Subroutine Find_Cluster_Core

Take TPC charged track and find the nearest hits to the predicted helix model of track.

This routine significantly used the calorimeter electronic cell structure database. It sets for the TESLA calorimeter - has to be rewritten for other calorimeter structures.

For every track it accumulates the information such as chisq, density, and it builds the particle hypothesis first approximation.

Detailed actions:

$\bullet$ Initialize COMMONS.

$\Rightarrow$ Loop along TPC tracks at the calorimeter face.

$\bullet$ Loops along ECAL and HCAL hits to select and collect hits at the one cell distance from predicted helix and distances from impact point and also calculate density of every collected hit. Track density calculation is made in the terms of one sensitive layer and it does not depends on the number of tiles in electronic cell of hadron calorimeter.

$\bullet$ Calculation of properties of collected track core cluster for further analysis, such as starting layer number along a track, final layer number, number of layers with one MIP in it, average density ...

$\bullet$ Analysis starts from the muon hypothesis chooser. The muon hypothesis is chosen when the core was no no gaps in ECAL and HCAL and if it has one MIP in every layer. All core hits are getting the hard assignment to this track.

$\bullet$ Next checked hypothesis is electron or positron. This hypothesis is chosen when the core has energy more then half of input energy (usual core energy is about 0.675-0.7 of input energy for $e^+, e^-$ in W-Si ECAL structure), first part of ECAL has 25% of input energy , core has a big average density (property of electromagnetic shower), core energy in ECAL less then input energy and number of collected HCAL hits are less then 15 (electrons with energy about 250 GeV make about 15 hits in HCAL due to the longitudinal leakage). The hits are getting the soft assignment to this track. The hard assignment is made for the core hits if its energy is within $\pm10\%/\sqrt{E}$ of input energy.

$\bullet$ Preparation of electron or positron hypothesis to the second iteration. There are few different cases were treated here for input energy less and more then 10 GeV (the electron shower with energy less then 10 GeV almost never can reach the HCAL).

$\bullet$ Next checked hypothesis is hadron that passed through the ECAL without hadron interaction. The hits are getting the soft assignment to this track. The hard assignment is made for the core hits if its energy is within $\pm30\%/\sqrt{E}$ of input energy.

$\bullet$ Then hypothesis where the hadron track has a MIP in the first 10 layers of ECAL.

$\bullet$ Then hypothesis where the hadron track has "exact" energy in $\pm20\%/\sqrt{E}$ range along helix prediction and the core energy is in $\pm30\%/\sqrt{E}$ range around input energy.

$\bullet$ Core energy is MORE then input energy (overlapping of showers). Remark: the core cylinder is very narrow (1 cell) if the energy that collected in such a cylinder more then input momentum then it has to be made the subtraction of energy from every hit along this track. The rest of hits is deassigned. There are several cases are treated here with different shapes of hadronic and overlapped showers.

$\bullet$ The track with core energy less then input energy goes to the second iteration.

$\Rightarrow$ Next TPC tracks at the calorimeter face.