The Wigner Function of Produced Particles in String Fragmentation

TL;DR

This paper models string fragmentation in QCD using a simplified 2D approach, revealing that particles are produced instantaneously across rapidity regions, challenging classical sequential pictures.

Contribution

It introduces a novel application of Schwinger QED2 to study the space-time dynamics of particle production in string fragmentation.

Findings

Particles are produced simultaneously across rapidity regions.

The model challenges classical space-momentum-time ordering in string fragmentation.

QCD4 can be approximated by QCD2 with transverse quark mass in certain limits.

Abstract

We show that QCD4 with transverse confinement can be approximately compactified into QCD2 with a transverse quark mass $m_{{}_T}$ that is obtained by solving a set of coupled transverse eigenvalue equations. In the limits of a strong coupling and a large number of flavors, QCD2 further admits Schwinger QED2-type bosonized solutions. We therefore examine phenomenologically the space-time dynamics of produced particles in string fragmentation by studying the Wigner function of produced bosons in Schwinger QED2, which mimics many features of string fragmentation in quantum chromodynamics. We find that particles with momenta in different regions of the rapidity plateau are produced at the initial moment of string fragmentation as a quark pulls away from an antiquark at high energies, in contrast to classical pictures of string fragmentation with longitudinal space-momentum-time ordering.