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The Annual State of RHIC Report

Steven Vigdor

Steven Vigdor

Let me take this opportunity to wish all of you and your families a happy and prosperous New Year, and to bring you up to date on 2011 RHIC highlights and plans and issues for 2012 and beyond.

Highlights of 2011

RHIC’s scientific productivity and impact continued at a high level in 2011, marked by a number of special achievements, honors and awards. Yasuyuki Akiba received the 2011 Nishina Memorial Prize for his work on the quark-gluon plasma within the PHENIX Collaboration, especially for his leadership in analyses of thermal dilepton spectra that led to a first measurement of the early collision temperature of the matter produced at RHIC. The RHIC-ATLAS Computing Facility team received one of nine Secretary’s Achievement Honor Awards given by Steven Chu for exceptional service to DOE and the American people. The STAR observation of antihelium-4, the heaviest antimatter nucleus ever observed, was published in Nature and highlighted by Discover Magazine as number 20 among its top 100 science achievements of the year. And earlier discoveries kept on giving: the PHENIX and STAR 2005 White Papers surpassed 1000 citations apiece, placing them among the 300 most-cited high-energy physics papers of all time in the SPIRES database (and among the top 20 published since 2004); Brookhaven National Laboratory received a 2011 Bulldog Award for Excellence in Media and Public Relations (an award judged by journalists) for the 2010 publicity initiative (including press releases and a press conference at the February 2010 APS meeting) surrounding the PHENIX measurement of early collision temperature and the STAR measurement of charged-particle correlations consistent with expectations for a sphaleron-induced event-by-event CP-violating electric dipole moment in the produced matter.

RHIC’s continuing productivity is summarized by the following quote from our June 2011 DOE Science and Technology Review: “Both experiments have been extraordinarily successful in generating interesting and even spectacular new physics results from their experiments at RHIC. Both experiments have demonstrated originality and creativity, enhancing the detector performance, utilizing improved luminosity, and creating new physics insights.” New RHIC results received wide attention at the Quark Matter 2011 Conference in Annecy last May, which represented a watershed for the field of relativistic heavy-ion collisions. Especially noteworthy were: the STAR and PHENIX results (along with analogous results from the three LHC experiments) for higher, including odd, multipoles of collective flow, pointing toward a path to improve greatly on the precision with which the degree of “perfection” of the near-perfect liquid can be established; first PHENIX results on the elliptic flow of direct photons; and first STAR results from the RHIC beam energy scan launched in 2010. Brookhaven, by the way, is the lead U.S. laboratory in the organization of Quark Matter 2012, which will take place in Washington, D.C. on August 12-18, 2012.

Run 11 at RHIC led to real progress in enhancing collider and detector performance. Although the 500 GeV p+p portion of the run fell far short of integrated luminosity goals, due primarily to several early major hardware failures completely unrelated to polarized beam operation, it nonetheless established new records for instantaneous luminosity and beam polarization. A p+p luminosity about 75% of the enhanced design goal at 500 GeV was reproducibly attained late in the run, and the 250 GeV beam polarization exceeded the 2009 value by a factor ≈ 1.3. Two significant sources of improvement in the polarization were the successful tuning of many tune-jump quadrupoles in the AGS and the operation of RHIC much closer to the 2/3 betatron resonance tune than was possible in 2009. The average observed polarization of 48% at 250 GeV still falls quite short of our design goal of 70%, but a series of auxiliary measurements made during the run at several beam energies provided critical diagnostics for assessing how to improve polarization in the future. In particular, the results indicate that the central polarization values within beam bunches and at the start of 250 GeV fills do not appear to suffer significant loss from the values attained out of the AGS. Rather, the losses are associated with a polarization profile that narrows on the acceleration ramp and, in small part, to a weak time decay of the polarization during a fill. We hope to ameliorate both these sources of polarization loss in the next few years, as well as to make further improvements to the polarization of beams out of the AGS.

Collider performance for Au+Au collisions in Run 11 was outstanding, far exceeding expectations for luminosity buildup at √sNN = 200 GeV, and thereby allowing us furthermore to complete the first phase of the beam energy scan started in Run 10. Planning for a second-phase return to the lower energies in future runs awaits results from the first phase, in particular bearing on the search for a critical point in the QCD phase diagram. In part, the excellent Run 11 luminosity performance for full-energy heavy-ion collisions arose from simultaneous operation of four planes of well-tuned stochastic cooling, following some retrofits to the stochastic cooling hardware between Runs 10 and 11. PHENIX took heavy-ion data with their new VTX silicon barrel installed, allowing a first look at separating charm from bottom quark production in assessing heavy quark energy loss and flow in the quark-gluon plasma. Other major equipment upgrade milestones reached during 2011, but without impact on Run 11, included completion of the new EBIS source and its first use for NASA Space Radiation Lab beams, and a successful CD-2/3 review that launched construction funding for the STAR Heavy Flavor Tracker.

Plans for RHIC Run 12

The completion of FY12 appropriations bills in Congress by the end of calendar year 2011 led to restoration of some RHIC operations funding that had been previously cut on the basis of the earlier Senate markup of the Energy & Water bill. This restoration permits us to run RHIC for about 20 cryo-weeks, and we have consequently reverted to previous plans to start cooldown of the RHIC rings below 45K on January 17. Physics production will start with 4 weeks of 200 GeV p+p operation, to provide transverse spin asymmetry data and new baseline data for earlier heavy-ion collisions that involved new subsystems, such as the PHENIX VTX. This will be followed by 500 GeV polarized proton collisions aimed at generating improved data for both gluon and sea antiquark polarization determination. The length of the 500 GeV run and the choice of heavy-ion collisions to follow it (between asymmetric Cu+Au operation or U+U collisions – both providing unprecedented capabilities) will be made during the run on the basis of judgments regarding machine performance and budget flexibility. The budget will likely not permit running both Cu+Au and U+U during 2012, but either can fuel exciting new programs to highlight at Quark Matter 2012, exploiting RHIC’s ability to vary initial collision geometry in illuminating ways.

We will continue in Run 12 RHIC’s tradition of commissioning substantial new systems during almost every run. Accelerator operations and cryo-system controls have been moved into a new Main Control Room in building 911, which should optimize communication among various support groups. The heavy-ion operation will provide the first opportunity to use the new EBIS source as RHIC’s pre-injector. Further improvements in beam intensities out of EBIS are anticipated via ongoing commissioning activities in the background, during the p+p portions of Run 12. Two additional planes of horizontal stochastic cooling have been added to RHIC, providing radial pickups and kickers to complete full three-dimensional cooling capabilities for high-energy heavy-ion operation. The 9 MHz rf cavity, which broke down during the final week of p+p operation in 2011, has been repaired for Run 12. In addition, we anticipate commissioning the RHIC spin flipper.

On the detector side, PHENIX has refurbished various ladders of the VTX detector and added the endcap silicon wheels that comprise the FVTX subsystem. Commissioning these subsystems fully during the p+p portions of the run should provide for enhanced heavy flavor detection capabilities in the later heavy-ion collisions. PHENIX has furthermore completed installation of its muon trigger upgrade, providing enhanced triggering for W production studies in 500 GeV p+p running. STAR has installed 14 of an eventual 24 sectors of its Forward GEM Tracker, to provide improved tracking resolution and charge sign discrimination for forward W decay electrons and positrons.

Outlook for FY2013 and beyond

Federal budget uncertainties, combined with expansive plans of the U.S. Nuclear Physics community, demand a delicate balancing act in planning RHIC’s future. On the one hand, the last year has been tremendously productive in advancing both scientific and technical progress in support of ongoing RHIC and future eRHIC operations. It is critical that we follow through aggressively on this progress, to produce a coherent strategy and to continue a cutting-edge R&D program for RHIC’s long-term future, in preparation for a possible NSAC Long Range Plan exercise that could take place as early as 2013. On the other hand, without a substantial increase in the federal funding level for Nuclear Physics, DOE will be hard pressed to support simultaneously the completion of the CEBAF 12 GeV upgrade, FRIB construction, ongoing RHIC operations and the full national research and facility operations portfolio. The uncertainties surrounding federal budgets make it difficult to predict if and when these funding challenges might reach a crisis stage. But this could happen as soon as FY2013. In his presentation at the December 1, 2011 NSAC meeting, Tim Hallman stated the following: “The initial OMB guidance for Nuclear Physics is very challenging. If that is how things turn out, the budget will most certainly not support the nuclear science vision articulated in the 2007 Long Range Plan. In that case one would anticipate some kind of community exercise early in 2012 to seek input on how to implement the program in light of the constraints.” As of this writing, we do not know yet if such an exercise will in fact be convened, but we clearly must be prepared in the very near future to make the strongest possible case for the criticality of ongoing RHIC operations to the short- and long-term health of U.S. nuclear science.

In reality, our preparations for either of these 2012-13 exercises began in earnest a couple of years ago with the commissioning of the new STAR and PHENIX Decadal Plans. It has been substantially advanced by the constructively critical feedback to those plans provided at the June 2011 Program Advisory Committee meeting, by the productive discussions about future strategy held with the user community at the June 2011 Users Meeting, and by recent upgrade collaboration meetings held by both PHENIX and STAR. Both collaborations have now adopted a staged approach, with substantial upgrades proposed for the second half of the current decade to advance the RHIC program, while remaining consistent with longer-term plans to make the detectors suitable for e+p and e+A collisions in the eRHIC era. We are taking a similar approach to machine upgrades, contemplating the early development to enhance RHIC capabilities of technology desirable for eRHIC in the long-term: examples include polarized 3He beams and coherent electron cooling (which could potentially dramatically improve p+p luminosities at RHIC, as well as e+p and e+A luminosities at eRHIC).

Furthermore, the scientific developments of the past year in heavy-ion collisions have helped enormously to pave the way toward quantifying properties of the quark-gluon plasma and of the QCD phase diagram, from below to above the deconfinement transition, and to highlight those unique capabilities at RHIC that would provide essential components of this quantification program. Among RHIC’s unique capabilities are an energy range that spans an apparent “sweet spot” encompassing the deconfinement transition (as hinted by early results from the 2010-11 beam energy scan), and the relative ease of providing asymmetric nuclear collisions that should shed light on the origin of odd multipoles of collective flow and on the path-length dependence of parton energy loss. More generally, the major focus on heavy-ion collisions at RHIC is crucial for the systematic studies needed to unravel the various intertwined dependencies that influence event evolution. The basic science questions still to be addressed by relativistic heavy-ion collisions remain compelling, centered on understanding how the very strongly correlated fluid behavior observed at RHIC and at LHC emerges from an asymptotically free quantum field theory. Krishna Rajagopal and Bill Zajc helped greatly in making the case for this compelling science to Bill Brinkman, when they accompanied me, Sam Aronson and Doon Gibbs (BNL’s Deputy Director for Science and Technology) on a very productive Sept. 21, 2011 meeting with the DOE Office of Science management team.

Planning for eRHIC

From my viewpoint, the scientific, technical and financial case for eRHIC is an essential component of the arguments for RHIC’s future. Even if the community has to deal with short-term budget crises, it is wise to consider where the community wants to be a decade or more from now, and to establish priorities that protect the most realistic paths to get to that long-term future.

A number of significant milestones in planning for an Electron-Ion Collider were reached in 2011, and we anticipate several more in 2012. Summer 2011 saw publication of a very detailed 550-page report of scientific progress made at the Fall 2010 10-week Institute for Nuclear Theory program on EIC science (arXiv:1108.1713). A Steering Committee appointed jointly by BNL and JLab is currently working on an EIC Science White Paper that will present the goals, approaches and simulations for an EIC at a level suitable for the general nuclear science community. The committee, representing more than 15 U.S. and foreign institutions, is co-chaired by Abhay Deshpande of Stony Brook, Jianwei Qiu of BNL and Zein-Eddine Meziani of Temple, and will produce a report for dissemination during 2012. The BNL design of eRHIC advanced considerably during 2011, and was the subject of a very successful technical (pre-conceptual) design review by an external team of accelerator physicists in August 2011. We are in the midst of a full cost estimation for this design, to be reviewed by an external panel in Spring 2012. We continue to pursue an aggressive suite of accelerator R&D projects relevant to eRHIC, and progress and plans for these were reviewed by DOE in December 2011. And we launched a generic EIC detector R&D program, using RHIC detector R&D funds, in 2011, which has led already to significant progress relevant to both BNL and JLab machine designs and to an expansion of the user community actively involved in EIC planning. In addition to incorporating plans for ep/eA operation into upgrade considerations for PHENIX and STAR, we continue to work as well on the design and costing of a new, dedicated eRHIC detector and intersection region. These approaches keep options open for trying to fit a first-phase EIC within constrained future budgets for the field.

My status as ALD

As many of you already know, I have announced my intention to retire from BNL at the end of calendar year 2012. My decision is dominated by personal considerations, and I gave BNL management three years’ notice of this intention. I am working to the extent possible to ensure that there will be a smooth transition to a new ALD. As the time for my retirement approaches more closely, I will fill you in on details of the transition. But in the meantime, as outlined above, we’ve still got a lot of irons in the fire, and I look forward to continuing to work closely with the RHIC user community to ensure a healthy and productive future for the facility.

2012-2813  INT/EXT  |  Media & Communications Office

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