A muon Veto for the Ultra-Cold Neutron Asymmetry Experiment Vince Bagnulo

A Muon Veto for the Ultra-Cold Neutron Asymmetry Experiment

• Vince Bagnulo

• LANL Symposium 2006

UCNA Experiment

What are cosmic ray muons?

• Muons are a fundamental particle, very similar to electrons, but heavier (m = 207 me)

• Cosmic rays are high- energy particles, mainly protons, from the sun and extra-solar sources

• Cosmic rays impinge on Earth's atmosphere, causing cascade of secondary particles – including muons

• At ground level, cosmic ray muons have the following parameters: - E  4 GeV - angular distribution  cos2() - flux  1 muon/ cm2/ min

Correcting for Muon Background

Proposed Muon Veto

• Goal: Intercept cosmic ray muons that will impinge on primary detectors with efficiency of at least 90%

• Solution: Surround primary detectors with plastic scintillator detectors:

Scintillator Detectors

• Scintillator re-emits energy deposited by ionizing radiation in the form of visible light.

• Visible light photons transmitted to photomultiplier tube (PMT) through use of total internal reflection

• A photomultiplier tube (PMT) attached to the plastic scintillator converts the light to an electronic signal and amplifies it

Initial State (beginning of summer 2006)

• One prototype muon veto paddle constructed

• Challenges: - veto paddles constructed out of salvaged scintillator (effectiveness uncertain) - PMTs located in 30 gauss field - scintillator paddles are large and unwieldy

My Task

• Measure efficiency of prototype veto paddle as a function of position: - establish testing procedure - help evaluate quality of scintillator

• Help evaluate feasibility of plastic scintillator veto concept

• Build production veto paddles

Developing a Testing Method

• Efficiency = detected muons/ incident muons

• Used cosmic ray muons to test efficiency

• Using one trigger paddle found efficiency  0%

• High singles rate due to gamma background:

Testing Method

• Add second trigger paddle and required coincidence to lower background

• Estimate double Compton scattering could occur to 0.1 - 1% of background gammas

• Two trigger paddle coincidence rate: 4.0 Hz

• Expected: 3.33 Hz

• Still not sufficient. Three trigger paddles might be necessary

Testing Results (two trigger paddles)

Conclusion

• Currently, performance of prototype veto paddle is not sufficient

• A new paddle is being constructed and will be tested

• If satisfactory, remaining paddles will be constructed

• If not, alternative methods of carrying out veto will be investigated