FT0: add threshold for crosstalk-induced low-amplitude digits

Author: Szymon Pulawski

Detectors/FIT/FT0/base/include/FT0Base/FT0DigParam.h

@@ -43,14 +43,15 @@ struct FT0DigParam : o2::conf::ConfigurableParamHelper<FT0DigParam> {
   float mNoiseVar = 0.1;              // noise level
   float mNoisePeriod = 1 / 0.9;       // GHz low frequency noise period;
   short mTime_trg_gate = 153;         // #channels as in TCM as in Pilot beams ('OR gate' setting in TCM tab in ControlServer)
-  short mTime_trg_vertex_gate = 100;  // #channels as in TCM as in Pilot beams ('OR gate' setting in TCM tab in ControlServer)
+  short mTime_trg_vertex_gate = 100;  // #channels as in TCM for VTX trigger 
   float mAmpThresholdForReco = 5;     // only channels with amplitude higher will participate in calibration and collision time: 0.3 MIP
   short mTimeThresholdForReco = 1000; // only channels with time below will participate in calibration and collision time
 
   float mMV_2_Nchannels = 2.;         // amplitude channel 7 mV ->14channels
   float mMV_2_NchannelsInverse = 0.5; // inverse amplitude channel 7 mV ->14channels (nowhere used)
 
-  float Cross_Talk_Frac = 0.05f;      // Crosstalk between channels
+  float Cross_Talk_Frac = 0.10f;      // Crosstalk between channels
+  float mAmpThresholdForCrossTalkDigit = 5.f; // Treshold for low crosstalk signals
 
   O2ParamDef(FT0DigParam, "FT0DigParam");
 };

Detectors/FIT/FT0/simulation/src/Digitizer.cxx

@@ -489,17 +489,24 @@ void Digitizer::storeBC(BCCache& bc,
       finalAmp[nb2] += directXtalk;
       finalAmp[diag] += diagXtalk;
 
-      auto propagateIfEmpty = [&](int dst) {
-        if (!chValid[dst]) {
-          chValid[dst] = true;
-          chTime[dst] = chTime[src];
-          chChain[dst] = chChain[src];
-        }
-      };
+      if (!chValid[nb1] && directXtalk >= params.mAmpThresholdForCrossTalkDigit) {
+        chValid[nb1] = true;
+        chTime[nb1] = chTime[src];
+        chChain[nb1] = chChain[src];
+      }
+
+      if (!chValid[nb2] && directXtalk >= params.mAmpThresholdForCrossTalkDigit) {
+        chValid[nb2] = true;
+        chTime[nb2] = chTime[src];
+        chChain[nb2] = chChain[src];
+      }
+
+      if (!chValid[diag] && diagXtalk >= params.mAmpThresholdForCrossTalkDigit) {
+        chValid[diag] = true;
+        chTime[diag] = chTime[src];
+        chChain[diag] = chChain[src];
+      }
 
-      propagateIfEmpty(nb1);
-      propagateIfEmpty(nb2);
-      propagateIfEmpty(diag);
     }
   }
 
@@ -512,6 +519,12 @@ void Digitizer::storeBC(BCCache& bc,
     if (amp > 4095.f) {
       amp = 4095.f;
     }
+    const bool hasPrimarySignal = (baseAmp[ipmt] > 0.f);
+    const bool isCrossTalkOnly = (!hasPrimarySignal && amp > 0.f);
+
+     if (isCrossTalkOnly && amp < params.mAmpThresholdForCrossTalkDigit) {
+       continue;
+    }
 
     const int smeared_time = chTime[ipmt];
     const int chain = chChain[ipmt];