Antihelium cores as messengers from the depths of the galaxy
#Antihelium #cores #messengers #depths #galaxy Welcome to Alaska Green Light Blog, here is the new story we have for you today:
New findings lay the foundation for the search for dark matter.
How do galaxies form and what holds them together? Astronomers assume that dark matter plays an essential role. However, it has not yet been directly proven that dark matter exists. A research team including scientists from the Technical University of Munich (TUM) has now for the first time measured the survival rate of antihelium nuclei from the depths of the galaxy – a necessary prerequisite for the indirect search for dark matter.
Much points to the existence of dark matter. The way galaxies move in galaxy clusters, or how fast stars orbit a galaxy’s center, leads to calculations that suggest there must be much more mass than we can see. For example, about 85 percent of our Milky Way consists of an invisible substance that can only be detected due to its gravitational effect. To date, the existence of this material has not been directly proven.
Several theoretical models of dark matter predict that it could be composed of particles that interact weakly with each other. This creates antihelium-3 nuclei, which consist of two antiprotons and one antineutron. These nuclei are also formed in high-energy collisions between cosmic rays and ordinary matter such as hydrogen and helium – albeit with different energies than would be expected from the interaction of dark matter particles.
In both processes, the antiparticles are formed in the depths of the galaxy, tens of thousands of light-years away from us. After their formation, some of them make their way in our direction. The permeability of the Milky Way for antihelium nuclei determines how many of these particles survive this journey undamaged and reach the vicinity of the earth as messengers of their formation process. So far, scientists have only been able to roughly estimate this value. However, an improved approximation of the transparency, a unit of measure for the number and energy of antinuclei, will be important for the interpretation of future antihelium measurements.
Particle accelerator LHC as an antimatter factory
Researchers from the ALICE collaboration have now carried out measurements with which they were able to determine transparency more precisely for the first time. ALICE stands for A Large Ion Collider Experiment and is one of the largest experiments in the world to study physics on the smallest length scales. ALICE is part of the Large Hadron Collider (LHC) at CERN.
The LHC can generate large amounts of light antinuclei such as antihelium. To do this, protons and lead atoms are each placed on a collision course. The collisions create showers of particles, which are then recorded by the detector of the ALICE experiment. Thanks to several subsystems of the detector, the researchers can then detect the antihelium-3 nuclei that have formed and follow their tracks in the detector material. This allows the probability that an antihelium-3 nucleus will interact with the detector material and disappear to be quantified. Scientists from TUM and the ORIGINS Cluster of Excellence made a significant contribution to the analysis of the experimental data.
Galaxy transparent for ancient cores
With the help of simulations, the researchers were able to transfer the findings from the ALICE experiment to the entire galaxy. The result: about half of the antihelium-3 nuclei that should be formed when dark matter particles interact would come close to Earth. So our Milky Way is 50 percent permeable to these antinuclei. For anti-nuclei produced in collisions between cosmic rays and the interstellar medium, the resulting transparency varies between 25 and 90 percent with increasing antihelium-3 momentum. However, these antinuclei can be distinguished from those created from dark matter because of their higher energy.
Antihelium nuclei can therefore not only travel long distances in the Milky Way, but also serve as important informants in future experiments: Depending on how many antinuclei arrive on earth with which energies, the origin of these well-travelled messengers can be thanks to the new Calculations can be interpreted as cosmic rays or dark matter.
Reference for future antinuclei measurements in space
“This is an excellent example of an interdisciplinary analysis that shows how measurements at particle accelerators can be directly linked to the study of cosmic rays in space,” says ORIGINS scientist Prof. Laura Fabbietti from the Faculty of Natural Sciences at TUM. The results of the ALICE experiment at the LHC are of great importance for the search for antimatter in space with the AMS-02 (Alpha Magnetic Spectrometer) module on the International Space Station (ISS). From 2025, the GAPS balloon experiment over the Arctic will also probe incoming cosmic rays for antihelium-3.
Reference: “Measurement of anti-3He nuclei absorption in matter and impact on their propagation in the Galaxy” by The ALICE Collaboration, 12 December 2022, Nature Physics.
In the work on the antihelium-3 interaction under the direction of Prof. Dr. Laura Fabbietti were research groups led by Prof. Dr. Alejandro Ibarra at TUM and Dr. Andrew Strong at the Max Planck Institute for Extraterrestrial Physics. This research was funded by the Federal Ministry of Education and Research and the German Research Foundation (DFG) via the Cluster of Excellence ORIGINS, EXC 2094 – 390783311 and the Collaborative Research Center SFB1258.