Pentaquark

A pentaquark is a hadron composed of four quarks and one antiquark, bound by the strong interaction. It is a type of exotic hadron beyond the familiar three-quark baryons and quark–antiquark mesons.

Quark: A fundamental particle that carries color charge and combines with other quarks through the strong interaction. Pentaquarks contain four quarks, whose flavors and charges help determine the particle's properties.
Quark model: A framework that classifies hadrons by their constituent quarks and quantum numbers. Its extended configurations allow hadrons with four quarks and an antiquark.
Harry J. Lipkin: An Israeli-American theoretical physicist known for work on particle physics and hadron spectroscopy. Lipkin proposed exotic baryon configurations in the 1960s, anticipating later pentaquark discussions.
Pc(4312): A hidden-charm pentaquark candidate observed by LHCb in the J/ψ proton mass spectrum. It is one of the narrow structures resolved in LHCb's 2019 analysis.
Pentaquark structure: The arrangement of quarks and antiquarks inside a pentaquark, including compact and molecular possibilities. Experiments have not established one universal internal structure for the observed candidates.
Antiquark: The antimatter counterpart of a quark, with opposite electric charge and color charge. Every pentaquark contains one antiquark alongside four quarks.
Hadron spectroscopy: The study of hadron properties through their masses, quantum numbers, and decay patterns. Pentaquark states are identified and compared through their spectral signatures.
H1 experiment: A particle-physics experiment at DESY that studied electron–proton collisions at the HERA accelerator. H1 reported a candidate pentaquark signal in 2004, though it was not confirmed broadly.
Pc(4440): A hidden-charm pentaquark candidate reported by LHCb near a mass of 4440 megaelectronvolts. It belongs to the three-peak structure that refined the original Pc(4450) observation.
Charmonium: A meson composed of a charm quark and a charm antiquark. Hidden-charm pentaquark candidates contain a charm–anticharm pair but are not ordinary charmonium.

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TetraquarkRelated: It is another exotic hadron, with one more valence constituent than a tetraquark.