Study of η→π⁺π^-l⁺l^-

2025/01/17 by BESIII Collaboration, M. Ablikim, М. Н. Ачасов +732
Computer Science · Mathematics · #Advanced Algebra and Geometry #Algebraic and Geometric Analysis #Coding theory and cryptography #FOS: Physical sciences #High Energy Physics - Experiment (hep-ex)

paper · pdf · doi:10.48550/arxiv.2501.10130

openalex publication_date 2025/01/17 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/29

Abstract

Using a sample of (10087±44)×10⁶ J/ψ events accumulated with the BESIII detector, we analyze the decays η→π⁺π^-l⁺l^- (l=e or μ) via the process J/ψ→γη. The branching fraction of η→π⁺π^-e⁺e^- is measured to be B(η→π⁺π^-e⁺e^-)=(3.07±0.12_\rmstat.±0.19_\rmsyst.) ×10^-4. No signal events are observed for the η→π⁺π^-μ⁺μ^- decay, leading to an upper limit on the branching fraction of B(η→π⁺π^-μ⁺μ^-)<4.0×10^-7 at the 90% confidence level. Furthermore, the CP-violation asymmetry parameter is found to be A_CP(η→π⁺π^-e⁺e^-)=(-4.04±4.69_\rmstat.±0.14_\rmsyst.)%, showing no evidence of CP-violation with current statistics. Additionally, we extract the transition form factor from the decay amplitude of η→π⁺π^-e⁺e^-. Finally, axion-like particles are searched for via the decay η→π⁺π^-a, a→ e⁺e^-, and upper limits on this branching fraction relative to that of η→π⁺π^-e⁺e^- are presented as a function of the axion-like particle mass in the range 5-200 MeV/c².

Related

• Measurement of the Electromagnetic Transition Form-factors in the decays η'→π⁺π^-l⁺l^-
• Improved measurement of the decays η' → π⁺π^-π⁺⁽⁰⁾π^-(0) and search for the rare decay η' → 4π⁰
• Measurement of the branching fraction of η→ μ⁺ μ^- and search for η→ e⁺ e^-
• Measurement of the η transition form factor through η' → π⁺π^-η decay
• Search for the lepton number violating decay η→ π⁺π⁺e^-e^- + c.c. via J/ψ→ϕη