?Dark matter detector: What do its strange findings mean
In 2020, the world's most sensitive dark matter detector (XENON1T) made an important detection not about dark matter but about something else, possibly neutrinos, solar axions, or radioactive contamination in the detector. Recently, another team of physicists came up with a different answer, saying that the signal might be consistent with dark energy rather than dark matter. If true, it represents an important milestone in the search for this mysterious power.
Dark energy is unknown to us, as is dark matter, which we call mass that we cannot detect directly. We infer its existence by observing a very large force of gravity in the universe, more than what we calculate from visible matter. Approximately 5% of the universe is natural matter, such as Stars, black holes, and planets, while dark matter constitutes about 21%.
The remaining percentage, which represents approximately 74%, is dark energy, which we could not detect directly either, but we inferred its existence from the accelerating expansion of the universe, as there is something that makes the universe spread faster than what can be calculated, counted, or explained, and we call it dark energy. .
“Both components are invisible, but we know more about dark matter, as its existence was proposed in the early 1920s, while dark energy was not discovered until 1998,” says cosmologist Sunni Vagnozzi of the Kavli Institute of Cosmology at the University of Cambridge. - Such as XENON1T - to directly detect dark matter, by searching for signs of dark matter colliding with ordinary matter, but dark energy is more difficult to obtain.
In practice, XENON1T is a tank filled with 3.2 metric tons of ultra-pure liquid xenon, and equipped with columns of photomultiplier tubes. This tank is completely sealed and completely dark, allowing researchers to detect the photoelectric luminescence flash caused by the interaction of particles, which produces a tiny shower of electrons from Xenon atoms in what is known as electronic bounce.
Because most of them result from known particle interactions, we have a roughly clear idea of how many electron bounce events to expect as part of the overall noise: about 232 ± 15 per year, but XENON1T detected 285 events from February 2017 to February 2018.
Scientists found that the most likely explanation was a type of hypothetical particle called a solar axon, first reported in the 1970s to solve a problem about keeping track of atomic forces in so-called straight charge symmetry, when most models say they don't need to.
But there's a problem: If the Sun can produce these axons, then all stars should as well. However, the heat loss observed in very hot stars places strict limits on the interactions of the axons with subatomic particles.
So, Vagnozzi and his team set out to test the possibility that dark energy might be responsible for the increase. Dark energy may be a mystery, but most physical models of dark energy lead to an unknown fifth force of nature, beyond electromagnetism, gravity, and the two nuclear forces.
Because the universe's accelerating expansion can only be detected on very large scales while gravity acts on local scales, any model of dark matter that suggests a fifth force would also need to explain why this force is not evident in our astronomical neighborhood.
Vagnozzi and his team have developed a methodology based on a mechanism called chameleon screening, which avoids the mess of explaining why we don't see the fifth force by assuming that it is very short-lived in dense environments like ours. "Our chameleon screening stops the production of dark energy particles in objects," Vagnozzi said. “It is very dense, which avoids the problems faced by solar axes, and also allows us to separate what happens in the local very dense universe from what happens on larger scales, where the density is very low.”
Their results showed that dark energy particles from the velocity line region (or tachocline, a strong magnetic region on the Sun between the inner radiative zone and the outer convective zone) may produce the signal observed in the XENON1T data, and this explanation is favored over the general noise with a confidence of 2.5 sigma.
It's still not as strong an explanation for solar axes, which had a confidence level of 3.5 sigma, or even neutrinos or radioactive contamination, which had a confidence level of 3.2 sigma.
It offers an alternative solution free of the thorny issues associated with others, and “this raises the tantalizing possibility that XENON1T may be the first to achieve a direct detection of dark energy,” the researchers wrote.
That is, of course, if the signal is real. We need another detection before we can be sure, and with the XENON1T currently undergoing improvements, we have some time to wait. Even if the signal does not appear in the next monitoring cycle, the research has laid the foundation for thinking outside the box when the discovery is eventually confirmed.
“It was really surprising that this excess was coming from dark energy, rather than dark matter,” Vagnozzi said. “When things work together like that, it’s really special.”
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