Spin-1 particles and perturbative QCD

TL;DR

This paper discusses the extraction of electromagnetic form factors for spin-1 particles using light-front dynamics, ensuring consistency with instant form calculations, and analyzes experimental data to test perturbative QCD predictions.

Contribution

It introduces a method to uniquely determine spin-1 electromagnetic form factors in light-front dynamics, accounting for zero-mode contributions, and applies it to experimental data for rho mesons.

Findings

Consistent form factor extraction across different current matrix elements.

Predictions on the energy scale where perturbative QCD becomes dominant.

Analysis of Babar data to test asymptotic QCD behavior.

Abstract

Due to the angular condition in the light-front dynamics (LFD), the extraction of the electromagnetic form factors for spin-1 particles can be uniquely determined taking into account implicitly non-valence and/or the zero-mode contributions to the matrix elements of the electromagnetic current. No matter which matrix elements of the electromagnetic current is used to extract the electromagnetic form factors, the same unique result is obtained. As physical observables, the electromagnetic form factors obtained from matrix elements of the current in LFD must be equal to those obtained in the instant form calculations. Recently, the Babar collaboration \cite{Aubert2008} has analyzed the reaction $e^+ e^-\rightarrow \rho^+ + \rho^-$ at $\sqrt{s}=10.58 GeV$ to measure the cross section as well as the ratios of the helicity amplitudes $F_{\lambda'\lambda}$. We present our recent analysis of the Babar data for the rho meson considering the angular condition in LFD to put a stringent test on the onset of asymptotic perturbative QCD and predict the energy regime where the subleading contributions are still considerable.