A possible structure of newly found exotic state $η_1(1855)$

Abstract

Recently, a hadronic state, named η 1 (1855), about 1.86 GeV was observed in BESIII experiment. This finding has a peculiar interest due to its exotic quantum number J P C = 1 −+ . In this paper, we examine the tetraquark interpretation for the structure of η 1 (1855) in the configurations of [1 c ] ss ⊗[1 c ] qq and [1 c ] sq ⊗ [1 c ] sq , and perform a mass spectrum calculation in the framework of QCD sum rules. The results show that the observed η 1 (1855) could be embedded into the [1 c ] ss ⊗ [1 c ] qq configuration.The possible tetraquark and hybrid decay modes are analyzed, which are critical in decoding its inner structure. By the same way, we evaluate as well the ssss molecular state with 1 −+ quantum number and find that there might exist two such ground states.

An updated review of the new hadron states

“…See Ref. [1065] for more QCD sum rule analyses. of a C-odd three-gluon glueball [934], given that two-gluon glueballs have been studied intensively but still difficult to be identified in experiments unambiguously.…”

Hyperon semileptonic decays in QCD sum rules

“…In our numerical calculations, related parameters of baryon octet are shown in table 2 and other inputs are adopted as follows [4,42,[50][51][52][53][54][55][56][57][58][59][60][61]: ⟨qq⟩ = −(0.24 ± 0.01) 3 GeV 3 , ⟨ss⟩ = (0.8 ± 0.1)⟨qq⟩,…”

Production of the $η_{1}(1855)$ through kaon induced reactions under the assumptions that it is a molecular or a hybrid state

“…Recently, the BESIII Collaboration observed η 1 (1855) in the J/ψ → γηη ′ decay [2]. Since the η 1 (1855) is an isoscalar resonance with exotic J PC = 1 −+ quantum numbers, different explanations of exotic states like hybrid [4][5][6], the K K1 (1400) molecular state [7,8], and tetraquark state [9] were proposed, which shows that this observation attracted theorist's attention in the past months. Besides decoding the nature of the observed η 1 (1855), establishing the η 1 (1855) in experiment is also crucial.…”

“…respectively. Obviously, the observed η 1 (1855) cannot be grouped into the conventional hadron, which is a good candidate of exotic states as indicated by some theoretical groups, where the η 1 (1855) was interpreted as a hybrid state [4][5][6], a molecular state [7,8], and a tetraquark state [9]. At present, the η 1 (1855) was only observed in the radiative decay J/ψ → γηη ′ , confirming this observation by others processes is an interesting experimental topic, which will be helpful to establish this exotic state in experiment and may provide some valuable information to reflect its inner structure.…”