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

[Anchovy]

In the context of cosmic rays?

 

[mfb]

Google knows the answer:

Muons resulting from charmed particle decays and other so-called prompt or direct processes, often referred to as X-processes, do not manifest the zenith angle dependence which is characteristic for muons from so-called normal processes, i.e., from pion and kaon decays

 

[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?

 

[mfb]

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.

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.

 

[jtbell]

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?)

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.)

 

[Anchovy]

OK thanks guys.