Future Muon Dipole Moment Measurements at a high

Future Muon Dipole Moment Measurements at a high intensity muon source A Precision Path to the Frontier B. Lee Roberts Department of Physics Boston University roberts@bu. edu http: //physics. bu. edu/roberts. html B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 1

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, HIFW 04, Isola d’Elba, 6 June 2004 2

Magnetic moments, g-factors B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 3

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, HIFW 04, Isola d’Elba, 6 June 2004 4

Lagrangian for MDM and EDM where α, β run from 0 to 3, and dμ is the electric dipole moment. We could also use the dipole operator D B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 5

Present EDM Limits Particle Present EDM limit (e-cm) SM value (e-cm) n future exp *projected 10 -24 to 10 -25 B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 6

Unlike the EDM, there is a large SM value for the MDM The Electron: to the level of the experimental error (4 ppb), Contribution of μ, (or anything heavier than the electron) is ≤ 4 ppb. For the muon, the relative contribution of heavier particles B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 7

Standard Model Value for (g-2) B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 8

Two Hadronic Issues: • Lowest order hadronic contribution • Hadronic light-by-light B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 9

Lowest Order Hadronic from e+e- annihilation Can hadronic lattice? decay data be used? Eventually from the B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 10

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, HIFW 04, Isola d’Elba, 6 June 2004 11

aμ 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, HIFW 04, Isola d’Elba, 6 June 2004 12

SUSY connection between Dμ , μ → e B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 13

Unlike the EDM, aμ is well measured. Comparing with e+e- data shows a discrepancy with the standard model of 2. 4σ the combined value is B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 14

Where we came from: B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 15

Today with e+e- based theory: All E 821 results were obtained with a “blind” analysis. B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 16

B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 17

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, HIFW 04, Isola d’Elba, 6 June 2004 18

aμ implications for the muon EDM This paper, published before our February 2001 announcement predicts a large muon EDM, and a corresponding SUSY contribution to aμ comparable to what we might be observing, with the e- EDM predicted to be 0. 1 of the present limit. B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 19

aμ implications for the muon EDM B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 20

Basis of the experiments: B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 21

Spin Precession Frequencies: 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, HIFW 04, Isola d’Elba, 6 June 2004 22

muon (g-2) storage ring B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 23

Technique for muon (g-2) use the magic γ = 29. 3 and electrostatic focusing. B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 24

Detectors and vacuum chamber B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 25

B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 26

B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 27

E 821 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, HIFW 04, Isola d’Elba, 6 June 2004 28

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, HIFW 04, Isola d’Elba, 6 June 2004 29

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. Possible Muon EDM Ring Parameters E B p 2 MV/m 0. 25 T 0. 5 Ge. V/c R 5 11μs 7 m B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 30

the lattice B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 31

Detectors above and below B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 32

up / down asymmetry put in updown/ up+d own time (μs) B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 33

NP 2 • the figure of merit is Nμ times the polarization. • we need to reach the 10 -24 e-cm level. B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 34

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, HIFW 04, Isola d’Elba, 6 June 2004 35

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, HIFW 04, Isola d’Elba, 6 June 2004 36

Deuteron EDM in a Storage Ring • • • Radial E-field to Control the g-2 Precession Intense Polarized Deuteron Beams Long Spin Coherence Time: 10 s Polarimeters: High Analyzing Power Clockwise and Counter-Clockwise Injection • Systematic Error: 10 -27 e cm • Statistical Error: 10 -27 e cm • Proposal This Summer to BNL, DOE/NSF B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 37

B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 38

Conclusions • • • The measured value of a differs from the SM value by ~2. 4 to 3 σ, and aμ will remain an important quantity. If SUSY is found, → tan β We propose to improve the precision of aμ. The muon EDM experiment can only be done at a high intensity muon source. We believe that a precision of 10 -24 – 10 -25 e-cm could be reached at a high intensity muon source. EDMs are an excellent opportunity to search for non-standard-model CP violation. B. Lee Roberts, HIFW 04, Isola d’Elba, 6 June 2004 39