ExperimentFAQ

Mu2e Newcomer FAQ: Physics and the Experiment

What is Mu2e trying to measure?
Mu2e is an experiment designed to measure the conversion of a muon into an electron (in the field of the nucleus) without the emission of the neutrinos. In the standard model, lepton conservation tells us that when a muon decays to an electron there should be an accompanying muon neutrino to conserve muon number in the decay and an anti-electron neutrino to conserve electron number.

Why put gold on the inside of the drift tubes and not copper?
Our first prototype tubes had copper on the inside but oxidation was quicker than previously thought. Copper oxides are generally insulating. An accumulation of charge on the tube inner walls will cause a spark and destroy that tube and probably neighboring tubes. Gold doesn’t oxidize and is very conductive. It should be noted that gold and aluminum from a compound at room temp., Au5Al2 , which is ~10 times less conductive than gold. A study showed that Au5Al2 is also okay.

What physics beyond the Standard Model could the experiment be sensitive to?
SUSY, etc. here for a test

Where did the idea originate? -- answer needed
testing

What competing and complementary measurements are being done by other experiments and what is the current best limit?
testing

Where do the muons come from?
testing

Why does the TS have two bends instead of one
The first bend separates positive and negative particles, negative goes up and positive goes down. In the middle section between the bends, upper part of beam goes through while lower part gets absorbed. Now the beam is primarily negative particles and it is slightly high. The second bend, realigns the beam by bringing it down to axis.

Why does the production target have fins?
The target heats up because of the proton beam. The temperature to which the target reaches is high enough to make the target sag. If part of the target is not on axis due to sagging, our pion and thereby muon yield is reduced. The fins add to rigidity (structural integrity) and increase radiative cooling. (link to docdc-doc)

What is the dead time of the CRV?
The dead time is about 3% (As of July 11, 2018). (link to doc)

Why use muons and not taus, don’t taus have lower rates than muons in many new physics models?
Yes, the taus have much lower rates, however, • They are more difficult to produce and harder to control. In mu2e we produce 10¹¹ muon per second, taus are produced ~ 10^¹⁰ per year. • Also, with muon to electron conversion, the standard model background rate is ~ 10^^-54 while the background for taus is ~10^-14. Background for mu2e is over 35 orders of magnitude away while taus are only 4-5 orders of magnitude away from the reach of the next generation of experiments (Belle II).

If the field is only along the axis of the transport solenoid (TS) what makes the muons direction of motion follow the bends of transport solenoid (TS)?
From Lorentz Force law, we can see that the plane of rotation is always perpendicular to the magnetic field direction. As the B-field changes orientation, so does the plane of rotation and hence forth the direction of the muon as is goes through the TS.

What are the primary experimental challenges?
testing

How can I learn more about the experiment?
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HELP! What does that acronym mean?
Muon to electron

How is the Project organized?
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How is the Collaboration Organized?
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How do collaborators communicate?
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Where can documentation be found?
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