A 1 ppm measurement of the positive muon lifetime

1. A 1 ppm measurement of the positive muon lifetime Qinzeng Peng Advisor: Robert Carey Boston University October 28, 2010 MuLan collaboration at BU: Robert Carey, James Miller, Lee Roberts, Kevin Lynch, Justin Phllips, William Earle Institutes: BU, UIUC, Univ. of Kentucky, JMU

2. Outline • Motivation and theory • MuLan experimental set up • 2006 data analysis • Systematic errors • Final results

3. MuLan Input parameters to the standard model and their precision measurements • The CKM mixing matrix • The masses of fermions and Higgs boson • 3 parameters to determine the strength of the interaction and the masses of the weak gauge bosons • Fine structure constant α • Z-boson massMZ • Fermi constant GF 0.71 ppb 23 ppm 8.6 ppm

4. Fermi Constant and g Contains all weak interaction loop corrections

5. Fermi Constant and τμ Contact interaction from Fermi theory Radiative corrections (maily QEC) In 1999, van Ritbergen and Stuart completed full 2-loop QED corrections reducing the uncertainty in GF from theory to < 0.3 ppm (it was the dominant error before)

6. A Graphical History of the Muon Lifetime Measurements

7. Experimental Concept • Traditional method: 1 muon decay each time • MuLan method: n muons decay each cycle need pulsed muon beam  kicker Accumulation period Measurement period -12.5 kV +12.5 kV

8. Experimental Setup • beam line • kicker • detector ball • WFD • DAQ • monitoring devices

9. Kicker • 2 sets of parallel plates • inside the vacuum pipe • high voltage at +/- 12.5 KeV • fast transition time (60 ns)

10. Target • Ferromagnetic target to dephase muons’ polarization during accumulation period. Polarization is both depolarized and dephased. • Arnokrome-3 (AK3) Target (~28% chromium, ~8% cobalt, ~64% iron) • 0.5 T internal magnetic field • Muons arrive randomly during 5 us accumulation period • Muons precess by 0 to 350 revolutions

11. Muon Corridor • Errant muons => vacuum pipe • AK-3 Target inside the pipe • AK3 liner

12. Target rotates out of beam Entrance Muon Counter to monitor beam profile

13. MuLan Detector Ball • 170 detector pairs = 20 hexagons + 12 pentagons

14. Detector elements

15. Waveform digitizer 2 Analog Pulses WFD 1 WFD 2 Anlog signal => Digitized samples ( ampitude and time)

16. More than 1012 muon decays in 2006 run >1 x 1012 coincidence pulses in 2006 data set >65 TBytes raw data

17. Data analysis • 3-parameter fit • 4-parameter fit • Artificial pile-up construction

18. Systematic studies • Early to late stability during 22 μs measuring period • Kicker stability • Background stability • Timing stability • Gain stability

19. Timing stability – with laser system • Need reference time, • Laser pulse is narrower than normal pulse • Reference PMT is NOT contaminated with experimental background

20. Laser system setup

21. Laser runs • 24 tile laser channels • 3305 laser runs in 2006 => 5E6 hits per channel • Combine the runs to study dt vs. time => 1.6E6 hits needed for 0.5 ppm error.

22. dt vs. run stability the scale of change is about 0.02 clock ticks In single run sigma of dt=0.13 clock ticks (in next slide)

23. Multi peaks combination

24. dT vs. time, single channel

25. dT vs. time, 24 channels c.t per c.t. Mean = -5E-9 c.t. per clock tick is close to 0 RMS = 6E-8 c.t. per clock tick as the timing shift Timing shift error: 0.06 ppm

26. Timing stability • Timing is pretty stable for MuLan experiment, at 0.1 ppm level

27. Gain stability • Gain shift == threshold shift • Gain shift => number vs. time shift • <amplitude> vs. time is studied

28. Gain shift to lifetime shift

29. Run selection Better region big fluctuation from run 33282 to 54318(index 1 to 225) slight change (10 ADC) from run 54330 to 55428 (index 225 to 400) Sigma of amplitude of single run is 10 -15 ADC

30. Ratio method • Ratio of amplitude of tile pulse to amplitude of the reference PMT • Ratio of amplitude of time bin I to amplitude of the last time bin

31. d(amp)/amp = (108-98)/98=0.1 d(amp_ratio)/amp_ratio = (0.68-0.655)/0.655 = 0.0382

32. Slope of ratio_bin_i vs. run – flat distribution

33. <ratio_bin_i> vs. time

34. 24 channels combined d(dG/G)/dt = 5E-5 per tau

35. Counts shift due to threshold change dN/N ≈ 3 x 10-4 for 1 ADC change in threshold

36. conclusion • Amp vs. time < 1 ppm

37. WFD Pulse Fitter Algorithm

38. Foucs on neighboring pulses

39. Test of PFA • Pile on effect, signal region and pedestal region

40. Effect of small pile on

41. Effect of pile on near threshold

42. Change vs. amplitude of pile on

43. Estimated pull of timing

44. B   MuSR effect • MuSR rotation results in an oscillation of the measurement probability for a given detector. B = 34 G

45. MuSR relaxation results in a reduction of the polarization magnitude.

46. The sum cancels muSR effects the difference accentuates the effect. counts arb. B   counts arb. Sum Difference/Sum counts arb.

47. conclusions • Timing shift => 0.1 ppm • Gain shift => < 1 ppm • PFA => < 0.1 ppm