Astronomers believe dark matter is crucial to the universe, but its existence has not yet been directly proven. Now, researchers at the Technical University of Munich (TUM) measured the survival rate of antihelium nuclei from the depths of the galaxy for the first time.
Measuring the antihelium nuclei is a requirement for the indirect quest for dark matter. Previous studies show that the way galaxies move in galactic clusters or how fast stars circle the center of a galaxy indicates there must be far more mass present than what is visible. Scientists believe that 85% of the substance in the Milky Way is invisible and can only be detected by its gravitational effects.
A general view of ALICE (A Large Ion Collider Experiment) cavern and detector during a behind the scenes tour at CERN, the World's Largest Particle Physics Laboratory on April 19, 2017 in Meyrin, Switzerland.
Antimatter Could Travel at Great Distance Without Being Absorbed
The worldwide ALICE (A Large Ion Collider Experiment) group proves in a paper, titled "Measurement of anti-3He nuclei absorption in matter and impact on their propagation in the Galaxy" published today in Nature Physics, that the antimatter equivalent of a light atomic nucleus may travel a great distance in the Milky Way without being absorbed.
The discovery will aid space- and balloon-based searches for antimatter that could have come from dark matter. It was made by putting data on antihelium nuclei created at the Large Hadron Collider (LHC) into models.
Particle accelerators on Earth have not yet been positively identified as emanating from space. So, space-based experiments such as AMS, built at CERN and placed on the International Space Station, as well as the planned GAPS balloon expedition, are seeking light antimatter nuclei in an effort to search for dark matter.
Scientists must ascertain the quantity or the "flux" of light antinuclei that are anticipated to arrive at the near-Earth site of these tests to assess whether dark matter is the cause of any prospective detections of light antinuclei from space.
This flux is determined by the specific type of antimatter source in our galaxy, the rate at which it generates antinuclei, and the rate at which the antinuclei should eventually vanish through annihilation or absorption when they come into contact with regular matter on their journey to Earth.
For the first time, ALICE researchers were able to gauge how quickly antihelium-3 nuclei vanish when they come into contact with regular matter. The material of the ALICE detector acts as the normal matter with which the antinuclei interact in this investigation.
The discovered disappearance rate was then included by the ALICE team in the freely accessible computer software GALPROP, which models the movement of cosmic particles throughout the Galaxy. They looked at two models for the flow of antihelium-3 nuclei that would be anticipated to get close to Earth after traveling from origins in the Milky Way.
The origins are either described as hypothetical dark-matter particles dubbed weakly interacting massive particles in one hypothesis or as cosmic-ray collisions with the interstellar medium in the other (WIMPs).
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ALICE Estimates the Milky Way's Antimatter Transparency
The ALICE team then calculated the Milky Way's transparency to antihelium-3 nuclei for each model, or the galaxy's capacity to permit the nuclei to pass through without being absorbed. To do this, they divided the flow produced by antinuclei disappearance and without it.
The results from the ALICE experiment were applied to the entire galaxy by the researchers using simulations, which showed that approximately half of the antihelium-3 nuclei that were anticipated to be produced by the collision of dark matter particles would end up in the area around the Earth.
Thus, these antinuclei can pass through Milky Way to the extent of 50%. With increasing antihelium-3 momentum, the transparency of antinuclei produced in collisions between cosmic radiation and the interstellar medium ranges from 25 to 90%. However, due to their increased energy, these antinuclei can be separated from those produced by dark matter.
The new calculations allow for the interpretation of the origin of these well-traveled messengers as cosmic rays or dark matter, depending on how many antihelium nuclei arrive at the Earth and with what energies. This means that antihelium nuclei can not only travel great distances in the Milky Way but also serve as significant informants in future experiments.
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