Observation of Resonance Structures in e^{+}e^{-}→π^{+}π^{-}ψ_{2}(3823) and Mass Measurement of ψ_{2}(3823)

Area of Science:

• Particle Physics
• High-Energy Physics
• Quantum Chromodynamics

Background:

• Understanding charmoniumlike states is crucial for comprehending the complex interactions governed by Quantum Chromodynamics.
• Previous studies have identified various charmonium states, but their precise nature and relationships remain areas of active investigation.
• The ψ₂(3823) is a vector charmoniumlike state whose properties are essential for refining theoretical models.

Purpose of the Study:

• To measure the product of the e⁺e⁻→π⁺π⁻ψ₂(3823) cross section and the branching fraction B[ψ₂(3823)→γχ<0xE2><0x82><0x9C>₁].
• To investigate the resonance structure in the cross section line shape of e⁺e⁻→π⁺π⁻ψ₂(3823).
• To determine the most precise mass and width for the ψ₂(3823) state.

Main Methods:

• Analysis of a data sample with an integrated luminosity of 11.3 fb⁻¹ collected at center-of-mass energies from 4.23 to 4.70 GeV using the BESIII detector.
• Fitting the energy-dependent cross section with models incorporating Breit-Wigner resonances.
• Precise measurement of the ψ₂(3823) mass using the observed decay products.

Main Results:

• First-time observation of resonance structure in the e⁺e⁻→π⁺π⁻ψ₂(3823) cross section line shape with a significance exceeding 5σ.
• A fit with two coherent Breit-Wigner resonances yielded masses M(R₁) = 4406.9 ± 17.2 ± 4.5 MeV/c² and M(R₂) = 4647.9 ± 8.6 ± 0.8 MeV/c², and widths Γ(R₁) = 128.1 ± 37.2 ± 2.3 MeV and Γ(R₂) = 33.1 ± 18.6 ± 4.1 MeV.
• The mass of the ψ₂(3823) state was measured as 3823.12 ± 0.43 ± 0.13 MeV/c², representing the most precise measurement to date.

Conclusions:

• The observed resonance structure deepens the understanding of the nature of vector charmoniumlike states.
• The precise mass measurement of ψ₂(3823) provides a critical benchmark for theoretical predictions.
• This study contributes significantly to the ongoing exploration of the hadronic spectrum in particle physics.