1. ZDC Status A.Mestvirishvili Iowa

2. Quite while we had some problems with ZDC, QIE saturations, Reflections, Noise etc. To improve the situation several different steps were taken. Since for the time being we can shoot laser light only in one arm of ZDC (ZDC-) another arm was completely disconnected to avoid any possible ground loops. Two ZDC’s have same HV grounding. For now we are working only with ZDC-. Channel 4 in HAD part is discconnected Laser+scope studies reviled a problem in a splitter box.

3. Red arrow - signal. Green arrow -Positive spike Splitter Box Reduced intensity

4. Signal shape without splitter Cable directly to scope Perfect signal – scale 10ns/division No reflections – scale 1us Modification – splitters were removed And signals were fed directly to QIE Signal is wide – width at base line is ~20ns And tail extends further, due to the very long cables used – 204m. This is perfectly Reflected in data.

5. Signal shape from data After all this exercises and simple modifications we started timing of ZDC- with laser Yesterday and today we were using HF partition for timing (ZDC is in HF partition) EM1EM2 EM3EM4 EM5HAD1 HAD2HAD3 HAD4 is disconnected. Signals from all connected channels Is seen. It is wide – expected. Had1 is unusually wide Due to the very high gain PMT. Reducing the Light bring right hand side tail down. Settings for L1ADelay and Pipeline length for ZDC- for now are L1ADelay=199 and Pipeline Length=80 Raw ADC counts vs TS, 500 Events, normalized to one event

6. Signal spectra and timing (rough calculations) Pedestal subtracted signal distribution Peds – av. Of first two time slice Signal – three TS, maximum, one before And one after Timing HAD1 – channel with high tail

7. Pedestal run We do not have a special configuration for ZDC pedestals A Laser configuration file was used Laser was pointing somewhere else and light was attenuated as much as possible (both attenuator wheels at position 12) 10000K Events were taken in this mode

8. Pedestals EM1EM2 EM3EM4 EM5HAD1 HAD2HAD4 To broad and strange pedestal distributions

9. Pedestals: Event by event In some cases pedestals within the event drops to zero: Event 16, TS 1-10 Four event in this plot

10. Conclusion and TODO Splitter was causing reflections, after removing the splitters good signal. ZDC- is timed in with lather. For now L1ADelay=199 and PL=80 (L1ADelay is likely to change) Same is needed to be done for ZDC+ ZDC+ and ZDC- has to be equalized, now one of the ZDC arm 141ns shorter in terms of lather light propagation to PMT. Strange behavior of the pedestals – noise? (most probably) needs to be understood