Detector Simulation Guidelines

Objectives

The tools to be provided by this working group are threefold:

• Parametric simulation: Provides the physics study groups with a fast and flexible simulation tool to evaluate the consequences of high luminosity with TESLA and to compare basic detector options.
• Ab initio simulation: To verify the correctness of parametric Monte Carlos and to determine their basic parameters, a full GEANT3 based simulation will be prepared for a slightly simplified version of the proto-detector described in the CDR.
• Long lived tools: In view of the long term needs for an assessment of the detector's capabilities for pattern recognition, particle identification and event reconstruction, object oriented tools will be developed using a GEANT4 based framework.

Status of existing tools

There are two versions of parametric Monte Carlo programs describing the basic properties of the CDR detector:

• SIMDET: A parametric Monte Carlo originally written by H.J. Schreiber from DESY Zeuthen. In its version used for the previous TESLA studies, the program applied Gaussian smearing to charged particle momenta and calorimeter cluster energies and directions. Particle impact information was also provided. The parameters of the program were taken from the CDR. SIMDET currently undergoes a major upgrade where shower parametrisations extracted from BRAHMS are introduced. The energy flow concept is being implemented.
• SGV: A fast simulation Monte Carlo written by Mikael Berggren from DELPHI. For details see the SGV web page for the LC version and the SGV web page.

There is a complete implementation of the CDR proto-detector available for ab initio Monte Carlo studies:

• BRAHMS: An ab initio Monte Carlo written by G. Blair using the GEANT3 framework. It implements a complete and only slightly simplified version of the CDR proto-detector. It is more intended for specialized studies on the properties of the proto-detector than for the general audience. For details on the implementation and usage see BRAHMS web page.

A migration to object oriented technology is foreseen for the medium term future. A study group is being formed to inspect current tools, including the GEANT 4 project, OO simulation development in the NLC project, based on GISMO. The study group will be less concerned with the simulation proper until GEANT 4 becomes publicly available. Its immediate concern will be to start design and test implementations of pattern recognition and reconstruction software. This is the only part of the project with long term perspectives, possibly beyond the machine proposal phase.

Interface Definitions

Interface definitions are needed at input towards the Event Generators and at output towards the programs for physics studies.

Input to detector simulation

Output from detector simulation

The proposed interface format is an extension of the existing SIMDET output structure. It allows the storage of calorimeter cluster information per energy flow object. For each event there are two lists:

1. List of generator particles (straight copy from input):
   • Number of particle records
   • Particle record:
     • status code, particle code, mother(s)
     • p_x, p_y, p_z, E, M
     • x, y, z, t of origin vertex
2. List of reconstructed energy flow objects:
   • Number of energy flow records
   • Energy flow record:
     • status code, object type, mother(s), fractional contribution
     • best estimate: p_x, p_y, p_z, E, M
     • tracker: p, theta, phi, DCA_xy, DCA_z, covariance
     • Ecal cluster: E, theta, phi, t, C_em
     • Hcal cluster: E, theta, phi, t, C_mip
     • Muon system: E, theta, phi, t, C_punch

The generator record is adapted from Hywel Phillips' proposal for the generators group. It contains the full information from the HEPEVT common and one direction of its cross reference table (daughter to mother only).

The list of reconstructed objects is a straight forward extension of the "smeared particle" output structure of SIMDET. The list of energy flow objects has a unique record for all objects. The object types are: electron, photon, muon, charged and neutral hadron or "jetlet" (see below). The "best estimate" is defined to allow a quick analysis without looking into details; it has the same format as a generator particle record.

The meaning of the tracker information (p, theta, phi, DCA) is obvious. A covariance matrix is stored for the tracker data only, since it makes much less sense for calormiteric information. The Ecal part contains a variable, C_em, characterising the electromagnetic properties of the associated cluster (e.g. a probability, chi**2, NN output, shape parameter etc.). There can of course be more than one such variables. Likewise, the Hcal part contains a variable, C_mip, characterising the compatibility of the cluster with a MIP signature. The muon system part quantifies the probability for the object to be a punch through by the variable C_punch.

The contents of the three parts depends on the object type. E.g. for photons, the tracker part is empty. For objects containing more than one track overlapping in the calorimeter such that no further separation is possible, the "jetlets", the cluster is associated to the highest momentum track only, all others have no Ecal and Hcal information. The status code is used to signal this case and point to the highest momentum track of the jetlet.