Leptons

For no particular reason, I felt like writing about leptons, so here you go! I suspect this will be followed up by a discussion of hadrons and possibly gauge bosons, but no guarantees! I'm also hoping to learn a bit about colloidal materials in the next few days and start writing about things other than particle physics and astrophysics.

Along with the electron and its corresponding neutrino that we all know and love, we also have antiparticles for both (unless the neutrino is a Majorana particle, which is a whole 'nother kettle of fish). These are the positron ($e^+$) and the anti electron neutrino.

In any case, the electron and the electron neutrino form the first 'generation' of the leptons. There are two more: the muon $\mu^-$ and the tau lepton $\tau^-$, along with their corresponding neutrinos. The muon has about 200 times the mass of the electron, and decays by
\[
\mu^- \to e^- + \nu_\mu + \overline{\nu}_e
\]
with a fairly reasonable lifetime of 2 microseconds. This makes it an awesome tool for experimental particle physics, but that is very much a topic for another day.
Similarly, the tau lepton has a lifetime of $10^{-13}$ seconds and can decay to either a muon or an electron, but it also has enough mass to produce some quarks/hadrons, so there are all sorts of interesting (nonleptonic) decay modes to look out for.

So here are the particles we have so far:
 \[
\begin{array}{|ccc|} \hline e^- & \mu^- & \tau^-\\ \nu_e & \nu_\mu & \nu_\tau\\ \hline \end{array}
\]
The leptons all have a quality called flavor, so they can interact by the weak force. The charged leptons can, of course, interact with other particles electromagnetically, while the neutrinos cannot. None of the leptons can interact strongly, though - that's just quarks and gluons.