Abstract
To take the full advantage of the ψ(3686) data set collected at e+e- collider at τ-charm energy region, a tag method is developed to directly measure the J/ψ meson decay branching fractions absolutely. The J/ψ meson decay can be measured with the J/ψ sample tagged by the two soft charged pions from the decay ψ(3686)→J/ψπ+π-. This method is illustrated by comparing the input and output branching fractions of J/ψ→γη with 106 million inclusive ψ(3686) Monte Carlo samples. The consistent result confirms the validity of the tag method.
Highlights
The firstly discovered charmonium J/ψ [1, 2], JPC = 1−−, is the lowest one among those which can be produced directly in e+e− annihilation
An energy scan experiment performed around the J/ψ resonance can solve the problem induced by interference effect, while it is not effective for the final states with undistinguishable backgrounds from other processes
The good photon candidate showers reconstructed from the barrel Electromagnetic Calorimeter (EMC) (| cos θ| < 0.80) must have a minimum energy of 25 MeV, while those in the end caps (0.86 < | cos θ| < 0.92) must have at least 50 MeV, where the energies deposited in nearby Time of Flight (TOF) counters are included
Summary
The summation of the measured J/ψ decay branching fraction is not more than 60% [15] without considering the interference between resonance and continuum amplitudes until now, which hampers the understanding of its properties. The J/ψ production and decay property are studied by using the data collected from e+e− collisions at the J/ψ resonance traditionally. At this energy, the events consist mostly of e+e− → J/ψ, e+e− → l+l− (l represents e, μ), with small amounts of three-flavor continuum and other processes such as γV, where V represents vector meson. Considering the large branching fraction of ψ(3686) → J/ψπ+π−, (34.67 ± 0.30)% [15], this sample can naturally be used to study the J/ψ decay. The feasibility of the method is verified by examining the input and output branching fractions of J/ψ → γη in the inclusive ψ(3686) Monte Carlo (MC) sample
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