Why can't we have a meson made of two quarks, why does there have to be the antiquark too?

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    $\begingroup$ Possible duplicates: physics.stackexchange.com/q/219710/2451 and links therein. $\endgroup$ – Qmechanic Mar 28 '19 at 18:05
  • $\begingroup$ Do you know about color confinement? $\endgroup$ – PM 2Ring Mar 28 '19 at 18:05
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    $\begingroup$ Possible duplicate of Why do quarks tend to bond in groups of three? $\endgroup$ – PM 2Ring Mar 28 '19 at 18:06
  • $\begingroup$ Actually, tetraquark states have been likely identified, of the $\bar{q} q \bar{q}q$ type, color singlets, of course, even though the distinction between a "mesonic molecule" (mesonic nucleus) and a hadron is not quite agreed upon. $\endgroup$ – Cosmas Zachos Mar 28 '19 at 19:11
  • $\begingroup$ @Cosmas Also pentaquarks. "One option is that they are truly made of five quarks, with all of them mixed together evenly within a single hadron. Another possibility is that the pentaquarks are really a baryon and a meson stuck together to form a loosely bound molecule" Although a genuine pentaquark would be kind of cool, I'm betting on option b. $\endgroup$ – PM 2Ring Mar 29 '19 at 11:40