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    User name X. Zheng

    Log entry time 10:56:12 on November 12, 2009

    Entry number 299174

    This entry is a followup to: 298609

    keyword=PVDIS DAQ - Right arm gas cherenkov threshold

    On 11/9 Ramesh doubled the GC threshold on the right arm from 30mV to 60mV (halog 298609). Below are two sets of plots showing the effect on R.cer.asum_c. Fig.1 is from run 4921 and Fig. 2 is from run 4853. Fig.3 and 4 are the unzoomed version. Run 4921 is after doubling and 4853 is before doubling. (Doubling happened after run 4892). The zoomed version shows only a slight increase from channel 80 to about 95. Since the single ph.e. peaks are aligned to channel 138 (halog 298147), we want this cutoff to appear near channel 200.

    Since increasing the threshold from 30mV to 60mV causes an increase of 15 channels, this means we need to increase the threshold further by 210mV (105 channels) to see a cutoff in channel 200. The new threshold should therefore be 60+210=270mV.

    Since 270mV sounds too high, Ramesh is looking at the ADC spectrum of the hardware-summed cerenkov signal to check the change in cutoff. And we could take a couple of short runs with different GC threshold to confirm it.

    Figure 1 Run 4921

    Figure 2 Run 4853

    Figure 3 Run 4921

    Figure 4 Run 4853