[Physics] What’s the meaning of “non-prompt” particle


I am currently studying methods for fake-rate determination, and as a source of the so-called reducible background "non-prompt" leptons coming from decays of heavy-flavor mesons & mis-reconstructed jets are mentioned.

What are "non-prompt" leptons?

Best Answer

As mentioned by knzhou, a prompt lepton is a lepton originating from the main collision taking place in the event, as a direct product of the particular decay you're after. An analysis looking for a particular final state containing leptons is really looking for prompt leptons.

Non-prompt leptons come later: either through the decay of the hadronized quarks (so-called jets), or a as a "mis-ID". The former basically means that e.g. a $B$-hadron coming from a $b$-quark might decay, before or within the detector, into one or more leptons. These will leave tracks and hits in the relevant parts of the detector as would a prompt lepton, but correlating those hits with nearby jets or $b$-tagged activity could be a way of removing those unwanted non-prompt leptons.

It could also be the case that due to a particular jet signature or a fault in a part of the detector, a jet is reconstructed as a lepton. These "mis-ID" or "fake" leptons are also considered non-prompt.

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