Brookhaven Lab leads the world in exploring how the matter that makes up atomic nuclei behaved just after the Big Bang. At that time, more than 13 billion years ago, there were no protons and neutrons—just a sea of “free” quarks and gluons, fundamental particles whose interactions are governed by nature’s strongest force and described by the theory of quantum chromodynamics (QCD). More than 1,000 scientists from around the nation and the world come to Brookhaven to recreate this “quark-gluon plasma” by accelerating heavy ions (atoms stripped of their electrons) to nearly the speed of light and smashing them together at the Lab’s Relativistic Heavy Ion Collider (RHIC). Detailed studies of the particles that stream out of these collisions have helped reveal surprising features of the early universe, and how the strong force shapes the structure of 99 percent of visible matter in the universe today—everything from stars to planets to people.
Research at RHIC, the only collider now operating in the U.S., has produced a series of stunning discoveries that have captured worldwide attention and showcased U.S. leadership in physics. First and foremost was the unexpected “perfect”-liquid nature of the 4-trillion-degree quark-gluon plasma that permeated the early universe. RHIC is now closing in on the transition from this hot quark-gluon plasma into ordinary matter made of protons and neutrons—namely everything we see in today’s world.
Other unexpected findings from RHIC include the observation of “bubbles” exhibiting local symmetry violations within the quark-gluon plasma—which may offer clues about why the early universe had more matter than antimatter—and the creation of exotic forms of antimatter at RHIC that may help scientists refine models of neutron stars and explore fundamental asymmetries in the early universe.
As the world’s only facility capable of colliding polarized protons, RHIC’s collisions are revealing for the first time that gluons make a significant contribution to proton spin, a property we use in magnetic resonance imaging (MRI) but that still holds many mysteries for physicists.
These discoveries have connections and relevance for scientists in many fields, including cosmology and astrophysics, as well as unexpected areas such as string theory, condensed matter physics, and high-temperature superconductivity.