FT0 crosstalk in digitizer#15466
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Please consider the following formatting changes to AliceO2Group#15466
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This PR introduces a neighbour-channel crosstalk model in the FT0 digitizer and adds a dedicated threshold to suppress very low-amplitude crosstalk-induced digits.
The crosstalk is applied at the digitizer level before trigger calculation, so that its effect is propagated consistently to channel digits, PM charge sums, and trigger decisions.
Main changes
Added configurable crosstalk fraction: float Cross_Talk_Frac = 0.10f;
Added configurable threshold for low-amplitude crosstalk-only digits: float mAmpThresholdForCrossTalkDigit = 5.f;
Implemented crosstalk propagation between channels within a 4-channel PMT grouping.
Crosstalk model: direct neighbouring channels receive f * A, diagonal channel receives (f / 3) * A, original source-channel amplitude is preserved.
Crosstalk is added before trigger calculation and therefore contributes to: channel digits, PM charge sums, central and semicentral trigger logic.
Channels with genuine primary signal are unaffected by the low-amplitude crosstalk threshold.
Channels activated only by crosstalk are rejected before digit creation if their final amplitude is below: mAmpThresholdForCrossTalkDigit
Motivation:
The neighbour-channel crosstalk model is introduced to improve the description of channel correlations observed in data.
However, crosstalk-induced signals are added after the standard hit-based signal formation chain. Without an additional protection, this can generate an excess of very small ADC signals in neighbouring channels. Such a low-amplitude tail is not observed in data.
The additional threshold suppresses these artificial low-ADC crosstalk-only digits while preserving larger crosstalk contributions relevant for detector response and trigger studies.
The new implementation significantly improves the FT0 signal description in Pb--Pb data while introducing only very small modifications in pp collisions.
Backward compatibility
When:
Cross_Talk_Frac = 0
the crosstalk contribution is disabled and the baseline digitizer behaviour is restored.
Validation
The implementation was tested by comparing FT0 channel-amplitude distributions with and without crosstalk. The additional threshold improves the low-ADC behaviour of MC while preserving the intended neighbour-channel crosstalk effect.
Related slides:
https://indico.cern.ch/event/1683590/contributions/7076968/attachments/3270462/5842052/20260507-%20Crosstalkv2.pdf