SIMDET has a built in an interface to PYTHIA for internal event generation via subroutine SIPYTH. Alternatively, events generated by other programs can be used for detector simulation; subroutine SIEVTI provides an input interface to events written by subroutine LCWRITE. If the structure of the generated events does not coincide with common /PYJETS/ of PYTHIA, subroutine SIPREP should fill the arrays K_PY(I,...), P_PY(I,...) and V_PY(I,...).
To allow for initial state radiation and beamstrahlung during event generation is in the responsibility of the event generator. Subroutine SIPYTH accounts for both radiations if wanted.
In all cases, NEVENT specifies the number of events to be processed.
The detector parameters used are defined in subroutine SIDETR. The naming convention is self explanatory.
After selection of all particles which might give a response in the detector (subroutine SIPART), charged particle tracking, impact parameter estimations and the covariance matrix are obtained from the subroutine SITRAK, subroutine SICDAS and subroutine SICOVM, respectively.
Detector resolution parameters for tracks are provided by the ab initio Monte Carlo program BRAHMS taking into account the complete tracking system.
Two options exist for the vertex detector (subroutine SIDCAS):
The calorimetric response is also based on detector studies using the ab initio Monte Carlo simulation package BRAHMS. The energy distributions of electrons and charged pions in adjacent cells were fitted and the parameters obtained are used for appropriate energy deposit simulations in the electromagnetic and hadronic calorimeters (subroutine SILEGO and subroutine SIDEPO). Afterwards, a cluster search algorithm (with some idealized assumptions) provides clusters (subroutine SICLUS_I) in the ECAL as well as the HCAL. Finally, an energy flow algorithm (subroutine SIFLOW_I) joins tracker and calorimeter informations such that as many single particles as possible are resolved. At this stage, the best estimate for charged particles is simply taken from the tracker, except for high energy electrons and positrons. Here, a proper weighting scheme of their tracker and calorimeter energies is applied (subroutine SIWGHT). Particle identification on the basis of shower shapes and matching between tracker and calorimeter information in space and momentum is emulated. Finally, best estimates of the energy flow objects are established.
In the very forward direction an instrumented mask, the low-angle tagger (subroutine SILOWT), and a low-angle luminosity calorimeter (subroutine SILCAL) are included as default devices. Their preliminary responses from BRAHMS simulation are included in SIMDET.
Particles not entering the calorimeters, e.g. low-pt tracks, are rescued in subroutine SIRSCU and added to the list of energy flow objects in subroutine SISTOR.
In addition, SIMDET allows for particle identification from specific energy losses dE/dx within the TPC (steered by subroutine SIDEDX).
Background events of the type
(and
later also of other sources) can be overlayed to each physical
event using the package hades
3.
The data card
IBKG enables this option provided the name of the
background file (data card BKGF) and the average number
of background events to be overlayed (data card NBKG)
are given by the user. Also the study of only background events
is possible. Formatted background files
resulting from the package GUINEA_PIG
exist for the TESLA collider at cms energies 170,
360, 500 and 800 GeV as well as for two CLIC options:
the nominal CLIC parameter option with a luminosity
at 3 TeV and an optimized version with
lower beamstrahlung and a luminosity of
.
It is the responsibility of the user to transform these files to
a local binary file using the program hades_import.
The CLIC option of SIMDET can be enabled
by the data card CLIC. If it equals 1, the process
selected in subroutine SIPYTH is simulated at the
predetermined cms energy, while CLIC 2 allows for
beamstrahlung effects if a luminosity spectrum file is provided on the
data card CLCF. This option reads the
electron and positron energies as obtained from GUINEA_PIG
for a nominal beam energy of 1500 GeV. If a different energy
is desired, the simulated 
energies are rescaled. In the case
of invoking a luminosity spectrum file, note that the file name
extension '.info' respectively '.ep' should not be given on the
data card CLCF. For more details we refer to 4.
The history of the events can be monitored either completely or in a restricted form. If the data card HISTORY is enabled, the complete event history is stored as described in the generated particle record, otherwise input quantities of only stable particles are kept, with a flag of being accepted by the detector or not.
Booking of histograms is provided in subroutine SIBOOK. A few standard histograms allow to monitor the detector response. They can be optionally filled and switched off or on by the data card PLOT.
The simulation finishes by providing all measured objects in the proposed common output structure in subroutine SISTOR.
If requested, the program allows to write (unformatted/formatted) all objects in either the standard structure or in a restricted structure (best estimates only) to an external file in subroutine SIWDST so that analysis can follow externally. It also offers to produce zipped output files (patchy use selection GZIO and data card GZIO) in order to save disk space. If this option is chosen, the extension .gz is added by the program to the file name. The required package is provided with the SIMDET code.
If no external file should be written, the array VECP(I,K) is optionally filled in subroutine SIVECS which allows to use directly the physics analysis package VECSUB (a product from SLAC/DELPHI). In this case, the components 1 to 7 of the array VECP involve the quantities as described in the VECSUB-DELPHI note 5, while the originally free locations 8, 9 and 10 of this array contain now the transverse and the longitudinal impact parameters, in units of sigma, and a simple numbering of the energy flow objects accepted.
Subroutine SIFFRE reads the set of data cards with the FFREAD package. Default settings in subroutine SIINIT and/or in subroutine SIDETR might be overwritten.
A user subroutine SIUSER (IFLAG) has been added. It is called during initialization (IFLAG=1), for each event before writing to output file (IFLAG=2) and during termination of the job (IFLAG=3).
The package exists as a CVS repository
as well as PATCHY/CMZ CAR
files. If the PATCHY distribution is chosen,
the desired code generation is steered
by 'use' selections. For the CVS repository
the selections are given as arguments to the
configure script.
SIMDET selects the standard simulation code, and with NOSIMU only all stable particles without any detector response are treated. This enables physics studies at the parton or generator level.
Further PATCHY 'use' options are:
CIRCE to allow for the beamstrahlung code,
COVMTX for the covariance matrix material,
GZIO to produce zipped output files,
IBKG to invoke additional code for background events and
CLIC for the CLIC linear collider option.
Please note that for HP platforms error handling routines are
included (forced by the 'use' selection HPUX).
Please link the CERNLIB libraries, the PYTHIA 6.1 library and, if selected, the enclosed GZIO library, as transparently illustrated by the installation script which can be used for different platforms (Linux, HP-UX, SunOS, OSF1).
A small utility package SIANAL has been added which can serve
as a template for further analyses. It contains routines to open and
read the SIMDET output file of the energy flow objects
written formatted or unformatted. For both types also
zipped files can be read. A zipped file is assumed if the file name has
the extension '.gz'. The file name is given in the command line to run
SIANAL,
eg. 'sianal.bin simdet_v4.evt.gz' .