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Observation of an Isoscalar Resonance with Exotic J^PC=1^(-+) Quantum Numbers in J/ψ→γηη'

2022-11-02 Author:
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The BESIII collaboration reported the observation of an isoscalar resonance with exotic JPC=1-+ quantum numbers. This research is published in Physical Review Letters [Phys. Rev. Lett. 129, 192002 (2022)], accompanied by a detailed companion paper in Physical Review D [Phys. Rev. D 106, 072012 (2022)]. This is an observation of a new category of hadronic matter, which is an important step forward in low energy QCD.

Study of QCD exotics beyond simple quark model provides critical information on the quantitative understanding of strong interaction and confinement in the low energy regime. Observation of states with exotic quantum numbers, such as JPC=1-+, has been of great experimental interest as it would be clear evidence for mesons beyond the simple q-qbar picture.
Based on a sample of 10 billion J/ψ events collected with the BESIII detector, a partial wave analysis of the decay J/ψ→γηη' is performed. An isoscalar state with exotic JPC=1-+ quantum numbers, denoted as η1(1855), has been observed for the first time with statistical significance larger than 19σ. Its mass is consistent with the predicted mass of 1-+ hybrid from Lattice QCD.
The observation of 1-+ isoscalar state η1(1855) has stimulate the interests of the community, since it cannot be grouped into the conventional hadron and has been interpreted as a candidate of hybrid, molecular state, and tetraquark state. Further measurements will be carried on to explore the internal structure of η1(1855) and to search for its possible partners.
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