J. G. Lu

Simulation and performance study of ceramic THGEM

The THGEMs based on ceramic substrate were developed successfully for neutron and single photon detection. The influences on thermal neutron scattering and the internal radioactivity of both ceramic and FR-4 substrates were studied and compared. The ceramic THGEMs are homemade of 200 um hole diameter, 600 um pitch, 200 um thickness, 80 um rim, and 50 mm*50 mm sensitive area. The FR-4 THGEMs with the same geometry were used for the reference. The gas gain, energy resolution and gain stability were measured in different gas mixtures by using the 5.9 keV X-rays. The maximum gain of single layer ceramic THGEM reaches 6*104 and 1.5*104 at Ne+CH4 = 95:5 and Ar+i-C4H10 = 97:3, respectively. The energy resolution is better than 24%. The good gain stability was obtained during more than 100 hour continuous test at Ar+CO2 = 80:20. By using the 239Pu source, the alpha deposited energy spectrum and gain curve of ceramic THGEM were measured.

Luminosity monitoring and calibration of BLM

The BEPC II Luminosity Monitor (BLM) monitors relative luminosity per bunch. The counting rates of gamma photons, which are proportional to the luminosities from the BLM at the center of mass system energy of the psi(3770) resonance, are obtained with a statistical error of 0.01% and a systematic error of 4.1%. Absolute luminosities are also determined by the BESIII End-cap Electro-Magnetic Calorimeter (EEMC) using Bhabha events with a statistical error of 2.3% and a systematic error of 3.5%. The calibration constant between the luminosities obtained with the EEMC and the counting rates of the BLM are found to be 0.84 +/- 0.03 (x10(26) cm(-2).count(-1)). With the calibration constant, the counting rates of the BLM can be scaled up to absolute luminosities.

Simulation of background reduction and Compton suppression in a low-background HPGe spectrometer at a surface laboratory

High-purity germanium (HPGe) detectors are well suited to analyse the radioactivity of samples. In order to reduce the environmental background for an ultra-low background HPGe spectrometer, low-activity lead and oxygen free copper are installed outside the probe to shield from gamma radiation, with an outer plastic scintillator to veto cosmic rays, and an anti-Compton detector to improve the peak-to-Compton ratio. Using Geant4 tools and taking into account a detailed description of the detector, we optimize the sizes of these detectors to reach the design requirements. A set of experimental data from an existing HPGe spectrometer was used to compare with the simulation. For the future low-background HPGe detector simulation, considering different thicknesses of BGO crystals and anti-coincidence efficiency, the simulation results show that the optimal BGO thickness is 5.5 cm, and the peak-to-Compton ratio of (40).K is raised to 1000 when the anti-coincidence efficiency is 0.85. In the background simulation, 15 cm oxygen-free copper plus 10 cm lead can reduce the environmental gamma rays to 0.0024 cps/100 cm(3) Ge (50 keV-2.8 MeV), which is about 10(-5) of the environmental background.

Measurements of the Mass and Width of the eta(c) Using the Decay psi (3686) -> gamma eta(c)

The mass and width of the lowest-lying S-wave spin singlet charmonium state, the η(c), are measured using a data sample of 1.06×10(8) ψ(3686) decays collected with the BESIII detector at the BEPCII storage ring. We use a model that incorporates full interference between the signal reaction, ψ(3686)→γη(c), and a nonresonant radiative background to describe the line shape of the η(c) successfully. We measure the η(c) mass to be 2984.3±0.6±0.6 MeV/c(2) and the total width to be 32.0±1.2±1.0 MeV, where the first errors are statistical and the second are systematic.

First measurement of the branching fraction of the decay ψ(2S)→τ+τ-

The branching fraction of the ψ(2S) decay into τ+τ− has been measured for the first time using the BES detector at the Beijing Electron-Positron Collider. The result is Bττ = (2.71± 0.43± 0.55)× 10−3 , where the first error is statistical and the second is systematic. This value, along with those for the branching fractions into e+e− and μ+μ− of this resonance, satisfy well the relation predicted by the sequential lepton hypothesis. Combining all these values with the leptonic width of the resonance, the total width of the ψ(2S) is determined to be (252±37) keV. PACS numbers: 13.20.Gd, 14.40.Gx, 14.60.-z, 14.60.Fg Typeset using REVTEX

Measurement of the branching fraction of [Formula presented] inclusive semileptonic decay [Formula presented]

The absolute inclusive semileptonic branching fraction of the D{sub s} meson has been measured based on 22.3 pb{sup {minus}1} of e{sup +}e{sup {minus}} collision data collected with the Beijing Spectrometer at {radical} (s) =4.03GeV. At this energy, the D{sub s} are produced in pairs: e{sup +}e{sup {minus}}{r_arrow}D{sub s}{sup +}D{sub s}{sup {minus}}. We reconstructed 171{plus_minus}21{plus_minus}15 D{sub s} events in five hadronic decay modes. In the recoil system of these events, several D{sub s} inclusive semileptonic decays were observed and the branching fraction is estimated to be B(D{sub s}{sup +}{r_arrow}e{sup +}X)=(7.7{sub {minus}4.3{minus}2.1}{sup +5.7+2.4}){percent}. {copyright} {ital 1997} {ital The American Physical Society}Author(s): Bai, JZ; Bardon, O; Bian, JG; Blum, I; Breakstone, A; Burnett, T; Chai, ZW; Chen, GP; Chen, HF; Chen, J; Chen, JC; Chen, SM; Chen, Y; Chen, YB; Chen, YQ; Cheng, BS; Cowan, RF; Cui, XZ; Ding, HL; Du, ZZ; Dunwoodie, W; Fan, XL; Fang, J; Fero, M; Gao, CS; Gao, ML; Gao, SQ; Gratton, P; Gu, JH; Gu, SD; Gu, WX; Gu, YF; Guo, YN; Han, SW; Han, Y; Harris, FA; He, J; He, JT; He, M; Hitlin, DG; Hu, GY; Hu, JL; Hu, QH; Hu, T; Hu, XQ; Huang, XP; Huang, YZ; Izen, JM; Jia, QP; Jiang, CH; Jin, S; Jin, Y; Jones, L; Kang, SH; Ke, ZJ; Kelsey, MH; Kim, BK; Kong, D; Lai, YF; Lan, HB; Lang, PF; Lankford, A; Li, J; Li, PQ; Li, Q; Li, RB; Li, W; Li, WD; Li, WG; Li, XH; Li, XN; Lin, SZ; Lu, F; Liu, HM; Liu, J; Liu, JH; Liu, Q; Liu, RG; Liu, Y; Liu, ZA; Lou, XC; Lowery, B; Lu, JG; Lu, JY; Luo, SQ | Abstract: The absolute inclusive semileptonic branching fraction of the [Formula presented] meson has been measured based on [Formula presented] of [Formula presented] collision data collected with the Beijing Spectrometer at [Formula presented] At this energy, the [Formula presented] are produced in pairs: [Formula presented] We reconstructed [Formula presented] [Formula presented] events in five hadronic decay modes. In the recoil system of these events, several [Formula presented] inclusive semileptonic decays were observed and the branching fraction is estimated to be [Formula presented]