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Register a new usera0+(980)-resonance production in the reaction pp -> dpi+eta close to the K(bar(K)) threshold
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The reaction pp -> dpi+eta has been measured at a beam energy of T=2.65 GeV (p=3.46 GeV/c) using the ANKE spectrometer at COSY-Juelich. The missing mass distribution of the detected dpi+ pairs exhibits a peak around the eta mass on top of a strong background of multi-pion pp -> dpi+(n(pi)) events. The differential cross section d^4(sigma)/d(Omega_d)d(Omega_pi+)d(p_d)d(p_pi+) for the reaction pp -> dpi+eta 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 sigma(pp -> da0+ -> dpi+eta)=(1.1 +/- 0.3_(stat) +/- 0.7_(syst)) microbarn for the production of pi+eta via the scalar a0+(980) resonance and sigma(pp -> dpi+eta) = (3.5 +/- 0.3_(stat) +/- 1.0_(syst)) microbarn for the non-resonant production. Using the same model as for the interpretation of recent results from ANKE for the reaction pp -> dK+(bar(K0)), the ratio of the total cross sections is sigma(pp -> d(K+(bar(K0)))_(L=0))/sigma(pp -> da0+ -> dpi+eta) = 0.029 +/- 0.008_(stat) +/- 0.009_(syst), which is in agreement with branching ratios in the literature.
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Using an effective Lagrangian approach as well as the Quark-Gluon Strings Model we analyze near-threshold production of a0(980)-mesons in the reaction NN -> d K bar{K} as well as the background of non-resonant Kbar{K}-pair production. We argue that the reaction pp -> d K^+ bar{K}^0 at an energy release Q<=100 MeV is dominated by the intermediate production of the a0(980)-resonance. At larger energies the non-resonant K^+bar{K}^0-pair production - where the kaons are produced in a relative P-wave - becomes important. Then effects of final-state interactions are evaluated in a unitarized scattering-length approach and found to be in the order of a 20% suppression close to threshold. Thus in present experiments at the Cooler Synchrotron COSY-Julich for Q<=107 MeV the a_0^+ signal can reliably be separated from the non-resonant K^+bar{K^0} background.
The reaction pp->d K+ Kbar0 has been investigated at an excess energy of Q=46 MeV above the (K+ Kbar0) threshold with ANKE at COSY-Juelich. From the detected coincident dK+ pairs about 1000 events with a missing Kbar0 were identified, corresponding to a total cross section of sigma(pp->d K+ Kbar0)=(38 +/- 2(stat) +/- 14(syst)) nb. Invariant-mass and angular distributions have been jointly analyzed and reveal s-wave dominance between the two kaons, accompanied by a p-wave between the deuteron and the kaon system. This is interpreted in terms of a0+(980)-resonance production.
The reaction pp -> d K^+ K^0-bar has been investigated at excess energies Q = 47.4 and 104.7 MeV above the K^+ K^0-bar threshold at COSY-Juelich. Coincident dK^+ pairs were detected with the ANKE spectrometer, and events with a missing K^0-bar invariant-mass subsequently identified. The joint analysis of invariant-mass and angular distributions reveals s-wave dominance between the two kaons, in conjunction with a p-wave between the deuteron and the kaon pair, i.e. K K-bar production via the a_0^+(980) channel. Integration of the differential distributions yields total cross sections of sigma(pp -> d K^+ K^0-bar) = (38 +/- 2(stat) +/- 14(syst)) nb and 190 +/- 4(stat) +/- 39(syst)) nb for the low and high Q values, respectively.
The real and imaginary parts of the bar K^0 d scattering length are extracted from the bar K^0 d mass spectrum obtained from the reaction pp to d bar K^0 K^+ measured recently at the Cooler Synchrotron COSY at Julich. We extract a new limit on the K^- d scattering length, namely Im a le 1.3 fm and |Re a| le 1.3 fm. The limit for the imaginary part of the K^- d scattering length is supported by data on the total K^- d cross sections.
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