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Muon Science Overview

Discover the groundbreaking research on muon-to-electron conversion including charged lepton flavor violation and related processes, with insights from R. Bernstein's work. Explore the rich history and promising future of muon physics.

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Muon Science Overview

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  1. Robert Bernstein Fermilab 30 June 2009 Muon Science Overview

  2. What is Muon-to-Electron Conversion? See Marciano et al., Annu. Rev. Nucl. Part. Sci. 2008. 58:315–41 • Muon converts to electron in the field of a nucleus: • Manifest Charged Lepton Flavor Violation • Related Processes: • m or t → eg, KL→me, and more • Searching at 6 X 10-17 at 90% CL • 104 improvement over existing limit DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  3. Al 1s state for m: • Bohr Radius ~ 20 fm • Radius of Al ~ 4 fm Experimental Signal 4 fm X 20 fm e- DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein • A Single Monoenergetic Electron • If Aluminum, Ee = 105. MeV • electron energy depends on Z of the Nucleus

  4. Who ordered that? (the question of flavor) (I.I. Rabi, 1936) After the μ was discovered, it was logical to think the μ is just an excited electron Expect BR(μ→eγ) ≈ 10-4 Unless another ν, in Intermediate Vector Boson Loop, cancels (Feinberg, 1958) DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  5. History of CLFV Searches DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  6. Processes Contributing to me Conversion DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  7. “Model-Independent” Picture DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  8. me Conversion and m→eg Project X Mu2e L(TeV) Mu2e 104 MEG 103 SINDRUM II MEGA k Mass Reach to ~104 TeV about x2 beyond MEG in loop-dominated physics Combination of experiments is powerful! DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  9. Mu2e, SUSY, and the LHC • Access SUSY through loops • Signal of Supersymmetry at LHC implies ~40 signal /0.4 bkg in Mu2e How does this play out in specific models? DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  10. Mu2e and Minimum Flavor Violation DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  11. Combining me Conversion and m→ eg me Conversion vs. m→eg MEG 10-11 me Conversion SINDRUM II 10-15 Mu2e m→eg 10-15 10-11 MEGA Mu2e MEG SO(10) models: C. Albright and M. Chen, arXiv:0802.4228, PRD D77:113010, 2008. DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  12. Endorsed by P5 in US Roadmap “The experiment could go forward in the next decade with a modest evolution of the Fermilab accelerator complex. Such an experiment could be the first step in a world-leading muon-decay program eventually driven by a next-generation high-intensity proton source. The panel recommends pursuing the muon-to-electron conversion experiment... under all budget scenarios considered by the panel” FNAL has proposed muon-electron conversion as a flagship program for the next decade DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  13. Accelerator Facilities at FNAL used by Mu2e • Booster • Accelerates protons to 8 GeV; used by NOnA as well • Recycler • Used by NOnA in 120 GeV program, and shared with Mu2e • Accumulator/Debuncher • Used in antiproton program; not needed after collider program ends, and Mu2e will adapt them to our needs DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  14. Why Fermilab 8 GeV Program? • Can re-use Accumulator/Debuncher complex after collider program ends (reduce, re-use, recycle!) • Fortunate coincidence: circumference of A/D ~ 1.7msec ~ muon lifetime • Mu2e does not interfere with NOnA • Uses Booster Batches NOnA can’t use • No conflict as at J-PARC with T2K vs. COMET or kaon program • Fermilab high intensity and bunched beam structure yield 104 improvement DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  15. Boomerang Scheme Mu2e Acc/Deb FNAL Main Injector And Recycler DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  16. Backgrounds Muon Total Lifetime = 864 nsec in Al 1/t = 1/t(capture) + 1/t(DIO) dN/dE ~10-17 within energy resolution ~10-17 within energy resolution (Emax- E)5 (Emax- E)5 g recoil tail 100 MeV nenm e- • Decay-In-Orbit: • if neutrinos have vanishingly small energy, the electron energy is the same as the conversion signal energy DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  17. Backgrounds, continued • Radiative p Capture: • Some pions don’t decay into muons are transported to the detector • Where they undergo capture, and the outgoing photon converts • The endpoint energy is mpand an asymmetric conversion can produce a 105 MeV e- DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  18. How Do We Manage Backgrounds? • DIO’s are handled by detector design, discussed later • Radiative p’s are managed by beam design: • FNAL’s pulsed beam is a key advantage over existing best experiment, SINDRUM, at PSI • The higher intensity of FNAL and the pulsed beam are the key reasons Mu2e is 104 better • After beam pulse, we wait 700 nsec for p’s to decay and other backgrounds to die out • And can’t have protons in between beam pulses at 10-9 : this is the extinction requirement DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  19. SINDRUM II • PSI beam is 10 nsec on, 10 off • Can’t wait for radiative p backgrounds to die off • Final SINDRUM-II on Au • Note Two Background Events beyond Signal Region DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  20. FNAL Pulsed Beam Time Structure 3 x 107 protons p’s arrive also and we wait for them to decay Recall tm= 864 nsec 700 nsec 1700 nsec DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  21. Overview of Experiment Three Superconducting Solenoids: Transport: select m- Detector: search for m-→e- conversions Production: create muons DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  22. Production Solenoid Initial protons Outgoing pions Muons into Transport solenoid 4 m x 0.3 m 8 GeV Protons in from left and strike target Producing p’s which decay into muons Graded field directs muons into transport solenoid DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  23. Transport Solenoid 13.1 m x 0.25 m “S”-shape splits m- from m+: in the curving solenoid,m- deflected up, m+ down Collimator eliminates m+ Second half brings m- back on-axis Thin window in center eliminates pbars DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  24. Detector Solenoid p = qBR low momentum particles and almost all DIO background (pT < 55 MeV/c) pass down center signal events pass through octagon of tracker and produce hits dN/dE Stopping Target (Al) ~10-17 within energy resolution (Emax- E)5 octagonal tracker surrounding central region: radius of helix proportional to momentum 100 MeV 10 m x 0.95 m DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  25. Expected Final Result: • For Rμe = 10-15 ~40 events / 0.4 bkg (LHC SUSY?) DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  26. What’s Next? Arbitrary normalization • Use Project X to • If a signal, study details of new physics: change Z of target • If not, push search up to two orders-of-magnitude DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  27. Muon Conversion Experiments and Project X • Project X can give us the intensity, • But for higher Z, muon lifetime is shorter: therefore must find some other way to eliminate radiative p background • But we need High Intensity Muon Beam Transport • e.g., helical cooling channels • AAC report mentioned Mu2e 54 times in report • If still searching, we will certainly need better resolution to eliminate Decay-in-Orbit backgrounds with higher intensity • Closely related to technologies for Neutrino Factories and Muon Colliders DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  28. Neutrino Factory, Muon Collider, and Mu2e Upgrades: New Design of Helical Cooling Magnet: Kashikhin-Yohehara at FNAL: HCC acceptance Mu2e acceptance Other schemes (see Shiltsev talk):Can we cool m+ and m-? DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein Just illustrative, not an endorsement!

  29. Thesis Topics • In Accelerator PhD Program: • Extinction Method • Extinction Measurement • Booster Upgrade • Slow Extraction with Large Tune Shift • … • In Conventional HEP/Nuclear Physics: • Mu2e Conversion with different reconstruction techniques • m-N(A,Z)→e+N(A,Z-2) (done by SINDRUM and interesting) • m+→e+e+e- (forming group to investigate) • Stopped Muon Rate • Shape and Normalization of DIO background • Radiative corrections to SM • Mu2e Normalization (nuclear capture) • Calibration Measurements • p+→e+n (monoenergetic line) • PSI stopped proton measurements • Detector Development • Good at foreign institutions DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

  30. Conclusions • Mu2e will either: • Reduce the limit for Rμe by more than four orders of magnitude (Rμe <6x10-17 @ 90% C.L.) • Rules out or sharply constrains many models • Discover unambiguous proof of Beyond Standard Model physics • In either case, Mu2e will provide important information either complementing LHC results or probing up to 104 TeV mass scales • With upgrades, we could extend the limit by up to two orders of magnitude or study the details of new physics • these upgrades are part of the path to a neutrino factory or muon collider DOE S&T Review, June 30 - July 2,2009: Muon Physics R. Bernstein

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