A next-generation dark matter detector has started operations, already
delivering its first results, which show it to be the most sensitive machine
of this type on Earth.
The machine could help unlock one of the biggest mysteries in physics —
the nature of dark matter — by directly detecting its constituent
particles for the first time.
Located deep below the Black Hills of South Dakota the LUX-ZEPLIN (LZ)
experiment — operated by a team of 250 scientists led by Lawrence Berkeley
National Lab (Berkeley Lab) — passed the check-up phase of its start-up
procedure with flying colors.
The LZ detector has been up and running since December 2021, and these first
results represent its first 60 days of live operations. "We're ready and
everything's looking good," Berkeley Lab senior physicist and past LZ
spokesperson Kevin Lesko said in a statement. "It's a
complex detector with many parts to it and they are all functioning well
within expectations."
Dark matter makes up around 85% of the matter in the known universe, but
because it doesn't interact with light it is practically invisible.
Likewise, whatever the constituent particles of dark matter are, they don't
interact strongly with other matter either.
In fact, the only way scientists can infer the presence of dark matter is
via its gravitational influence which literally holds together most
galaxies, preventing their constituent stars from flying apart as they spin.
This means researchers know dark matter isn't made up of protons and
neutrons like the everyday matter — or baryonic matter — we see around us on
an everyday basis.
The LUX-ZEPLIN detector is set up to specifically search for a hypothesized
type of dark matter called weakly interacting massive particles, or WIMPs.
These particles are expected to collide with matter very rarely and interact
extremely weakly when they do.
No dark matter particles have currently been directly detected, but the hope
is that the LZ detector could change that by detecting the faint
interactions of these mysterious particles with xenon atoms. This requires a
sensitive detector with all possible noise that could interfere with
detection eliminated.
The LZ experiment's xenon is in two nested titanium tanks containing ten
tons of the element in its liquid state. These tanks are monitored by two
photomultiplier tube (PMT) arrays which are poised to detect faint sources
of light.
The tanks and their attendant detectors also sit within a larger detection
system that can catch any particles that could mimic the signal of dark
matter and eliminate this from the hunt for real dark matter.
To spot these weak interactions the xenon tanks must be maintained at minus
148 degrees Fahrenheit (minus 100 degrees Celsius). Additionally, the LZ
team must remove all natural background radiation from the detector. A water
tank surrounds the experiment from the natural radiation emitted by
radiation from the lab's walls.
The underground location of the dark matter detector helps protect it from
high-energy protons and atomic nuclei that move through space at nearly the
speed of light and originate from the sun and beyond the solar system called
cosmic rays.
The LZ detector's sensitivity will be further boosted over the coming 1000
days, meaning this is just the beginning for the experiment.
"We plan to collect about 20 times more data in the coming years, so we're
only getting started," LZ spokesperson from the University of California
Santa Barbara, Hugh Lippincott, said in a statement.
"There's a lot of science to do and it's very exciting!"
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