Point Maker


After obtaining the clusters for 4 subdetectors, we need to obtain the information about the incident shower by making the proper matching between clusters from different subdetectors.

It should be mentioned that, because of the better energy resolution and higher depth BEMC is to be used for obtaining the energy of the shower. SMDs on the other hand will be used for obtaining the position of the showers because of their better position resolution.

Currently Preshower detector (PSD) has not been included in the scheme of matching, so we discuss here the details of the method adopted for matching other 3 sub detectors.

Following steps are adopted to obtain proper matching:

  • The clusters obtained from different sub detectors are sorted to obtain the clusters in a single subsection of the SMD phi.
    • Each module of SMD phi consists of 10 subsections. 
      • Each subsection consists of 15 strips along eta, giving phi positions of the clusters for the eta-integrated region of 0.1. 
    • In SMD eta same subsection region consists of 15 strips along phi and the same region consists of 2 x 2 towers. 
  • In the present scheme of matching, we match the clusters obtained in 3 sub detectors in each of this SMD phi subsection.
  • There are two levels of matching:
    • SMD eta - SMD phi match
      • First matching aims to obtain the position of the shower particle in (eta, phi). Because of the integration of signals in SMD etas in the SMD phi subsection region, (i.e.. each SMD eta strip adds the signal in 0.1rad of phi and each SMD phi strip adds the signal in delta eta=0.1 region.) For this type of configuration of detectors, we have decided to get the position matching for each SMD phi subsection. Even though for cases like 1 cluster in SMD eta and 1 cluster in SMD phi in the subsection, we have mostly unique matching of (eta, phi), but for cases where SMD eta/SMD phi subsection consists of more than 1 cluster (see figure) then the possibility of matching does not remain unique. the task is handled from the following standpoint, The number of matched (eta, phi) pairs are taken as minimum of (number of clusters in SMD eta, number of clusters in SMD phi). The (eta, phi) assignment for the pairs are given considering the pair having minimum of (E1-E2)/(E1+E2), where E1, E2 are the cluster energy of SMD eta and SMD phi clusters.
    • Position - energy match
      • It should be mentioned that position/energy matching is done only when there exists a cluster in BEMC for the subsection under study. Because of the large dimension of towers, the clusters obtained in BEMC is made up of more than one incident particles. In case of AuAu data, where particle density is very large, the definition of clusters in towers become ambiguous, especially for low energy particles. In the present scheme, as we have discussed earlier, we have followed the method of peak search for finding clusters, where maximum cluster size is 4 towers. 4 towers make the region of one SMD phi subsection, so we have obtained the energy for the pairs obtained in (SMD eta, SMD phi) from the cluster energy of BEMC cluster in the same subsection. For the cases where we have 1 cluster in BEMC, 1 cluster in SMD eta, 1 cluster in SMD phi, we assign the BEMC cluster energy to (eta, phi) pairs. But for the cases when the number of matched pairs is more than one, then we need to split the BEMC cluster energy. Presently it is done according to the ratio of the strengths of (eta, phi) pair energies. This method of splitting has the drawback of using SMD energies, where energy resolution is worse compared to BEMC energy resolution.

Codes for the point maker are found in StRoot/StEpcMaker