1. 1 Muon Physics Project X Workshop Fermilab 17 November 2007

2. 2 Questions Is the physics compelling in the light of LHC, prospects for ILC, other opportunities? Are there experimental techniques that require or can make use of the very high intensity? Can it be done cheaper, faster, better elsewhere?

3. 3 Potential Program Muon and electron number violation (  - N→e - N,   →e +  ) – Best match to accelerator properties (energy, time structure, intensity) for  - N→e - N –   →e +   →e + e + e -  better done at PSI (DC beam, plenty of muons, no clear upgrade path requiring higher intensity) Muon anomalous magnetic moment – 8 GeV is probably too low for efficient 3.5 GeV pion production Muon electric dipole momentum – Could be a candidate – No clear advantage with respect to PSI, JPARC, BNL Muon lifetime Concentrate on charged lepton flavor violation in  - N→e - N

4. 4 Is the physics of muon conversion compelling? Covered by Joe Lykken and Hitoshi Murayama in the context of having set the supersymmetry mass scale in the early LHC running Has no Standard Model background – signal is unambiguous evidence for new physics Addresses directly question of flavor mixing in a class of supersymmetry models – not easily addressed with LHC In the event that LHC sees nothing beyond SM Higgs, it is one of the few ways to see evidence for something new (particularly in accelerator based particle physics). Could be unique in its discovery potential in the context of other new physics not addressed at LHC – Heavy Z' boson – Leptoquarks – Multiple Higgs

5. 5 Explore dependence of   N  →e - N rate on new physics in model independent way using following Lagrangian Contributions are magnetic-moment-type operator  =0 ) and effective four fermion interaction (  → ∞ ).  interpolates between these limits in cases where both types of operators are present. Illustrates relative power of conversion and decay in model independent way. Is the physics compelling?

6. 6 Sindrum2 (Au) mu2e/MECO PRIME COMET Project X?

7. 7 Is the physics case compelling? From the model of J. Hisano and D. Nomura, Phys. Rev. D59 (1999): MSW large angle Just so Possible interpretations of solar  deficit MEG  →e  goal MECO/mu2e  - N→e - N goal Just so MSW small angle MSW large angle MSW small angle  m 2 [eV 2 ] M R2 [GeV/c 2 ] BR(  →e  ) sin 2 (2  ) MEGA  →e  limit Mass relevant for lepto-genesis

8. 8 Is the physics compelling? If CLFV is observed at any stage with sufficient rate We can map out CLFV physics by comparing rate for  - N→e - N to that for  → e  and  → eee. More information derives from rates with different targets. If new states are discovered at the LHC CLFV provides complementary information from both positive and negative results. For example, presence of CLFV in MSUGRA-type world would reveal that seesaw scale is high, lack of CLFV would point to lower seesaw scale. CLFV offers a strong (perhaps unique) link between the new physics uncovered by neutrino experiments and the new physics uncovered at the LHC. If no new states other than the SM Higgs boson is discovered at the LHC CLFV among the deepest probes of new physics beyond the LHC reach. CLFV still has potential to elucidate the physics uncovered by neutrinos.

9. 9 Can it be done cheaper, faster, better elsewhere? Fermilab phase 1 – 8 GeV synchrotron – Storage rings for time structure of beam (1.6  s pulse spacing) – 20 kW beam power with small impact on  program Fermilab phase 2 – 8 GeV linac – Storage rings for time structure of beam (1.6  s pulse spacing) – 200 kW beam power without impact on  program JPARC phase 1 – 8 GeV synchrotron (de-rated from 40 GeV) – 50 kW beam power, inconsistent with  program – Time structure in accelerator (1.2  s pulse spacing) JPARC phase 2 – 40 GeV synchrotron – >1 MW beam power, inconsistent with  program – Time structure from FFAG muon storage ring, low repetition rate PSI – 600 MeV cyclotron – 1.2 MW beam power (but too low energy for efficient pion production) – Pulsing only by chopping beam – inconsistent with other users Brookhaven National Laboratory – 8 GeV synchrotron (de-rated from 27 GeV) – Time-sharing with use as RHIC injector – 25 kW beam power (radiation limited) – Time structure in accelerator (1.35  s pulse spacing )

10. 10 Can it be done faster, better, cheaper elsewhere? Sindrum2 (Au) mu2e/MECO PRIME COMET Project X?

11. 11 Can it be done better, faster, cheaper elsewhere? Considerations of potential sources of fake backgrounds specify much of the design of the beam and experimental apparatus. SINDRUM2 currently has the best limit on this process: Expected signal Cosmic ray background Prompt background Experimental signature is105 MeV e - originating in a thin stopping target. Muon decay

12. 12 Can it be done cheaper, faster, better elsewhere? Mu2e/MECO based on detailed performance simulation, design and cost analysis that has been extensively reviewed – beam and accelerator modifications for Fermilab implementation is in early stages, but no show stoppers. It could be built at existing complex with modest tax on protons for neutrino physics or at Project X with no tax (Jim Miller). COMET is based on similar muon beam design, with novel detector geometry that is designed to reduce detector rates. Running COMET and the JPARC neutrino program are incompatible (Yoshi Kuno). PRISM (beam) / PRIME (experiment) is based on very different muon beam driven by a fast extracted beam and an FFAG muon storage ring with phase rotation. It has very high instantaneous stopping rates and a experimental geometry designed to reduce detector rates (Yoshi Kuno). Schedule, cost, manpower are not given.  - N → e - N at Project X not yet studied. It would have no negative impact on a neutrino program. Muon beam intensity could be >10x what could be done earlier at Fermilab. Muon beam advances based on new technology (e.g. for muon colliders) should be studied (Chuck Ankenbrandt). A phased approach starting with mu2e is being studied (Jim Miller).

13. 13 Straw Tracker Crystal Calorimeter Muon Stopping Target Muon Beam Stop Superconducting Production Solenoid (5.0 T – 2.5 T) Superconducting Detector Solenoid (2.0 T – 1.0 T) Superconducting Transport Solenoid (2.5 T – 2.1 T) Collimators Can it be done better, faster, cheaper elsewhere? Fermilab mu2e based on MECO design Single event sensitivity ~2x10 -17

14. 14 Can it be done better, faster, cheaper elsewhere?

15. 15 Can it be done better, faster, cheaper elsewhere? JPARC

16. 16 Can we use the high intensity provided by Project X?  - N → e - N at Project X is not yet studied in detail. Project X would eliminate any negative impact on neutrino program from proton economics. Muon beam intensity could be >10x what could be done earlier at Fermilab, more if muon beam techniques that are being pursued in context of muon collider studies can be used. Detector would require upgrades to improve rate-handling capabilities, resolution in measuring electron momentum. A phased approach starting with mu2e based on MECO design with sensitivity < 10 -16 starting before Project X and a goal of approaching sensitivity of 10 -18 is being studied. PRISM/PRIME approach could be studied in Fermilab context.

17. 17 The Physics Case for a mu to e conversion experimental now and after the start of the LHC Rates for CLFV processes in the SM plus massive Dirac neutrinos are expected to be vanishingly small. This is also true in the case of Majorana neutrinos if the new physics responsible for neutrino masses is close to the GUT scale (or very weakly coupled) -- Observation of CLFV in any channel implies the existence of new physics. In the case of new physics at the TeV scale, CLFV rates are generically expected to be very close to current experimental bounds. This is especially true given our current understanding of neutrino mixing (potentially mild mass hierarchies, large mixing angles).