Measurement of the Positive Muon Lifetime to 1 ppm

1. Measurement of the Positive Muon Lifetime to 1 ppm David Webber Preliminary Examination March 31, 2005

2. Outline • Basics and theory • How is the muon lifetime measured? • MuLan experiment’s main components • Systematics and design considerations • Analysis cross-checks • Personal contribution • Conclusion

3. Basics Log(counts) time

4. Why is the muon lifetime important?

5. Why is the muon lifetime important? + … + … The theoretical uncertainty on GF as extracted from the muon lifetime is < 0.3 ppm.

6. Why is the Muon Lifetime Important? 9 ppm 0.06 ppm The goal of the Muon Lifetime Analysis (MuLan) experiment is to reduce the experimental uncertainty on GF to 0.5 ppm by measuring the muon lifetime to 1 ppm. …it is extremely difficult to predict, even in the relatively short term, the accuracy to which fundamental parameters will be determined and it is important that these be extracted to the limits that the current theoretical and experimental technology allows. (Ritbergen and Stuart, hep-ph/9904240)

7. How is the muon lifetime measured? N=1

8. How is the muon lifetime measured? N=10

9. How is the muon lifetime measured? N=100

10. How is the muon lifetime measured? N=100

11. How is the muon lifetime measured? N=104

12. How is the muon lifetime measured? N=106

13. How is the muon lifetime measured? N=1012

14. How long will it take? • ~1012 events necessary for 1 ppm measurement Source Muon rate Time to 1012 m+ Cosmic rays 1 / 50 cm2 s 1 / hand s ~104 years e+ Scint. PMT p+ Continuous beam 20 kHz ~1.6 years beam time m+ PMT PMT Water e+ Pulsed beam (usable) ~ 3 weeks beam time

15. BEAM m+ DETECTORS DIGITIZERS DAQ #4 The MuLan Experiment

16. The MuLan Experiment - Beamline • Key Beamline Elements • Production target • Separator • Kicker • Entrance muon chamber • Depolarizing target

17. The MuLan Experiment - Detector

18. 2 Analog Pulses The Mulan Experiment – Readout Plan for 2005-2006 runs Waveform Digitizers x2

19. Systematics Early-to-late systematics • Clock stability • Pileup • 2 pulses appear as one • Muon spin precession • Others • Sneaky muons • Instrumental changes • Kicker noise “early” “late” The most dangerous systematic effects occur “early-to-late”

20. Clock Stability • A single clock drives the waveform digitizers • The clock is tunable, and the analyzers only know the 4 most significant digits (500 ppm)

21. Pileup Reduction • Highly segmented detector (170 detector pairs) • Analog readout by waveform digitizers • Depolarize the collected muons

22. Good Pulse Phototube Breakdown The importance of waveform digitizers • Identify false pulses • No missed pulses from pileup • Pileup identification vs. Pulse Area (outer) 2 pulses become 1 large pulse Pulse Area (inner)

23. Muon Spin Precession • Muons are highly polarized and can remain so when they stop in the target • Muon decay violates parity • Muons precess in a magnetic field. • Example: the Earth’s magnetic field will change the preferred decay direction by one detector in one muon lifetime

24. Front Back Silver Target Muon Spin Precession - Fixes • Point-like symmetric detector ball • Depolarizing target • Sulfur has ~8% residual polarization • Arnokrome-3 (30% chromium, 10% cobalt, 60% iron) has 0.5 T internal field • Ring magnet on sulfur dephases ensemble during accumulation

25. Cross-Checks • Multiple identical detectors • LED system • Test-fire the detector • Check for timing shifts • Stable clock system • Blind analysis • Analysis checks • Start-time scan • Stop-time scan Plots courtesy: D. Chitwood

26. Personal Contribution

27. MULAN Continuous Data Acquisition Waveform Digitizer frontends fiberoptic Waveform Digitizers fiberoptic TDC frontend Ball Discriminators TDCs ADC/SCALER # fills protons hits in detector Online Monitor camac CAMAC frontend fiberoptic Flight Simulator frontend Ethernet PSI Archive LED Drivers Flight Simulators serial port High Voltage frontend High Voltage RAID and TAPE: Data Storage and Offline Analysis Gigabit Switch Backend Entrance Muon Chamber fiberoptic EMC frontend Discriminators TDCs Marker Pulses enhanced parallel port Kicker Programmable gate generator Programmable gate generator frontend infinite persistence scope Note: Yellow – Frontend programs Green – Frontend computers Beamline frontend Beamline network Muon Production Target

28. The MuLan Experiment - Software “Good” “2 AM Phone Call”

29. High-rate, Entrance Muon Chamber I helped design the green boards (above), commissioned the chamber and readout electronics (above right), and wrote the real-time online beam profiler to the right.

30. Conclusion • Basics of muon decay • The MuLan experiment • Systematics • Personal contribution • Last muon lifetime measurements  1984 • Muon decay gives best determination of GF • Muon lifetime gives the dominant error onGF • It is time to measure the muon lifetime again

31. Thank you!

32. References • Ritbergen and Stuart, hep-ph/9904240. • Chitwood, Dan. “Measuring the Positive Muon Lifetime to 1 ppm.” Preliminary Exam Paper. September 23, 2002. • R. M. Carey et al. MuLan Proposal. http://www.npl.uiuc.edu/exp/mulan/proposal/MuLan.ps

33.  5 mLan goal History of the Muon Lifetime

34. Positron Michel Sprectrum Michel Spectrum Relative Intensity 53 MeV Positron energy

35. Why is the Muon Lifetime Important?

37. Model-independent extraction of GF General Analysis Restricted Analysis

38. Other “Early-to-Late” Effects • Sneaky Muons • Fix: Entrance Muon chamber • Instrumental Changes • Fix: LED test-firing system • Kicker Noise • Recently reduced by 103 • Under investigation

39. 2 Analog Pulses The Mulan Experiment – Readout Now 2 Analog Pulses Discriminator Time to Digital Converter 20-bit time word Planned for 2005-2006 Runs Waveform Digitizer

40. What is the Muon Lifetime?