Large-Area Scintillator Hodoscope with 50 ps Timing Resolution Onboard   BESS
  We describe the design and performance of a large-area scintillator hodoscope onboard the BESS rigidity spectrometer; an instrument with an acceptance of 0.3 m^{2}sr.   The hodoscope is configured such that 10 and 12 counters are respectively situated in upper and lower layers.   Each counter is viewed from its ends by 2.5 inch fine-mesh photomultiplier tubes placed in a stray magnetic field of 0.2 Tesla.   Various beam-test data are presented.   Use of cosmic-ray muons at ground-level confirmed 50 ps timing resolution for each layer, giving an overall time-of-flight resolution of 70 ps rms using a pure Gaussian resolution function.   Comparison with previous measurements on a similar scintillator hodoscope indicates good agreement with the scaling law that timing resolution is proportional to 1/$\sqrt{N_{\rm pe}}$, where $N_{\rm pe}$ is the effective number of photoelectrons. 
Y. Shikaze, S. Orito, T. Mitsui, K. Yoshimura, H. Matsumoto, H.   Matsunaga, M. Nozaki, T. Sonoda, I. Ueda, T. Yoshida