The Past 6 Weeks for Nuclear, Particle Physics at BNL
By Steve Vigdor
Dear RHIC and AGS Users,
The past 6 weeks have been an extremely busy period for Nuclear and Particle Physics at Brookhaven. On April 28, Sam Aronson and the upper BNL management presented a 10-year BNL plan to DOE, in which both nuclear and particle physics played crucial roles. On May 2, we hosted a symposium to honor the 50th anniversary of the classic BNL experiment by Maurice Goldhaber, Lee Grodzins and A.W. Sunyar measuring the helicity of the neutrino. On May 6-7, we hosted the first TECHQM (Theory-Experiment Collaboration for Hot QCD Matter) meeting, established to foster a coherent effort to quantify the interpretation of relativistic heavy-ion collisions. The RHIC/AGS Program Advisory Committee met at BNL on May 8-9. A May 12 symposium to honor Larry Trueman upon the occasion of his retirement was followed in rapid succession by a review of the national LQCD Project on May 13-14 and a DOE review in Germantown of the BNL heavy-ion research groups on May 14. A return visit to Germantown on May 19 to discuss planning for RHIC’s future was followed by the Electron-Ion Collider Workshop at Hampton University May 19-23. Many of you attended the annual RHIC/AGS Users Meeting at Brookhaven May 27-30, which occurred in parallel with the Washington, DC meeting of the High-Energy Physics Advisory Panel to consider the report of the P5 Panel on a ten-year plan for US High Energy Physics. There was an internal BNL management retreat on June 3-4, a PHENIX VTX project review on June 9-10, a Daya Bay project CD-3b review on June 10-11 and a meeting of the US/Japan Committee for Cooperation in the Field of High-Energy Physics on June 12-13, all at BNL. (Exhausted yet?) Now I have just returned from a June 16-17 Gluon Polarization Workshop at the University of Illinois, and am planning for the upcoming (July 7-9) DOE Science and Technology Review of RHIC. I have finally found a moment or two to summarize for you some of the important aspects of the above meetings. But there’s so much to summarize that I’ll break it up into two RHIC Newsletter articles, the other one devoted only to PAC recommendations and their impact on running schedules for the next several years.
TECHQM Workshop: The workshop at BNL was very well attended and marked by lively discussions regarding both the status and needs of modeling of relativistic heavy-ion collision dynamics and the structures that might be used to foster cooperative work on these problems. The assembled theorists and experimentalists decided to launch the efforts by breaking up into two working groups, one focused first on reconciling different theoretical approaches to partonic energy loss in hot QCD matter, and a second working on bulk evolution of the matter, with an early emphasis on progress toward viscous hydrodynamics treatments. Considerable progress on the latter subject had already been made just prior to the TECHQM Workshop in a program at BNL sponsored by the RIKEN-BNL Research Center. I consider efficient and timely progress on collision modeling critical to the future health of RHIC, and specifically to meeting the advertised RHIC-II goal of quantifying properties of the “perfect” liquid matter produced in RHIC collisions. I therefore look forward to a continuing meeting of the minds and of the milestones established at this first meeting. The workshop web page is here and the wiki page for ongoing work within this cooperative agreement can be found here.
Planning RHIC’s Future
Derek Lowenstein, Tom Ludlam and I met with staff from the DOE Office of Nuclear Physics, at Jehanne Simon-Gillo’s request, on May 19. We discussed (primarily) the scope of accelerator improvements to be considered as fostering the RHIC-II science program, plus our initial thoughts about possibilities for staging an Electron-Ion Collider (EIC) at BNL. I summarized some aspects of these considerations for users in my concluding talk at the Special Symposium on RHIC & Its Impact on Nuclear Science (webpage) held during the recent Users Meeting at BNL. In that talk, I stressed that securing a long-term future for RHIC is likely a play with three acts. We are well under way in Act 1, pushing the time scale for getting to the RHIC-II science program much earlier than that envisioned in the 2007 Nuclear Physics Long Range Plan, thanks to the success in developing stochastic cooling of bunched beams. Act 3 requires making both the science and technical feasibility cases for EIC much more compelling on the time scale of the next Nuclear Physics Long Range Plan, presumably to be developed in ~2012-13, and would culminate with a full EIC implementation at RHIC some time in the 2020’s.
The time gap between Acts 1 and 3 requires that we begin now to develop a detailed plan for Act 2, an intermediate upgrade plan that could be implemented in parallel with making RHIC-II science measurements during the second half of the next decade. The most attractive options might serve as a serious step toward realization of the EIC. At the Users Meeting I presented three possibilities. The first would be a preliminary stage of EIC, involving polarized electron-proton and electron-ion collisions at one intersection point of RHIC, at lower energy and luminosity (hence, much lower cost) than the final EIC. Energy and luminosity upgrades to reach EIC could then be added in subsequent stages, after an initial foray into the science of matter at high gluon densities. The idea of staging was also discussed at the EIC Workshop at Hampton University. While the idea was controversial, it led to constructive discussion and, I think, has launched more serious thought about how staging might be optimally implemented. Much work has yet to be done on fleshing out a science program achievable with a sensible first stage, which will certainly influence strongly the preferred staging implementation.
The second possibility I presented for upgrades during the second half of the next decade centered on an improvement to polarized proton collision luminosities at RHIC that might be achievable if we can successfully demonstrate that the promising concept of coherent electron cooling (CeC) works in practice to enhance high-energy hadron beam luminosities. CeC utilizes Free Electron Laser amplification of density modulations in an electron beam from a high-brightness Energy Recovery Linac (ERL) to facilitate a technique that is a hybrid between conventional electron cooling and stochastic cooling. We plan to use the R&D ERL under development at RHIC for a proof-of-principle demonstration of CeC during the next five years. If the present limit anticipated on RHIC p+p luminosities from beam-beam tune spread could be relaxed to take advantage of coherent cooling (and the RHIC detectors could handle the rates and the pileup), a number of previously considered RHIC spin measurements could be made feasible. This option would also take us along a path to EIC, where CeC represents one of the techniques that might allow reaching the ambitious luminosity goals.
The third option I presented involved precision physics experiments at the AGS, including a storage ring experiment to measure or place stringent limits on an intrinsic electric dipole moment of the deuteron. This experiment was proposed and considered at the recent PAC meeting. My presentation of upgrade options was considered provocative by many users, because it did not include heavy-ion collision enhancements beyond the luminosity and detector upgrades under way for the next five years or so. The absence of this item reflects the absence to date of clear input to me from the RHIC collaborations concerning longer-term needs for heavy-ion upgrades. If you have a compelling plan to enhance the heavy-ion program at reasonable cost during the 2nd half of the next decade, now is the time to let me and your collaboration know and discuss this plan!
The P5 Report and BNL Particle Physics Plans
The report of the Particle Physics Project Prioritization Panel (P5), in response to a charge from DOE issued last Fall, was presented to HEPAP, and approved, on May 29-30. The P5 plan (available here) is strongly supportive of BNL plans for the next decade in particle physics, as we presented them to P5 (here) in the March 6-8 meeting at BNL. In particular, the P5 Plan adopts for the entire field the three-frontier (energy, intensity, cosmology) theme toward which BNL plans are directed, and recommends funding for all of our major projects under any of the funding scenarios they were asked to consider. The suite of these projects was presented, under the rubric “Physics of the Universe”, as one of four major BNL activities going forward, in an April 28 presentation by Sam Aronson to Ray Orbach and DOE covering the BNL Business Plan. (The other three major activities are Collective QCD Phenomena, incorporating the RHIC, RHIC-II and eRHIC science programs, Photon Science centered around the NSLS-II project, and Energy Sciences.) The highlights of Physics of the Universe, as pursued by BNL, include: the search for supersymmetric partner particles, including potential dark matter candidates, at ATLAS; the search for CP violation in the neutrino sector, with implications for the matter-antimatter asymmetry in the universe, via oscillation experiments in Daya Bay and then with a long baseline from Fermilab to the Homestake Mine (DUSEL) in South Dakota; improving constraints on the nature of dark energy with the ground-based Large Synoptic Survey Telescope (LSST); and R&D on muon colliders as a candidate for a next-generation energy frontier machine to pursue precision understanding of physics and early-universe symmetries beyond the current Standard Model.
There is enormous mutual benefit to the RHIC program and to the BNL particle physics program if we can keep both efforts at the forefront of their scientific subfields. I look forward to your continuing help in doing just this.