Univ Sci & Technol China, Dept Modern Phys, Hefei 230026, Peoples R China
; CAS, Inst High Energy Phys, Beijing 100049, Peoples R China
The Endcap TOF (ETOF) of Beijing Spectrometer (BES III) consists of 2 x 48 pieces of trapezoidal scintillator (BC408). Its main physics goal is to reach the intrinsic time resolution of 80ps and to realize the 2 sigma pi/k separation at momentum up to 1 GeV/c. In this paper, the performance of one ETOF module under different conditions, such as with different packing material, operating voltage and shape of scintillator, is tested by the beam of 800MeV electrons at IHEP. The primary results show that the intrinsic time resolution of ETOF with Tyvek paper wrapping is between 70-90ps.