nLab pentaquark

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

The pentaquark is a bound state of 5 quarks (as opposed to just 3 in baryons and 2 in mesons) which after a long history of theoretical prediction and inconclusive experimental signatures was finally observed beyond doubt by the LHCb collaboration.

Detection due to

LHCb collaboration, Observation of $J/\psi b$ resonances consistent with pentaquark states in $\Lambda^0_b \to J/\psi K^- p$ decays, Phys. Rev. Lett. 115, 072001 (2015) (arXiv:1507.03414)

Review in