23 November 2019 | New Scientist | 11A NEW clue to the existence of
a fifth fundamental force of
nature may have emerged.
It comes from Attila
Krasznahorkay at the Atomki
Institute of Nuclear Research,
Hungary, and his team. They
spent years studying the decay
of beryllium-8, a radioisotope,
and, in 2016, published details
of an odd finding, suggesting
it was caused by an unknown
particle. This was later proposed
to be a hint of a fifth force.
Now, the same researchers
have found another anomaly,
this time in an energy transition
involving an excited state of the
helium nucleus, and say that it
points to the same particle.
They calculate that the new
particle has a mass of around
17 megaelectronvolts, or about
33 times that of an electron, and
have called it X17 as a result.
The particle appears to carry
energy away from an atomic
nucleus, and then decay into an
electron-positron pair, which the
team’s experiment can detect.
Normal physics predicts
that the electron and positron
should be emitted in roughly
the same direction. But in the
beryllium-8 experiment, the
two particles diverged at an
angle of 135 degrees, while
the new helium result gives
a similar detection bump at
an angle of 115 degrees
(arxiv.org/abs/1910.10459).
This difference is crucial
because the helium transitions
take place at a higher energy to
the beryllium one. The higher
the energy, the smaller the
expected angle. “If the bump is
produced by a new particle, it
has to move in exactly this way,”
says Jonathan Feng, a theoretical
particle physicist at the
University of California, Irvine.
He investigated the original
claim in 2016. At the time,
he proposed that the X
particle must only be capable
of interacting with neutrons,
otherwise it would have been
detected already. But for this
to be true, the particle can’t be
using any known force of nature.
Instead, it must be interacting
through a force unrelated to
gravity, electromagnetism or the
two nuclear forces we know of.
Feng says that the latest
result corroborates the first
and has got people excited.
“I sent a one-line email to my
collaborators with the link and
one word: ‘Wow’,” he says.
For his part, Krasznahorkay
is looking to other, independent
groups to confirm whether the
particle really exists. “If the
existence is settled, that would
open up a new avenue in particlephysics,” he says. X17 could
be the link between ordinary
matter and dark matter.
The Positron Annihilation into
Dark Matter Experiment (PADME)
in Frascati, Italy, is also looking
for X17. Its researchers collected
data this year and will run their
experiment again next year with
improved performance. PADME
spokesperson Mauro Raggi says
to expect the analysis around
spring 2021.
“The beryllium-8 anomaly
is a result published by a very
qualified journal and the helium
[result] will soon have the same
destiny,” says Raggi. “We need
to seriously consider these two
results. The question is whether
it is connected to a new particle
or not and this is what PADME
may help to clarify.” ❚Particle physics
Stuart Clark
A TRANSPARENT battery could
replace glass in windows. The
battery still has a low output, but
may eventually add extra energy
storage to cars or smart glasses.
Most battery research focuses
on increasing power output or
energy density, a measure of how
much energy can be stored in a
certain volume. But Hironobu
Minowa and his colleagues at
Japanese communications giant
NTT sought instead to make a
battery that was as inconspicuous
as possible.
To do this, the team had to
create new versions of battery
components to lower overall light
absorption and reflection. The
result is a battery the size of an
A4 or a US letter sheet of paper that
is as see-through as window glass.
The battery lacks the capacity
of a conventional one: it holds
only 1 milliamp hour compared
with more than 1000 in an
AA battery. But it lets 69 per cent
of light pass through it, which is
at the lower end of what window
glass achieves.
Its output is still enough to
power an LED or a digital clock,
says Minowa, who demonstrated
the battery at NTT’s R&D Forum
in Tokyo this month.Transparent battery
looks like glass
TechnologyEdd GentNTT^ DAT
AAs homes fill up with sensors
and small smart devices, used
for everything from monitoring
temperature to optimising
lighting, transparent batteries
like this could help clear up the
associated mess of wires and
battery packs.
Since building the prototype
battery last year, the team has
already doubled its output and
tripled its transparency, says
Minowa. Although the team
can’t yet make batteries any
larger than an A4 sheet, it is
possible to link multiple panes
together to boost capacity.
The ability to turn a
window into a battery could
be revolutionary, says Kevin
Curran at Ulster University,
UK. Transparent batteries
could also have applications
in smart glasses, in vehicles and
even in sensor-packed contact
lenses, he says.
“No one desires ugly cables,”
says Curran. Having transparent
batteries would open up the
possibility of having much more
beautiful devices, he says. ❚Hironobu Minowa sought
to create a battery that
was inconspicuousX
The name of a hypothetical new
particle that is exciting physicistsAnother surprise
hint of a fifth
force of nature