ATGEN interface to event generation and analysis: structuring and reusing common procedures

Paper: 298
Session: A (poster)
Presenter: Amorim, Antonio, LIP, Lisbon
Keywords: simulation, simulation tools, GUI's, world-wide collaboration, WWW applications

ATGEN interface to event generation and analysis:
structuring and reusing common procedures.

A. Amorim

LIP and CFNUL, Av. Gama Pinto 2, 1699 Lisboa, Portugal
The ATLAS Software Group


Event generators will play and important role in extracting the physical
meaning of LHC data.
The ATGEN package interfaces to generators of both the parton shower
{\small (PHYTHIA,ISAJET,HERWIG)} and matrix elements type
{\small (NJETS,VECBOS)} in a manner that tries to simplify the required
changes in user behavior to go from one generator to the other while
strictly respecting their physics contents. It allows data to be stored
and feed both into the {\small GEANT } detector simulation and analysis.

While the analysis is easily extensible to the different generators,
creating large problem specific user routines does not encourage the
writing of reusable code that could be shared efficiently, helping to
define relevant detailed analysis information.

To obviate this problem, generic analysis routines are included in the
package and their input control statements form the prototype of a
syntax that selects particles in the event record and computes the
required kinematic variables including reconstructed decays.
Event selection at generation level is implemented by requiring that
particles meeting specified conditions must be present. Simple
parameterisations of detector performances are also available.
Although some very specific problems still have to be coded in the
user routines, one finds that simple input statements can do large
chunks of the analysis automatically, structuring the procedures in
reusable form.

The interface input syntax has to cope with both a large number of
options and parameters to tune each event generator and the
specificity of driving the user analysis for different channels.
Using WWW, a simple CGI graphic tool was designed that assists in
building the input statements while providing direct links to the
generator documentation. It is also managing a database of user
procedures that further simplifies the diffusion of relevant
detailed information on analysis for each channel.

The long time scale involved in LHC stresses the importance of being
able to reproduce previously simulation data implying, as part of our
work, a code management mechanism for the different generators.

The importance of event generation for LHC, together with the
necessity to spread the task oven an unprecedented large
community of users, makes it necessary to have the tools to
avoid lengthy user specific code whose options may not be
structured and documented. The ATGEN program, together with its CGI
interface are a first attempt to evaluate the requirements of a
future system were abstraction and re-usability together with
directly documented tuning should be the main goals.
An option being investigated would evolve the CGI interface into a
simple case tool, writing user code according to the specified
options that may be compatible with future OO class libraries.