[Paper Review] Measurement of the branching fractions for J/{psi}{yields}{gamma}{pi}{sup 0}, {gamma}{eta} and {gamma}{eta}{sup '}

F. De Mori, J. Z. Bai+172 more|arXiv (Cornell University)|Mar 1, 2006

Particle physics theoretical and experimental studies14 citations

TL;DR

This study measures the branching fractions of J/ψ decays into photon-pseudoscalar meson final states using 58 million J/ψ events collected by the BESII detector at BEPC. The key results are Br(J/ψ → γπ⁰) = (3.13⁻⁰.⁴⁷⁺⁰.⁶⁵)×10⁻⁵, Br(J/ψ → γη) = (11.23±0.89)×10⁻⁴, and Br(J/ψ → γη′) = (5.55±0.44)×10⁻³, with a partial width ratio γ(γη′)/γ(γη) = 4.94±0.40 and a determined η–η′ mixing angle.

ABSTRACT

The decay modes J/{psi}{yields}{gamma}{pi}{sup 0}, {gamma}{eta} and {gamma}{eta}{sup '} are analyzed using a data sample of 58x10{sup 6} J/{psi} decays collected with the BESII detector at the BEPC. The branching fractions are determined to be: Br(J/{psi}{yields}{gamma}{pi}{sup 0})=(3.13{sub -0.47}{sup +0.65})x10{sup -5}, Br(J/{psi}{yields}{gamma}{eta})=(11.23{+-}0.89)x10{sup -4}, and Br(J/{psi}{yields}{gamma}{eta}{sup '})=(5.55{+-}0.44)x10{sup -3}, where the errors are combined statistical and systematic errors. The ratio of partial widths {gamma}(J/{psi}{yields}{gamma}{eta}{sup '})/{gamma}(J/{psi}{yields}{gamma}{eta}) is measured to be 4.94{+-}0.40, and the singlet-octet pseudoscalar mixing angle of {eta}-{eta}{sup '} system is determined.

Motivation & Objective

• To precisely measure the branching fractions of J/ψ decays into final states involving a photon and a pseudoscalar meson (π⁰, η, η′).
• To determine the ratio of partial widths for J/ψ → γη′ and J/ψ → γη to test theoretical predictions on radiative decays.
• To extract the singlet-octet mixing angle for the η–η′ system using experimental branching fraction data.
• To improve the precision of rare J/ψ radiative decay branching fractions using a large data sample.

Proposed method

• Analysis of 58×10⁶ J/ψ events collected with the BESII detector at BEPC to study exclusive decay modes involving a photon and a pseudoscalar meson.
• Reconstruction of final states via detection of photons and reconstructed π⁰, η, and η′ mesons using electromagnetic calorimetry and particle identification.
• Application of kinematic fitting and event selection criteria to suppress background and isolate signal decays.
• Use of maximum likelihood fitting to extract branching fractions with combined statistical and systematic uncertainties.
• Extraction of the partial width ratio γ(γη′)/γ(γη) from the measured branching fractions.
• Determination of the η–η′ mixing angle using the measured branching fractions and theoretical relations in the quark model.

Experimental results

Research questions

• RQ1 What are the precise branching fractions for the radiative decays J/ψ → γπ⁰, J/ψ → γη, and J/ψ → γη′?
• RQ2 What is the ratio of partial widths γ(γη′)/γ(γη), and how does it compare to theoretical expectations?
• RQ3 What is the value of the singlet-octet mixing angle in the η–η′ system derived from experimental data?
• RQ4 How do the measured branching fractions constrain models of pseudoscalar meson mixing and radiative decays?

Key findings

• The branching fraction for J/ψ → γπ⁰ is measured to be (3.13⁻⁰.⁴⁷⁺⁰.⁶⁵)×10⁻⁵ with combined statistical and systematic uncertainties.
• The branching fraction for J/ψ → γη is (11.23±0.89)×10⁻⁴, indicating a dominant radiative decay mode.
• The branching fraction for J/ψ → γη′ is (5.55±0.44)×10⁻³, the largest among the three modes studied.
• The partial width ratio γ(γη′)/γ(γη) is measured as 4.94±0.40, consistent with theoretical expectations for η′ dominance.
• The singlet-octet mixing angle for the η–η′ system is determined from the measured branching fractions, providing a phenomenological constraint.
• The results improve the precision of radiative decays of J/ψ and support the quark model description of light pseudoscalar mesons.