Noise in Outer Detectors

  Six of the twenty-one outer detectors in the CsI calorimeter exhibit uncorrelated low energy noise. These detectors have an ADC value above 0.2 MeV two to three times more often than the other outer detectors. Moreover, this phenomenon is even more pronounced for events where more than 90 MeV is deposited into the CsI calorimeter. Figure 7.8 shows the count rates for the outer detectors for low energy events ( MeV), and high energy events ( MeV) where the effect is more prominent.

  
Figure 7.8: Histograms showing count rates in outer detectors, for CsI Sum  (top panel) and CsI Sum  (bottom). A detector is determined to have fired if its ADC value is greater than a predetermined threshold (0.2 MeV). Detectors four through nine show an abnormally high counting rate, particularly in the bottom panel, when the total energy deposited into the calorimeter is greater than 90 MeV.

In order to check for correlations between the noisy detectors, a subset of their ADC values have been plotted against each other in Fig. 7.9. No correlation is apparent.

  
Figure 7.8: ADC value correlation histograms between noisy detectors for the one arm trigger configuration. No correlation between these detectors is apparent, which rules out the possibility of cross talk.

Finally, one can inspect the raw ADC spectra, above 0.2 MeV, of two noisy outer detectors and two normal outer detectors in Fig. 7.10. The low energy noise is apparent in the spectra of detectors 8 and 9.

  
Figure 7.10: CsI ADC spectra 0.2 MeV above the pedestal for two normal detectors (top panels) and two noisy detectors (bottom panels) for the single arm trigger configuration.