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Detector Simulation Guidelines


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

Status of existing tools

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

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

A rudimentary reconstruction package to support BRAHMS users is under development. This includes a track fitting program as well as a cluster finder for the calorimeters. Energy flow algorithms will be implemented later.

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

The standard output for event generators as proposed by the Event Generators working group is adopted for all above mentioned simulation tools. Implementations exist for BRAHMS and are being prepared for SIMDET and SGV.

Output from detector simulation

It is proposed to use energy flow objects as the basic building blocks for an output interface of the simulation. These objects are: electrons, photons, muons, charged and neutral hadrons and clusters. The last category comprises all objects that cannot be separated further but are recognized to contain more than one particle.

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):
  2. List of reconstructed energy flow objects:

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.