YSM Issue 95.1

Physics
NEWS
HELLO
HALOSCOPES
A new detection method
for dark photons
IMAGE COURTESY OF PIXABAY
BY ISABEL TRINDADE
Dark matter is known to permeate our universe, but its exact
nature has long remained a mystery. Now, new research
from the Wright Laboratory at Yale sheds light on the
presence of dark photons, a candidate for dark matter. The team,
led by Sumita Ghosh, a graduate student in the Department of
Applied Physics at the Wright Laboratory, developed new methods
of analyzing existing data sets from devices known as haloscopes,
which have previously been used to detect particles known as
axions. This new method of detecting dark photons could help
answer long-standing questions about dark matter.
Ghosh says that she had previously read about dark photons but
had not studied them in her research before. Her greatest motivation,
she says, coincided with the pandemic. “I couldn’t do my regularly
scheduled work anymore,” Ghosh said. Thus, she decided to focus
on this project combining algebra, probability, and coding, all
of which she could do at home. Ghosh was inspired by previous
research on dark photons, including two studies in particular: one
by Arias et al. on WISPy Dark Matter, and another by Caputo et
al., “Dark photons: a cookbook.” “[The Caputo paper] is absolutely
brilliant,” said Ghosh, “and inspired me to do a more rigorous job
on one of the experiments [she analyzed], the CAPP haloscope.”
This research is part of an ongoing scientific investigation into
the nature of dark matter. Previous astrophysical observations
indicate that around eighty-five percent of the matter in the
universe is dark matter, the nature of which is still, for the most
part, unknown. However, most of the previous research in dark
matter has pointed to certain characteristics of dark matter: it is
massive, stable, and manifests primarily through interactions with
the observable universe, particularly gravitational interactions.
One candidate for the basic, or elementary, dark matter particle is
the axion, which is identified using detectors known as haloscopes. A
haloscope is a device made of a strong magnetic field in a microwave
cavity, within which we search for signals matching the range of axion
frequencies. Haloscopes can also detect the presence of dark photons,
which are another dark matter candidate. Not much is yet known about
dark photons, but according to Ghosh, they are a possible “flavor” of the
photon and the mediator of a “dark electromagnetic force.”
“All particles in particle physics have parameters, including
mass, charge, and other properties with a numeric value,” said
Ghosh. Particles such as axions and dark photons, which we know
less about, have is a range of possible values for each property.
The combination of these ranges in vector form is known as the
parameter space. This study describes a procedure to convert
haloscope data from axion parameter space into dark photon
parameter space, thus allowing for more potential detection of
dark photons using haloscopes.
Dark photon fields can be uniformly or non-uniformly polarized,
both of which are considered in this study. “The method outlined
in this work for using a single cavity haloscope as a dark photon
detector may be applicable to any haloscope that employs a similar
analysis procedure,” Ghosh said. Regarding the viability of the dark
photon as a dark matter candidate, they have several mechanisms
that allow them to naturally produce relic abundance—the amount
of a particle that is still around after the Big Bang—of dark matter.
However, Ghosh said, “the motivation for dark photons is not
contingent on their comprising all of dark matter.”
This research is significant because there are many materials
that dark matter could consist of, each of which has a large
parameter space. “It’s important to try to narrow that down
faster than we’re currently able to,” said Ghosh. “Each
experiment built is so expensive, and it would be amazing if we
could make them all more productive by being able to interpret
the same data in many different ways.” Ghosh also noted
that, since the publication of her research, other researchers
have contacted her about ways to extend the results of their
experiments, paving the way for further exploration of other
particles beyond standard-model photons.
Future research in the direction of this study may include
potential improvements in the signal strength detected by the
haloscopes. In addition, the dark photon limits in the polarized
case may be enhanced by tailoring the method of conversion to
each haloscope experiment’s analysis method. “This technique will
be greatly enhanced by single photon detection, similarly to axion
detection,” Ghosh said. ■
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March 2022 Yale Scientific Magazine 11