Observation of the doubly radiative decay η′→γγπ0

Abstract

respectively. In addition, the M 2 γγ-dependent partial widths of the inclusive decay are also presented.

Search for the decay η′→γγη

“…Thus the uncertainty associated with the five reconstructed photons is 3% (0.6% per photon) by weighting the uncertainties according to the polar angle distribution of the five photons from data. The uncertainties associated with the other selection criteria, e.g., kinematic fit with χ 2 5C < 30, the number of photons equal to 5, π 0 veto (jMðγγÞ − mðπ 0 Þj > 18 MeV=c 2 ) and cos θ decay , are studied using the J=ψ → γη 0 → γγω, ω → γπ 0 decay control sample [9]. The systematic uncertainty for each of the applied selection criteria is numerically estimated from the difference of the number of events with and without the corresponding requirement.…”

“…The uncertainty due to the signal shape is considered by convolving a Gaussian function to account for the difference in the mass resolution between data and MC simulation. In the fit to the γγη distribution, the signal PDF is the signal MC shape convolving a Gaussian function with a fixed width of 1.5 MeV [9], and the changes of the signal yields is taken as the uncertainty due to the signal shape.…”

“…Recently using 1.31 × 10 9 J=ψ events, BESIII reported the study of η 0 → γγπ 0 for the first time, and the branching fraction of η 0 → γγπ 0 was determined to be ð32.0 AE 0.7 AE 2.3Þ × 10 −4 [9]. By excluding the intermediate contributions from ωðρ 0 Þ → γπ 0 , the so-called nonresonant branching fraction of η 0 → γγπ 0 was determined to be ð6.16 AE 0.64 AE 0.67Þ × 10 −4 [9], which confirmed the theoretical prediction and indicated that this decay was dominated by the VMD processes. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license.…”

Theoretical analysis of the doubly radiative decays η(′)→π0γγ and Escribano1, Gonzàlez-Solís2, Jora3 et al. 2020Phys. Rev. D

“…At present, while there is only a course estimation for the branching ratio of the η 0 → π 0 γγ decay [8,9], there is no calculation or theoretical prediction for the η 0 → ηγγ branching ratio. Second, the BESIII Collaboration has recently reported the first measurements for the decays η 0 → π 0 γγ [10] and η 0 → ηγγ [11], thus making the topic of timely interest [12]. Third, the analysis of these decays could help extract relevant information on the properties of the lowest-lying scalar resonances, in particular, the isovector a 0 ð980Þ from the two η ð0Þ → π 0 γγ processes and the isoscalars σð500Þ and f 0 ð980Þ from the η 0 → ηγγ decay, thus complementing other investigations such as the studies of V → P 0 P 0 γ decays (V ¼ ρ 0 ; ω; ϕ and P 0 ¼ π 0 ; ηÞ [13], D and J=ψ decays, central production, etc.…”

“…The latest PDG states a fit value of BR ¼ ð2.56 AE 0.22Þ × 10 −4 [14]. For the η 0 → π 0 γγ decay, the BESIII Collaboration has recently reported for the first time the associated m 2 γγ invariant mass distribution [10]. The measured branching fraction is BR ¼ ð3.20 AE 0.07 AE 0.23Þ × 10 −3 , superseding the upper limit BR < 8 × 10 −4 at 90% CL determined by the GAMS-2000 experiment [24].…”