Observation of a State X(2600) in the π^{+}π^{-}η' System in the Process J/ψ→γπ^{+}π^{-}η'

Area of Science:

• Particle Physics
• Hadron Spectroscopy
• Quantum Chromodynamics

Background:

• The J/ψ meson is a crucial probe for studying the spectrum of hadrons.
• Understanding the nature of resonances provides insights into the strong interaction.
• The η' (eta prime) meson is a key particle in studying light meson spectroscopy.

Purpose of the Study:

• To search for new resonances in the J/ψ→γπ+π−η' decay.
• To investigate the properties of the newly observed X(2600) state.
• To explore the connection between the X(2600) and structures in the π+π− invariant mass spectrum.

Main Methods:

• Analysis of (10087±44)×10^6 J/ψ events collected by the BESIII detector.
• Study of the J/ψ→γπ+π−η' process using two dominant η' decay channels: η'→γπ+π− and η'→ηπ+π− (with η→γγ).
• Simultaneous fit to the π+π−η' and π+π− invariant mass spectra.

Main Results:

• Observation of a new resonance, X(2600), with a statistical significance > 20σ in the π+π−η' invariant mass spectrum.
• The X(2600) state has a measured mass of 2618.3±2.0(stat)−1.4+16.3(syst) MeV/c² and a width of 195±5(stat)−17+26(syst) MeV.
• A correlation was found between the X(2600) and a structure near 1.5 GeV/c² in the π+π− invariant mass spectrum.

Conclusions:

• The discovery of the X(2600) provides a new candidate for understanding exotic hadrons.
• The observed properties of X(2600) warrant further theoretical and experimental investigation.
• This finding contributes to the ongoing exploration of the complex hadron spectrum within the Standard Model.