Polarization and Spin Alignment in Multihadronic Z0 Decays

TL;DR

This paper analyzes polarization and spin alignment phenomena in hadronic Z0 decays, revealing polarization in baryons and spin preferences in mesons, providing insights into the hadronization process and non-perturbative QCD effects.

Contribution

It presents detailed measurements of polarization and helicity density-matrix elements in various hadrons produced in Z0 decays, highlighting unexplained spin alignment mechanisms.

Findings

Lambda_b baryons and Lambda hyperons show longitudinal polarization.

Light mesons and D*+ exhibit a preference for helicity-zero states at high energy.

Some mesons display non-diagonal elements indicating coherence effects.

Abstract

The large statistics of millions of hadronic Z0 decays, accumulated by the four LEP experiments between 1989 and 1995, allowed for detailed investigations of the fragmentation process. Inclusive Lambda_b baryons and Lambda hyperons at intermediate and high momentum have been found to show longitudinal polarization. This may be related to the primary quark and antiquark polarization and the hadronization mechanism which produces the leading baryons. Helicity density-matrix elements have been measured for a variety of vector mesons produced inclusively in hadronic Z0 decays. The diagonal elements of some of the light mesons and the D*+- show a preference for a helicity-zero state if the meson carries a large fraction of the available energy. The mechanism which produces such spin alignment in the non-perturbative hadronization of the primary partons to the vector mesons is so far unexplained. For the B* the results are consistent with no spin alignment, which is expected in a picture based on HQET. For some meson species non-diagonal elements have been measured indicating coherence phenomena due to final-state interaction between the primary quark and antiquark.