A tiny graphene device could detect neutrinos from the big bang

Neutrinos from the early universe have never been detected directly but a device that uses the atom-thick material graphene might be able to change that.

A particle detector made from extremely thin sheets of carbon may be able to spot never-before-seen neutrinos from the time of the big bang. If the design works, detecting these so-called ultra-low energy neutrinos could help us to better understand the first moments of the universe.

Detecting any neutrinos is challenging because they normally move through matter without affecting it – trillions of them are passing through you right now. They are some of the most abundant particles but they are nearly massless and don’t have electric charge. To spot even high energy neutrinos created in cataclysmic events like explosions of nearby stars, researchers have to build huge detectors kilometres across.

Hugo Tercas at University of Lisbon and Carlo Alfisi at Polytechnic University of Milan have come up with a much smaller detector design that would be able to spot ultra-low energy neutrinos. Their detector would be shaped like an elongated box only a few centimetres in size and composed of dozens or more layers of graphene – essentially carbon sheets that are only one atom thick.

The pair calculated that if a few thousand ultra-low energy neutrinos entered the detector that would make the electrons inside the graphene form a hot, charged liquid-like state called plasma. From the way the plasma behaves, they would be able to deduce how fast and how heavy the neutrinos are.

Electrons in materials other than graphene wouldn’t combine into plasma after interacting with low energy neutrinos. “Physics-wise, we had to think completely out of the box here,” says Tercas. So far researchers have only built detectors for very energetic neutrinos.

“This is really kind of a new way of listening to the universe,” says Christopher Tully at Princeton University. He and collaborators are in the early stages of building a different detector where neutrinos collide with the radioactive version of hydrogen called tritium and make it decay into helium.

Actually building the new graphene-based detector will require advances in engineering and material science, says Tercas. For instance, it is currently difficult to make centimetre-sized graphene sheets free of imperfections that would influence the plasma’s behaviour and consequently make neutrino detection glitchy.

Irene Tamborra at the University of Copenhagen says the detector could be used to test theories about the early universe. Where neutrinos were and how fast they were moving right after the big bang may have influenced where whole galaxies formed later. Currently, physicists also have many questions about neutrinos themselves, Tamborra says, like what exactly their mass is and whether they’re their own antiparticles.

Reference: 

arXiv preprint, DOI: 2204.12002

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