nLab proton radius problem

Contents

matter field fermions (spinors, Dirac fields)

flavors of fundamental fermions in the standard model of particle physics:
generation of fermions	1st generation	2nd generation	3d generation
quarks ( $q$ )
up-type	up quark ( $u$ )	charm quark ( $c$ )	top quark ( $t$ )
down-type	down quark ( $d$ )	strange quark ( $s$ )	bottom quark ( $b$ )
leptons
charged	electron	muon	tauon
neutral	electron neutrino	muon neutrino	tau neutrino

bound states:
mesons	light mesons: pion ( $u d$ ) ρ-meson ( $u d$ ) ω-meson ( $u d$ ) f1-meson a1-meson	strange-mesons: ϕ-meson ( $s \bar s$ ), kaon, K-meson ( $u s$ , $d s$ ) eta-meson ( $u u + d d + s s$ ) charmed heavy mesons*: D-meson ( $u c$ , $d c$ , $s c$ ) J/ψ-meson ( $c \bar c$ )	bottom heavy mesons: B-meson ( $q b$ ) ϒ-meson ( $b \bar b$ )
baryons	nucleons: proton $(u u d)$ neutron $(u d d)$

hadrons (bound states of the above quarks)

bosinos:

dark matter candidates

Exotica

auxiliary fields

Idea

What is called the ptoton radius problem or proton radius puzzle is an apparent disagreement of computations in QCD and its effective field theories with experiment, akin to the proton spin crisis (see there for more), but concerning the proton‘s radius.

Gil Paz, The Proton Radius Puzzle (arXiv:1909.08108)
Clara Peset, Antonio Pineda, Oleksandr Tomalak, The proton radius (puzzle?) and its relatives (arXiv:2106.00695)