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.