GERDA...

From Nature: “The inner walls of the water tank are covered by a reflecting foil improving the light detection. This permits the identification of cosmic muons.” Image: K. Freund, GERDA collaboration

Topics: Antimatter, Big Bang, Cosmology, Neutrinos, Particle Physics

You and me, we’re matter. Everyone you know is matter. Everything on Earth, spare a few particles, is matter. Most of the things in space are matter. But we don’t have convincing reasons why there should be so much more matter than antimatter. So where’s all the antimatter?

A team of European scientists have taken a major step in understanding this conundrum, using a house-sized detector called the Germanium Detector Array, or GERDA, buried inside a mountain in Grand Sasso, Italy. GERDA’s scientists are looking for a strange behavior in radioactive atoms, called “neutrinoless double beta decay” (I’ll get to that in a second). Some versions of the rules of particle physics says this behavior could help explain where all the antimatter went. But for now, the experiment is reporting some important results: it works.

“A discovery of [neutrinoless double beta] decay would have far-reaching consequences for our understanding of particle physics and cosmology,” the researchers write in the paper, published today in the journal Nature. It’s important that we understand why there is more matter than antimatter today. The Big Bang probably should have created equal amounts... but it didn't.

Neutrinos, they’re weird. Scientists don’t know how much they weigh, but even at the upper limit of what we guess their mass is, they’re many times lighter than electrons. They’re also really common—for example, the sun sending almost a hundred billion of them per square centimeter of your body every second. They don’t interact via electromagnetism, though, so they don’t harm us in any way. If they were their own antiparticle, what scientists call “Majorana particles,” they should annihilate one another. Most extensions of our main theory of particle physics, called the Standard Model, say this is true.

That’s what GERDA is looking for. They’re watching 35.6 kilograms of a special form of germanium, the shiny semiconducting metal, sitting inside a vat of liquid argon inside a bigger vat of water, waiting however long it takes for it to experience a neutrinoless double beta decay. No, they haven’t found any evidence of the process yet. But their experiment works really, really well—there’s no background noise, which is an incredible feat. Otherwise, we might see a false signal. And there’s radiation that could set off the detector everywhere, from the sun to the air we breathe.

Gizmodo:
Scientists Are Getting Closer to Understanding Where All the Antimatter Has Gone
Ryan F. Mandelbaum