Abstract
Exotic hadronic states beyond the conventional quark model (called charmoniumlike/bottomoniumlike states or XYZ particles) have been searched for and many candidates were proposed including glueballs, hybrids, multi-quark states, hadron molecules, etc. Dramatic progress was made in the study of the exotic states after the running of the two B -factories, i.e., Belle at KEK and BaBar at SLAC. In my review report, I present the most recent results on the study of the XYZ states from the BESIII, Belle, BaBar, LHCb, CMS experiments, etc., including (1) X states: the observation of the X(3872) in e + e − → γX (3872) at around 4.26 GeV; searches for the X b state; (2) Y states including the updated results for the Y (4008), Y (4260), Y (4360), Y (4660), etc; (3) Z states including the observations of the Z (4430), Z 1 (4050), Z 2 (4250), Z c (3900), Z c (4020), Z c (4200); the evidence for the Z c (4050) ± → π ± ψ (2 S ); search for the Z cs in e + e − → K + K − J/ψ .
Highlights
It has been prospering for dozen years that lots of the “XYZ" particles mainly were observed by Belle, BaBar, and BESIII Collaborations
In the latter the invariant mass distribution of π+π−π0 indicated that the sub-threshold decay into ωJ/ψ is dominated [9] with the rate comparable to that of the π+π− J/ψ decay mode
There is a broad structure at high energy with a possible local maximum at around 4.23 GeV. (2) Based on data samples collected at 9 center-of-mass energies from 4.21 to 4.42 GeV, BESIII searched for the production of e+e− → ωχc0 [39], where χc0 was reconstructed with π+π− and K+K− decay modes
Summary
It has been prospering for dozen years that lots of the “XYZ" particles mainly were observed by Belle, BaBar, and BESIII Collaborations. Most of them above the open charm threshold can not be described well by quark potential models, which decay into the final states containing a charmonium and light hadrons, but not open charm pairs with a detectable rate as expected [1, 2]. Their underlying exotic properties have been stimulating significant interests in theoretical studies, and indicate several possible popular interpretations such as tetraquarks, molecules, hybrids, hadrocharmonia, or glueballs [1, 2]. I present the most recent results on the study of the “XYZ" states from the BESIII, Belle, BaBar, LHCb, CMS experiments, etc
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