# What is the meaning of the term 'prompt muon'?

1. Nov 28, 2015

### Anchovy

In the context of cosmic rays?

2. Nov 28, 2015

### Staff: Mentor

3. Nov 28, 2015

### Anchovy

Ahh, good find. So there are short-lived particles containing c quarks in the atmosphere (which ones specifically and what are they doing there in the first place?) that rapidly decay (hence 'prompt') to muons.

And these muons arrive at the surface with no directional preference... but I'm not fully clear on why... The $\pi, \hspace{1 mm} K$ that decay to produce the usual atmospheric muons might approach from wide zenith angles, and must therefore pass through much more atmosphere than those from small zenith angles, thus scattering more before they decay... but the parent particles of the prompt muons barely pass through any atmosphere regardless of angle... so they don't tend scatter before they decay? And the muons themselves don't scatter much once they've been created?

4. Nov 28, 2015

### Staff: Mentor

High-energy collisions can produce heavy quarks, typically as quark+antiquark pair.

Those muons also have a directional preference (most notably, they don't go up), but the angular dependence is different from the normal processes. Their higher typical energy might be related to it.

5. Nov 28, 2015

### Staff: Mentor

I'm not familiar with cosmic-ray studies. However, a long time ago I had a small involvement with an accelerator-based "beam dump" experiment in which a high-energy proton beam was sent into a block of metal. Among the many particle-antiparticle pairs produced in such interactions are some charm-anticharm pairs which produce prompt muons. I suspect you have a similar situation with high-energy cosmic-ray interactions.

(edit: mfb beat me to it while I was typing.)

6. Nov 28, 2015

### Anchovy

OK thanks guys.