THE MUON IAN BRUBAKER

DR. DARREL SMITH

• Upper Atmosphere Collisions

• Proton- nucleus collisions in

the upper atmosphere create

pos. & neg. pions

• After pions decay ~15km above the Earth’s surface, muons are created

• The process for a pion decay is:

HOW ARE MUONS CREATED?

( ) ( )or

• How do the Particles reach us?

• The muon decay times can range from

a few nanoseconds to 12 µs

• Mean lifetime is = 2.2 µs

• Knowing the muon travels near c, let’s do a quick

calculation

Then, how do the muons reach the

earth’s surface?

The answer is time dilation. t = g to

tµ

RAINING DOWN TO EARTH

6 8(2.2 10 ) (3 10 / ) 660s m s m

The scintillator absorbs

the energy lost by the

muon and produces light

omni-directionally.

• Some muons will lose all

their kinetic energy and

"come to rest” inside the

detector.

• 2 pulses of light occur; the

first pulse when the muon

comes to rest; the second

pulse when it decays.

HOW DO WE OBSERVE THE MUONS?

µ plus decay:

5 gallon bucket containing CH2 doped with liquid scintillator

AN INTERLUDE FOR THE PMT

• 2 photo multiplier tubes (PMTs) were used for the experiment and a base was

created specifically for our PMT model.

• 2 PMTs were used to reduce “false signals” due to noise

• Specifics for our PMTs

• Hamamatsu R2083 2” flat-faced PMT.

• No bases are manufactured for these tubes.

• Students built the bases and circuit boards.

• Voltage divider circuit with 50W termination.

• Typical Vop = 1900 volts Gain ~ 3x105

• Typical rise times ~ 1.0 ns

BLUE LED PULSER

“Simple techniques for generating nanosecond blue light pulses from

light emitting diodes.” Omar Veledar, et al. 2007 IOP Publishing Ltd.

• Students built the circuit (Fig. 4 plus circuit “a”) and connected

it to a frequency generator.

• It generated low light levels (by varying Vcc) to measure the single pe

response of the PMT.

LED

LIGHT PRODUCTION + QUANTUM EFFICIENCY

Where the PMT is most sensitive

Hamamatsu R2083 EJ-321H Liquid Scintillator

Scintillator produces maximum light ~ 420 nm

The pulses collected from the PMTs are sent to a discriminator

to create a digital pulse which is sent to a logic gate…

COLLECTING DATA

Trigger logic with digital

pulses

The digitized pulses are then sent to the oscilloscope (PicoScope).

The PicoScope displays the following

output. We export the pulse times and

analyze the lifetimes of thousands of

stopping-muon events.

COLLECTING DATA CONTINUED

∆t

Trigger pulse

from logic gate

OUR DATA

*Note the mean lifetime is

not the accepted 2.2µs

/tAe ct

/tAe ct

Function for out fit line:

The data was taken over

261.5 hours

passing µ/sec

stopping µ/sec

5.6 .008

3 56 10 8.6 10

WHAT SKEWS THE MEASURED LIFETIME?

• Keep in mind, the particles spend some of their lifetime outside of the detector.

p n g

The µ minus in matter, matters

µ minus radiative capture

When a negatively charged muon comes to rest in our detector, it can be captured

into the K shell of a carbon atom thus affecting its lifetime.

Adding to the fit We will replace our constant “C” in the fitting equation with

the term shown to right since the captured µ minus has a

different lifetime tc. / ctBe

t

1 1 12.06

meas cap

s

t t t

WHAT IS NEXT?

• In the immediate future, we plan to measure the radiative muon capture rate

• This will be accomplished by extending our baseline time measurement from 9µs to

150µs to measure the lifetime of the captured µ minus.

• We will also determine the charge ratio of the muons being observed

Charge Ratio =

obs

obs

N

N

t tt

t t t

THE MICHEL SPECTRUM

( )ee

Endpoint Energy = 52.8MeV

Future experiments will measure the Michel

spectrum of the muon

Michel electron

This isn’t our plot,

but it should look

something like this.

THANK YOU! QUESTIONS?