High statistics study of the reaction $\gamma p\to p\;2\pi^0$

TL;DR

This study provides detailed measurements of the $ ext{γ}p o p 2 ext{π}^0$ reaction, analyzing cross sections, polarization, and resonance properties to enhance understanding of nucleon resonance decays into multi-pion states.

Contribution

It offers the first comprehensive analysis of the $ ext{γ}p o p 2 ext{π}^0$ reaction with polarization data and resonance branching ratios using partial wave analysis.

Findings

Determined resonance contributions to the $p ext{π}^0 ext{π}^0$ final state.

Measured differential and total cross sections across photon energies.

Identified key decay channels including $ ext{Δ}(1232) ext{π}$ and $N(1440)1/2^+ ext{π}$.

Abstract

The photoproduction of 2$\pi^0$ mesons off protons was studied with the Crystal Barrel/TAPS experiment at the electron accelerator ELSA in Bonn. The energy of photons produced in a radiator was tagged in the energy range from 600\,MeV to 2.5\,GeV. Differential and total cross sections and $p\pi^0\pi^0$ Dalitz plots are presented. Part of the data was taken with a diamond radiator producing linearly polarized photons, and beam asymmetries were derived. Properties of nucleon and $\Delta$ resonances contributing to the $p\pi^0\pi^0$ final state were determined within the BnGa partial wave analysis. The data presented here allow us to determine branching ratios of nucleon and $\Delta$ resonances for their decays into $p\pi^0\pi^0$ via several intermediate states. Most prominent are decays proceeding via $\Delta(1232)\pi$, $N(1440)1/2^+\pi$, $N(1520)3/2^-\pi$, $N(1680)5/2^+\pi$, but also $pf_0(500)$, $pf_0(980)$, and $pf_2(1270)$ contribute to the reaction.