Further prediction on the possible double-peak structure of the X17 particle

Abstract

The [Formula: see text] particle, discovered by [A. J. Krasznahorkay et al., Phys. Rev. Lett. 116, 042501 (2016), doi:10.1103/PhysRevLett.116.042501] at ATOMKI, was recently confirmed in the [Formula: see text] invariant mass spectra by [K. U. Abraamyan, C. Austin, M. I. Baznat, K. K. Gudima, M. A. Kozhin, S. G. Reznikov and A. S. Sorin, arXiv:2311.18632] at JINR. We notice with surprise and interest that the [Formula: see text] seems to have a double-peak structure. This is in a possible coincidence with our QCD sum rule study of [H.-X. Chen, arXiv:2006.01018], where we interpreted the [Formula: see text] as a tetraquark state composed of four bare quarks ([Formula: see text]), and claimed that “A unique feature of this tetraquark assignment is that we predict two almost degenerate states with significantly different widths”. These two different tetraquark states are described by two different chiral tetraquark currents [Formula: see text] and [Formula: see text]. To verify whether the tetraquark assignment is correct or not, we replace the up and down quarks by the strange quarks, and apply the QCD sum rule method to study the other four chiral tetraquark currents [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text]. We calculate their correlation functions, and find that non-perturbative QCD effects do not contribute much to them. Our results suggest that there may exist four almost degenerate tetraquark states with masses about [Formula: see text] MeV. Each of these states is composed of four bare quarks, either [Formula: see text] or [Formula: see text].