A Study of Spin Alignment of rho(770)+- and omega(782) Mesons in Hadronic Z Decays

TL;DR

This study measures the helicity density matrix elements of rho(770)+- and omega(782) mesons produced in Z decays, finding results compatible with a statistical mix of helicity states across the energy range.

Contribution

It provides the first measurements of rho[00] for these mesons in Z decays and compares them with other vector mesons, enhancing understanding of meson spin alignment.

Findings

Measured rho[00] values are consistent with 1/3 across the energy range.

At high energy, rho(770)+- has rho[00] ~ 0.373, omega ~ 0.142.

Results align with a statistical mixture of helicity states.

Abstract

The helicity density matrix elements rho[00] of rho(770)+- and omega(782) mesons produced in Z decays have been measured using the OPAL detector at LEP. Over the measured meson energy range, the values are compatible with 1/3, corresponding to a statistical mix of helicity -1, 0 and +1 states. For the highest accessible scaled energy range 0.3 < x_E < 0.6, the measured rho[00] values of the rho(770)+- and the omega are 0.373 +- 0.052 and 0.142 +- 0.114, respectively. These results are compared to measurements of other vector mesons.