Simulation example of multiplicity-triggered Pythia8

Author: preghenella

MC/config/common/external/trigger/multiplicity.C

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+// multiplicity trigger
+//
+//   usage: o2sim --trigger external --extTrgFile trigger_multiplicity.C
+// options:                          --extTrgFunc "trigger_multiplicity(-0.8, 0.8, 100)"
+//
+
+/// \author R+Preghenella - February 2020
+
+#include "Generators/Trigger.h"
+#include "TParticle.h"
+#include "TParticlePDG.h"
+
+o2::eventgen::Trigger
+  trigger_multiplicity(double etaMin = -0.8, double etaMax = 0.8, int minNch = 100)
+{
+  auto trigger = [etaMin, etaMax, minNch](const std::vector<TParticle>& particles) -> bool {
+    int nch = 0;
+    for (const auto& particle : particles) {
+      if (particle.GetStatusCode() != 1)
+        continue;
+      if (!particle.GetPDG())
+        continue;
+      if (particle.GetPDG()->Charge() == 0)
+        continue;
+      if (particle.Eta() < etaMin || particle.Eta() > etaMax)
+        continue;
+      nch++;
+    }
+    bool fired = nch >= minNch;
+    return fired;
+  };
+
+  return trigger;
+}

MC/config/examples/ini/trigger_multiplicity.ini

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+### The setup uses an external even generator trigger which is
+### defined in the following file and it is retrieved and configured
+### according to the specified function call
+
+[TriggerExternal]
+fileName=${O2DPG_ROOT}/MC/config/common/external/trigger/trigger_multiplicity.C
+funcName=trigger_multiplicity(-0.8, 0.8, 100)
+
+### This part configures Pythia8
+
+[GeneratorPythia8]
+config = ${O2DPG_ROOT}/MC/config/common/pythia8/generator/pythia8_inel.cfg

MC/run/examples/trigger_multiplicity.sh

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+#!/usr/bin/env bash
+
+### This script run the simulation of Pythia8 pp INEL events with a multiplicity trigger.
+### The details of the configuration are defined in the INI config files (--configFile).
+
+set -x
+
+MODULES="PIPE ITS TPC"
+EVENTS=20
+NWORKERS=8
+
+o2-sim -j ${NWORKERS} -n ${EVENTS} -g pythia8 -m ${MODULES} -o sim \
+       --configFile ${O2DPG_ROOT}/MC/config/examples/ini/trigger_multiplicity.ini \
+       > logsim 2>&1