MUON EXPERIMENT

Xinjun Guo

Dec. 16, 2009

Cosmic Rays

Primary: protons( ), light nuclei

Secondary: , , others

Decay product: , ,

K

e

%79

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 .

sm2/240

GeV2

s/25ms40

Muons lose energy: Muons stopping in scintillators

, of the flux going through the

detector, namely, stopping rate .

Mean liftime:

2/2 gcmMeV

MeV50%3.0

s/077.0

s 00004.019703.2

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.

2nst 20

s

t

tnPR aa /0073.0

,

Measurement without coincidence

Calibration

Measurement without coincidence

Background rate

CtNtN o /exp()(

6.133

2641

)024.0

C

N

s

o

sRa /0089.0min5000

206.133

Measurement with coincidence

Measurement with coincidence

Background rate

CtNtN o /exp()(

8.125

2570

)015.0121

C

N

s

o

sRa /0056.0min7500

208.125

Correction for Muon lifetime

Capture reaction: The effective mean lifetime is shortened, The corrected measured value in this

experiment is .

*)1(ZZ

ce

111

s

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.

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.

Reference

1. Muon Experiment, Lab Manual,2. A. Melissinos, Experiments in Modern

Physics, Academic Press, New York(1996)

3. Zhen Ye, Muon Experiment Lab Report4. T. K. Gaisser, T. Stanev, Cosmic Rays,

Particle Data Group website5. Wikipedia

Thank you!