image: Comparison between D0Ds*- invariant mass spectrum and D0Ds*- femtoscopic correlation function in the three scenarios of resonant/virtual/bound states.
Credit: ©Science China Press
The strong interaction is one of the four fundamental interactions in nature and contributes to the vast majority of the mass of visible matter in the universe. The fundamental theory describing the strong interaction is Quantum Chromodynamics (QCD), based on quarks and gluons. However, due to color confinement, only color-singlet hadrons can be observed. According to the quark model, hadrons are typically classified as mesons (composed of a quark and an antiquark) or baryons (composed of three quarks). Since 2003, a series of exotic hadron states that are difficult to explain by the conventional quark model have been discovered experimentally, providing new opportunities for in-depth studies of the strong interaction. In 2013, the BESIII and Belle collaborations observed the hidden-charm tetraquark candidate Zc3900± in the J/ψπ± invariant mass spectrum of the e+e-→J/ψπ+π- process. In 2020, the BESIII collaboration reported the first hidden-charm tetraquark candidate with strangeness, Zcs3985-, in the recoil-mass spectrum of the K+ meson from the e+e-→K+(D*0Ds-+D0Ds*-) process. The quark contents of the Zc3900-/Zc3900+ and Zcs3985- states are ccdu/ccud and ccsu, respectively; the latter is often interpreted as the strangeness partner of the former. Extensive and in-depth discussions have been conducted regarding the nature of the tetraquark candidates Zc(3900)/Zcs(3985). Particularly within the "hadronic molecular" picture, significant divergence remains on whether their nature corresponds to a resonance, a virtual state, or a bound state near the D0D*-/D0Ds*- thresholds.
The authors of this paper propose for the first time that femtoscopy in large hadron collider experiments, specifically by measuring the momentum correlation functions of D0D*-/D0Ds*-, can effectively distinguish between these three scenarios. Based on effective field theory methods and the Koonin-Pratt formalism, their calculations reveal that in the low-momentum region, the correlation functions exhibit distinct momentum-dependent behaviors for the three cases, with these differences being particularly pronounced in proton-proton collision experiments. Furthermore, in the higher momentum region, the correlation function for the resonance case shows non-trivial structures closely related to the behavior of the scattering phase shift. The authors further point out that the phase-space suppression effect is the main reason for the difficulty in distinguishing the near-threshold states using the invariant mass spectrum alone. Consequently, they suggest combining studies of correlation functions and invariant mass spectra as a new strategy for future studies of exotic hadron states.
Journal
Science Bulletin