OpenStax College Physics for AP® Courses, Chapter 33, Problem 17 (Test Prep for AP® Courses)

This is College Physics Answers with Shaun Dychko. A meson is composed of two quarks so you can think of a meson as a package containing a one quark, let's suppose an anti-up quark and a down quark; this is the pi minus meson and so the word meson means two quarks and so if you were to shoot high energy electrons at this particle, you would find that the electrons bounce off at oblique angles when hitting these quarks directly whereas they will go through relatively unscattered anywhere else through the meson and so most of this meson volume will be empty space with the exception of two particularly dense pieces inside and so these pieces are the quarks and this is the reason why quarks are considered to exist is because an experiment like this shooting high energy electrons at a meson will bounce off to point-like particles inside the meson. And for baryon, it would bounce off three point-like particles.