Prospects for searching the η→e^+e^- rare decay at the CSR

We study the possibility of searching the η→e＋e- rare decay on the Cooling Storage Ring （CSR） at Lanzhou. The main features of the proposed Internal Target Experiment （ITE） and External Target Facility （ETF） are included in the Monte Carlo simulation. Both the beam condition at the CSR and the major physics backgrounds are carefully taken into account. We conclude that the ITE is more suitable for such a study due to better detector acceptance and higher beam density. At the maximum designed luminosity （1034cm-2s-1 ）, η→e＋e- events can be collected every～400 seconds at the CSR. With a mass resolution of 1 MeV, the expected signal-to-background （S/B） ratio is around 1.

Observation of a p mass threshold enhancement in ψ′→π+π-J/ψ(J/ψ→γp) decay

The decay channel ψ′→ π 〉＋π^-J/ψ（J/ψ 〉 γp^-p） is studied using a sample of 1.06 × 10^8 ψ′ events collected by the BESIII experiment at BEPCII. A strong enhancement at threshold is observed in the p^-p invariant mass spectrum. The enhancement can be fitted with an S-wave Breit-Wigner resonance function with a resulting peak mass of M = 1861-13^＋6 （stat）-26^＋7 （syst） MeV/c^2 and a narrow width that is Г 〈 38 MeV/c^2 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.

Determination of the number of ψ' events at BES Ⅲ

The number of φ＇ events accumulated by the BESIII experiment from March 3 through April 14, 2009, is determined by counting inclusive hadronic events. The result is 106.41×（1.00±0.81%）×10^6. The error is systematic dominant; the statistical error is negligible.

A GEANT4 simulation study of BESⅢ endcap TOF upgrade

A GEANT4-based Monte-Carlo （MC） model is developed to study the performance of endcap time- of-flight （ETOF） at BESIII. It＇s found that the multiple scattering effects, mainly from the materials at the MDC endcap, can cause multi-hit on the ETOF＇s readout cell and significantly influence the timing property of ETOF. A multi-gap resistive plate chamber （MRPC） with a smaller readout cell structure is more suitable for the ETOF detector due to significantly reduced multi-hit rate （per channel）, from 71.5% for currently-used scintillator-based ETOF to 21.8% or 16.7% for MRPC-based ETOF, depending on the readout pad size used. The timing performance of an MRPC ETOF is also improved. These simulation results suggest and guide an ETOF upgrade effort at BESIII.

Measurement of the integrated luminosities of the data taken by BESⅢ at √s=3.650 and 3.773 GeV

Data sets were collected with the BESⅢ detector at the BEPCⅡ collider at the center-of-mass energy of √s=3.650 GeV during May 2009 and at √s=3.773 GeV from January 2010 to May 2011. By analyzing the large angle Bhabha scattering events, the integrated luminosities of the two data sets are measured to be （44.49±0.02±0.44） pb-1 and （2916.94±0.18±29.17） pb-1, respectively, where the first error is statistical and the second error is systematic.

Determination of the number of J/ψ events with J/ψ → inclusive decays

The number of J/ψ events collected with the BES detector at the BEPC from June 12 to July 28, 2009 is determined to be （225.3 ± 2.8） × 10^ 6 using J/ψ→inclusive events, where the uncertainty is the systematic error and the statistical one is negligible.