The Relativistic Heavy Ion Collider, or “rick” as it is commonly referred to, is comprised of a 2.4-mile tunnel underneath the small hamlet of Uptown, NY. Directly on top sits Brookhaven National Lab where some of the most groundbreaking experiments and studies are conducted to further scientific knowledge in a variety of fields.
RHIC is a particle accelerator, meaning its principle function revolves around taking elementary particles and sending them smashing into each other at relativistic speeds, or speeds that are near that of light, and then studying the after effects. A recent experiment by RHIC allowed researchers to probe the ever-deepening mystery behind proton spin, a characteristic that describes a particle’s intrinsic angular momentum.
The discoveries made by particle accelerators have been making headlines in the past few years due in part to the initial operations of the Large Hadron Collider in Geneva, Switzerland. The LHC is the largest particle accelerator ever created and was successfully turned on Sept. 8, 2008.
But not all particle accelerators are colliders, like RHIC and LHC.
“If you think about car crashes, a car running into the wall is bad, but it’s not nearly as bad as a head-on collision because in a head-on collision they both bring energy,” said Barbara Jacak, a disguised professor of physics at Stony Brook and a principle researcher at RHIC. “…So you get a lot more energy you can use to produce heat or remove particles. That’s why the colliders are exciting and useful.”
While there are many similarities between the LHC and RHIC, one major difference makes Brookhaven an especially unique center for discovery.
“At RHIC, we can collide polarized protons, which the Large Hadron Collider can’t do,” said Jacak. The method Jacak is referring to is what allowed RHIC to make its recent discoveries involving proton spin.
Jacak is also the spokesperson for PHENIX, one of four detectors placed around RHIC that is designed to digest specific aspects of the collisions. PHENIX is the largest detector, coming it at around 4,000 tons, while STARR the second largest, is 1,200 tons. The two smaller detectors, named PHOBOS and BRAHMS, have finished their designated experiments and are currently not in use.
Researching proton spin is only one half of RHIC’s capabilities. The other half deals with its ability to generate such enormous temperatures that mysterious new types of matter are created, which is an ability that RHIC does share with the LHC (though on a smaller level considering the LHC, nearly 17 miles long, can reach energy levels more than 20 times that of RHIC).
“On the heavy-ion side, that’s where we take nuclei and heat them to 4 trillion degrees,” said Jacak. These enormous temperatures allow scientists to observe properties of elementary particles around “one or two microseconds after the Big Bang,” Jacak added.
What they discovered was contrary to a previously held belief. “We expected that it would be like a gas of quarks and gluons, but the surprise is that the stuff seems to be behave more like a liquid,” said Jacak. This new substance, referred to as quark-gluon plasma, is spurring questions on the development of the universe, among other wide-ranging inquiries.
Future experiments at RHIC will continue to probe the mystery of proton spin, as well as the continuation of heavy ion collisions.
“The mystery of the proton spin is not only still with us, it’s even deeper,” said Jacak. She explained that there were many levels to the spin research, which first focused on quarks, which make up protons, and then gluons, which make up quarks.
“We did experiments for a few years, we looked at the gluons, and all the gluons that we could actually access…they don’t carry the spin either.” So Jacak and fellow scientists turned to the creation of the W-boson in their most recent experiment.
“W-bosons because those probe the motion of the anti-quarks, which briefly exist inside the nuclei. So we’re going to see what those do.”