2 00 1 Has the E 791 experiment measured the pion wave function profile ?

The cross section of hard diffractive dissociation of the pion into two jets is calculated. It is obtained that the distribution of longitudinal momenta for jets is not simply proportional to the profile of the pion wave function, but depends on it in a complicated way. In particular, it is shown that, under the conditions of the E791 experiment, the momentum distribution of jets is similar in its shape for the asymptotic and CZ wave functions, and even the ratio of the differential cross sections is not far from unity. We argue therefore that, unfortunately, the E791 experiment has not yet measured the profile of the pion wave function. For this, the experimental accuracy has to be increased essentially. 1. The E791 experiment at Fermilab [1] has recently measured the cross section of the hard diffractive dissociation of the pion into two jets. In particular, the distribution of the total longitudinal momentum into fractions y 1 and y 2 , (y 1 + y 2) = 1, between jets has been measured. The main purpose was to obtain in this way the information about the leading twist pion wave function φ π (x 1 , x 2), which describes the distribition of quarks inside the pion in the longitudinal momentum fractions x 1 and x 2 , (x 1 + x 2) = 1. The hope was based on the theoretical calculations of this cross section [2]. It has been obtained in these papers that the cross section is simply proportional to the pion wave function squared: dσ/dy 1 ∼ |φ π (y 1)| 2. In such a case, it would be sufficient to measure only the gross features of dσ/dy