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The Case for Muons at a Fermilab Proton Driver Facility

The Case for Muons at a Fermilab Proton Driver Facility. Unique Features of the Proton Driver The Physics Case Lepton Flavor Violation (LFV) m - A  e - A m +  e + g m +  e + e - e + Muon Electric Dipole Moment (EDM) Muon Anomalous Dipole Moment (g-2) The Experiments.

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The Case for Muons at a Fermilab Proton Driver Facility

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  1. The Case for Muons at a Fermilab Proton Driver Facility • Unique Features of the Proton Driver • The Physics Case • Lepton Flavor Violation (LFV) • m-A  e-A • m+ e+g • m+ e+ e- e+ • Muon Electric Dipole Moment (EDM) • Muon Anomalous Dipole Moment (g-2) • The Experiments R. Ray for the muon working group, Fermilab Proton Driver Workshop

  2. Unique Features of the Proton Driver • Only a small fraction of the beam from a new 8 GeV PD needed • fill MI. The remainder could be used for a low energy m • program that runs simultaneous with a 120 GeV n program. • The Recycler Ring could be used to repackage the proton beam • to the desired bunch structure • Fill Recycler with 1.5 x 1014 protons every 100 ms (one missing pulse every 1.5 s for MI) ~1.4 x 1022 protons/yr at 8 GeV • Gradually empty in 100 ms intervals between PD pulses • Extraction could be DC or in bursts • Recycler can chop 1.5 x 1014 protons into 588 bunches of 0.25 x 1012 protons and a pulse width of 3 ns. • Extract one bunch at a time with a fast kicker R. Ray for the muon working group, Fermilab Proton Driver Workshop

  3. Muon Source • Detailed m source design does not exist • Straw man design worked out for the front end of a n factory • supported by extensive MARS simulations • 1.4 x 1022 protons/year at 8 GeV yields ~3 x 1021 muons/year. Charged particle spectra at end of decay channel R. Ray for the muon working group, Fermilab Proton Driver Workshop

  4. Muon Source (cont.) • Muonshave large Dp and transverse phase space • at end of channel. An interface between the • decay channel and experiments is required • A PRISM-like FFAG ring downstream of the • decay channel can reduce the momentum • spread and make efficient use of the muon flux • Detailed design work required, particularly to develop a cost estimate • Could be the first step towards a n factory based on a m storage ring R. Ray for the muon working group, Fermilab Proton Driver Workshop

  5. General Statements • We have learned many important things from m • The m is a clean laboratory for new physics • We know that n oscillate and have mass • Neutral lepton flavor violation • LFV in m decays that result directly from n mass/mixings are suppressed by small n mass. • Implies charged LFV at high mass scales • Enhanced by new dynamics at TeV scale (SUSY?) R. Ray for the muon working group, Fermilab Proton Driver Workshop

  6. General Statements (cont.) • We expect CP violation in the lepton sector • Manifested in EDMs as well as n oscillations • Possible connection with cosmology (leptogenesis) • Muon g-2 is a very precise test of SM • Sensitive to any new particles that couple to muons • 2.7s signal from BNL g-2 exp. Hint of new physics? R. Ray for the muon working group, Fermilab Proton Driver Workshop

  7. The Physics Case • Scenario 1 - SUSY discovered at LHC • LFV muon decays, EDM and g-2 should all be enhanced by SUSY. • To understand the detailed nature of SUSY, measurements such as these will have to be made as many of the model’s parameters are only accessible from low-energy experiments. R. Ray for the muon working group, Fermilab Proton Driver Workshop

  8. Lepton Flavor Violation • No LFV in the SM • Non-zero masses of n can be explained via the seesaw • mechanism with massive right-handed n • LFV in charged lepton processes is negligibly small for a simple seesaw neutrino model. • The SUSY seesaw extension to the SM can produce • LFV at significant rates R. Ray for the muon working group, Fermilab Proton Driver Workshop

  9. SUSY and LFV SUSY contains new sources of flavor mixing in the mass matrices of sleptons and squarks. LFV processes are induced by the off-diagonal terms in the slepton mass matrixes g-2: the diagonal term EDM: complex phases LFV: the off-diagonal term Off-diagonal terms depend on how SUSY breaking is generated and what kinds of LFV interactions exist at the GUT scale. R. Ray for the muon working group, Fermilab Proton Driver Workshop

  10. Experimental Bound Goal of MEG Right-handed selectron mass m  eg branching ratio SU(5) SUSY GUT J. Hisano et al., Phys. Lett. B391 (1997) 341 Small (<10) tan b values are highly disfavoured by combined LEP data. (ALEPH, DELPHI, L3 & OPAL Collaborations, hep-ex/0107030) The branching ratio can be large. The SO(10) SUSY GUT model is ~10-100x larger R. Ray for the muon working group, Fermilab Proton Driver Workshop

  11. 10 -11 10 -13 10 -15 10 -17 10 -19 10 -21 SUSY predictions ofm-A  e-A From Barbieri, Hall, Hisano … Rme MECO single event sensitivity PRIME single event sensitivity 100 200 300 100 200 300 •  eg& m-A  e-ABranching Ratios are linearly correlated Complementary measurements(discrimination between SUSY models) R. Ray for the muon working group, Fermilab Proton Driver Workshop

  12. Muon g-2 A very precise test of the SM am = (g - 2)/2 amexp = 116592080(58) x 10-11 (BNL, m+m- combined) amSM = amQED + amhad + amweak = 116591829(73) x 10-11 amexp - amSM = 251(93) x 10-11 (2.7 s) Big effect! Larger than EW contribution. Depending on the details of SUSY breaking, amSUSY can be larger than the EW contribution 215 x 10-11 < amNP < 637 x 10-11 R. Ray for the muon working group, Fermilab Proton Driver Workshop

  13. SUSY and g-2 Chargino and neutralinos contribute to g-2 and EDM at the one loop level Large tanb limit  For tan b between 4 - 40 This is right where SUSY particles are generally expected! If sparticle masses are measured at the LHC, amNP can be used to extract tanb and constrain SUSY mixing. R. Ray for the muon working group, Fermilab Proton Driver Workshop

  14. Muon EDM • SM contribution is heavily suppressed. Observation is • unambiguous evidence for new physics. • Current bound is O(10-19) e cm • Conventional scaling arguments from more sensitive • e- EDM search: • dm = (mm/me)de < 3.3 x 10-25 e cm (90% CL) • EDM is CPV (assuming CPT). Sensitive to new physics. Possible • connection to leptogenesis. • EDM arises from operators similar to g-2, so possible • observation of amNP also motivates search for EDM. R. Ray for the muon working group, Fermilab Proton Driver Workshop

  15. SUSY and EDMs Deviations from lepton mass scaling occur naturally in SUSY For SUSY + seesaw, same mechanism responsible for nR mass can enhance dm to the level of 5 x 10-23 e cm, even for small tanb (hep-ph/0006329) m EDM greatly enhanced for non- degenerate heavy neutrinos Leptogenesis requires non-degenerate heavy neutrino masses amNP 0 can induce an EDM: A measurement of dm = 10-24 probes |tan fCP| > 3 x 10-3 R. Ray for the muon working group, Fermilab Proton Driver Workshop

  16. The Physics Case • Scenario 2: LHC finds SM Higgs at a reasonable mass and nothing else. g-2 discrepancy is the only indication of new physics beyond non-zero neutrino masses. • Precision measurements come to the forefront since they are sensitive to heavier virtual physics. • m-e conversion and g-2 are particularly sensitive to a range of new physics beyond SUSY R. Ray for the muon working group, Fermilab Proton Driver Workshop

  17. Sensitivity to Different Muon Conversion Mechanisms Supersymmetry Compositeness Predictions at 10-15 Second Higgs doublet Heavy Neutrinos Heavy Z’, Anomalous Z coupling Leptoquarks After W. Marciano R. Ray for the muon working group, Fermilab Proton Driver Workshop

  18. Mass Limit 86 TeV/c2 21 TeV/c2 365 TeV/c2 Limits on Muon Number Violating Processes m-e conversion has the greatest mass reach and is more sensitive to nearly all new physics contributions that are not mediated by a photon. m eg is ~ 300 times more sensitive to processes mediated by a photon. Relative rates for eg and -Ne-N give information on underlying physics A significant rate for eg with polarized m could give additional information on mechanism R. Ray for the muon working group, Fermilab Proton Driver Workshop

  19. g-2 is sensitive to a wide range of new physics besides SUSY • Muon substructure • Anomalous couplings • Extra Higgs bosons • Leptoquarks • Many other things (extra dimensions, etc.) R. Ray for the muon working group, Fermilab Proton Driver Workshop

  20.  • Choose g, B and E so that precession due to first 2 terms sums to zero • Only precession due to EDM remains.  Radial E causes rotation of spin in vert. plane for non-zero EDM e+ emitted preferentially along m spin vector Signal is an up-down asymmetry in the number of e+ that grows linearly with time. The Experiments New Approach to m EDM Precession of m in storage ring R. Ray for the muon working group, Fermilab Proton Driver Workshop

  21. m EDM • m EDM search is a fundamentally novel measurement where no future • progress will be made until a high-intensity polarized m source is available. • Sensitivity of 10-24 e•cm can be achieved for NP2 = 1016 •  1 year of running. • Measurement is rate limited. Need many short pulses separated • by > 500 ns. Well suited to PD + recycler ring. • SUSY calculations range from 10-22 to 10-32 e cm, so more muons help • Sensitivity of 10-26 achievable, but rates in detectors become high. • Integrate detector signals instead of using single pulses. R. Ray for the muon working group, Fermilab Proton Driver Workshop

  22. m+ e+g • Present upper limit (1.2 x 10-11) expected to be reduced to 10-13 • (or observed) by MEG - start data taking in 2006 • Exploiting higher intensities a nontrivial challenge, limited by accidentals. • Continuous beam required. • New concepts, advances in detector design needed for further progress. • For example: • Thinner target subdivided into a row of thin foils • Require e+ and g to originate from same target • Use silicon pixels to measure e+ and e+e- pair from converted g • Development of thinner pixel detectors required • A 2 - 3 order of magnitude improvement possible * • * F. DeJongh - FERMILAB-TM-2292-E, CERN-TH/2001-231 R. Ray for the muon working group, Fermilab Proton Driver Workshop

  23. m eee • Current sensitivity bound of 1 x 10-12 • (SINDRUM - 1988) • Powerful constraints on vertex quality • and location reduce accidentals • Rate of 1010m+/s needed for a • sensitivity of 10-16 • High rate tracking and triggering • is the challenge. R. Ray for the muon working group, Fermilab Proton Driver Workshop

  24. m-A e-A • Signal is a single monochromatic 105 MeV electron • Accidentals not an issue • Requires pulsed beam with small extinction and small Dp/p • Current limit of 6.1 x 10-13 should be pushed to 10-17 by MECO • PRIME at JPARC could reach 10-19 using an FFAG ring • Sensitivity dominated by performance of pulsed beam. • Measurement can continue to benefit from increased beam intensity. R. Ray for the muon working group, Fermilab Proton Driver Workshop

  25. Future Progress in g-2 • E969 at BNL: 0.5 ppm accuracy • 0.27 ppm sys (0.17 ppm B-field, 0.21 ppm precession frequency) • Statistical uncertainty (1999, 2000, 2001 data sets) 0.46 ppm Measurements still statistics-limited. Still room to reduce systematics. • Plans for upgrade (not funded): 0.5  0.20 ppm • Reduce sys. error by x 2 • Increase statistical sample by x 9 • Near-term improvement in theory  Significant confrontation with SM • A R. Ray for the muon working group, Fermilab Proton Driver Workshop

  26. A New g-2 Experiment at a Future High Flux Facility • Goal: Factor of 10 improvement  0.05 ppm uncertainty • Statistical uncertainty: 0.03 ppm (increase statistics by x200) • Systematic uncertainty: 0.04 ppm (reduce systematic error by x7) • Open inflector ends to reduce multiple scattering • More magnetic quadrupoles in beamline • Backward muon beam to eliminate flash • Longer p  m decay beamline • Better phase space matching of beamline to ring • Redesign inflector with larger aperture • Li lens • Maximum flux of 5.4 GeV/c m from backward p with small Dp/p • Pulsed beam (width < 20 ns) • High rep rate • Min 1 ms between pulses R. Ray for the muon working group, Fermilab Proton Driver Workshop

  27. Desirable Beam Characteristics hep-ph/0109217 R. Ray for the muon working group, Fermilab Proton Driver Workshop

  28. Summary • Important m physics experiments can be executed at a PD facility • LFV • g-2 • muon EDM • The physics case for these measurements is solid • These measurements are complementary to other methods • that explore the frontier beyond the Standard Model • Depending on what is found at the LHC, they may be the only • way to get at this information. • In either case, they will provide essential information in our • attempt to discover and understand physics beyond the • Standard Model R. Ray for the muon working group, Fermilab Proton Driver Workshop

  29. Summary (cont.) • The combination of a new PD and the existing Recycler can • provide a unique facility with unmatched intensity and flexibility • An 8 GeV m program could run simultaneous with a 120 GeV • MI program • Some effort needs to be put into the design of a muon source • to understand cost and feasibility issues. • This could be the first step towards a n factory R. Ray for the muon working group, Fermilab Proton Driver Workshop

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