Analysis of Data from Experiment E895 at the Alternating Gradient Synchrotron
Dieter Best, Gulshan Rai, and Hans-Georg Ritter, Lawrence Berkeley National Laboratory
Research Objectives
The physics goal of experiment E895 at Brookhaven National Laboratory's Alternating Gradient Synchrotron (AGS) is to study multiparticle correlations -- especially collective effects -- as well as particle production and other phenomena in a variety of heavy ion collisions (up to Au + Au) over a range of incident beam energies.
Computational Approach
E895 relies heavily on the HPSS mass storage system and NERSC's Parallel Distributed Systems Facility (PDSF). All the raw data -- consisting of several thousand files of about 500 MB each (about 2 TB total) -- are stored on HPSS. The data analysis proceeds as follows: A UNIX shell script copies raw data from HPSS to the PDSF data vaults using FTP, making maximum use of the available disk space. A second shell script checks all workstations for active jobs. When an inactive workstation is found, a job is started and assigned to work on one of the raw data files. This way many files are analyzed in parallel. The output per job is around 100 MB, which is copied back to HPSS.
Accomplishments
The total data at beam energies 2 and 4 AGeV were analyzed in 1998, along with about 10-20% of the data at 6 and 8 AGeV. The data processing will continue for at least another year. Concurrently a large number of simulated data will be analyzed for calibration purposes. Preliminary results for E895 have been presented at many conferences worldwide. Manuscripts on directed and radial flow will be submitted shortly to Physical Review Letters.
Significance
E895, which began at the Equation of State Time Projection Chamber (EOS TPC) in the Berkeley Lab Bevalac, charts new territory at the AGS in two important respects.
This central Au on Au collision at 4 GeV/nucleon kinetic energy comes from the January 1996 run of E895. Ionization clusters in the EOS Time Projection Chamber are shown in red. In this event, some 18,000 clusters are distributed over the 2+ million pixels of the TPC.
First, we can measure and identify most produced particles and nuclear fragment species over a substantial fraction of 4 pi solid angle. Second, our measurements will build upon the detailed excitation functions already measured by the EOS TPC and seamlessly extend them up to the higher beam energies.
Publications
N. N. Ajitanand et al., "Collective flow in Au + Au collisions between 2-8 AGeV at AGS," Nuclear Physics A 638, 451 (1998).