1 Does the E 791 experiment have 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 jets in longitudinal momenta 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 form for the asymptotic and CZ wave functions, and the ratio of cross sections differs from unity only within a factor of two. We argue therefore that, unfortunately, the E791-experiment have not measured yet 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 measured recently the cross section of hard diffractive dissociation of the pion into two jets. In particular, the distribution of jets in longitudinal momentum fractions y 1 and y 2 , (y 1 + y 2) = 1, 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 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