Study of the quasi-free $np\to np{\pi }^{+}{\pi }^{-}$ reaction with a deuterium beam at 1.25 GeV/nucleon

Abstract

The tagged quasi-free $np\to np{\pi }^{+}{\pi }^{-}$ reaction has been studied experimentally with the High Acceptance Di-Electron Spectrometer (HADES) at GSI at a deuteron incident beam energy of 1.25 GeV/nucleon ($\sqrt{s}\sim$ 2.42 GeV/c for the quasi-free collision). For the first time, differential distributions for ${\pi }^{+}{\pi }^{-}$ production in $np$ collisions have been collected in the region corresponding to the large transverse momenta of the secondary particles. The invariant mass and angular distributions for the $np\to np{\pi }^{+}{\pi }^{-}$ reaction are compared with different models. This comparison confirms the dominance of the $t$-channel with $\Delta \Delta$ contribution. It also validates the changes previously introduced in the Valencia model to describe two-pion production data in other isospin channels, although some deviations are observed, especially for the ${\pi }^{+}{\pi }^{-}$ invariant mass spectrum. The extracted total cross section is also in much better agreement with this model. Our new measurement puts useful constraints for the existence of the conjectured dibaryon resonance at mass M$\sim$ 2.38 GeV and with width $\Gamma \sim$ 70 MeV.

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• Measurement of the $\vec{n}p\to d{\pi }^0{\pi }^0$ Reaction with Polarized Beam in the Region of the $d^{\ast }(2380)$ Resonance
• Determination of N* amplitudes from associated strangeness production in p+p collisions
• Search for an Isospin I =3 Dibaryon
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• Analysis of the exclusive final state npe${}^{+}$e${}^{-}$ in quasi-free np reaction
• Differential Cross Sections for Neutron-Proton Scattering in the Region of the $d^{\ast }(2380)$ Dibaryon Resonance
• On the Production of an Isotensor Dibaryon in the $pp\to pp{\pi }^{+}{\pi }^{-}$ Reaction
• Branching Ratios for the Decay of $d^{\ast }(2380)$
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