

42 THE END B. Lee Roberts, APPEAL07, CAST, 19 February p. 42/34

Lifetime and Dipole Moments

Precision Measurements with the Muon: Lifetime and Dipole Moments B.L. Roberts Department of Physics Boston University roberts @bu.edu http://physics.bu.edu/roberts.html B. Lee Roberts, Workshop on Precision