B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 1/39 Future Muon Dipole Moment Measurements at a high intensity muon source B. Lee Roberts Department of Physics Boston University A Precision Path to the Frontier

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 2/39 Outline theory and motivation of dipole moments, including the transition moment for μ→e conversion muon (g-2) present and future muon EDM summary and conclusions

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 3/39 Magnetic moments, g-factors

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 4/39 Electric and Magnetic Dipole Moments Transformation properties: An EDM implies both P and T 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, HIFW04, Isola d’Elba, 6 June p. 5/39 Lagrangian for MDM and EDM where α, β run from 0 to 3, and d μ is the electric dipole moment. We could also use the dipole operator D

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 6/39 Present EDM Limits ParticlePresent EDM limit (e-cm) SM value (e-cm) n future exp to *projected

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 7/39 Unlike the EDM, there is a large SM value for the MDM The Electron: to the level of the experimental error (4ppb), Contribution of μ, (or anything heavier than the electron) is ≤4 ppb. For the muon, the relative contribution of heavier particles

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 8/39 Standard Model Value for (g-2)

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 9/39 Two Hadronic Issues: Lowest order hadronic contribution Hadronic light-by-light

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 10/39 Lowest Order Hadronic from e + e - annihilation Can hadronic decay data be used? Eventually from the lattice?

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 11/39 Hadronic light-by-light This contribution must be determined by calculation. While there have been issues with this contribution, things are settling down. a lattice calculation might improve things further, and give confidence in the models. the knowledge of this contribution limits knowledge of theory value.

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 12/39 a μ is sensitive to all virtual particles which couple to the muon, e.g. SUSY a toy model with equal susy masses gives: If SUSY is discovered at LHC, then (g-2) will give a 20% determination of tan β

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 13/39 SUSY connection between D μ, μ → e

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 14/39 Unlike the EDM, a μ is well measured. the combined value is Comparing with e + e - - data shows a discrepancy with the standard model of 2.4σ

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 15/39 Where we came from:

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 16/39 Today with e + e - based theory: All E821 results were obtained with a “blind” analysis.

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 17/39

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 18/39 Discrepancy with e + e - based theory What might this mean? It all depends on your religion… –if you believe in SUSY, then it is the predicted effect, and evidence for SUSY. –if you are a non-believer then this discrepancy is interesting, or a fluctuation… Whatever you believe, muon (g-2) provides a wonderful test of the standard model.

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 19/39 a μ implications for the muon EDM This paper, published before our February 2001 announcement predicts a large muon EDM, and a corresponding SUSY contribution to a μ comparable to what we might be observing, with the e - EDM predicted to be 0.1 of the present limit.

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 20/39 a μ implications for the muon EDM

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 21/39 Basis of the experiments:

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 22/39 Spin Precession Frequencies: The EDM causes the spin to precess out of plane. The motional E - field, β X B, is much stronger than laboratory electric fields.

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 23/39 muon (g-2) storage ring

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 24/39 Technique for muon (g-2) use the magic γ = 29.3 and electrostatic focusing.

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 25/39 Detectors and vacuum chamber

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 26/39

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 27/39

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 28/39 E821 will improve muon EDM however, the EDM signal is sitting on top of a large background from g-2. we need to eliminate this background. use a radial E field to turn off g-2 precession

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 29/39 EDM – up/down Asymmetry run off the magic γ and use a radial E-field to turn off (g-2) precession Place detectors above and below the vacuum chamber and look for an up/down asymmetry which builds up with time

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 30/39 The EDM ring run with both μ + and μ -. there must be regions of combined E+B along with separate focusing elements. There needs to be a scheme to inject CW and CCW. EBpR 2 MV/m0.25T0.5 GeV/c511μs7 m Possible Muon EDM Ring Parameters

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 31/39 the lattice

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 32/39 Detectors above and below

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 33/39 up / down asymmetry time (μs) asymmetry put in up- down /up+d own

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 34/39 NP 2 the figure of merit is N μ times the polarization. we need to reach the e-cm level.

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 35/39 Future Plans: (g-2) we are preparing a proposal to BNL to improve on our error from 0.5 ppm to ≤ 0.25 ppm. –proposal ready late July –defend in late September This will require upgrades and ~28 weeks of beam time. Longer term, if theory can support it, we believe that at a high-intensity μ source we could reach 0.06 ppm.

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 36/39 Future Plans: Muon EDM The muon EDM experiment needs a high intensity source, along with a polarized D beam to test systematic errors. A letter of intent was submitted to JPARC. A separate proposal to search for a Deuteron EDM is being prepared (J. Miller, E. Stephenson and Y. Semertzidis spokespersons).

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 37/39 Deuteron EDM in a Storage Ring Radial E-field to Control the g-2 Precession Intense Polarized Deuteron Beams Long Spin Coherence Time:  10s Polarimeters: High Analyzing Power Clockwise and Counter-Clockwise Injection Systematic Error:  e  cm Statistical Error:  e  cm Proposal This Summer to BNL, DOE/NSF

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 38/39

B. Lee Roberts, HIFW04, Isola d’Elba, 6 June p. 39/39 Conclusions The measured value of a differs from the SM value by ~2.4 to 3 σ, and a μ will remain an important quantity. If SUSY is found, → tan β We propose to improve the precision of a μ. The muon EDM experiment can only be done at a high intensity muon source. We believe that a precision of – e-cm could be reached at a high intensity muon source. EDMs are an excellent opportunity to search for non-standard-model CP violation.