Precision measurement of the branching fractions of $η^\prime$ decays

Abstract

Based on a sample of (1310.6 ± 7.0) × 10 6 J/ψ events collected with the BESIII detector, we present measurements of J/ψ and η ′ absolute branching fractions using the process J/ψ → γη ′ . By analyzing events where the radiative photon converts into an e + e − pair, the branching fraction for J/ψ → γη ′ is measured to be (5.27 ± 0.03 ± 0.05) × 10 −3 . The absolute branching fractions of the five dominant decay channels of the η ′ are then measured for the first time and are determined to be B(η ′ → γπ + π − ) = (29.90±0.03±0.55)%, B(η ′ → ηπ + π − ) = (41.24±0.08±1.24)%, B(η ′ → ηπ 0 π 0 ) = (21.36±0.10±0.92)%, B(η ′ → γω) = (2.489±0.018±0.074)%, and B(η ′ → γγ) = (2.331±0.012±0.035)%, where the first uncertainties are statistical and the second systematic.

Precision tests of fundamental physics withηandη′mesons

“…The PDG value for the branching ratio B(η → ωγ) = 2.62(13)% [54] is dominated by a BESIII measurement [330], updated most recently to B(η → ωγ) = 2.489(76)% [55].…”

“…[512,513] for preliminary results of the same investigation). Similar to what was found for η → π 0 γγ, vector-meson exchange (by ρ 0 , ω, and φ) was identified as the dominant mechanism; the main difference to the η decay is that in particular the ω can go (almost) on-shell (to the extent its width can be neglected), i.e., η → π 0 γγ for instance can proceed as two real sequential two-body decays, according to η → ωγ (with branching ratio 2.489(76)% [55]) with subsequent ω → π 0 γ (branching ratio 8.40( 22)%). The theoretical calculation of Refs.…”