The secret of antimatter creation in cosmic collisions revealed
At the Quark Matter conference and the Rencontres de Moriond conferences, the LHCb collaboration presented an analysis of particle collisions at the Large Hadron Collider (LHC) that could help determine whether the antimatter seen by experiments in space whether or not it comes from the dark matter that holds galaxies like the Milky Way together.
Space experiments such as the Alpha Magnetic Spectrometer (AMS), which was assembled at CERN and installed on the International Space Station, have detected the fraction of antiprotons, the antimatter counterparts of protons, in high-energy particles called cosmic rays. . These antiprotons could be created when dark matter particles collide, but they could also form in other cases, such as when protons collide with atomic nuclei in the interstellar medium, which is mostly hydrogen. and helium.
To know whether or not one of these antiprotons comes from dark matter, physicists must therefore estimate the frequency of production of antiprotons in collisions between protons and hydrogen as well as between protons and helium. Although some measurements of the former have been made and LHCb reported in 2017 the very first measurement of the latter, this LHCb measurement only involved rapid production of antiprotons, i.e. antiprotons produced right where the collisions took place.
In their new study, the LHCb team also looked for antiprotons produced some distance from the collision point, by the transformation, or “decay”, of particles called antihyperons into antiprotons. To perform this new and previous measurement, LHCb researchers, who usually use proton-proton collision data for their investigations, instead used proton-helium collision data obtained by injecting helium gas at the point where the two LHC proton beams normally collide.
By analyzing a sample of some 34 million proton-helium collisions and measuring the ratio between the rate of production of antiprotons from antihyperon decays and that of instantaneous antiprotons, LHCb researchers found that at collision energy scale of their measurement, antiprotons produced via antihyperon decays contribute much more to the total antiproton production rate than the amount predicted by most models of antiproton production in proton-nucleus collisions .
“This result complements our previous measurement of rapid antiproton production and will improve model predictions,” said Chris Parkes, LHCb Spokesperson. “This enhancement may in turn help space experiments find evidence of dark matter.”
“Our LHCb collision point gas injection technique was originally designed to measure the size of proton beams,” explains Niels Tuning, LHCb Physics Coordinator. “It’s really nice to see again that this also improves our knowledge of how often antimatter should be created in cosmic collisions between protons and atomic nuclei.”
