1. Kevin Lynch MuLan Collaboration Boston University CIPANP 2006 A new precision determination of the muon lifetime Berkeley, Boston, Illinois, ITU, James Madison, Kentucky, KVI, PSI

2. KRL, CIPANP, June 20062 Why measure the lifetime ? MuCap The Fermi Constant can be extracted from the free muon lifetime log(counts) time μ+μ+ μ – MuLan The lifetime difference with negative muons in hydrogen gives the nucleon pseudoscalar coupling

3. KRL, UIUC, 2006/05/17-193 Time for a new measurement? 18 ppm90 ppb< 1 ppm 1 ppm Mulan Goal

4. KRL, CIPANP, June 20064 Experimental Concept Create a “radioactive” source ● Electrostatically chopped muon beam ● 5 ms on – 22 ms off ● Muon beams are highly polarized ● Spin depolarizing/dephasing target environment ● Minimize materials between muon source and target

5. KRL, CIPANP, June 20065 Experimental Concept Surround it with a positron detector Create a “radioactive” source ● High rates demand pileup reducing design ● Highly segmented, symmetric detector ● 500 MHz flash waveform digitization

6. KRL, CIPANP, June 20066 Experimental Concept Create a “radioactive” source Surround it with a positron detector Build decay time histogram

7. KRL, CIPANP, June 20067 2004 Physics Results The 7-parameter fit function includes: ● The muon lifetime, ● A flat background, and ● An independently validated electronics oscillation (with low correlation to the lifetime) The analyzers are blind to the clock frequency

8. KRL, CIPANP, June 20068 Fit Consistency The fit residuals show no structure...

9. KRL, CIPANP, June 20069 Fit Consistency... an FFT of the residuals finds no structure...

10. KRL, CIPANP, June 200610 Fit Consistency... fit start and stop time scans show drift consistent with statistics... Results reported with an additional blind offset to protect analyzers from each other

11. KRL, CIPANP, June 200611 Fit Consistency... and a host of other variables argue for consistency of the global fit.

12. KRL, CIPANP, June 200612 Truth in advertising We've found at least one area of inconsistency, but we think we understand the source and are actively addressing the issue...

13. KRL, CIPANP, June 200613 Systematics Remain... ● Background flatness and stability ● PMT gain and timing stability ● Discriminator threshold stability ● PMT afterpulsing ● Instrumental backgrounds ● Dead time and pileup correction ● Residual Polarization and non-target stops

14. KRL, CIPANP, June 200614 Pileup Raw Spectrum Pileup Corrected Pileup Time Distribution Normal Time Distribution ● Same probability ● Statistically reconstruct pileup time distribution ● Correct and fit Correction large but controlled to better than statistical uncertainty

15. KRL, CIPANP, June 200615 Non-target stops

16. KRL, CIPANP, June 200616 Status ● 2004 Physics Analysis nearing completion ● Around 10 10 decays in data set ● 8 ppm statistics ● Should publish this fall ● 2005 Engineering Run validated the full experimental setup and collected about 10 11 decays ● 2006 Physics Run should collect about 10 12 decays ● 1-2 ppm statistics

17. KRL, CIPANP, June 200617

18. KRL, CIPANP, June 200618 A brief history... The last precision measurements are over 20 years old and ripe for improvement

19. KRL, CIPANP, June 200619 Fit Consistency Fits are also consistent across time...

20. KRL, CIPANP, June 200620 Fit Consistency... target material...

21. KRL, CIPANP, June 200621 Pileup Accuracy? Are we under or over correcting? Apply a scale factor to the pileup correction and measure the slope...

22. KRL, CIPANP, June 200622 Pileup Accuracy?... compare the zero slope crossing with the original correction; the discrepancy gives you a measure of the accuracy The pileup correction is well controlled, with a residual uncertainty well below the statistical uncertainty of the data set.