In a former salt mine at the Department of Energy’s Waste Isolation Pilot Plant near Carlsbad New Mexico, all that matters is antimatter. In this deep underground cavern (pictured on bottom right) physicists are putting the finishing touches on a new particle detector, the Enriched Xenon Observatory (EXO).
In the spirit of Halloween, think of antimatter as matter’s ghostly counterpart, a doppelganger with an equal but opposite charge. Every particle has its own antiparticle ghost-twin, for example the antiparticle of the negatively charged electron is the positively charged positron, all other properties (mass, spin, etc.) remain deceptively the same.
But everyone learns at some point that the universe appears to be made entirely out of matter (lesson learned when I ran smack dab into a glass sliding door at the age of six). Which begs the question, if every bit of matter has an equal but opposite antimatter counterpart, why is there so more much matter around us? Where did the antimatter go? In true ghostly fashion, it seems to have vanished.
The EXO experiment is gearing up to find answers to those questions, the parts of physics that explain the puzzling imbalance of matter and antimatter in our universe. Frankly, imbalance is agood thing, no matter how ghostly. When particles and antiparticles draw close, they destroy or annihilate each other, leaving only the energy they were made of behind in the form of radiation. If during the evolution of our universe there were equal amounts of matter and antimatter, annihilation would have resulted in a desolate swamp of leftover radiation and not much else.
Of course, things get muddled when considering neutrinos, fundamental particles that have no charge. Scientists believe neutrinos are also antineutrinos. They act as their own antiparticles, little untraceable neutral ghosts. Experiments like EXO are hoping to discover what makes matter and antimatter behave differently, despite all their similarities. The answer may lie in neutrinos.
The ton-scale experiment is searching for a special type of nuclear decay called neutrinoless double beta decay in the 136 isotope of Xenon. Yet to be observed, neutrinoless double beta decay occurs when two neutrons in a nucleus are simultaneously converted to protons that emit two electrons without emitting any antineutrinos. In normal beta decay (first observed in 1986), two neutrons become protons that emit two electrons along with two antineutrinos.
Seeing neutrinoless double beta decay would prove that the neutrino really is its own antiparticle. Moreover, obtaining a measurement of the neutrinoless double beta decay half-life would allow scientists to determine the exact mass of the neutrino.
There are actually numerous experiments around the world focusing on differences in the decays of particles, like NEMO at the Frejus Underground Laboratory, the CUORE at the Cryogenic Underground Observatory for Rare Events, and COBRA at the Cadmium- Telluride O-neutrino double- Beta Research Apparatus, to name a few.
So this Halloween, while gorging on matter in the form of candy, think of a yet-to-be-discovered strange antiworld of antimatter. Scary!