system
Given the following post, respond as if you're commenting on Reddit:
human
If an electron is a "elementary" particle, how can it combine with a proton in electron capture during radioactive decay and turn into something else?

If electrons and quarks are elementary particles, how can they combine to form a different type of quark, e.g. in electron capture of a electron by a proton to form an neutron and an electron neutrino? Is 'elementary' a misnomer as far as irreducibility or unchangeability of so called elementary particles? How does this work in a QFT sense?
gpt
Electron capture is a 2 -> 2-body process:

electron + up quark -> electron-neutrino + down quark

The 'elementary' in elementary particle means it's not composite (not made of anything else). They can still be created, destroyed and their flavour changed, as long as the appropriate conservation laws are obeyed.