Dynamics of 1S0 diproton formation in the reactions pp-> (pp)_s+pi0$ and pp-> (pp)_s+gamma in the GeV region

TL;DR

This paper analyzes proton-proton reactions producing a proton pair in the singlet state with neutral pion or gamma emission at GeV energies, explaining observed energy dependencies via the Δ-isobar contribution within a one-pion exchange model.

Contribution

It introduces a detailed analysis of $pp$ reactions involving diproton formation and photon emission at GeV energies, highlighting the role of the Δ-isobar in these processes.

Findings

Broad maximum in $ ext{pi}^0$ production at 0.5-0.6 GeV

Rapid increase in $ ext{gamma}$ production cross section at 0.3-0.55 GeV

Δ-isobar contribution explains energy dependence patterns

Abstract

COSY-ANKE data on the cross section of the reactions $pp\to \{pp\}_s\pi^0$ and $pp\to \{pp\}_s\gamma$, where $\{pp\}_s$ is the proton pair in the $^1S_0$ state at small excitation energy $E_{pp}<3$ MeV, are analyzed at beam energies $0.5 - 2.0$ GeV within the one-pion exchange model. The model includes the subprocesses $\pi^0 p\to \pi^0 p$ and $\pi^0 p\to \gamma p$ for the pion- and photo-production, respectively, and accounts for the final state pp-interaction. A broad maximum in the energy dependence of the $\pi^0$ production at $\sim 0.5 -0.6$ GeV and fast increase of the $\gamma$-production cross section at $0.3 - 0.55$ GeV observed in the data are explained by the $\Delta$-isobar contribution. An analogy with the dynamics of the deuteron breakup reaction $pd\to \{pp\}_sn$ in the $\Delta$-region is outlined.