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↗

DOE OSTI2017

Observation of χ c 2 → η ' η ' and χ c 0 , 2 → η η '

Using a sample of 448.1×10 6 ψ(3686) events collected with the BESIII detector in 2009 and 2012, we study the decays χ c 0,2 → η ' η ' and η η ' . The decays χ c 2 → η ' η ' , χ c 0 → η η ' and χ c 2 → η η ' are observed for the first time with statistical significances of 9.6 , 13.4 and 7.5 , respectively. The branching fractions are determined to be B( χ c 0 → η ' η ' ) = (2.19 ± 0.03 ± 0.14) × 10 -3 , B( χ c 2 → η ' η ' ) = (4.76 ± 0.56 ± 0.38) × 10 -5 , B( χ c 0 → η η ' ) = (8.92±0.84±0.65)×10 -5 and B( χ c 2 → η η ' ) = (2.27±0.43±0.25)×10 -5 , where the first uncertainties are statistical and the second are systematic. The precision for the measurement of B( χ c 0 → η ' η ' ) is significantly improved compared to previous measurements. Based on the measured branching fractions, the role played by the doubly and singly Okubo-Zweig-Iizuka disconnected transition amplitudes for χ c 0 , 2 decays into pseudoscalar meson pairs can be clarified.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2017

Improved measurements of two-photon widths of the χ c J states and helicity analysis for χ c 2 → γ γ

Based on 448.1 x 10 6 ψ(3686) events collected with the BESIII detector, the decays ψ(3686) → γχ cJ ,χ cJ → γγ(J = 0,1,2) are studied in this paper. The decay branching fractions of χ c0,2 → γγ are measured to be β(χ c0 → γγ) = (1.93 ± 0.08 ± 0.05 ± 0.05) x 10 -4 and β(χ c2 → γγ) = (3.10 ± 0.09 ± 0.07 ± 0.11) x 10 -4 , which correspond to two-photon decay widths of Γ γγ (χ c0 ) = 2.03 ± 0.08 ± 0.06 ± 0.13 keV and Γ γγ (χ c2 ) = 0.60 ± 0.02 ± 0.01 ± 0.04 keV with a ratio of R = Γ γγ (χ c2 )/Γ γγ (χ c0 ) = 0.295 ± 0.014 ± 0.007 ± 0.027, where the uncertainties are statistical, systematic and associated with the uncertainties of β(ψ(3686) → γχ c0,2 ) and the total widths Γ(χ c0,2 ), respectively. For the forbidden decay of χ c1 → γγ, no signal is observed, and an upper limit on the two-photon width is obtained to be Γ γγ (χ c1 ) < 5.3 eV at the 90% confidence level. Finally, the ratio of the two-photon widths between helicity-zero and helicity-two components in the decay χ c2 → γγ is also measured to be f 0/2 = Γ λ=0 γγ (χ c2 )/Γ λ=2 γγ (χ c2 ) = (0.0 ± 0.6 ± 1.2) x 10 -2 , where the uncertainties are statistical and systematic, respectively.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Search for the rare decay D + → D 0 e + ν e

Using a data set with an integrated luminosity of $2.93\text{ }\text{ }{\mathrm{fb}}^{{-}1}$ collected at $\sqrt{s}=3.773\text{ }\mathrm{GeV}$ with the BESIII detector operating at the BEPCII storage rings, we search for the rare decay ${D}^{+}{\rightarrow}{D}^{0}{e}^{+}{{\nu}}_{e}$. No signal events are observed. We set the upper limit on the branching fraction for ${D}^{+}{\rightarrow}{D}^{0}{e}^{+}{{\nu}}_{e}$ to be $1.0\times{}1{0}^{{-}4}$ at the 90% confidence level.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗