- 4569 - DARK MATTER - discoveries in new experiment? - Dark matter is thought to account for 85% of mass in the Universe, but because it barely interacts with ordinary matter and doesn’t interact at all with light, it is notoriously difficult to observe directly. Several research teams have tried to catch a glimpse of the elusive substance, but only the DAMA/LIBRA experiment has claimed to have seen it for real.
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- DARK MATTER -
discoveries in new experiment?
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- It’s a mystery that has had physicists
scratching their heads for more than 20 years. The DAMA/LIBRA experiment at the
Gran Sasso National Laboratory (LNGS) near L’Aquila, Italy, has been recording
an annual fluctuation of light flashes in its detector that appears to be a
sign of dark matter. But no one has been able to definitively replicate the
findings.
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- Beneath a mountain in Jeongseon, South
Korea, researchers are scaling up an experiment that could finally lay the
controversial dark-matter claim to rest. In June, researchers will finish
installing a revamped detector in a brand-new facility called “Yemilab”. If all
goes to plan, the upgraded COSINE-100 experiment will be running by August,
2024.
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- DAMA/LIBRA’s observations of the distinct
annual pattern is consistent with what physicists would expect with Earth’s
relative position in the galaxy throughout the year. As the Earth orbits the
Sun, the Sun orbits the black hole at the center of the Milky Way. In June, the
Earth hurtles through the Milky Way in the same direction as the Sun,
increasing its relative speed through the haze of dark matter.
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- But in December, the Earth travels with the
flow of dark matter as it moves in the opposite direction to the Sun. As
expected, the number of signals recorded by DAMA/LIBRA’s detector are highest
in June and lowest in December.
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- To reproduce DAMA/LIBRA’s results
scientists were using similar methods and materials in their detectors,
including the same type of sodium iodide crystals that emit tiny flashes of
light when they are hit with subatomic particles. Among them is “COSINE-100”,
which has been running since 2016 at Yemilab’s predecessor, the Yangyang
Underground Laboratory (Y2L) in South Korea.
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- But none have produced results that match
those of the original experiment, raising questions about whether the yearly
swing in signals is because of something else, such as the detector itself or
from errors in the analysis methods used. This is a puzzle that’s still there
after 20 years.
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- To confirm or rule out DAMA/LIBRA’s claims
for good, experiments need to match the original as much as possible. Although the COSINE-100 detector uses the
same type of sodium iodide crystals, they contain up to three times more
radiation than the ones used in DAMA/LIBRA, which can muddy the faint signals
of potential dark-matter particles and make it difficult to produce definitive
results.
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- The upgraded experiment will use the same
crystals as those used in the earlier COSINE-100 experiment, but with some
extra enhancements to boost their sensitivity. The team are also developing a
set of sodium iodide crystals that will be even more radiopure than
DAMA/LIBRA’s for the next phase of the experiment, COSINE-200. With even lower
radioactivity levels, the hope is to generate enough data over a shorter period
of time to reach a more solid conclusion about DAMA/LIBRA’s results, and also
search for low-mass dark matter.
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- “COSINE-100” will be housed in the brand
new 3,000-square-metre Yemilab. The $23 million facility lies around 1
kilometer underground and surpasses “Y2L” in both depth and volume. Since
September 2023, researchers have been moving all Y2L experiments to Yemilab,
where they will begin their next phase by the end of this year.
-
- Yemilab also offers a better-shielded
environment for detecting elusive particles besides dark matter. The facility
will also hunt for neutrinos, chargeless particles that barely have mass. The
second phase of an experiment called “AMoRE” will search for signs of two
neutrons decaying into protons and electrons without emitting a neutrino.
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- This hypothesized process is called
“neutrinoless double β decay” and if observed, it will demonstrate that
neutrinos are their own antiparticle. This could offer clues about their mass
and explain why there is more matter than antimatter in the Universe.
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- The upgraded neutrino detector will use
around 160 kilograms of crystals embedded with molybdenum-100, a naturally
occurring radioisotope. When AMoRE-II starts running at the end of this year,
2024, it will be 100 times more sensitive than the previous version of the
experiment.
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- Whether the two experiments succeed or fail
at detecting the rare events they are looking for, they are nevertheless set to
raise more questions. If both will
deliver only null results, we should seriously start rethinking the Universe.
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October 3, 2024 DARK MATTER
- discoveries in new experiment? 4569
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