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Steve Vigdor is the Associate Laboratory Director for Nuclear and Particle Physics at Brookhaven National Laboratory.

RHIC Funding, Operating Schedule Update

By Steven Vigdor

I have now secured enough funds to run RHIC for a total of 19 cryoweeks, i.e., until mid-March, allowing essentially 6 weeks beyond the end of the d+Au portion of the run. Everyone agreed that this was insufficient time to permit a meaningful addition to precision of constraints on gluon polarization from incremental longitudinal spin asymmetries in 200 GeV pp. STAR presented a plan focused on using nearly all of the 6 weeks for 200 GeV pp measurements, with a primary emphasis on providing reference data for d+Au correlation data being taken presently with FMS triggers (and secondary benefits mentioned below). PHENIX presented an alternative plan devoted primarily to getting a start on 500 GeV polarized proton collision studies, where 6 weeks might produce, in addition to demonstration of machine capabilities and tuning of detector gains, cross section measurements for hadron production, polarimeter calibration, perhaps a first view of a W production peak in the central arms (via electron/positron detection) and assessment of background for W measurements in the muon arms. STAR also requested a couple of days of additional tests for low-energy Au+Au operation. Possible ways of combining the various requests were also discussed.

I have decided based on what I heard to suggest the following plan for the remainder of Run 8:

  1. Terminate d+Au running on Jan. 29. This is 2 days short of 13 weeks, to allow for 2 days of low-energy Au+Au tests (though they will be scheduled for later in the run to accommodate QM2008 travel schedules). It represents the earliest time by which it seems prudent to expect STAR to have completed its d+Au goals and proton beam readiness for the pp run. PHENIX should have attained its d+Au goals somewhat earlier.
     
  2. Switch to 200 GeV pp collisions, using the new working point. We anticipate readiness for 200 GeV pp physics production then by about Feb. 12.
     
  3. This leaves about 4 weeks for 200 GeV pp production, followed by 2 days of low-energy Au+Au luminosity tests.
     
  4. If a compelling case can be made for what we could gain with 2 weeks of 500 GeV pp (1 week of commissioning + 1 week of data-taking), I can try to secure additional funding for a 20th cryoweek. This would permit the 2 weeks of 500 GeV running if it looks as though 200 GeV goals can be accomplished in 3 weeks of production, rather than 4.

Let me explain my reasons for this choice to provide some calibration of how I think about these things for future reference:

  1. The most convincing case I heard for urgency of science impact was to provide the pp reference data for the CGC test with STAR’s FMS. It would clearly be beneficial for RHIC to produce a definitive test of CGC predictions before the LHC heavy ion program is launched.
     
  2. Getting a start on 500 GeV pp running is in everyone’s interest and is “new”, but the case for urgency is less strong because a first 500 GeV pp run was never in the plans before FY09. A 500 GeV run in FY09 of comparable length to that PHENIX argued for in FY08 would still provide an opportunity to address the Japanese funding agency 2011 milestone regarding W production, and might benefit from additional simulations for W analysis that can be performed in the meantime.
     
  3. The secondary benefits of an FY08 200 GeV pp run for the spin program are substantial: it permits a meaningful test of the new working point needed to improve pp luminosity for a long longitudinal asymmetry run in FY09 (with some time to respond before FY09 if things do not work as anticipated); it also allows for significant new transverse spin asymmetry data to be taken with expanded forward coverage, where inclusive asymmetries are known to be sizable.
     
  4. Although PHENIX argued that the transverse asymmetry data they could acquire at 200 GeV in Run 8 were not of very high priority, they also indicated they might well ask to measure transverse asymmetries at 200 GeV early in Run 9 (if the remainder of Run 8 were devoted to 500 GeV pp). Any transverse run in Run 9 could not likely be significantly longer than the 4 production weeks available in Run 8, and still be consistent with the Run 9 pp run length needed for the higher-priority longitudinal asymmetry measurements. Thus, 200 GeV transverse asymmetry measurements in Run 8, followed by 200 GeV longitudinal asymmetry measurements and a first 500 GeV run in Run 9, seems a viable, though not preferred, plan for PHENIX.

I wish that federal funding allowed more sensible planning, so we could avoid these wrenching annual decisions of what important science goals to cut in light of reduced (and very late) budgets. But the above represents my best attempt to optimize RHIC’s scientific impact within the budget we have been given for FY08. We can do this well only because the machine performance has been so good thus far in Run 8 – at least for this, and for C-AD’s efforts in providing this performance, we should be thankful.