Signs of ‘neutrino fog’ are emerging, complicating searches for dark matter
Signs of ‘neutrino fog’ are emerging, complicating searches for dark matter
By Don Lincoln | Published: 2024-11-11 15:47:00 | Source: Hard Science – Big Think
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According to the theory favored by most scientists, the stars and galaxies that dot the night sky are only a small fraction of the universe’s mass and energy budget. A form of matter is called Dark matter It is thought to be five times more prevalent than regular matter. Over the past several decades, the sensitivity of experiments searching for dark matter has increased by more than a million-fold, but they have found no direct evidence of its existence.
One complication in dark matter searches is that dark matter detectors with sufficient sensitivity can also observe neutrinos. Neutrinos They are subatomic particles commonly created in nuclear reactions, and the largest nuclear reactor in existence is the Sun. The Earth is bathed in solar neutrinos. When dark matter detectors become able to see these messengers from the Sun, the signal will overwhelm any expected dark matter events – and this will greatly complicate future efforts to detect dark matter. In two separate papers (Sheet 1 and Sheet 2), two experimental groups have reported that they have begun to see solar neutrinos.
Solar neutrinos
Starting in the 1930s, and with more sophisticated confirmation in the 1970s, astronomers made an unexplained observation: galaxies rotate faster than can be explained by visible matter and the known laws of physics. While several possible explanations were considered, the research community settled on the explanation that seemed to fit the data best. In this interpretation, galaxies contain an invisible form of matter called dark matter. Dark matter contributes to the gravitational properties of galaxies, which explains their rapid rotation. However, as its name suggests, dark matter does not emit light and therefore cannot be seen with telescopes.
Although dark matter has not been observed directly, several different models of dark matter have been proposed, each with different properties. A common model is called weakly interacting massive particles, or… weak. Inert particles (WIMPs) are electrically neutral, stable particles with masses ranging from a few times the mass of a proton to perhaps 10,000 times the mass of a proton. In this model, each galaxy is surrounded by what one can imagine to be a cloud of weakly interacting massive particles (WIMPs). As planets orbit their stars, they move through the WIMP cloud. This is the motion that astronomers rely on in their weakly interacting massive particle (WIMP) detection efforts.
Many different techniques are used to detect weakly interacting massive particles (WIMPs). The common feature is that the detector is cooled to very low temperatures – low enough that the atoms and molecules in the detectors do not move very quickly. If a WIMP particle moves through the device, there is a chance it will hit an atom in the detector, causing it to bounce off. Through a variety of means, the motion of the atom is detected, indirectly revealing the passage of dark matter.
Dark matter interactions are expected to be extremely rare, requiring the protection of external interaction detectors. They are made of low-radioactive materials and are found frequently Deep undergroundoften in abandoned mines.
“neutrino fog”
One complicating factor in searches for dark matter is the presence of neutrinos, which arise from both sun High-energy cosmic protons hitting the Earth Atmosphere. Although neutrinos interact very rarely, there are a large number of them: every second, approximately 70 billion neutrinos from the Sun pass through every square centimeter of the Earth’s surface. If only a small fraction of these neutrinos interacted in dark matter detectors, they would completely dwarf dark matter interactions. Researchers call this flood of neutrinos “neutrino fog.”
Neutrinos coming from the Sun come from a variety of different fusion processes. The most common comes from the fusion of two protons. However, this fusion process produces very low-energy neutrinos. However, there is a much rarer fusion process that involves the element boron. This process accounts for only about 0.1% of solar neutrinos, but these neutrinos have much higher energy, making them easier to detect. These are called high-energy neutrinos 8B neutrinos.
Two highly sensitive dark matter detectors recently published data showing hints of dark matter detection 8B neutrinos. The first is called Xenontwhich uses 5.9 tons of liquid xenon, located in a laboratory deep in the Apennine Mountains in Gran SassoItaly. It is called the second detector Panda X-4T. Liquid xenon is also used to try to detect dark matter and neutrinos. PandaX-4T is located at Jinping’s deep underground laboratory In Sichuan, China.
Both experimental collaborations use a specific process to research 8B neutrinos, called “Scattering of coherent elastic neutrino nucleiWhile neither detector has conclusively claimed to have observed a neutrino fog, both claim to have seen the first hints of a neutrino fog. 8B neutrinos. The significance of the XENONnT claim is 2.73 standard deviations and 8b Neutrino flux 4.7 × 106 Neutrinos per square centimeter per second, with an uncertainty of +3.6 × 106 And -2.3 x 106. In contrast, the PandaX-4T paper claims a standard deviation of 2.63, with a standard deviation value of 2.63 8b Neutrino flux of (8.4±3.1) × 106 Neutrinos per square centimeter per second.
Thus, the two experiences agree. Moreover, the two measurements are roughly consistent with a more precise measurement made by a vision-enhanced detector 8B neutrinos. This more accurate measurement has been reported by researchers in Sudbury Neutrino Observatory (SNO) and its size is approximately (2.5±0.3) x 106 Neutrinos per square centimeter per second. While the SNO instrument can see neutrinos, it cannot see dark matter.
The future of dark matter research
that it standard In particle physics it requires a minimum significance of 3 standard deviations to claim evidence of a phenomenon, and 5 standard deviations to claim observation, so neither experimental set reached this level of statistical significance. However, the fact that both experimental groups reported similar results gives us reason to believe that the era will soon come when dark matter experiments become sensitive to neutrino fog.
This sensitivity will greatly complicate future searches for dark matter. Researchers will need to perform more complex analyzes to pull potential dark matter signals out of the noise, based on measurements of the energy spectrum of the observed dark matter candidates. WIMP searches will soon become more difficult.
This imminent observation of neutrino fog will not make future searches for dark matter impossible. After all, there is These are other possible models of dark matter Which are not WIMPs. However, this new research will certainly mean that the future of dark matter research will become even more interesting.
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