Analysis of the pi^+pi^-pi^+pi^- and pi^+pi^0pi^-pi^0 Final States in Quasi-Real Two-Photon Collisions at LEP

TL;DR

This study investigates the gamma gamma to four-pion final states at LEP, revealing the dominance of specific spin-parity states and providing detailed analysis of their helicity structures within a broad energy range.

Contribution

It provides the first detailed spin-parity-helicity analysis of these final states in two-photon collisions at LEP energies, highlighting the dominance of the 2+ helicity 2 state.

Findings

Dominance of the 2+ helicity 2 state in rho rho systems

Observation of 0+ and 0- contributions

Negligible 2- and zero-helicity 2+ contributions

Abstract

The reactions gamma gamma -> pi^+pi^-pi^+pi^- and gamma gamma -> pi^+pi^0pi^-pi^0 are studied with the L3 detector at LEP in a data sample collected at centre-of-mass energies from 161GeV to 209GeV with a total integrated luminosity of 698/pb. A spin-parity-helicity analysis of the rho^0 rho^0 and rho^+ rho^- systems for two-photon centre-of-mass energies between 1GeV and 3GeV shows the dominance of the spin-parity state 2+ with helicity 2. The contribution of 0+ and 0- spin-parity states is also observed, whereas contributions of 2- states and of a state with spin-parity 2+ and zero helicity are found to be negligible.