The majority of matter in the Universe is made up of a mysterious invisible mass called Dark Matter. There are a number of ways we could look for this invisible mass soon. One theory is that Dark Matter particles could collide and destroy each other in order to create Cosmic rays that can be seen throughout the universe.
This theory could be tested in the near future thanks to research conducted using the ALICE experiment. ALICE is designed to study the results from nuclei that travel very close to light. According to new research by the ALICE Collaboration, dedicated instruments could detect anti-helium-3 nuclei (the anti-matter counterpart to He 3 ) as they reach Earth's atmosphere and provide evidence forDM.
The theory of Dark Matter came to light in the 1960s when telescopes were used to observe General Relativity. The curvature of spacetime is predicted to be altered by the presence of a large object. Einstein's Rings, Crosses, and Arcs can be seen when light from a distant source is warped. Astronomers observed that the curvature of the Universe was much greater than expected.
Either Einstein was wrong or there must be mass in the Universe that we can't see. Finding direct evidence of Dark Matter has always been a challenge for physicists. They stated in their study that antinuclei could be detected, depending on the nature of the DM. The ALICE Collaboration used a leading theoretical profile called Weakly-Interacting Massive Particles.
The weak nuclear force is what causes the particles to interact with each other. The theory states that interaction between these particles causes them to destroy one another and produce anti-He 3 nuclei. Cosmic rays, high-energy particles that originate from beyond our Solar System and collide with our atmosphere, are known as antinuclei.
Anti-He 3 nuclei can be created by other types of Cosmic rays colliding with theISM. This source of antinuclei is unrelated to DM so it's the background for searches. In an email to Universe Today, Laura Serksnyte said that she was one of the experts on the study.
“The expected number of low-energy antihelium-3 nuclei coming from dark matter annihilation is expected to be much larger than from the background contribution. Thus the detection of even a few low-energy antihelium-3 nuclei in cosmic rays would provide a smoking gun signal for the dark matter, meaning that the antihelium-3 is a very ‘clean’ probe for dark matter searches.”
As anti-He 3 nuclei interact with gas in the ISM, it could be difficult to find this smoking gun. Anti-He3 nuclei would disappear before they reached Earth's atmosphere due to inelastic interaction. The only way to make and study antinuclei with high precision is to use high-energy particle accelerators. Serksnyte said that the ALICE instrument came into use here.
“Our experiment studied the inelastic interactions of antihelium-3 (produced in the collisions at the LHC) with matter, where ALICE detector itself is used as a target. Our work thus provided the first ever measurement of inelastic antihelium-3 cross-section, which constrains how probable it is for the antihelium-3 to disappear if it collides with matter.”
After measuring the anti-He3 produced in the LHC, the team applied their measurements to see how these antinuclei would interact with the gas in the ISM. They were able to estimate the fraction that would be detected by our instruments by calculating the level of antinuclei that disappear while traveling from their point of origin to detectors in Earth's atmosphere. Serksnyte said the results were positive.
“Our results show that the transparency of our galaxy to the passage of antihelium-3 cosmic rays is high, and thus such antinuclei could indeed reach Earth and be measured by dedicated experiments. Thus confirming that antihelium-3 is a promising candidate for Dark Matter searches. Our measurement of the disappearance probability of the antihelium-3 nuclei interacting with matter will also be used by the scientists to understand the antihelium-3 cosmic ray fluxes once they are measured and to put constraints on the Dark Matter models.”
One of the most pressing mysteries in astrophysics can be solved by placing tighter constraints on what scientists can look for. The detection of Dark Matter would show where 85% of the matter is hidden. It would confirm that General Relativity is correct, as well as validation of a key part of the most widely accepted theory of cosmology. It won't be the end of the mysteries but it will lead to a better understanding.
There is further reading on nature.
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