A proposed billion-dollar American particle collider has received enthusiastic backing from the US National Academies of Sciences, Engineering, and Medicine, according to a newly released report.
This proposed “electron-ion collider,” or EIC, would serve as a state-of-the-art facility designed to answer some of the deepest questions about our Universe. The National Academies “finds a compelling scientific case for such a facility,” according to its report released today.
“We can view the EIC,” and the nuclear physics it will study, “as the last frontier of Standard Model physics,” Ani Aprahamian, professor of experimental nuclear physics at the University of Notre Dame, said in a National Academies webinar on Tuesday.
An electron-ion collider would smash a beam of polarized electrons with a beam of polarized protons at high luminosity, meaning the particles in each beam have aligned spins and the beams are squeezed to maximize the collisions. Such an experiment is meant to study the structure inside atomic nuclei and protons. Plenty of mysteries remain on this front—like how protons get their nuclear spins in the first place, or why they weigh over 100 times more than the sum of their parts (called quarks), for example.
The electron-ion collider would essentially act like an electron microscope, where electrons serve as probes into the interior of atoms.
The report is an important next step in the experiment’s story, after a 2015 report from the Nuclear Science Advisory Committee “strongly recommended” the EIC’s construction. The National Academies report concludes that the accelerator would be important both for nuclear physics, other research areas, and accelerator science in general: “[T]he answers to these fundamental questions about the nature of the atoms will also have implications for particle physics and astrophysics and possibly other fields. Because an EIC will require significant advances and innovations, the impact of constructing an EIC will affect all accelerator-based sciences,” it says.
At present, two labs with half of the puzzle each are vying for the collider. One particle accelerator, the Relativistic Heavy Ion Collider in Brookhaven National Lab (BNL) in New York, already has a ring that accelerates polarized protons, and would just need an electron ring. Another, the Thomas Jefferson National Accelerator Facility (JLab) in Virginia, has an electron accelerator, and would need the proton ring.
For now, the labs are working together. According to a joint statement from BNL and JLab: “We are very pleased to see the results of the NAS report. We fully support the committee’s findings and thank its members for their efforts. We look forward to DOE and NSF adopting the committee’s findings, and to working with those agencies and the worldwide nuclear physics community to make the EIC a reality.”
No decision has been made as to which lab will build the experiment, nor has a cost been determined, but a 2015 report from Nature listed estimates around $1 million to $1.5 billion. Adrian Cho, writing for Science, points out that the Department of Energy, who would fund the project, is currently building a nuclear physics facility at Michigan State University that will cost $730 million, so the EIC probably isn’t in the DOE’s sights just yet.
The new report “is important because it lays out the science case for a nuclear facility that will usher in the next era studying the structure of everyday matter in terms of its fundamental constituents,” said Christine Aidala, a professor of nuclear physics at the University of Michigan.
The consensus is clear: American nuclear physicists really, really want an electron-ion collider.
Disclosure: I did some EIC-related research at Brookhaven National Lab as an undergraduate student.