Target and beam-target asymmetries for the $\gamma p \to \pi^0 \pi^0 p$ reaction

TL;DR

This paper investigates target and beam-target polarization asymmetries in the photoproduction of neutral pion pairs from protons, providing insights into nucleon resonance decays and advancing analysis techniques for multi-meson final states.

Contribution

It presents experimental measurements and model analysis of polarization observables in the $\,\gamma p \to \pi^0 \pi^0 p$ reaction, highlighting systematic uncertainties and methodological approaches.

Findings

Measured polarization asymmetries Py and Px in the reaction.

Analyzed asymmetries with three independent methods.

Identified systematic uncertainties in the measurements.

Abstract

Background: Photoproduction of pion pairs allows to study sequential decays of nucleon resonances via excited intermediate states. Such decays are important e.g. for states which in the quark model have both oscillators excited and de-excite them in a two-step process. However, analyses of multi-meson final states is difficult and requires more than unpolarized cross section measurements. Purpose: Experimental study and model analysis in view of resonant contributions of target and beam-target polarization observables for the reaction $\gamma p \to \pi^0 \pi^0 p$. Methods: Investigated were target (single) and beam-target (double) polarization asymmetries in dependence of several parameters. The experiments were performed at the Mainz Microtron (MAMI) using circularly polarized photon beams and transversally polarized solid-state butanol targets. The reaction products were analyzed with the Crystal Ball and TAPS detectors. Results: Studied were the polarization observables Py (unpolarized beam, target polarized in y direction) and Px (circularly polarized beam, target polarized in x direction), which are similar to T (target asymmetry) and F (beam-target asymmetry) for single pion production. The asymmetries were analyzed with three independent methods, revealing systematic uncertainties.