The Eta and Eta Prime Mesons

<p><strong>The Field Guide to Particle Physics : Season 2<br></strong><a href="https://pasayten.org/the-field-guide-to-particle-physics">https://pasayten.org/the-field-guide-to-particle-physics</a><br>©2022 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><a href="https://pasayten.org/the-field-guide-to-particle-physics/eta-eta-prime"><strong>The Eta and Eta Prime Mesons</strong></a><strong><br></strong><br>The Eta and Eta Prime particles are a pair of electrically neutral particles that were - for a moment anyway - the center of a fierce debate among physicists. That debate ended as quantum chromodynamics - the mathematical theory which describes how quarks and gluons interact - was enshrined into the standard model of particle physics.</p><p>Those mathematical details involved in describing eta and eta prime are almost as fierce as the debate over how they worked. And those details are what we’ll describe today.</p><p>With the strange quark, three are three kinds of quarks that can combine into all sorts of particles: up, down and strange. Of course, they each have antiparticle partners: antiup, antidown and antistrange with opposite electric charge.</p><p>Mesons are particles that mix quarks and antiquarks. The neutral pion is a pretty clean mixture of direct quarks/antiquarks pairs: up-antiup with down-anti-down.</p><p>Nature can also make nice, clean, symmetric combinations of all three quarks: up-antiup, down-antidown, strange-antistrange. Actually, it can make two of them, because, you know, strangeness. Those two combinations are known as the eta and eta-prime mesons, respectively.</p><p>Like the pi0, both eta and eta prime have zero electric char