Trigger Timing

As a byproduct of this study, shown in Fig. 9 is the time of flight distribution for recoil protons from the reaction $^9$Be $(\gamma ,p\eta ')\,^8$X. Only hits from $60^o$ to $90^o$ in polar angle have been included so that all tracks have about the same path length from the target to the scintillators. The time-of-flight r.m.s. spread of about 700ps comes almost entirely from the velocity spread of the protons. From this plot one can judge what time resolution is needed for the BSD readout. The multi-hit TDC (LeCroy 1877) with a specified r.m.s. resolution of 400ps is quite adequate, and the improvement to be had with a high-resolution TDC for these events is marginal.

Figure 9: Time of flight distribution for recoil protons from the reaction $^9$Be $(\gamma ,p\eta ')\,^8$X. Only hits between polar angles of $60^o$ and $90^o$ are included in this spectrum.