Using a sample of 1.06 × 10 8 ψ ′ decays collected by the BESIII detector, χ c0 and χ c2 decays into π 0 π 0 and ηη are studied. The branching fraction results are Br(χ c0 → π 0 π 0 ) = (3.23 ± 0.03 ± 0.23 ± 0.14) × 10 −3 , Br(χ c2 → π 0 π 0 ) = (8.8 ± 0.2 ± 0.6 ± 0.4) × 10 −4 , Br(χ c0 → ηη) = (3.44 ± 0.10 ± 0.24 ± 0.2) × 10 −3 , and Br(χ c2 → ηη) = (6.5 ± 0.4 ± 0.5 ± 0.3) × 10 −4 , where the uncertainties are statistical, systematic due to this measurement, and systematic due to the branching fractions of ψ ′ → γχ cJ , respectively. The results provide information on the decay mechanism of χ c states into pseudoscalars.

We present measurements of the charmonium state h(c)(1P(1)) made with 106x10(6) psi' events collected by BESIII at BEPCII. Clear signals are observed for psi'-->pi0 h(c) with and without the subsequent radiative decay h(c)-->gamma eta(c). First measurements of the absolute branching ratios B(psi'-->pi0 h(c)) = (8.4+/-1.3+/-1.0) x 10(-4) and B(h(c)-->gamma eta(c)) = (54.3+/-6.7+/-5.2)% are presented. A statistics-limited determination of the previously unmeasured h(c) width leads to an upper limit Gamma(h(c))<1.44 MeV (90% confidence). Measurements of M(h(c)) = 3525.40+/-0.13+/-0.18 MeV/c2 and B(psi'-->pi0 h(c)) x B(h(c)-->gamma eta(c)) = (4.58+/-0.40+/-0.50) x 10(-4) are consistent with previous results.

The decay channel Ψ′ → π+π− J/Ψ(J/Ψ → γpp̄) is studied using a sample of 1.06 × 108 Ψ′ events collected by the BESIII experiment at BEPCII. A strong enhancement at threshold is observed in the pp̄ invariant mass spectrum. The enhancement can be fitted with an S-wave Breit–Wigner resonance function with a resulting peak mass of M = 1861+6−13 (stat)+7−26 (syst) MeV/c2 and a narrow width that is Γ < 38 MeV/c2 at the 90% confidence level. These results are consistent with published BESII results. These mass and width values do not match with well established mesons.

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The top hat electrostatic analyzer is widely used to measure ion and electron fluxes variation in the relatively small region of space. The goal of this investigation is to report our findings about the difference of the analyzer constant K determined by two methods that are respectively the theory (K the ) and simulation (K sim ). Firstly, an analyzer is designed with the radius R 1 = 30 mm and the gap d = 2 mm, and the performance parameters of analyzer are obtained, including the analyzer constant K, energy resolution ∆E/E k , and pixel geometric factor GF through the theory model and simulation. Since the analyzer constant K can be obtained both from theory (K the ) and simulation (K sim ), a difference between the two has been obtained and, in particular, K the has resulted greater than K sim . Analyzing the structure of top hat electrostatic analyzer, we drew as a conclusion that the non-uniform electrostatic field in the region of top hat accelerates the incident ions and generates the difference for the analyzer constant K. To analysis and take into account the difference between K the and K sim , a function f(R 0 /d), which depends on the design parameters, are derived from the simulated results. K: Very low-energy charged particle detectors; Particle tracking detectors; Plasma diagnostics -charged-particle spectroscopy; Instrumentation for radioactive beams (fragmentation devices; fragment and isotope, separators incl. ISOL; isobar separators; ion and atom traps; weak-beam diagnostics; radioactive-beam ion sources) 1Corresponding author.