The Tau

<p><strong>The Field Guide to Particle Physics <br></strong><a href="https://pasayten.org/the-field-guide-to-particle-physics">https://pasayten.org/the-field-guide-to-particle-physics</a><br>©2021 The Pasayten Institute <a href="https://creativecommons.org/licenses/by-sa/4.0/">cc by-sa-4.0</a><br>The definitive resource for all data in particle physics is the Particle Data Group: <a href="https://pdg.lbl.gov/">https://pdg.lbl.gov</a>.</p><p>The Pasayten Institute is on a mission to build and share physics knowledge, without barriers! <a href="http://pasayten.org/heysean">Get in touch</a>.</p><p><strong>The Tau<br></strong><br>The tau is a very heavy species of elementary particle that aren’t quite as common as the <a href="https://pasayten.org/the-field-guide-to-particle-physics/electron">electron</a> or the <a href="https://pasayten.org/the-field-guide-to-particle-physics/muon">muon</a>. Nevertheless, just as the muon shares many of the properties with the electron, so too does the tau.</p><p><br>Like all elementary particles, taus have no known size. But they do have a known mass. At 1776.86 MeV, it’s a pretty big mass. That’s well over 3000 times the mass of the electron, or just shy of 17 times the mass of the muon. That large mass is key to understanding the tau, especially how it decays.</p><p><br>Taus are not stable. Heavy particles rarely are. Taus decay to all kinds of other stuff. Generally, heavier particles can decay into lighter particles so long as things like electric charge are conserved. Muons aren’t terribly heavy, and so decay primarily to electrons because there’s not much else to decay to. Taus by contrast, are so heavy they can decay into all kinds of things.</p><p><br>Because taus are so heavy, they can decay to hadrons - a fancy name for all that nuclear junk - and those decays happen quickly. Very quickly. There are just so many options. On average the taus only live for about 2.9×10^-13 seconds. Forget nanoseconds. That’s less than a <a href="https://en.wikipedia.org/wiki/Pico-"