Hydrogen is a neutral atom. Its single electron orbits a single proton, and the net effect is no electrical charge. But what about hydrogen’s antimatter counterpart, antihydrogen? Made of a positron that orbits an antiproton, the antihydrogen atom should be neutral too. Various results have indicated as much, but because the charge of antiatoms is
Theory and observations support the view that antimatter experiences gravity just as ordinary matter does, but the evidence so far has been indirect. Indeed, some theorists speculate that antimatter is antigravitational, that it may fall “up” instead of “down.” Led by Berkeley Lab physicists, the ALPHA Collaboration at CERN has made direct measurements of the gravitational mass of atoms of antihydrogen, testing how they fall and in what direction.
Neutrinos may be even stranger than they seem, if indeed they are the only fermions (particles of matter) that are their own antiparticles. Proof would be a rare form of radioactive decay called neutrinoless double-beta decay, which could only be seen if there’s virtually no background interference. The MAJORANA DEMONSTRATOR now under construction at the Sanford Underground Research Facility in the Black Hills of South Dakota aims to prove these near-perfect conditions can be met.
Scientists at Lawrence Berkeley National Laboratory have played leading roles in designing and operating ALPHA, the CERN experiment that was the first to capture and hold atoms of antihydrogen, a single antiproton orbited by a single positron. Now, by measuring antihydrogen’s hyperfine structure, ALPHA has achieved another first in antimatter science with the very first measurements of the energy spectrum of an anti-atom.
Physicists in Berkeley Lab’s Accelerator and Fusion Research Division are key members of the international ALPHA Collaboration at CERN in Geneva, which has succeeded in storing a total of 309 antihydrogen atoms, many of them for as long as 1,000 seconds (almost 17 minutes) and some for much longer — more than enough time to perform meaningful scientific experiments on confined anti-atoms.
Antimatter nuclei of helium-4, the heaviest antiparticles ever found, have been created by the STAR experiment at Brookhaven’s Relativistic Heavy Ion Collider. Eighteen examples of the antihelium particles were detected by STAR’s Time Projection Chamber, designed and built at Berkeley Lab, in debris from a billion high-energy collisions of gold nuclei.
Atoms of antimatter have been trapped and stored for the first time by the ALPHA collaboration, an international team of scientists working at CERN in Switzerland. Berkeley Lab researchers made key contributions to the effort, including the design of the trap’s crucial component—an octupole magnet—and computer simulations needed to identify real antihydrogen annihilation events against a noisy background.
There’s nothing fictional about antimatter. It’s all around us, all the time. Researchers know how to create and store antiparticles, and members of Berkeley Lab’s Accelerator and Fusion Research Division have even helped make antihydrogen atoms at CERN. But gathering enough to fuel a rocket or make a bomb would take so much energy that no one (including the Vatican) needs to worry.