PhotonTransport

Contents

Contact Name

Nathaniel Tagg. n.tagg1@physics.ox.ac.uk

Overview

PhotonTransport provides the Monte-Carlo simulation of scintillator and optical fibre in the MINOS detectors.  Either GMINOS or the new MinosMC package tracks particles through the detector, depositing energy in the scintillator. These energy depositions are taken by PhotonTransport, which computes how much light is created by each hit, tracks the scintillator light through the strip until it hits a wavelength shifting fibre. Then it tracks the photon refraction into the WLS fibre core, where the photon is (probably) absorbed.  The WLS fluror then decays, emitting photons isotropically, some of which are trapped in the fibre and transmitted down it.  Photons are attenuated in the fibre and finally reach the PMT photocathode, where they generate photoelectrons.

Each of these steps can be done by pluggable modules which are configured at run-time.

Input/Output

Input Objects

PhotonTransport looks for a list of DigiScintHits in the SimSnarlRecord in Mom.  These Hits are used to generate the resulting light. PhotonTransport doesn't use any other information (besides the SimSnarlRecordHeader).

Output Objects

PhotonTransport creates a list of DigiPEs in the SimSnarlRecord as it's output.  In addition, it creates a PhotonEventResult record in the SimSnarl which can be used to compile statistics on things like tracking errors.

Database Access

PhotonTransport makes heavy use of databases through the Plex, UgliGeometry, and Calibrator packages. It also uses several custom tables for things such as spectral information and PMT quantum efficiency as functions of wavelength. At present, these tables include:
  PHOTONBLUESPECTRUM           
  PHOTONFASTBLUESPECTRUM       
  PHOTONFIBREABSORB            
  PHOTONGREENSPECTRUM          
  PHOTONPMTQUANTUMEFFICIENCY   
  PHOTONPROTONRANGE            
  PHOTONSCINTATTEN             
  PHOTONTIO2PAINTREFLEC        
 
Last, the PHOTONPROTONRANGE table is used to compute the range of protons in scintillator. (This is done as a fix to the problem that GEANT does not properly track very small track lengths, resulting in infinite dE/dx when calculating Birk's supression.)

Configuring & Running

There are many ways of running PhotonTransport. In particular, the package can be set up for "fast" simulation, "simple" simulation (meaning straightforward algorithms, not simple to use), and "full" simulation. Most users will want to run the simulation in the "fast" mode, the default.   The other modes are useful mostly for cross-checking and validation of the fast mode.

PhotonTransport has many configurable options, but the defaults should be sufficient for most users. The simplest macro for setting up DetSim and Photon Transport is available at $SRT_PUBLIC_CONTEXT/PhotonTransport/macros/simple.C.

Configurable options are fully described in the macro file $SRT_PUBLIC_CONTEXT/PhotonTransport/macros/mc.C, which lists all the available options, set to their defaults.

These two macro files are always kept up-to-date and serve as the basic documentation for configuring the package

Further Links

See also:
    DetSim Overview
    Digitization Overview  
    Description of DetSim and PhotonTransport (older)
    Also, see the slides of my talks at the June 2004 (Ely) and Sept 2004 (FermiLab)


Nathaniel Tagg Last Modified: $Date: 2004/10/05 14:33:54 $