Physicists at Rice University and their collaborators have detected the antimatter partner of the helium nucleus, antihelium-4. This newly observed particle is the heaviest antimatter particle ever detected.
Scientists at Rice's Bonner Lab designed and built the new time-of-flight detector that identified antihelium-4. The $7.5 million detector was built by a U.S.-China collaboration led by Rice, with Chinese scientists contributing $2.5 million to the project. The new detector was installed as part of the STAR experiment at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory in New York. STAR scientists announced their find today in the journal Nature.
Antimatter is the yang to matter's yin. Both were created in ostensibly equal amounts at the time of the Big Bang, but because matter and antimatter annihilate each other upon contact, most of it disappeared almost instantly. But there was an apparent imbalance that favored matter, which makes up nearly all that we see (and are) today.
Why this is so remains one of the great mysteries in physics. Scientists hope the study of antimatter created in particle accelerators, which attempt to mimic conditions at the beginning of the universe, will offer clues to why nature allows humans to exist.
Last year at Brookhaven, shortly after the long-planned time-of-flight detector was fully installed, evidence of 15 antihelium-4 nuclei (aka anti-alphas) was found among the trillions of particles released when heavy gold ions were collided at nearly the speed of light. These nuclei contain two antiprotons and two antineutrons and do not undergo radioactive decay.
The collisions produce a quark gluon plasma which, when cooled, transitions into a hadron gas that contains protons, neutrons and their antimatter equivalents among many other fundamental particles. This rapidly expanding cloud of particles is where the team found antihelium-4.
|Contact: David Ruth|