Exclusive Measurement of the $pp \to nn\pi^+\pi^+$ Reaction at 1.1 GeV

TL;DR

This study presents the first exclusive measurements of the $pp o nn o ext{pi}^+ ext{pi}^+$ reaction at 1.1 GeV, revealing discrepancies with existing theories and indicating a different dominant process involving a higher-lying $ ext{Delta}$ state.

Contribution

It provides new experimental data challenging current theoretical models by identifying a different dominant excitation process in proton-proton collisions.

Findings

Total and differential cross sections differ from predictions.

Data suggest $ ext{Delta}(1600)$ excitation dominates at 1.1 GeV.

Results imply need to revise theoretical models.

Abstract

First exclusive data for the $pp \to nn\pi^+\pi^+$ reaction have been obtained at CELSIUS with the WASA detector setup at a beam energy of $T_p$ = 1.1 GeV. Total and differential cross sections disagree with theoretical calculations, which predict the $\Delta\Delta$ excitation to be the dominant process at this beam energy. Instead the data require the excitation of a higher-lying $\Delta$ state, most likely the $\Delta(1600)$, to be the leading process.