Add counter to ParticleMassMonitor

Re-add counter to ParticleMassMonitor to know how many events have a mass within 1 mass sigma, that is defined by the user. The counter is used by the bremsstrahlung test Moore!2373 (merged).

Goes with Moore!2373 (merged), lhcb-datapkg/PRConfig!367 (merged)

FYI: @cmarinbe

Phys/ParticleMaker/src/ParticleMassMonitor.cpp

@@ -75,6 +75,8 @@ private:
 
   // Flag for tuple generation
   Gaudi::Property<bool> m_generateTuples{this, "GenerateTuples", false};
+  // counters
+  mutable Gaudi::Accumulators::Counter<> m_n1sigma{this, "Candidates in 1 sigma"};
 
   // Daughter particles
   std::string m_daughter1;
@@ -121,6 +123,7 @@ DECLARE_COMPONENT( ParticleMassMonitor )
 
 // Algorithm
 void ParticleMassMonitor::operator()( LHCb::Particle::Range const& particles ) const {
+  auto b_1sig = m_n1sigma.buffer();
   for ( const auto& p : particles ) {
     const double m         = p->momentum().M();
     const auto   daughters = p->daughtersVector();
@@ -129,6 +132,10 @@ void ParticleMassMonitor::operator()( LHCb::Particle::Range const& particles ) c
 
     // Mass plots
     auto& mass_histo = m_histograms_mass.at( 0 );
+
+    // count candidates in 1 sigma
+    if ( std::abs( m_mass - m ) / m_sigma < 1 ) b_1sig++;
+
     ++mass_histo.CandidateMass[m];
     ++mass_histo.MassvsPt[{pt, m}];
     ++mass_histo.MassvsP[{mom, m}];