The Neutral Pion

<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 Neutral Pion<br></strong>In many ways, the neutral pion - sometimes call the π0 meson - is closely related to the charged pions. In others, the neutral pion is a truly bizarre little beast.</p><p>There are so many kinds of pions because there are so many ways to combine up and down quarks into particle/antiparticle pairs. The neutral pions are kind of a mixed bag of <a href="https://pasayten.org/the-field-guide-to-particle-physics/up-and-down-quarks">up quarks</a> paired with antiup quarks, and <a href="https://pasayten.org/the-field-guide-to-particle-physics/up-and-down-quarks">down quarks</a> paired with antidown quarks. The electric charges are always canceled between these antiparticle partners. The neutral pion is a great example of how antimatter isn’t always a destructive thing.</p><p>Owing to this special structure, the neutral pion is its own antiparticle. π0 mesons decay much, much faster than their charged siblings, a literal billion times faster. They only stick around for about 8.5×10^−17 =0.000000000000000085 seconds. Yikes! That’s so small it probably doesn’t mean anything to most of us! By particle standards, it’s a properly fast decay.</p><p><br>The charged pions decay via the weak nuclear force. The neutral pions decay via the <a href="https://pasayten.org/the-field-guide-to-particle-physics/photon">electromagnetic force</a>, which is much, much stronger. Which is why they decay much