Direct measurement of the pion valence quark momentum distribution, the pion light-cone wave function squared

TL;DR

This paper reports the first direct experimental measurement of the pion valence quark momentum distribution, linking it to the pion light-cone wave function squared, using high-energy diffractive dissociation data.

Contribution

It provides the first direct measurement of the pion valence quark distribution and compares it with perturbative QCD predictions for the light-cone wave function.

Findings

The asymptotic light-cone wave function describes the data well at high Q^2.

The measured transverse momentum distribution of di-jets was obtained.

Results support perturbative QCD models for pion structure.

Abstract

We present the first direct measurements of the pion valence quark momentum distribution which is related to the square of the pion light-cone wave function. The measurements were carried out using data on diffractive dissociation of 500 GeV/c $\pi^-$ into di-jets from a platinum target at Fermilab experiment E791. The results show that the $|q\bar {q}>$ light-cone asymptotic wave function, which was developed using perturbative QCD methods, describes the data well for $Q^2 \sim 10 ~{\rm (GeV/c)^2}$ or more. We also measured the transverse momentum distribution of the diffractive di-jets.