Precision measurement of the mass difference between light nuclei and anti-nuclei

The measurement of the mass di erences for systems bound by the strong force has reached a very high precision with protons and anti-protons1,2 . The extension of such measurement from (anti-)baryons to (anti-)nuclei allows one to probe any di erence in the interactions between nucleons and antinucleons encoded in the (anti-)nuclei masses. This force is a remnant of the underlying strong interaction among quarks and gluons and can be described by e ective theories3 , but cannot yet be directly derived from quantum chromodynamics. Here we report a measurement of the di erence between the ratios of the mass and charge of deuterons (d) and anti-deuterons (d), ¯ and 3He and 3He nuclei carried out with the ALICE (A Large Ion Collider Experiment)4 detector in Pb–Pb collisions at a centre-of-mass energy per nucleon pair of 2.76 TeV. Our direct measurement of the mass-over-charge di erences confirms CPT invariance to an unprecedented precision in the sector of light nuclei5,6 . This fundamental symmetry of nature, which exchanges particles with anti-particles, implies that all physics laws are the same under the simultaneous reversal of charge(s) (charge conjugation C), reflection of spatial coordinates (parity transformation P) and time inversion (T).