a0+ (980)-resonance production in the reaction pp → dπ+η close to the $$K\bar K$$ threshold

AbstractThe reaction pp → dπ+η has been measured at a beam energy of Tp = 2.65 GeV (pp = 3.46 GeV/c) using the ANKE spectrometer at COSY-Julich. The missing-mass distribution of the detected dπ+ pairs exhibits a peak around the η mass on top of a strong background of multipion pp → dπ+(nπ) events. The differential cross section d4σ/dΩddΩπ+dpddpπ+ for the reaction pp → dπ+η has been determined model independently for two regions of phase space. Employing a dynamical model for the a0+ production allows one then to deduce a total cross section of σ(pp → da0+ → dπ+η) = 1.1 ± 0.3stat ± 0.7syst µb for the production of π+η via the scalar a0+(980) resonance and σ(pp → dπ+η) = 3.5 ± 0.3stat ± 1.0syst µb for the nonresonant production. Using the same model as for the interpretation of recent results from ANKE for the reaction $$pp \to dK^ + \bar K^0 $$ , the ratio of the total cross sections is $$\sigma (pp \to d(K^ + \bar K^0 )_{L = 0} )/\sigma (pp \to da_0^ + \to d\pi ^ + \eta ) = 0.029 \pm 0.008_{stat} \pm 0.009_{syst} $$ , which is in agreement with branching ratios in the literature.