Abstract
We report the progress in the study of the exotic hadrons, also called XYZ states, at BESIII experiment with its unique data samples in e+ e− annihilation at center-of-mass energies of 3.8–4.6 GeV. The talk covers the observation of the Zc(3900) and Zc(4020) and new measurements related to them; updated measurement of the resonant parameters of the Y(4260) in e+ e−→ π+π− J/ψ and discovery of its new decay modes π+π−ψ(2S), ωχc0, π+π−hc, and D0D∗−π++c.c.; and observation of X(3872) in e+e− annihilation.
Highlights
In the conventional quark model, mesons are composed of one quark and one anti-quark, while baryons are composed of three quarks
BaBar and Belle experiments finished their data taking in 2008 and 2010, respectively, and the data are still used for various physics analyses
We focus on the measurements of the three mostly studied XYZ states, i.e., the X(3872), the Y(4260), and the Zc(3900), at BESIII [5]
Summary
In the conventional quark model, mesons are composed of one quark and one anti-quark, while baryons are composed of three quarks. Many charmonium-like states were discovered at two B-factories BaBar and Belle in the first decade of this century [2] Whereas some of these are good candidates of charmonium states, many other states have exotic properties, which may indicate that exotic states, such as multi-quark state, hadronic molecule, or hybrid, have been observed [3]. The BESIII experiment studied the e+e− → π+π− J/ψ process at a center-of-mass (c.m.) energy of 4.26 GeV using a 525 pb−1 data sample [6], with J/ψ decays into a pair of e+e− or. A structure at around 3.9 GeV/c2 was observed in the π± J/ψ invariant mass distribution with a statistical significance larger than 8σ, which is referred to as the Zc(3900).
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