# $\Delta$(1232) Dalitz decay in proton-proton collisions at T=1.25 GeV measured with HADES

## TL;DR

This paper reports the first identification of the $ ext{Delta}(1232)$ Dalitz decay in proton-proton collisions at 1.25 GeV, measuring its branching ratio and testing sensitivity to N-$ ext{Delta}$ transition form factors.

## Contribution

The study provides the first experimental observation of the $ ext{Delta}(1232)$ Dalitz decay and measures its branching ratio, enhancing understanding of baryon resonance decays.

## Key findings

- First identification of $ ext{Delta}(1232)$ Dalitz decay.
- Measured branching ratio: (4.19 ± 0.62 (syst.) ± 0.34 (stat.)) × 10^{-5}.
- Validated analysis through $ ext{pi}^0$ Dalitz decay reconstruction.

## Abstract

We report on the investigation of $\Delta$(1232) production and decay in proton-proton collisions at a kinetic energy of 1.25 GeV measured with HADES. Exclusive dilepton decay channels $ppe^{+}e^{-}$ and $ppe^{+}e^{-}\gamma$ have been studied and compared with the partial wave analysis of the hadronic $pp\pi^{0}$ channel. They allow to access both $\Delta^+ \to p\pi^0(e^+e^-\gamma)$ and $\Delta^+ \to pe^+e^-$ Dalitz decay channels. The perfect reconstruction of the well known $\pi^0$ Dalitz decay serves as a proof of the consistency of the analysis. The $\Delta$ Dalitz decay is identified for the first time and the sensitivity to N-$\Delta$ transition form factors is tested. The $\Delta$(1232) Dalitz decay branching ratio is also determined for the first time; our result is (4.19 $\pm$ 0.62 syst. $\pm$ 0.34 stat.) $\times $ 10$^{-5}$, albeit with some model dependence.