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As of AtlfastCode-01-03-02 Atlfast ClusterMaker may produce Massive aswell as massless clusters that are then used to construct Jets.
The original massless Cluster Code in ClusterConeStrategy.h summed up the lorentz vectors calculated from the eta phi and energy of the Atlfast::Cells and then assigned the Cluster the HepLorentzVector as follows:
theta = atan( exp( - this->eta() ) ) * 2.0
t = this->eT() / sin( theta ) ;
x = this->eT() * cos( this->phi() ) ;
y = this->eT() * sin( this->phi() ) ;
z = t * cos( theta ) ;
return HepLorentzVector( x, y, z, t ) ;
This is still the default option in Atlfast. However, a new method can now be selected that calculates the Clusters HepLorentzMomentm directly from the sum of the cells, this then does not assume massless Jets and Clusters and the Jets and clusters will have an approximate mass from the sum:
t = m_momentum_sum.e();
x = m_momentum_sum.px();
y = m_momentum_sum.py();
z = m_momentum_sum.pz();
return HepLorentzVector( x, y, z, t ) ;
This option can be selected as follows
ClusterMaker.MasslessJets = false;