Multiquark Hadrons

TL;DR

Recent experimental results from BESIII, Belle, and LHCb provide evidence for multiquark hadrons, including tetraquark and pentaquark states, expanding our understanding of complex substructures beyond traditional mesons and baryons.

Contribution

The paper reviews recent experimental discoveries of multiquark hadrons, highlighting new candidate states with four- and five-quark substructures in various high-energy physics experiments.

Findings

Observation of near-threshold behavior in e+e- --> Lambda Lambda-bar

Identification of Z(4430)+ as a four-quark state

Discovery of P_c(4380) and P_c(4450) as five-quark pentaquark candidates

Abstract

A number of candidate multiquark hadrons, i.e., particle resonances with substructures that are more complex than the quark-antiquark mesons and three-quark baryons that are prescribed in the textbooks, have recently been observed. In this talk I present: some recent preliminary BESIII results on the near-threshold behavior of sigma(e+e- --> Lambda Lambda-bar) that may or may not be related to multiquark mesons in the light- and strange-quark sectors; results from Belle and LHCb on the electrically charged, charmoniumlike Z(4430)^+ --> pi^+ psi ' resonance that necessarily has a four-quark substructure; and the recent LHCb discovery of the P_c(4380) and P_c(4450) hidden-charm resonances seen as a complex structure in the J/psi p invariant mass distribution for Lambda_b --> K^-J/psi p decays and necessarily have a five-quark substructure and are, therefore, prominent candidates for pentaquark baryons.