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

The total cross section for interaction of ultrarelativistic positronium atoms ({ital A}{sub 2{ital e}}) with carbon atoms has been measured. The source of ({ital A}{sub 2{ital e}}) is decay of the neutral pion {pi}{sup 0}{r arrow}{gamma}+{ital A}{sub 2{ital e}}. In the momentum range investigated the {gamma} factor of the atoms (800{lt}{gamma}{lt}2000) is three orders of magnitude greater than achieved in other experiments on study of atom-atom collisions. In this range of {gamma} factors the cross section should be equal to its asymptotic value. The measured total interaction cross section is {sigma}{sub tot}=(16{sup +16}{sub {minus}6}){center dot}10{sup {minus}19} cm{sup 2}/atom. The cross-section value obtained is consistent with the calculated value {sigma}{sup th}{sub tot}=5.7{center dot}10{sup {minus}19} cm{sup 2}/atom determined by the Coulomb interaction of {ital A}{sub 2{ital e}} with carbon. At the same time comparison of the values of {sigma}{sub tot} and {sigma}{sup th}{sub tot} does not exclude existence of other mechanisms of ionization or excitation of ultrarelativistic {ital A}{sub 2{ital e}} by matter which lead to a substantial increase of the cross section.