Welcoming a New Era of Discovery at the 2024 RHIC & AGS Users' Meeting

Annual meeting recaps science highlights and lays out plans for the future

July 2, 2024

By Kelly Zegers, Karen McNulty Walsh, and Amber Aponte

Scientists and supporters of the Relativistic Heavy Ion Collider (RHIC) and Alternating Gradient Synchrotron (AGS), key components of the collider-accelerator complex at the U.S Department of Energy’s (DOE) Brookhaven National Laboratory, gathered at Brookhaven for their annual users' meeting June 11-14, 2024.

This year’s meeting focused on fulfilling the recommendations laid out in the 2023 Long Range Plan for Nuclear Science, which plots a path for the next decade for nuclear physicists in the U.S. Top priorities from the plan — “A New Era of Discovery,” released in October 2023 by the Nuclear Science Advisory Committee (NSAC) — include completing RHIC’s science mission and ensuring a swift transition to the Electron-Ion Collider (EIC).

The first two full days of the conference featured workshops on the use of machine learning and artificial intelligence for running colliders and experiments and for analyzing data, along with a wide range of physics topics. There were a slew of sessions addressing particle flow from various collisions systems, presentations of findings offering insight into spin physics and cold nuclear matter, commentary on how ultraperipheral collisions — where speeding ions interact without colliding — can be used to explore the properties of nuclear matter, and discussions of jets and RHIC’s Beam Energy Scan (BES). Scientists also discussed the important interplay of nuclear physics experiments with theory, as well as connections between RHIC physics and experiments at the Large Hadron Collider (LHC) and the future EIC.

“In its 24^th year of operations, RHIC remains a cornerstone of Brookhaven’s science program,” Brookhaven Lab Director JoAnne Hewett said as she welcomed users attending the meeting’s first plenary session on day three. “Over its lifetime, RHIC has collided various configurations of beams with 10 different particle species over a wide range of center of mass energies. This is a first for any collider, and it’s nothing short of spectacular.”

Meeting attendees heard updates on the status of the current run, which is still ongoing, and plans for converting RHIC to the EIC after its next run in 2025. The EIC is a state-of-the-art facility that will explore a new frontier in nuclear physics and will be built in partnership with DOE’s Thomas Jefferson National Accelerator Facility (Jefferson Lab). Once the RHIC program is complete, “we must start construction of the Electron-Ion Collider in earnest,” Hewett said.

The EIC is already off to a good start, Hewett noted. In just the last few months, the project received the go-ahead to procure key components needed for the construction and celebrated a $100 million investment from New York State that will support EIC design and construction over the next four years.

Between the turn-off of RHIC and the start of EIC operations, there will be an unavoidable gap in collecting new science data, she noted. Still, there will be a lot of RHIC data to analyze and much to do in the meantime.

“The final analysis of RHIC data will last for six to eight years,” Hewett said. “It will take that long at least to sift through the data and mine it for every piece of physics that you can get.”

Plus, the construction of a new EIC detector will be a fun, exciting once-in-a-lifetime opportunity for scientists, postdocs, and students. There are also chances to collaborate with heavy ion physicists conducting experiments at the LHC at CERN, Europe’s laboratory for nuclear and particle physics, Hewett said.

“There will be a lot of exciting heavy ion physics during this period,” Hewett said. “And then, the EIC will turn on!”

Updates from RHIC Run 24

RHIC Run 24 kicked off in April, focused on collecting critical data from polarized proton collisions. Scientists will use the data to investigate proton spin and the arrangement of fundamental building blocks — quarks and gluons — within protons. The run will also provide comparisons for data collected from other types of RHIC collisions.

The run’s organizers also aim to capture gold-gold ion collisions for dataset goals carried over from a shortened Run 23.

“So far, Run 24 has been an exciting and interesting run,” said Kiel Hock of the Collider-Accelerator Department (C-AD), run coordinator for Run 24.

Before the run began, C-AD physicists and engineers carried out upgrades and repairs needed after Run 23. With the run well underway, both of RHIC’s detectors, STAR and sPHENIX, had taken less data than projected by the time of the users’ meeting, Hock noted. But C-AD is working diligently to provide the experiments with higher luminosity, or collision rates, to support meeting their physics goals. Members of the STAR and sPHENIX collaborations were encouraged by the increasing luminosity in the weeks leading up to the meeting.

Overall, STAR’s data-taking for proton-proton collisions at 200 billion electron volts (GeV) has seen “smooth operations” with “good use of beam time,” said Jaroslav Adam, a STAR collaborator from Czech Technical University in Prague.

The detector is making use of recently installed components that are seeing proton-proton collisions at this energy for the first time, as well as upgrades to its triggers — a combination of hardware and algorithms that decide which collision events to record. Adam noted that the experiment’s data acquisition systems are currently capturing 5,000 events per second. “This is three orders of magnitude better than when STAR first started operating in 2000,” he said.

“In just over two weeks [during intentionally low luminosity collision conditions early in the run], we were able to get nice data for interesting physics,” he said.

Jamie Nagle, an sPHENIX collaborator from the University of Colorado, Boulder, applauded the efforts of C-AD to produce the collision conditions needed to collect proton-proton data while describing the successes — and challenges — of running the newest RHIC detector.

“It was a packed shutdown schedule — basically from the minute the last run ended all the way up to April,” he noted, with “heroic efforts by C-AD and heroic efforts by sPHENIX” to get the accelerator and detector ready for the run’s first proton-proton events. “Collisions began on the full moon night of April 26,” he said. “It brought me back to 1999, when RHIC first had beam!”

Nagle’s talk covered how one full suite of sPHENIX detectors is “in very good shape, sampling everything C-AD can give us. This is the beginning of our physics data-taking,” he said.

Even so, Nagle noted the sPHENIX collaboration’s ongoing efforts to improve the stability of the experiment's 240-million-pixel silicon vertex detector, the MVTX, and its main tracking detector, the time projection chamber (TPC). Changes to the way the MVTX data is read out — implemented the day before Nagle’s talk — have been very successful. Nagle also noted that the team planned to adjust the gas mixture that fills the TPC. That effort has improved TPC performance in the weeks since the Users’ Meeting.

“We have been doing a lot of diagnostic work, cooperative work with C-AD, and STAR has been very helpful. Things are progressing,” he said. With cautious optimism, he noted that C-AD’s efforts to achieve higher bunch intensities and squeeze the proton beams to increase the likelihood of collisions “might get us to our proton-proton data goal.”

Science highlights from RHIC

Haiyan Gao, Brookhaven’s outgoing associate laboratory director for nuclear and particle physics, covered highlights from RHIC’s science programs during her opening remarks at the plenary session. Abhay Deshpande, director of EIC science, has assumed the role of interim associate lab director as of July 1.

“This community has been extremely productive and talented,” Gao said, noting major accomplishments since the last NSAC Long Range Plan in 2015. “The highlights are really a bounty,” she said.

Here’s a snapshot of what she and additional plenary speakers from STAR, sPHENIX, and PHENIX — a former RHIC detector that is no longer running but is still publishing results from data taken through 2016 — presented:

• STAR’s results on magnetic fields generated in RHIC’s off-center gold-gold collisions revealed these to be potentially the most powerful magnetic fields in the universe. Gao noted that these findings garnered widespread media attention, which she used to point out the value of clear science communication.
• A range of results from the now-completed BES — a series of experiments exploring gold-gold collisions over a wide range of energies — made progress in exploring the properties of quark-gluon plasma. This free-flowing state of quarks and gluons, visible matter’s fundamental building blocks, mimics the state of the early universe, before protons and neutrons formed. BES data are helping STAR physicists map out the phases as quark-gluon plasma transforms into ordinary matter and look for signs of a critical point in this transition.
• PHENIX’s results on gluon polarization revealed that the spins of these force-carrier particles are positively aligned with the spin of the proton they are in. This was a long-sought result and a culmination of the PHENIX spin physics program.
• New PHENIX analyses of data from small collisions systems continue to offer intriguing evidence that such systems can create quark-gluon plasma.
• Preliminary results and tantalizing hints of signals from the decays of pions, kaons, and lambda particles as well as jets highlight the precision of sPHENIX’s subsystems — and the bright future of this detector’s physics program.

Gao pointed out that Brookhaven’s Nuclear Theory group has been highly visible and impactful in guiding not only RHIC physics but also heavy ion experiments at the LHC and the future EIC experimental program. And she emphasized that staff from Brookhaven’s Scientific Data and Computing Center continue to meet the computing needs of the RHIC community while collaborating with Jefferson Lab on computing efforts for the EIC.

She also pointed out the importance of maintaining the Lab’s collider-accelerator complex in a ready state for future EIC operations and to operate isotope production and space radiation research facilities, which use particles extracted from the same chain of accelerators as RHIC and the EIC, during the RHIC-to-EIC transition.

Exciting EIC opportunities ahead

The transition from RHIC to the EIC was a major topic throughout the meeting and the focus of a series of dedicated talks that summarized progress and scientific opportunities.

Jim Fast, a physicist at Jefferson Lab and the EIC associate project manager, gave an update on the EIC project, which is hitting milestones and increasing its national and international support, with over half of the scientific participants coming from outside the U.S.

At last count, the EIC Users Group, formed in 2016, has 1,529 collaborators from 40 countries and nearly 300 institutions — including 80 U.S. universities. The EIC detector collaboration — known as ePIC, for its electron-Proton-Ion Collider experiment detector design — was formed in 2022. It now has 650 active collaborators from 25 countries and 173 institutions. 

“The EIC was intended to be an international project since its inception,” Fast noted. “We cannot be successful without everyone on board. All systems [detector, accelerator, and science] have international participation. Momentum is building,” Fast said.

Since reaching the major milestone approving long-lead procurements — the purchase of materials and/or components that will take a significant amount of time to design and manufacture — the EIC project has been working to execute about $90 million in these purchases. Prominent items include normal conducting magnets for the Rapid Cycling Synchrotron, the accelerator that will bring electrons up to speed for collisions with protons or heavier ions at the EIC. 

Daniel Brandenburg, a RHIC and EIC collaborator from Ohio State University, spoke about the opportunities for exploring spin physics at the EIC. Spin is a fundamental property of matter. Yet, physicists still don’t understand how quarks and gluons combine their spins to generate the overall spin carried by the proton. 

Brandenburg noted that while RHIC provides an ideal testing ground for a wide range of aspects of the “spin puzzle,” the EIC will make precise measurements that solve the spin mystery. “Exciting opportunities lie ahead,” he said. 

Kong Tu, a Brookhaven Lab member of the ePIC Collaboration, gave an overview of the planned EIC detector — including its massive superconducting solenoid and sensitive calorimeters — and how it will build on questions pursued at RHIC. These “big questions” center around the origin of mass and spin, the 3D internal structure of protons and nuclei, and the question of whether gluons reach a steady state of saturation at high energy. 

“The ElC will probe the fundamental structure of matter with unprecedented precision,” Tu said. “It will allow us to see the fundamental structure of matter and what we are made of.”

He noted how the detector’s sophisticated components will take “snapshots” that help scientists reconstruct the dynamic interactions of quarks and gluons within protons and nuclei.

While ePIC will be located at the current location of STAR, Anselm Vossen of Duke University spoke on behalf of a subset of the EIC Users Group that is continuing to make the case for constructing a second EIC detector at the current location of sPHENIX.

Vossen pointed out that most accelerator facilities have two detectors to provide independent verification as well as complementarity in technology and strength, and he emphasized that the large EIC community can support two detector collaborations.

“In addition to confirming the precision of measurements and any unexpected effects, a second detector could expand physics opportunities,” Vossen said.

Deshpande added, “I was delighted to see such enthusiasm for the EIC amongst the RHIC and AGS users and the ever-increasing momentum it has resulted in for the EIC and the ePIC detector — and that user-driven discussions for the science case for the second detector have started.”

Comments from funding agencies

RHIC and the EIC are awaiting finalized budgets for fiscal year 2025. Both receive funding allocated by Congress and the DOE Office of Science. Individual RHIC users may also receive funding from the National Science Foundation (NSF). 

In an update from DOE’s Office of Nuclear Physics, Physics Research Division Director Sharon Stephenson noted that the fiscal year 2025 President’s Request is 3.6% above fiscal year 2024’s budget, with the caveat that appropriations from Congress may not match that request.

The Office of Nuclear Physics is working to support the priorities outlined in the 2023 NSAC Long Range Plan within the constraint of annual appropriations, Stephenson said.

This includes the recommendations to expediently complete the EIC and to construct facilities that support neutrino-less double beta decay. Both heavily depend on international partnership, she said.

With respect to the Long Range Plan, the DOE Office of Science requested that an NSAC subcommittee assess the scientific importance and construction readiness of new, major nuclear physics facilities, Stephenson said. Among the projects, the subcommittee considered the EIC to be “absolutely central” and “ready to initiate.” The DOE Office of Science leadership is assessing that report.

Beyond budget outlooks and future plans, Stephenson encouraged users to reach out and share their current work so it can be celebrated and distributed.

“I have opportunities to blow the horn of success for our research community often and in different places,” she said.

Stephenson also emphasized a commitment to advancing belonging, accessibility, justice, equity, diversity, and inclusion across the activities sponsored by the Office of Nuclear Physics and the Office of Science. A number of ongoing and new programs support students, early career researchers, and visiting faculty by offering research opportunities at national labs.

Senta “Vicki” Greene, NSF program director for nuclear physics, also spoke to efforts that support and grow an inclusive workforce. She highlighted NSF’s interest in funding early-career scientists through its Early Faculty Career Development Program. The program awards early career scientists who have the potential to serve as academic role models in research and education and to lead to advances in the mission of their department or organization. Untenured assistant professors who are at least 50% tenure track are eligible.

On the budget, Greene noted that fiscal year 2024 was a challenging year for NSF but she’s hoping for an increase in physics funding in line with the President’s request.

“A steady increase is better than up and down,” Greene said.

Notes on diversity, equity, inclusion, and accessibility

During a Wednesday afternoon workshop covering diversity, equity, inclusion, and accessibility (DEIA) as well as potential career directions, attendees had a chance to discuss challenges and opportunities.

Brookhaven Lab Chief Diversity Officer Noel Blackburn spoke about how the Lab’s DEI Office has been introducing different DEIA topics under the Focus Themes program, from emotional intelligence and inclusion to psychological safety and respect in the workplace.

With this latest theme, he said, “Our primary focus will be respect as we continue to engage our staff, understand how to better retain employees, and pursue different ways of diverse talent recruitment.”

He emphasized the need for treating coworkers and collaborators courteously and fairly, which includes valuing their beliefs, contributions, and ideas. He noted that the Lab would continue to pursue the present set of DEIA programmatic activities while developing sound metrics to evaluate their effectiveness.

Blackburn also described an ongoing DEIA effort across the Lab that's focusing on encouraging staff to be their “authentic selves,” enabling their success in a respectful workplace, increasing productivity, and pushing the Lab to be the best that it can be. 

Additional speakers discussed ways that the RHIC & AGS Users’ Executive Committee and the American Physical Society’s Inclusion, Diversity & Equity Alliance could potentially provide support.

Attendees were also offered diverse career advice, including from a former RHIC physicist who is now pursuing an “off the path” job running a hedge fund, a professional managing data science for Home Depot, and a person developing the latest PET scan detector technology. All these fields use skills that RHIC collaborators learn and can bring with them to a variety of careers.

Campus notes, awards, and thanks

Tom Daniels, Brookhaven’s associate laboratory director for facilities and operations, shared updates that users may notice over the next year, including the new Science and User Support Center currently under construction at the Lab’s entrance. The new facility will expedite check-ins for Lab guests and user scientists and provide new meeting spaces. Daniels also outlined recent and upcoming improvements to the Lab’s on-site housing and transportation options. He took questions and suggestions for improving users’ experiences into the future.

Each year, the users’ community celebrates Ph.D. students and scientists recognized by the Users’ Executive Committee for outstanding thesis and research in either theory or experiment related to RHIC, AGS, the NASA Space Radiation Laboratory, the Tandem Van de Graaff, the Accelerator Test Facility, the Brookhaven Linac Isotope Producer, and/or EIC facilities. View the results of the merit awards and thesis awards online.

In addition, Zachary Sweger from the University of California received the best poster award for his research: “How Not to Measure a False Critical Point.”

Users’ Executive Committee Chair Marzia Rosati and Chair-Elect Anders Knospe wrapped the meeting by thanking Brookhaven’s Guest, User & Visitor Center staff for their help coordinating another successful event.

Research at RHIC and the facility’s operations, and the EIC project, are all funded by the DOE Office of Science, with additional contributions from NSF towards sPHENIX, STAR, and the research at RHIC. RHIC is a DOE Office of Science user facility, as will be the future EIC.

Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit science.energy.gov.

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