STAR Simulations, Reconstruction and Calibration Software

  The Simulations and Analysis Software (SAS) group in STAR provides ongoing service and support for the STAR project. This includes contributions to the detector design by way of simulation studies and helping to understand the performance of the detector hardware and electronics by providing analysis software and manpower for analyzing test data. Starting in 1999 SAS will be responsible for analyzing the first ion-ion collision data and for carrying out large scale simulations to determine detector acceptances, reconstruction efficiencies and backgrounds. This section provides a brief summary of the mission, requirements and general design plan for the offline simulations and analysis software. Several useful programming guides are listed for those interested in developing new code or improving existing modules.

PURPOSE:

The purposes of the STAR offline simulations, reconstruction and calibration software are:

1.

To simulate the particle production from nucleus + nucleus, proton + nucleus, and proton + proton collisions, as well as that from background sources and from special calibration procedures.

2.

To simulate the propagation, scattering, energy deposition, decay and secondary particle production throughout the detector from all the preceding sources of particle production, in both the active and inactive parts of the detector.

3.

To simulate the physical (ionization, charge drift and collection, light production and propagation, photo-electron production, etc.) and electronic (pre-amp, shaper, analog-to-digital conversion (ADC), time sampling, etc.) response of each detector to the passage of ionizing particles and energy deposition in the active portions of the detectors.

4.

To realistically simulate fluctuations and non-uniformities in order to facilitate the development of calibration and correction procedures and software.

5.

To reconstruct the collision event from either the simulated or real data to a sufficient extent that the physics goals of STAR and the physics capabilities of the subdetectors can be realized.

6.

To analyze calibration and correction data, both simulated and real, in order to provide corrections which remove the effects of instrumental fluctuations and non-uniformities from the data.

7.

To sufficiently evaluate and visualize the results to determine the adequacy and correctness of the simulation, event reconstruction, calibration and physics analysis software.

8.

To simulate, analyze, evaluate and develop trigger algorithms which can be used in the on-line trigger system.

9.

To generate acceptance and reconstruction efficiency tables and to facilitate studies of backgrounds for the full range of physics observables for STAR.

REQUIREMENTS:

The requirements of the offline software are driven by the physics goals of STAR and by the performance capabilities of the various detectors. However, detailed specification of the required performance of a given software component is quite difficult. For example, the performance of the TPC event reconstruction software can be measured in terms of track finding efficiency, tracking purity, momentum resolution, impact parameter resolution, particle identification accuracy and efficiency, two-track resolution, etc. For each performance criteria the requirements vary considerably depending on the physics issue being considered. Temperature and mean transverse momentum determination, for example, is not particularly demanding of the tracking software whereas strange particle reconstruction (V0 decays) and Hanbury-Brown and Twiss (HBT) interferometry analyses are very demanding of the software and place high performance criteria on most aspects of TPC tracking. The varied physics goals of STAR impose a wide range of performance requirements on the software.

FUNCTIONALITY:

The essential functionality includes:

• Simulations:

  1.

  Generate simulated pp, pA, and AA collision events

  2.

  Realistic simulation of ``hits'' in the active detector volumes

  3.

  Realistic simulation of the digitized output from each detector

• Event Reconstruction:

  1.

  Track reconstruction for TPC, SVT and FTPC

  2.

  Primary vertex determination; decay vertex reconstruction with loose cuts.

  3.

  dE/dx and time-of-flight information for post-DST particle ID analyses.

  4.

  Neutral and charged particle energies using tracking and the EMC.

  5.

  Global event reconstruction

  6.

  Event characteristics and QA parameters

  7.

  First pass identification of background tracks

• Calibration and Corrections:

  1.

  Magnetic field map corrections

  2.

  Pedestal determination and monitoring

  3.

  Gain and time offset corrections

  4.

  Energy deposition calibration for EMC and Shower Maximum Detector (SMD).

  5.

  Space point position distortion corrections in all tracking detectors.

  6.

  Beam-beam intersection luminosity profiles

  7.

  Local and global alignment corrections

• Calibration Software Must Handle:

  1.

  Laser tracks

  2.

  Cathode emission

  3.

  Direct charge injection

  4.

  Tracks from radioactive sources

  5.

  Direct light injection into photo-multiplier tubes/scintillators.

  6.

  Magnetic field off, straight tracks from collisions

  7.

  Cosmic ray tracking

  8.

  Wire pulsing

  9.

  Gas monitor chambers

  10.

  Magnetic field NMR and Hall probe monitors

  11.

  Slow controls and other monitoring data; time dependences throughout run.

The list of SAS deliverables to the project include analysis modules, data structures or tables, linked STAF executables, run time procedural control scripts for running STAF which presently are KUIP macro (kumac) files, event generator codes and event files, Geant implementation for STAR or GSTAR as well as output files, detector geometry files, event reconstruction output files including DSTs, first pass physics analysis results and web based documentation.

GENERAL DESIGN:

Beginning in late 1995 selected members of SAS conducted an intensive design effort for the offline simulations, reconstruction and calibration software for STAR. The first version of the STAR Offline Simulations and Analysis Software Design Document was completed in early 1997 and was released both as a STARNOTE (#281) and as an html document. See the URL:

http://www.rhic.bnl.gov/STAR/html/sas_l/design/sas_main_html.html

The purpose of this design work was to specify the basic requirements, the essential functionality, and the general content of the major data structure interfaces for the offline software. Additional functionality and data information will inevitably be required as the software continues to develop and this design framework is intended to be flexible and amenable to change. While the document outlines the required functionality of the software it does not fully described the actual algorithms, data objects or runtime control scripts which constitute the actual implementation of this design plan. Plenty of opportunities for original contributions remain. It is intended that this document evolve in parallel with the actual software, both guiding its development and documenting its overall structure. Upon completion, this document will provide an overview and top-level description of the actual offline software for STAR.

The scope of the initial version 1.0 includes simulations, event reconstruction and calibrations. The document specifies, in a general way, the necessary computational processes (to be implemented in PAMs and kumac files) and data structure interfaces which are implemented as STAF tables.

The document presents the offline software in a convenient, hierarchical organization. It is important for those new to STAR offline computing to realize that the actual software library is not organized in this way. Later STAR libraries (e.g. SL98a) are reorganized to be more like the design document but still differ from it. Each section in the report contains the following: (1) description of the purpose, requirements and essential functionality of the specific subsection, (2) functional model or data flow diagrams, (3) execution flow charts for a few cases, (4) glossary defining, in a general way, the computational processes and data structures, and (5) a brief status of software update.

The STAR Note version is available on the web starting from the STAR Home page, selecting ``general documents,'' then ``STAR Notes,'' then ``Keyword Search,'' and by entering SN0281 in the dialog box. A convenient, html version is also available HERE or directly at the preceding listed URL.

STAF PROGRAMMING GUIDES

Several useful STAF PAM programming guides are available:

• Fortran 77 and C analysis module Templates generated by Stic from specific PAM.idl files. The salient features of these templates include the (1) documentation header, (2) the STAF callable function declaration statement, (3) required #include statements, (4) variable type declarations, (5) an example of how to return the STAF condition value, and (6) some trivial, example lines of code. These templates can be generated from the PAM.idl file by typing `stic PAM.idl' at the UNIX prompt in the PKG/src subdirectory.
• STAR Coding Style Manual for Fortran 77, C and C++ analysis modules in STAF. This version was revised in Sept. 1996 and specifies the current, adopted coding standards for offline STAR software. The manual attempts to spell out the agreed upon style for code which is to be contributed to the STAR software library. It consists mostly of encouragement to use good coding practices for ease of code readability, maintenance and compilability on different machines. The reasons for the coding rules are given along with each rule. The accepted programming languages are FORTRAN 77 (with VAX extensions), C and C++ (preferred). FORTRAN 77 with VAX extensions are acceptable except for the prohibitions listed in this manual. Fortran90 is not an accepted language in STAR. Sample code templates are also provided in this manual but are incomplete. Please use the Stic generated templates instead.
• The STAR Coding Style Checker is a SOFI tool which provides automated checking of Fortran 77 and C analysis modules for compliance with the STAR Coding Style Manual rules. It issues error messages and warnings. Compliance with these standards is voluntary so far. Documentation is available HERE or explicitly at the URL:

  
  

          http://www.rhic.bnl.gov/STAR/html/ssd_l/cds_l/cds_usage.html
  
  
  

  or by following the path from the STAR Home page, to Computing, to Offline Software, to Offline Software Packages - SYS, to cds, and finally to Usage.

• Useful tips and important rules for proper initialization of analysis modules and for correct usage of the STAF table keys is given HERE or at the URL:

  
  

    http://www.rhic.bnl.gov/STAR/html/sofi_l/info/margetis/key-usage.html
  
  
  

  or by following the path from the STAR Home page, to Computing, to Offline Software, and to Design and Development - ``Rules and tools for PAM Intialization and Foreign Key Usage.''