1. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys A Muon to Electron Experiment at Fermilab Eric Prebys Fermilab For the Mu2e Collaboration

2. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys R.M. Carey, K.R. Lynch, J.P. Miller*, B.L. Roberts - Boston University W.J. Marciano, Y. Semertzidis, P. Yamin - Brookhaven National Laboratory Yu.G. Kolomensky - University of California, Berkeley W. Molzon - University of California, Irvine C.M. Ankenbrandt, R.H. Bernstein*, D. Bogert, S.J. Brice, D.R. Broemmelsiek, R.M. Coleman, D.F. DeJongh, S. Geer, D.A. Glezinski, D.F. Johnson, R.K. Kutsche, M.A. Martens, S. Nagaitsev, D.V. Neuffer, M. Popovic, E.J. Prebys, R.E. Ray, V.L. Rusu, P. Shanahan, M.J. Syphers, R.S. Tschirhart, H.B. White Jr., K. Yonehara, C.Y. Yoshikawa – Fermi National Accelerator Laboratory K.J. Keeter, E. Tatar - Idaho State University P.T. Debevec, G.D. Gollin, D.W. Hertzog, P. Kammel - University of Illinois, Urbana-Champaign V. Lobashev - Institute for Nuclear Research, Moscow, Russia D.M. Kawall, K.S. Kumar - University of Massachusetts, Amherst R.J. Abrams, M.A.C. Cummings, R.P. Johnson, S.A. Kahn, S.A. Korenev, T.J. Roberts, R.C. Sah - Muons, Inc. A.L. de Gouvea - Northwestern University F. Cervelli, R. Carosi, M. Incagli, T. Lomtadze, L. Ristori, F. Scuri, C. Vannini - Instituto Nazionale di Fisica Nucleare Pisa M.D. Cororan - Rice R.S. Holmes, P.A. Souder - Syracuse University M.A. Bychkov, E.C. Dukes, E. Frlez, R.J. Hirosky, A.J. Norman, K.D. Paschke, D. Pocanic - University of Virginia J. Kane – College of William and Mary Mu2e Collaboration 2

3. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Acknowledgement This effort has benefited greatly from over a decade of voluminous work done by the MECO collaboration, not all of whom have chosen to join the current collaboration. 3

4. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Outline Theoretical Motivation Experimental Technique Making Mu2e work at Fermilab Sensitivities Future Upgrades Conclusion 4

5. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys General The study or rare particle decays allows us to probe mass scales far beyond those amenable to direct searches. Among these decays, rare muon decays offer the possibility of experimentally clean and unambiguous evidence of physics beyond the current Standard Model. Such searches are a natural part of the “Intensity Frontier”, which is being proposed for Fermilab after the end of the current collider program. In the case of muon conversion, we can take advantage of a great deal of work that has already been done in the planning of the Muon to Electron Conversion Experiment (MECO), which was proposed at Brookhaven. 5

6. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys  ->e CLFV in the SM Forbidden in Standard Model Observation of neutrino mixing shows this can occur at a very small rate Photon can be real (  ->e  ) or virtual (  N->eN) Standard model B.R. ~ O (10 -50 ) First Order FCNC: Higher order dipole “penguin”: Virtual mixing 6

7. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Beyond the Standard Model Because extensions to the Standard Model couple the lepton and quark sectors, lepton number violation is virtually inevitable. Charged Lepton Flavor Violation (CLFV) is a nearly universal feature of such models, and the fact that it has not yet been observed already places strong constraints on these models. CLFV is a powerful probe of multi-TeV scale dynamics: complementary to direct collider searches Among various possible CLFV modes, rare muon processes offer the best combination of new physics reach and experimental sensitivity 7

8. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Generic Beyond Standard Model Physics ? ? ? Flavor Changing Neutral Current Mediated by massive neutral Boson, e.g.  Leptoquark  Z’  Composite Approximated by “four fermi interaction” Dipole (penguin) Can involve a real photon Or a virtual photon ? ? ? 8

9. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Muon-to-Electron Conversion:  +N  e+N Similar to  e  with important advantages:  No combinatorial background  Because the virtual particle can be a photon or heavy neutral boson, this reaction is sensitive to a broader range of BSM physics Relative rate of  e  and  N  eN  is the most important clue regarding the details of the physics  105 MeV e - When captured by a nucleus, a muon will have an enhanced probability of exchanging a virtual particle with the nucleus. This reaction recoils against the entire nucleus, producing the striking signature of a mono-energetic electron carrying most of the muon rest energy 9

10. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys  e Conversion vs.  e  Courtesy: A. de Gouvea ? ? ? Sindrum II MEGA MEG proposal We can parameterize the relative strength of the dipole and four fermi interactions. This is useful for comparing relative rates for  N  eN and  e  10

11. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys History of Lepton Flavor Violation Searches 1 10 -2 10 -16 10 -6 10 -8 10 -10 10 -14 10 -12 1940 1950 1960 1970 1980 1990 2000 2010 Initial mu2e Goal   - N  e - N  +  e +   +  e + e + e - K 0    + e - K +    +  + e - SINDRUM II Initial MEG Goal  10 -4 10 -16 11

12. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Example Sensitivities* Compositeness Second Higgs doublet Heavy Z’, Anomalous Z coupling Predictions at 10 -15 Supersymmetry Heavy Neutrinos Leptoquarks *After W. Marciano 12

13. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Sensitivity (cont’d) Examples with  >>1 (no  e  signal):  Leptoquarks  Z-prime  Compositeness SU(5) GUT Supersymmetry:  << 1 Littlest Higgs:   1 Br(  e  ) Randall-Sundrum:   1 MEG mu2e 10 -12 10 -14 10 -16 10 -11 10 -13 10 -15 R(  Ti  eTi) 10 -13 10 -11 10 -9 Br(  e  ) 10 -16 10 -10 10 -14 10 -12 10 -10 R(  Ti  eTi) 13

14. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Decay in Orbit (DIO) Backgrounds: Biggest Issue Very high rate Peak energy 52 MeV Must design detector to be very insensitive to these. Nucleus coherently balances momentum Rate approaches conversion (endpoint) energy as (E s -E) 5 Drives resolution requirement. N Ordinary: Coherent: 14

15. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Previous muon decay/conversion limits (90% C.L.) Rate limited by need to veto prompt backgrounds!  >e Conversion: Sindrum II LFV  Decay: High energy tail of coherent Decay-in-orbit (DIO) 15

16. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Mu2e (MECO) Philosophy Eliminate prompt beam backgrounds by using a primary beam with short proton pulses with separation on the order of a muon life time Design a transport channel to optimize the transport of right-sign, low momentum muons from the production target to the muon capture target. Design a detector to strongly suppress electrons from ordinary muon decays ~100 ns ~1.5  s Prompt backgrounds live window 16

17. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Signal Single, monoenergetic electron with E=105 MeV, coming from the target, produced ~1  s (   Al ~ 880ns) after the “  ” bunch hits the target foils Need good energy resolution: ≲ 0.200 MeV Need particle ID Need a bunched beam with less than 10 -9 contamination between bunches 17

18. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys negligible 95.56 MeV10.08 MeV.0726  s~0.8-1.5Au(79,~197) 0.16 0.45 Prob decay >700 ns 104.18 MeV 104.97 MeV Conversion Electron Energy 1.36 MeV.328  s1.7Ti(22,~48) 0.47 MeV.88  s1.0Al(13,27) Atomic Bind. Energy(1s) Bound lifetime R  e (Z) / R  e (Al) Nucleus  Aluminum is nominal choice for Mu2e Choosing the Capture Target Dipole rates are enhanced for high-Z, but Lifetime is shorter for high-Z  Decreases useful live window Also, need to avoid background from radiative muon capture  Want M(Z)-M(Z-1) < signal energy 18

19. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys mu2e Muon Beam and Detector MECO spectrometer design for every incident proton 0.0025   ’s are stopped in the 17 0.2 mm Al target foils 19

20. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Production Region Axially graded 5 T solenoid captures low energy backward and reflected pions and muons, transporting them toward the stopping target Cu and W heat and radiation shield protects superconducting coils from effects of 50kW primary proton beam Superconducting coils Production Target Heat & Radiation Shield Proton Beam 5 T 2.5 T 20

21. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Transport Solenoid Curved solenoid eliminates line-of-sight transport of photons and neutrons Curvature drift and collimators sign and momentum select beam dB/ds < 0 in the straight sections to avoid trapping which would result in long transit times Collimators and pBar Window 2.5 T 2.1 T 21

22. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Detector Region 1 T 2 T Axially-graded field near stopping target to sharpen acceptance cutoff. Uniform field in spectrometer region to simplify momentum analysis Electron detectors downstream of target to reduce rates from  and neutrons Stopping Target Foils Straw Tracking Detector Electron Calorimeter 22

23. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Magnetic Field Gradient Production Solenoid Transport Solenoid Detector Solenoid 23

24. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Transported Particles E~3-15 MeV Vital that e- momentum < signal momentum 24

25. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Tracking Detector/Calorimeter 3000 2.6 m straws   (r,  ) ~ 0.2 mm 17000 Cathode strips   z) ~ 1.5 mm 1200 PBOW4 cyrstals in electron calorimeter   E/E ~ 3.5% Resolution:.19 MeV/c 25

26. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Sensitivity R  e = 10 -16 gives 5 events for 4x10 20 protons on target 0.4 events background, half from out of time beam, assuming 10 -9 extinction  Half from tail of coherent decay in orbit  Half from prompt Coherent Decay-in-orbit, falls as (E e -E) 5 26

27. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys A long time coming 1992MELC proposed at Moscow Meson Factory 1997 MECO proposed for the AGS at Brookhaven as part of RSVP (at this time, experiment incompatible with Fermilab) 1998-2005 intensive work on MECO technical design: magnet system costed at $58M, detector at $27M July 2005RSVP cancelled for financial reasons 2006 MECO subgroup + Fermilab physicists work out means to mount experiment at Fermilab June 2007mu2e EOI submitted to Fermilab October 2007LOI submitted to Fermilab Fall 2008mu2e submits proposal to Fermilab November 2008Stage 1 approval. Formal Project Planning begins 2010technical design approval: start of construction 2014?first beam 27

28. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Enter Fermilab  Fermilab  Built ~1970  200 GeV proton beams  Eventually 400 GeV  Upgraded in 1985  900GeV x 900 GeV p-pBar collisions  Most energetic in the world ever since  Upgraded in 1997  Main Injector-> more intensity  980 GeV x 980 GeV p-pBar collisions  Intense neutrino program  Will become second most energetic accelerator (by a factor of seven) when LHC comes on line ~2009  What next??? 28

29. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys The Fermilab Accelerator Complex MiniBooNE/BNB NUMI 29

30. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Preac(cellerator) and Linac “Preac” - Static Cockroft-Walton generator accelerates H- ions from 0 to 750 KeV. “Old linac”(LEL)- accelerate H- ions from 750 keV to 116 MeV “New linac” (HEL)- Accelerate H- ions from 116 MeV to 400 MeV 30

31. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Booster Accelerates the 400 MeV beam from the Linac to 8 GeV Operates in a 15 Hz offset resonant circuit Sets fundamental clock of accelerator complex From the Booster, 8 GeV beam can be directed to The Main Injector The Booster Neutrino Beam (MiniBooNE) A dump. More or less original equipment 31

32. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Main Injector/Recycler The Main Injector can accept 8 GeV protons OR antiprotons from Booster The anti-proton accumulator The Recycler (which shares the same tunnel and stores antiprotons) It can accelerate protons to 120 GeV (in a minimum of 1.4 s) and deliver them to The antiproton production target. The fixed target area. The NUMI beamline. It can accelerate protons OR antiprotons to 150 GeV and inject them into the Tevatron. 32

33. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Present Operation of Debuncher/Accumulator Protons are accelerated to 120 GeV in Main Injector and extracted to pBar target pBars are collected and phase rotated in the “Debuncher” Transferred to the “Accumulator”, where they are cooled and stacked Not used for NOvA 33

34. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Available Protons: NOvA Timeline Roughly 6*(4x10 12 batch)/(1.33 s)*(2x10 7 s/year)=3.6x10 20 protons/year available MI uses 12 of 20 available Booster Batches per 1.33 second cycle Preloading for NOvA Available for 8 GeV program Recycler Recycler  MI transfer 15 Hz Booster cycles MI NuMI cycle (20/15 s) 34

35. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Delivering Protons: “Boomerang” Scheme Deliver beam to Accumulator/Debuncher enclosure with minimal beam line modifications and no civil construction. Recycler (Main Injector Tunnel) MI-8 -> Recycler done for NOvA New switch magnet extraction to P150 (no need for kicker) 35

36. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Momentum Stacking Inject a newly accelerated Booster batch every 67 mS onto the low momentum orbit of the Accumulator The freshly injected batch is accelerated towards the core orbit where it is merged and debunched into the core orbit Momentum stack 3-6 Booster batches T<133ms T=134ms T=0 Energy 1 st batch is injected onto the injection orbit 1 st batch is accelerated to the core orbit T<66ms 2nd Batch is injected T=67ms 2 nd Batch is accelerated 3 rd Batch is injected 36

37. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys June 3, 2008 37 Booster-Era Beam Timelines for Mu2E Experiment Base line scenario. Numerous other options being discussed.

38. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Rebunching in Accumulator/Debuncher Momentum stack 6 Booster batches directly in Accumulator (i.e. reverse direction) Capture in 4 kV h=1 RF System. Transfer to Debuncher Phase Rotate with 40 kV h=1 RF in Debuncher Recapture with 200 kV h=4 RF system  t ~40 ns 38

39. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Resonant Extraction Exploit 29/3 resonance Extraction hardware similar to Main Injector  Septum: 80 kV/1cm x 3m  Lambertson+C magnet ~.8T x 3m 39

40. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Extinction in the Rings RF noise, gas interaction, and intrabeam scattering cauase beam to “wander out” of the RF bucket. D is the dispersion function:  Transverse Offset = ΔE/E × D Anticipate installation of collimator in region with dispersion, removing off- momentum particles:  Momentum scraping Mu2e/PAC Meeting - 5 March 2009 40

41. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys External Extinction (AC-Dipole Scheme) Possible change from baseline in proposal: two stage collimation  Dipoles at 0  and 360   Collimators at 90  and 180  Mu2e/PAC Meeting - 5 March 2009 41 Baseline design, single collimator

42. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Proposed Location Requires new building. Minimal wetland issues. Can tie into facilities at existing experimental hall. 42

43. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys What we Get Proton flux1.8x10 13 p/s Running time2x10 7 s Total protons3.6x10 20 p/yr   stops/incident proton0.0025   capture probability0.60 Time window fraction0.49 Electron trigger efficiency0.90 Reconstruction and selection efficiency0.19 Detected events for R  e = 10 -16 4.5 43

44. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Three Types of Backgrounds Muon decay in orbit:   → e  E e < m  c 2 – E NR – E B N  (E 0 - E e ) 5 Fraction within 3 MeV of endpoint  5x10 -15 Defeated by good energy resolution Radiative muon capture:   Al →  Mg  endpoint 102.5 MeV 10 -13 produce e - above 100 MeV 1. Stopped Muon Induced Backgrounds 44

45. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Backgrounds (continued) 2. Beam Related Backgrounds Suppressed by minimizing beam between bunches –Need ≲ 10 -9 extinction –(see previous slides) Muon decay in flight:   → e  Since E e 77 GeV/c Radiative   capture:   N → N* ,  Z → e  e  Beam electrons Pion decay in flight:   → e  e 3. Asynchronous Backgrounds Cosmic rays suppressed by active and passive shielding 45

46. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys The Bottom Line Roughly half of background is beam related, and half interbunch contamination related Total background per 4x10 20 protons, 2x10 7 s:0.43 events Signal for R  e = 10 -16 :5 events Single even sensitivity: 2x10 -17 90% C.L. upper limit if no signal:6x10 -17 Blue text: beam related. 46

47. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Present areas of research Beam delivery schemes  Try to minimize charge in Accumulator at one time.  Generally a trade-off that increases instantaneous rate. Recalculating rates and backgrounds  Models and data on low energy pion production have come a long way in recent years. Optimizing magnet design  Original design based on SSC superconductor, which has since mysteriously vanished.  Is magnetic mirror worth it? New detector options  Investigating low pressure drift chamber Similar mass and less probability of fakes Calibration schemes  How can we convince the world we can measure something at a < 10 -16 BR? Siting optimization and synergy with other programs  g-2  Muon collider R&D 47

48. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Possible Future: “Project X” One 5 Hz pulses every 1.4 s Main Injector cycle = 2.1MW at 120 GeV This leaves six pulses (~860 kW) available for 8 GeV physics These will be automatically stripped and stored in the Recycler, and can also be rebunched there. 48

49. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Accelerator Challenges for using Project X beam Beam delivery  Accumulator/Debuncher (like initial operation)? How much beam can we put into the Accumulator and Debuncher and keep the beam stable? Radiation issues (already a problem at initial intensities).  Directly from Recycler? Not enough aperture for conventional resonant extraction. Investigating more clever ideas 49

50. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Experimental Challenges for Increased Flux Achieve sufficient extinction of proton beam.  Current extinction goal directly driven by total protons Upgrade target and capture solenoid to handle higher proton rate  Target heating  Quenching or radiation damage to production solenoid Improve momentum resolution for the ~100 MeV electrons to reject high energy tails from ordinary DIO electrons.  Limited by multiple scattering in target and detector planes  Requirements at or beyond current state of the art. Operate with higher background levels.  High rate detector Manage high trigger rates All of these efforts will benefit immensely from the knowledge and experience gained during the initial phase of the experiment. If we see a signal a lower flux, can use increased flux to study in detail  Precise measurement of R  e  Target dependence  Comparison with  e  rate 50

51. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys However, the future has some uncertainty! (from Dep. Director Y-K Kim) 51

52. High Energy Physics Seminar, Princeton University, April 15, 2009 E Prebys Conclusions We have proposed a realistic experiment to measure Single event sensitivity of R  e =2x10 -17 90% C.L. limit of R  e <6x10 -17 This represents an improvement of more than four orders of magnitude compared to the existing limit, or over a factor of ten in effective mass reach. For comparison –TeV -> LHC = factor of 7 –LEP 200 -> ILC = factor of 2.5 Potential future upgrades could increase this sensitivity by one or two orders of magnitude ANY signal would be unambiguous proof of physics beyond the Standard Model The absence of a signal would be a very important constraint on proposed new models. 52