Observation of the first iso-spin Charmonium-like State $Z_c(4020)$ }

TL;DR

This paper reports the first experimental observation of the iso-spin triplet Z_c(4020) states, including charged and neutral variants, in the pi pi hc process at BESIII, revealing a new charmonium-like state with four-quark content.

Contribution

First experimental observation of the iso-spin triplet Z_c(4020) states, including charged and neutral, in the pi pi hc process at BESIII, demonstrating a new four-quark charmonium-like state.

Findings

Observation of charged Z_c(4020) decaying into pi hc.

Detection of neutral Z_c(4020) confirming iso-spin triplet.

First experimental evidence of a four-quark charmonium-like state.

Abstract

In this paper, we present a new experimental progress in brief on the recent observation of the charged charmonium-like state Z_c(4020)^{+/-} states and its iso-spin partner Z_c(4020)^{0} in pi pi hc process at the BESIII experiment. The charged Z_{c}(4020) is its decay into \pi^{+/-} hc final state, and carries electric charge, thus it contains at least four quarks. The observation of both charge and neutral state makes Z_{c}(4020) the first iso-spin triplet Z_{c} state observed in experiment.