a{sub 0}{sup +} (980)-resonance production in the reaction pp {sup {yields}} d{pi}{sup +}{eta} close to the KK-bar threshold

The reaction pp {sup {yields}} d{pi}{sup +}{eta} has been measured at a beam energy of T{sub p} = 2.65 GeV (p{sub p} = 3.46 GeV/c) using the ANKE spectrometer at COSY-Julich. The missing-mass distribution of the detected d{pi}{sup +} pairs exhibits a peak around the {eta} mass on top of a strong background of multipion pp {sup {yields}} d{pi}{sup +}(n{pi}) events. The differential cross section d{sup 4}{sigma}/d{omega}{sub d}d{omega}{sub {pi}}{sup +}dp{sub d}dp{sub {pi}}{sup +} for the reaction pp {sup {yields}} d{pi}{sup +}{eta} has been determined model independently for two regions of phase space. Employing a dynamical model for the a{sub 0}{sup +} production allows one then to deduce a total cross section of {sigma}(pp {sup {yields}} da{sub 0}{sup +} {sup {yields}} d{pi}{sup +}{eta}) = 1.1 {+-} 0.3{sub stat} {+-} 0.7{sub syst} {mu}b for the production of {pi}{sup +}{eta} via the scalar a{sub 0}{sup +}(980) resonance and {sigma}(pp {sup {yields}} d{pi}{sup +}{eta}) = 3.5 {+-} 0.3{sub stat} {+-} 1.0{sub syst} {mu}b for the nonresonant production. Using the same model as for the interpretation of recent results from ANKE for the reaction pp{yields}dK{sup +}K-bar{sup 0}, the ratio of the total cross sections is {sigma}(pp{yields}d(K{sup +}K-bar{sup 0}){sub L=0})/{sigma}(pp{yields}da{sub 0}{sup +}{yields}d{pi}{sup +}{eta})=0.029= {+-}0.008{sub stat}{+-}0.009{sub syst},more » which is in agreement with branching ratios in the literature.« less