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

Abstract

The tagged quasi-free np → npπ + π − 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 ( √ s ∼ 2.42 GeV/c for the quasi-free collision). For the first time, differential distributions of solid statistics for π + π − 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 → npπ + π − reaction are compared with different models. This comparison confirms the dominance of the t-channel with ∆∆ 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 π + π − 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∼ 2.38 GeV and with width Γ ∼ 70 MeV.

Branching ratios for the decay of d*(2380)

“…Our result also is compatible with available measurements for this channel, see Ref. [6], including the newest results from HADES [26].…”

Proton distributions in dp dielectron production within Regge theory

“…For analysis of the exclusive production of one or two pions in NN or πN interactions the one-pion exchange reggeized (OPER) model was suggested [2]. For example, recently the OPER was successfully applied [3,4] to describe the experimental data on two-pion production in np collisions at incident kinetic energies E kin of about 1-5 GeV [3,5,6,7] and the HADES data at E kin = 1.25 GeV [4]. One of the most interesting goals in the HADES program is the study of e + e − -pair production in np interactions.…”