Charged lepton flavor violation has never been observed

lepton_chartQuarks_and_Leptons_Top_Trumps_PreviewParticle physicists use “generation” and “flavor” interchangeably, “generation” and “flavor” refer to the same property.

first generation leptons: electron and electron-type neutrino
second generation leptons: muon and muon-type neutrino
third generation leptons: tau and tau-type neutrino

Reminder: each one of these 6 elementary particles have anti-particles.

Neutrinos do not carry electrical charge, so the charged leptons are

first generation charged lepton: electron
second generation charged lepton: muon
third generation charged lepton: tau

Reminder: the anti-particles of these 3 are: positron which is the anti-electron, anti-muon an anti-tau.

Charged lepton flavor violation has never been observed. This means that muons do not turn into electrons directly. This is a confusing statement. We know that muons are unstable. Muons decay in micro-seconds. When a muon decays we see an electron plus muon-type neutrino and an electron-type antineutrino as decay products. So, isn’t this a violation of charged lepton flavor? Well, the correct statement should be:

Neutrino-less charged lepton flavor violation has never been observed.

The decay process where a muon decays into 2 electrons plus a positron without any neutrinos showing up has never been observed. The decay process where muon decays into an electron plus photon has never been observed.

Similarly taus decaying into muons or electrons without any neutrinos showing up have never been observed.

There are experiments looking for a charged lepton flavor change (see the links below) but so far the results are negative.

Reminder: in these decays a) electric charge is conserved b) lepton number is conserved.


About Suresh Emre

I have worked as a physicist at the Fermi National Accelerator Laboratory and the Superconducting Super Collider Laboratory. I am a volunteer for the Renaissance Universal movement. My main goal is to inspire the reader to engage in Self-discovery and expansion of consciousness.
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