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First Measurement of the Absolute Branching Fraction of η_{c}→γγ
M Ablikim1, M N Achasov2, P Adlarson3
1Institute of High Energy Physics, Beijing 100049, People's Republic of China.
Abstract:
We apply a tag-and-probe method to precisely measure the absolute branching fraction of the decay η_{c}→γγ with the BESIII experiment at BEPCII. Starting with a large initial sample of (2712.4±14.3)×10^{6} ψ(3686) events, a sample of 0.16×10^{6} η_{c} events is tagged via the golden channel ψ(3686)→π^{0}h_{c}, h_{c}→γη_{c}, effectively avoiding interference effects. The absolute branching fraction of η_{c}→γγ is measured for the first time to be B(η_{c}→γγ)=(2.45±0.48_{stat}±0.09_{syst})×10^{-4}. Using the world average value of the total width of the η_{c}, the partial decay width of η_{c}→γγ is calculated to be Γ(η_{c}→γγ)=(7.48±1.48_{stat}±0.30_{syst}) keV.
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