Algorithm

The new cluster-track matching program first identify electrons and muons with external particle-ID devices. Then EM-cluster-$e^\pm$-track matching is performed which is followed by HD-cluster-hadron-track matching. The cluster-track matching proceeds as follows. We first form global calorimetric clusters, which are contiguous calorimeter blocks with nonzero energy deposites (see Fig.1.1).

 

Figure 1.1:  Global cluster and corresponding tracks

When such a global cluster contains no matched charged track, the cluster is recognized as a pure neutral particle and we assign a 4-momentum:

$$\begin{array} {lll} E^{N\mu} = (E^G, E^G \cdot \bar{{\bf x}}_G/\left\vert\bar{{\bf x}}_G\right\vert)\end{array}$$ (1)

assuming it is a single massless neutral particle.

On the other hand, when the energy of the global cluster E^G is consistent with the energy of the corresponding charged tracks E^C:

$$\begin{array} {lll} E^G - E^C \le n \cdot \sigma,\end{array}$$ (2)

the global cluster is taken as consisting entirely of charged particles. We thus discard this global cluster and use only tracking information.

When the above matching condition is not satisfied:

$$\begin{array} {lll} E^G - E^C \gt n \cdot \sigma,\end{array}$$ (3)

the global cluster is recognized as a mixed cluster consisting of both charged and neutral particles. In this case, we use all the charged tracks in this global cluster, while treating the energy difference as a single massless neutral particle with a 4-momentum:

$$\begin{array} {lll} E^{N\mu} = (E^N,{\bf E}^N),\end{array}$$ (4)

where

$$\begin{array} {lll} E^N & = & E^G - E^C \cr {\bf E}^N & ... ...- \sum \vert{\bf p}_i\vert {\bf x}_i^p\right\vert }.\end{array}$$ (5)