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[eRHIC Project Overview]

Simulations and EIC Computing How-To

[e+A Working Group]
BNL Task Force Membership

Detector simulation for eRHIC project

To run detector simulations for eRHIC we suggest you to use our simulations framework , esim. It is based on Geant3 with a special language to describe different detector geometries. Geometrical description of a detector, of a part of the detector system, is written as a separate module which is dynamically compiled and loaded into the framework.

More details on the simulation framework can be found here ESIM system manual.

How to get started

Basic Simulation Software for a Linux machine can be found in this tar file. After you download it, untar it (tar xfvz in a directory which is in your default PATH.

Alternatively, if you have an EIC account, you can run the program version installed in the directory /afs/ Add this directory to your path with:

setenv PATH /afs/$PATH

After this, you can just use the esim executable from any directory.

To make sure everything is installed correctly you can run a built-in test simulating a room with two chairs which have a screw as a sensetive detector. This should help you to understand the basics of detector simulations with esim.

This is how your first session may look like:

  • mkdir mysim
  • cd mysim
  • tar xfvz <somewhere>/
  • setenv PATH .:$PATH
  • - or -
  • setenv PATH /afs/$PATH
  • cp -p /afs/ .
  • - then -
  • esim.exe -w 1
  • esim> debug on
  • esim> make roomgeo
  • esim> gclose all
  • esim> gkine 100 5 0 10
  • esim> switch 2 3
  • esim> trig

Running zero-approximation guess of the EIC detector

  • First super simple example:

A very first eRHIC detector layout (really zero approximation!) can be simulated using file. After downloading it (or, if you have an EIC account, you can copy it from /afs/, you can run as following:

  • esim.exe -w 1
  • make edicgeo.age
  • dcut edic x 0.1 10 10 0.01 0.01

You should get this layout.

  • Preliminary Detector Design:

Running PYTHIA in ESIM

It is possible to run PYTHIA event generator (version 6.4.21) directly in ESIM using this tar file. If you have a ERIC account you can get it from /afs/ area.

After you download and untar it, you just do "make apythia" in ESIM. This command compiles the Pythia code and the interactive interface and load them into ESIM as share library. The steering is done with simple commands, described in the interactive help menue ("help pythia"). The generated events are stored in the standart Pythia common block HEPEVT and are directly accessible for detector simulations. They can also be save in a file for subsequent input.

An example of a simple session is below:

tar xfvz /afs/ 
esim.exe -w 0
  • esim> make apythia
  • esim> help pythia
  • esim> frame CMS
  • esim> beam e- p+
  • esim> ener 900
  • esim> msel 1
  • esim> trig 1
  • esim> call pylist(1) - to see the whole parton tree
  • esim> gprint kine - to see only the particles going into detector

Running Rapgap Generated Events in ESIM

THIS SECTION IS UNDER DEVELOPMENT Events generated in the RAPGAP environment can be replicated in ESIM using the file "esimread.age". Using this example you will see constant magnetic fiels for the solenoid and dipoles. Copies of all relevant files can be found in /afs/

An example of a simple session is below:

 esim.exe -w 1
  • esim> make edicgeo
  • esim> make mflegeo
  • esim> debug on
  • esim> gclose all
  • esim> make esimread
  • esim> swit 2 3
  • esim> gkine -1 0 0 1 -6 6 0 6.3
  • esim> gfile u testevents.txt e
  • esim> dcut edic x .1 10 10 .2 .2 -this is a zoomed in view of the ip, you can manipulate the variables for different views
  • esim> trig