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PHENIX Run 7 Startup

by John Haggerty

The PHENIX experiment has been preparing for Au+Au collisions for many months now, under the leadership of this year's Run Coordinator, Mike Leitch from Los Alamos National Laboratory. 24x7 shift operation began on January 9, 2007, with shift takers converging on the PHENIX counting house from all over the world to prepare the detector, electronics, and software for a new season of data taking with heavy ions. This will be the first Au+Au run since Run 4, and the continuing evolution and refinement of the detector promises to offer many new opportunities for physics in this run.

Mike Leitch, a Fellow of the American Physical Society, moved to Brookhaven to serve as run coordinator in October, and has been working hard to organize the shift taking and juggle the demands of operating the experiment and testing and debugging the detector. Although it looked for a while during the budget deliberations like he might be the first run coordinator with no run to coordinate, during all the uncertainty PHENIX kept taking shifts, accumulating cosmic ray data, and refining the detector. Mike came to Los Alamos in 1979, after receiving a Ph.D. in physics from MIT, and he has served as spokesman of the Fermilab E866 collaboration before joining the Dimuon collaboration which eventually became part pf the PHENIX collaboration.

For Run 7, PHENIX has an ambitious program of upgrades under way, spearheaded by the operation of four new detectors--a new time of flight system on the west carriage, a hadron blind detector in the central region, a second arm of forward calorimetry, and a reaction plane detector. The time of flight detector, built at Vanderbilt University with electronics built at Columbia University, benefits greatly from R&D done by STAR and ALICE, and is designed to extend the PHENIX capabilities in high pT particle identification when used in concert with the Ring Imaging Cerenkov Counter and Aerogel Cerenkov counter on the west arm. The Hadron Blind Detector is an innovative Cerenkov counter, which detects photoelectrons from a CsI photocathode with a Gas Electron Multiplier (GEM), whose major component is a foil with very small holes in which a large electric field causes avalanche amplification. This detector was built by collaborators from the Weizmann Institute of Science in Israel, and Stony Brook and Brookhaven physicists, with electronics also designed and built at Columbia University.

The beginning of a run in PHENIX is always a time of great activity, starting from the "Blue" and "Pink" sheet checkout of the safety systems before the experiment is given approval to operate by the Collider-Accelerator Department, to the deployment of new data acquisition hardware and software, to turning on detector high voltage, sometimes for the first time in many months. There are always some surprises along the way; this year, a number of broken wires were found in the drift chamber, one of the detectors critical for the detection and momentum measurement of charged particles, which necessitated the repair of the detector by Stony Brook and Petersburg Institute of Nuclear Physics (PNPI) physicists.

FIGURE: This is an event display of a cosmic ray muon going through the PHENIX muon tracker (the circular pie slices) and the muon identifier. The muon tracker consists of three layers of cathode strip chambers built at Los Alamos National Laboratory, and the muon identifier consist of five layers of Iarocci tubes built at Oak Ridge National Laboratory. A trigger, made with electronics built at Iowa State University, is used to select events with hits in the muon identifier, and the event is recorded by the data acquisition system, with hardware and software provided by Columbia University and Brookhaven National Laboratory.

Today, PHENIX stands ready to start taking data, with flammable gas turned on to the tracking detectors, and five person shift crews set to control and monitor the operation of the experiment. The daily shift change meeting at 3:30 is replete with discussions of the vagaries of the software and electronics, and the atmosphere is much like the beginning of a new sporting season. The technicians are preparing themselves for being called in to help with some critical repair, the engineers wonder what last minute changes they'll be asked to design, and the Data Acquisition group wonders what late night oddities they'll be called upon to explain. The only sure thing is that PHENIX has some interesting times ahead.

The Relativistic Heavy Ion Collider at Brookhaven National Laboratory is a world-class scientific research facility primarily funded by the U.S. Department of Energy Office of Science. Hundreds of physicists from around the world use RHIC to study what the universe may have looked like in the first few moments after its creation. What physicists learn from these collisions may help us understand more about why the physical world works the way it does, from the smallest subatomic particles, to the largest stars.