Measurement of the cross section for interaction of ultrarelativistic positronium atoms with carbon

The total cross section for interaction of ultrarelativistic positronium atoms (A2e) with carbon atoms has been measured. The source of (A2e) is decay of the neutral pion π0→γ+A2e. In the momentum range investigated the γ factor of the atoms (800<γ<2000) is three orders of magnitude greater than achieved in other experiments on study of atom-atom collisions. In this range of γ factors the cross section should be equal to its asymptotic value. The measured total interaction cross section is σtot=(16+16-6)·10-19 cm2/atom. The cross-section value obtained is consistent with the calculated value σthtot=5.7·10-19 cm2/atom determined by the Coulomb interaction of A2e with carbon. At the same time comparison of the values of σtot and σthtot does not exclude existence of other mechanisms of ionization or excitation of ultrarelativistic A2e by matter which lead to a substantial increase of the cross section