International Conference on Exotic Atoms and Related Topics - EXA2017

The measurement of the mass-to-charge ratio difference between nuclei and anti-nuclei probes the possibility of subtle differences between the way protons and neutrons bind together in nuclei compared with how their respective anti-particles form anti-nuclei. Such a study provides a quantitative verification of the matter/anti-matter symmetry in the context of the nuclear forces, a remnant of the underlying strong interaction between quarks and gluons. Relativistic heavy ion collisions at the CERN Large Hadron Collider (LHC) provide a copious source of matter and anti-matter particles. They create suitable conditions for producing light nuclei and anti-nuclei with nearly identical abundances. Thanks to its excellent tracking and particle identification capabilities, the ALICE experiment allows the investigation of these produced (anti-)matter states at LHC. The experiment makes accurate measurement of the curvature of particle tracks in the detector's magnetic field and of the particles' time of flight, and this information is used to determine the mass-to-charge ratio mu = m/z for nuclei and anti-nuclei. The precision comparison of the deuteron and anti-deuteron, and the 3He and 3Hebar nuclei mass-to-charge ratio will be presented. The precision of the measurement of the relative differences Δmu_ddbar/mu_d = [0.9 ± 0.5 (stat.) ± 1.4 (syst.)] x 10^-4 and Δmu_3He3Hebar/mu_3He = [-1.2 ± 0.9 (stat.) ± 1.0 (syst.)] x 10^-3 improves by one to two orders of magnitude with respect to analogous results obtained more than 40 years ago. Combining these results with existing measurements of the masses of the anti-nucleons, the relative binding energy differences are extracted, Δe_ddbar/e_d = -0.04 ± 0.05 (stat.) ± 0.12 (syst.) and Δe_3He3Hebar/e_3He = 0.24 ± 0.16(stat.) ± 0.18 (syst.). These results test, to an unprecedented precision, the CPT invariance in the sector of light (anti-)nuclei. Interestingly, these results are obtained in a high energy physics experiment at LHC designed for other purposes. Perspectives of improved limits with a future larger data set will be also discussed.