Using a sample of 448.1×10 6 ψ(3686) events collected with the BESIII detector, a search for the isospin violating decay η c → π⁺π⁻π⁰ via ψ(3686) → γ η c is presented. No signal is observed, and the upper limit on B(ψ(3686) → γ η c ) × B( η c → π⁺π⁻π⁰) is determined to be 1.6 × 10 -6 at the 90% confidence level. In addition, a search for η (1405) → f 0 (980)π 0 in (3686) radiative decays is performed. No signal is observed, and the branching fraction B(ψ(3686) → γη(1405))×B( η (1405) → f 0 (980)π 0 ) × B(f 0 (980) → π⁺π⁻ is calculated to be less than 5.0 × 10 -7 at the 90% confidence level.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2017

Branching fraction measurement of J / ψ → K S K L and search for J / ψ → K S K S

Using a sample of 1.31×10 9 J/ψ events collected with the BESIII detector at the BEPCII collider, we study the decays of J/ψ→ K S K L and K S K S . The branching fraction of J/ψ→ K S K L is determined to be B(J/ψ→ K S K L ) = (1:93 0:01 (stat:) 0:05 (syst:))×10 -4 , which signi cantly improves on previous measurements. No clear signal is observed for the J/ψ→ K S K S process, and the upper limit at the 95% con dence level for its branching fraction is determined to be B(J= ! K S K S ) < 1:4×10 -8 , which improves on the previous searches by 2 orders in magnitude and reaches the order of the Einstein-Podolsky-Rosen expectation.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2017

Search for the rare decays J / ψ → D 0 e + e - + c . c . and ψ ( 3686 ) → D 0 e + e - + c . c .

Using the data samples of (1310.6 ± 7.2) × 10 6 J / ψ events and (448.1 ± 2.9) × 106 (3686) events collected with the BESIII detector, we search for the rare decays J / ψ → D 0 e + e - + c.c. and (3686) → D 0 e + e - + c.c.. No significant signals are observed and the corresponding upper limits on the branching fractions at the 90% confidence level are determined to be B( J / ψ → D0e+e- + c.c.) < 8.5 × 10 -8 and B( (3686) → D0e+e- + c.c.) < 1.4 × 10 -7 , respectively. Our limit on B( J / ψ → D 0 e + e - + c.c.) is more stringent by two orders of magnitude than the previous results, and the B( (3686) → D 0 e + e - + c.c.) is measured for the first time.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2017

Observation of the helicity-selection-rule suppressed decay of the χ c 2 charmonium state

The decays of χ c 2 → K + K - π 0 , K S K ± π ∓ , and π + π - π 0 are studied with the ψ ( 3686 ) data samples collected with the Beijing Spectrometer (BESIII). For the first time, the branching fractions of χ c 2 → K*$\bar{K}$ , χ c 2 → $a_2^±$(1320)π ∓ /$a_2^0$(1320)π 0 , and χ c 2 → ρ( 770 ) ± π ∓ are measured. Here, K*$\bar{K}$ denotes both K* ± K ∓ and its isospin-conjugated process K* 0 $\bar{K}$ 0 +c.c., and K* denotes the resonances K*(892), $K_2^*$(1430), and $K_3^*$(1780). The observations indicate a strong violation of the helicity selection rule in χ c 2 decays into vector and pseudoscalar meson pairs. The measured branching fractions of χ c 2 → K*(892)$\bar{K}$ are more than ten times larger than the upper limit of χ c 2 → ρ ( 770 ) ± π ∓ , which is so far the first direct observation of a significant U -spin symmetry breaking effect in charmonium decays.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗