James WestoverDan Linford

Background Production and Lifetime The Apparatus Discussion of our procedure and results Questions

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?

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 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?

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 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.

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 muon is going fast enough at the detector to be relativistic. So lets consider the problem a bit more generally.

Figure from http://hyperphysics.phy-astr.gsu.edu/hbase/Relativ/muon.html

RelativisticMuon

RelativisticGround

Non-Relativistic

Distance 2km 10km 10km

Time in microseconds 6.8 34 34

Half-lives 4.36 4.36 21.6

Surviving out of 1000000

49000 49000 .3

So what does each of these pieces do?

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.

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.

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.

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.

But the trouble was they were too frequent. Here is what the curve should have looked like:

Here is what our data looked like:

Part of the story got left out. The most likely explanation:

TDC Malfunction