0+ fully-charmed tetraquark states

Jian-Rong Zhang

doi:10.1103/physrevd.103.014018

Abstract

Motivated by the LHCb's new observation of structures in the $J/\psi$-pair invariant mass spectrum, for which could be classified as possible $cc\bar{c}\bar{c}$ tetraquark candidates, we systematically study $0^{+}$ fully-charmed tetraquark states through QCD sum rules. Making the development of calculation techniques to fourfold heavy hadronic systems, four different configuration currents with $0^{+}$ are considered and vacuum condensates up to dimension $6$ are included in the operator product expansion (OPE). Finally, mass values acquired for $0^{+}$ $cc\bar{c}\bar{c}$ tetraquark states agree well with the experimental data of the broad structure, which supports that it could be a $0^{+}$ fully-charmed tetraquark state.

Highlights

The topic of the fully-charmed tetraquark state has attracted much attention
As one reliable way to evaluate nonperturbative effects, the QCD sum rule [58] is firmly established on the basic theory, and it has been widely applied to hadronic systems
Motivated by the exciting and significant structures observed in the di-J=ψ mass spectrum, we follow the previous QCD sum rule studies [63,64,65] of hadrons containing one or two heavy quarks and devote ourselves to developing the corresponding calculation techniques to fourfold heavy hadronic systems

Summary

INTRODUCTION

The topic of the fully-charmed tetraquark state has attracted much attention. For example, a variety of phenomenological models were employed to predict the existence of some states merely made up of four heavy quarks [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28]. On 0þ cccc ̄ tetraquark states, there are some existing works [11,12,31,41,50] on different versions of the QCD sum rules. There are some other QCD sum rule analyses of fully heavytetraquark states involving condensate contributions up to dimension four in the operator product expansion (OPE), especially choosing the axial-vector–axial-vector configuration current in Ref. Motivated by the exciting and significant structures observed in the di-J=ψ mass spectrum, we follow the previous QCD sum rule studies [63,64,65] of hadrons containing one or two heavy quarks and devote ourselves to developing the corresponding calculation techniques to fourfold heavy hadronic systems. We intend to systematically study 0þ fully-charmed tetraquark states with QCD sum rules by taking into account four possible configuration currents and calculating condensates up to dimension six. The following forms of currents could be constructed for 0þ cccc ̄ tetraquark states with j 1⁄4 ðQTa Cγ5QbÞðQaγ5CQ Tb Þ

Published by the American Physical Society

After equating

SUMMARY