1. Xinjun Guo Dec. 16, 2009

2. Cosmic Rays  Primary: protons( ), light nuclei  Secondary:,, others  Decay product:,,

3. Muons  Mean energy near the ground:  Total flux crossing unit horizontal area:  The singles rate crossing the scintillator is, and the mean time between counts is.

4. Muons lose energy: Muons stopping in scintillators, of the flux going through the detector, namely, stopping rate. Mean liftime:

5. Accidental stops If the singles rate is too high, then the stop pulse may not be due to the decay of the muon that started the TAC, but to a different muon entering the scintillator. Using the Poisson distribution for and, we find the accidental rate, which is ten times smaller than the stopping rate, and does not affect the determination of the mean life.

6. Measurement without coincidence

7. Calibration

8. Measurement without coincidence Background rate

9. Measurement with coincidence

10. Background rate

11. Correction for Muon lifetime Capture reaction: The effective mean lifetime is shortened, The corrected measured value in this experiment is.

12. Conclusion By collecting muon decay events using two methods, we get two mean values for the mean lifetime, both of which are close to the value published. We can also see that the value obtained with coincidence technique is more accurate.

13. Acknowledgement I am pleased to have Ares as my experimental partner all through this semester. I would also like to give my thanks to Dean, Gaitskell, Bob, Angus and Terri for their great help in the experiment.

14. Reference  Muon Experiment, Lab Manual,  A. Melissinos, Experiments in Modern Physics, Academic Press, New York(1996)  Zhen Ye, Muon Experiment Lab Report  T. K. Gaisser, T. Stanev, Cosmic Rays, Particle Data Group website  Wikipedia

15. Thank you !