After disscution with Xin, now I have some idea about the BB Cherenkov signal.
All the figures are from the run#3713 & 3714, which are taken on BeO target, 1uA, with a threshold as -0.1V. The number of total events is about 0.7M.
In Fig1 the black line is the Cherenkov TDC signals trigged by T1 or T6. The red line has an additional cut. as pre-shower energy is larger than 600 to choose electron, while for the green line the cut is less than 600. The flatness of green one tells us that the peak is really caused by electron. Xin pointed out that in ADC. channel only signals in this peak make sense, the others are totally junk. So below I only plot the ADC channel. within this narrow timing window.
In Fig2 they are the ADC signals within this window, under a reasonable cut on tracking vertex. The red one still stand for electrons which are choosed by cuts on preshower while the green one is for pion choosed by the same way. The fact that green peaks and red peaks are roughly in the same position tells that even in the narrow timing window there are still a lot of junk. I think it is caused by crazy radiation background, which makes the the amplitude of. our PMD do not tell us how many Cherenkov photons go into it. Maybe better shielding can partly solve this problem.
Fig3 also comes from ADC signal, in the same timing window but trigged by T3 or T5 or EDTM. This tells us the absolutely junk can also give us the same shape in ADC channels. Fortunately we see only little events in the last 10 channels which. are located farther from beam line. So the Cherenkov is not totally hopeless.
A copy of this log entry has been emailed to: email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com