Bepcii and Besiii
The Beijing Electron Collider has been upgraded (BEPCII) to a two-ring collider with a design luminosity of $1 \times 10^{33}$cm$^{-2}$ s$^{-1}$ at a center-of-mass energy of 3.78 GeV. It will operate between 2 and 4.6 GeV in the center of mass. With this luminosity, the BESIII detector will be able to collect, for example, 10 billion $J/\psi$ events in one year of running. This will be a unique facility in the world opening many physics opportunities. BEPCII and BESIII are both currently being commissioned, first events have been obtained, and data taking will take place in fall 2008.
Electronics of BESIII TOF monitor system
This paper describes the control electronics for the TOF (Time of Flight) monitor system of BESIII. A 9U VME module is designed as an interface between the TOF monitor laser box and BESIII data acquisition (DAQ) system. It enables the laser source, sends trigger signals to the laser driver, switches the optic path, and measures the charge and arrival time of pulses from two reference phototubes (Ref. PMT) as well. After sending each trigger pulse to the laser source, the monitor electronics module also sends a L1 (Level 1) trigger to the TOF readout system. The whole interface and control logic is implemented in an Altera FPGA (Field Programmable Gate Array) mounted on the Monitor module, and signals from the Ref. PMTs of the laser system are digitized with the CERN HPTDC technique. According to a serial of experimental tests, the time resolution of monitor electronics is better than 25ps, and the relative methodical error of charge measurement is less than 0.5% after quadratic fitting. The TOF monitor system was installed at the end of 2007, and has been operated continuously since then. A total time resolution of about 70ps and a charge resolution of about 4% of the TOF counters have been obtained during field monitor tests.
Hadronic production by e+e− collisions at the energy 990 MeV with the Orsay storage ring
Abstract Data were taken at the energy 2 E = 990 MeV to search for multibody events, with the same large solid angle detector which has been used for the measurement of the ϱ , ω and φ production by e + e − annilations. Assuming a π + π − π 0 π 0 production by the quasi two-body process e + e − → ϱ → ωπ 0 we give the correspondi ng cross section σ (e + e − → π + π − π 0 π 0 ) = (1.1 ± 0.5) 10 −32 cm 2 . Since no events with 3 and 4 charged pions have been observed σ (e + e − → π + π − π 0 π − ) ⩽ 1.5 × 10 −33 cm 2 .