4.1 URHI overview
J.G. Cramer and T.A. Trainor
The University of Washington URHI group carries out collaborative experimental programs with two large-acceptance heavy ion experiments - STAR, a large solenoidal detector presently under construction and scheduled to commence operation at RHIC in 1999, and NA49, a fixed-target multi-TPC experiment that has been operating since 1994 at the CERN SPS. The Fall-1995 run of NA49 was the first in which all detector components were in operation, including four large TPCs using 180,000 electronics channels. About 10 Tbytes of data were recorded, representing about 700,000 central Pb-Pb events at 158 GeV/nucleon.
After a year of analysis the first NA49 physics results are becoming available. Surprises have appeared in several areas, including the high degree of nuclear stopping and the relative abundance of flow in central and peripheral collisions. One of the main goals of the NA49 and STAR experimental programs is event-by-event physics analysis. Much of the recent effort of the URHI group has been directed toward development of new event-by-event analysis techniques. In addition, with DOE capital equipment funds we have recently purchased two new HP 'Skyhawk' parallel-processor workstations providing greater computational power for extensive offline analysis of NA49 data.
The UW has had a leadership role in the production of main TPC tracking software for NA49. This software is completed and has passed through a quality assurance program. It is presently being used for full-scale production of data summary tapes for the 1995 NA49 data. This is the largest data volume ever processed at CERN, easily exceeding in a few weeks of detector operation the combined data volumes of all the LEP experiments to date.
A novel multitarget correlation analysis technique developed at the UW was used to determine the precise relative location of all NA49 detectors to about 100 micrometers and 100 microradians, thus virtually eliminating system geometry as a source of experimental error.
The main NA49 data display facility for tracking analysis and optimization, developed at the UW, permits one to 'fly' through a visual representation of the tracking data. It also facilitates direct access to data structures used by the tracking code. One of the images generated by this display was featured on the 1996 GSI calendar.
Investigations of multiparticle Bose-Einstein interferometry have advanced on several fronts in the past year. A new analysis procedure has been developed which offers the capability for distinguishing between the effects of source coherence and particle contamination. The 'ripples' produced by non-Gaussian source shapes have been investigated. A new Monte-Carlo event-generator code has been developed which can include Bose-Einstein and Coulomb correlation effects for up to order 6.
Work continues on STAR trigger algorithms, with a transition from level-1 algorithms emphasizing one-dimensional charged-particle multiplicity distributions on pseudorapidity to level-2 algorithms emphasizing two-dimensional EM calorimeter energy distributions applicable to jet and other high-pt physics.
The slow control program SControl has been further improved and integrated into the NA49 detector systems and was used with good results in the Fall-95 run. We have completed an EPICS-based computer control system for the STAR TPC high voltage supply which interacts with the STAR slow controls system and stabilizes the TPC electron drift speed to about one part in 100,000.