QCD sum rule studies on the possible double-peak structure of the $X17$ particle

Abstract

The $X17$ particle, discovered by Krasznahorkay et al. at ATOMKI, was recently confirmed in the $\gamma \gamma$ invariant mass spectra by Abraamyan et al. at JINR. We notice with surprise and interest that the $X17$ seems to have a double-peak structure. This is in a possible coincidence with our QCD sum rule study of [arXiv:2006.01018], where we interpreted the $X17$ as a tetraquark state composed of four bare quarks ($u\bar{u}d\bar{d}$), 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 ${\bar{u}}_L{\gamma }_{\mu }{d}_L{\bar{d}}_L{\gamma }^{\mu }{u}_L$ and ${\bar{u}}_L{\gamma }_{\mu }{d}_L{\bar{d}}_R{\gamma }^{\mu }{u}_R$. 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 ${\bar{u}}_L{\gamma }_{\mu }{s}_L{\bar{s}}_L{\gamma }^{\mu }{u}_L$, ${\bar{u}}_L{\gamma }_{\mu }{s}_L{\bar{s}}_R{\gamma }^{\mu }{u}_R$, ${\bar{d}}_L{\gamma }_{\mu }{s}_L{\bar{s}}_L{\gamma }^{\mu }{d}_L$, and ${\bar{d}}_L{\gamma }_{\mu }{s}_L{\bar{s}}_R{\gamma }^{\mu }{d}_R$. 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 $236\sim 296$ MeV. Each of these states is composed of four bare quarks, either $u\bar{u}s\bar{s}$ or $d\bar{d}s\bar{s}$.

11 pages, 1 figure, revised version to be published in MPLA

References in corpus (8)

• Collider Probes of Axion-Like Particles
• Particle Physics Models for the 17 MeV Anomaly in Beryllium Nuclear Decays
• The light U boson as the mediator of a new force, coupled to a combination of Q, B, L and dark matter
• New anomaly observed in ${}^{12}$C supports the existence and the vector character of the hypothetical X17 boson
• Exotic Tetraquark ud bar[s] bar[s] of J^P=0^+ in the QCD Sum Rule
• QED Meson Description of the X17 and Other Anomalous Particles
• Anomalies in ${}^8$Be nuclear transitions and $(g-2{)}_{e,\mu }$: towards a minimal combined explanation
• The new interaction suggested by the anomalous ${}^8$Be transition sets a rigorous constraint on the mass range of dark matter