Transcript Lifetime of Cosmic Muon - University of Rochester

James Westover
Dan Linford
LIFETIME OF COSMIC MUON
OUTLINE
Background
 Production and Lifetime
 The Apparatus
 Discussion of our procedure and results
 Questions

BACKGROUND
What is a Muon?
 It’s an elementary particle.
 It’s a lepton with the same charge as an
electron.
 Discovered by Carl D. Anderson in 1936
 But cosmic Muon why cosmic?

COSMIC MUONS
Muons are massive 105MeV/c^2
 Radioactive decay, Nuclear fission, and Nuclear
fusion are not energetic enough to produce
particles of that mass.
 So if these processes cannot produce muons
then how are they produced?

COSMIC RAYS AND PRODUCTION OF MUONS
Cosmic rays consist primarily of protons.
 Those protons strike nuclei in the upper
atmosphere.
 Which form Pions which quickly decay within
meters into Muons and Neutrinos.
 So Pions decay quick. So how long do these
Muons hang around?

LIFETIME
Previous experiments put Muons lifetime at a
value of 2.2 microseconds.
 The atmosphere is about 10 km thick.
 So even at c they could only make it 660
meters!
 So how could we observe them at sea level?

SPECIAL RELATIVITY

Special relativity allows for time dilation.
This effect is only significant for fast moving
objects.
 Lets get an idea of what that speed is at the
detector.

THE NUMBERS

If we are going to use a relativistic effect we
should verify that our particle is traveling close
to c

So we are in the right ballpark.
THE NUMBERS CONT’D
The muon is going fast enough at the detector
to be relativistic. So lets consider the problem a
bit more generally.
 Figure from http://hyperphysics.phyastr.gsu.edu/hbase/Relativ/muon.html

SUMMING IT UP
Distance
Time in
microseconds
Half-lives
Surviving out of
1000000
Relativistic
Muon
Relativistic
Ground
Non-Relativistic
2km
10km
10km
6.8
34
34
4.36
4.36
21.6
49000
49000
.3
THE APPARATUS
So what does each of these pieces
do?
SCINTILLATOR
A scintillator is a substance that absorbs high
energy charged particles then, in
response, fluoresces photons.
 Our scintillator was connected directly to a
photomultiplier which converts the photons to
an electrical signal which reflect in voltage the
energy of the photons.

DISCRIMINATOR
Takes the signal from the scintillator and picks
out pulses based on their voltage.
 Then re-emits a pulse of a defined width.
 This device is essential to separating the muon
events from the gamma events which are much
more frequent.

TDC
The TDC is the interface between the computer
and the discriminator.
 The computer uses a program which uses the
output of the discriminator to start, stop, and
reset a sensitive timer.

DISCUSSION ABOUT EXPERIMENT
Setting up the apparatus and tuning it properly is
challenging.
 After careful work using an oscilloscope to check
each piece we got a result much like this.
 After that point we let the TDC start collecting
more data to try and tune the additional
parameters in the program. After much trial and
error with the discriminator settings and those
parameters we got a setting that yielded frequent
results of 2.2 microseconds.

HERE COMES TROUBLE
But the trouble was they were too frequent.
Here is what the curve should have looked like:
 Here is what our data looked like:

WHAT WENT WRONG?
Part of the story got left out.
 The most likely explanation:

 TDC
Malfunction
QUESTIONS?