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Sources of cross-talk

Two sources of cross-talk are expected:

1. global cross-talk in the AMPLEX chips is known [30] to be negative and proportional to the total charge received by the chip.
2. negative cross-talk due to capacitive coupling between pads through the detector board.

The AMPLEX group performed test measurements [30] where detector board cross-talk was eliminated by disconnecting two pairs of channels adjacent to the stimulated one on each side of it, but in the actual experimental application this source of cross-talk should be expected. Its magnitude was not a priori clear. In the AMPLEX test measurements [30], -1.5% global cross-talk in the chip was observed. The experts admit [30]: ``The origin of this effect is not yet understood''. They found the adjacent cross-talk to be negligible. Our channel-to-channel correlation analysis of the NA44 central $PbPb$ data, discussed in detail in this section, reveals 9% adjacent cross-talk. The global cross-talk was seen with event displays, although rarely, and did not manifest itself in the channel-to-channel correlation analysis.