Brookhaven HENP Program Advisory Committee

Recommendations on BRAHMS, PHENIX, PHOBOS, & STAR

March 24, 2000

Spokespersons for the BRAHMS, PHENIX, PHOBOS and STAR experiments presented the status and preparations of their detectors for the first physics run of RHIC, scheduled to start in May 2000. The PAC was very impressed by the progress that has been made on the construction and installation of all four detectors. All four RHIC experiments are on target in their preparations for data taking. The goals, priorities and recommendations of last year's PAC report remain unchanged because technical accelerator problems prevented data taking since that time.

The delay has reduced the first year's physics running time to 8 weeks with an integrated luminosity that may reach only a few inverse microbams. This precludes measurements of rare probes, but should be adequate to start mapping the global features of nuclear reactions in this uncharted energy domain. This first survey should provide important constraints on the initial conditions (baryon density, energy density) that can actually be achieved in nuclear collisions at collider energies. The PAC reiterates its recommendation that high priority be given by all four RHIC experiments to the timely completion of data analysis and publication of these first data.

Given the very limited running time available during the first year and the importance of a highly successful physics outcome, the PAC recommends that Laboratory management keep searching for ways and resources necessary to extend that time as long as possible. The anticipated quadratic growth of integrated luminosity puts a premium on any such extensions. It is now anticipated that the year one run will begin with colliding Au beams at 70 A-GeV. Depending on progress with accelerator performance, the beam energy may be increased to 100 A-GeV later in the run. We recommend that the decision whether or not to change beam energies should be based on the ability of the experiments to generate data sets that are sufficient to obtain useful physics results.

We also recommend that the Laboratory try to coordinate the polarized proton beam commissioning with a short run on p-p collisions. The p-p data obtained in such a parasitic mode would help the experiments to compare p+p with heavy ion data.

The PAC feels that Laboratory management and experimental groups should keep in mind the opportunity afforded by the upcoming Nuclear Science Long Range Plan to advance long range proposals for accelerator and detector upgrades for RHIC physics over the next five year period. The long lead times needed to fund major new proposals necessitate that planning of the next generation of RHIC experiments occurs concurrently with data taking and analysis of the present round of experiments.