Observation of a charged charmoniumlike structure in e+ e- → (D* D*)± π∓ at √s = 4.26  GeV

Area of Science:

• Particle Physics
• High-Energy Physics
• Quantum Chromodynamics

Background:

• Investigating exotic hadrons provides crucial insights into the complex dynamics of the strong nuclear force.
• The Belle II experiment and BESIII detector are key facilities for exploring new particle physics phenomena.

Purpose of the Study:

• To study the process of electron-positron annihilation into (D* D*)± π∓ at a center-of-mass energy of 4.26 GeV.
• To search for and characterize new resonant structures in the (D* D*)± π∓ final state.
• To measure the properties of any observed structures, including mass, width, and production ratios.

Main Methods:

• Utilized a large dataset of 827 pb⁻¹ collected with the BESIII detector at the Beijing Electron Positron Collider.
• Employed a partial reconstruction technique to analyze the π∓ recoil mass spectrum.
• Performed a quantitative analysis to determine the Born cross section and production ratios.

Main Results:

• Measured the Born cross section for e+ e- → (D* D*)± π∓ to be (137±9±15) pb.
• Observed a significant structure, denoted as Zc±(4025), near the (D* D*)± threshold.
• Determined the mass and width of the Zc±(4025) to be (4026.3±2.6±3.7) MeV/c² and (24.8±5.6±7.7) MeV, respectively.
• Calculated the production ratio of Zc±(4025) to be 0.65±0.09±0.06.

Conclusions:

• The discovery of the Zc±(4025) provides evidence for a new exotic hadron state.
• Its properties suggest a complex structure possibly related to molecular states or other non-conventional hadronic configurations.
• Further theoretical and experimental studies are needed to fully understand the nature of the Zc±(4025).