Near-threshold production of a0(980) mesons in the reaction pp -> d K^+ \bar{K}^0

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 K\bar{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-J\"ulich for Q<=107 MeV the a_0^+ signal can reliably be separated from the non-resonant K^+\bar{K^0} background.Comment: 14 pages, 12 figures, submitted to EPJ

a0(980)-f0(980) mixing and isospin violation in the reactions pN -> d a0, pd -> 3He/3H a0 and dd -> 4He a0

It is demonstrated that f_0-a_0 mixing can lead to a comparatively large isospin violation in the reactions pN -> da_0, pd -> ^3He/^3H a_0 and dd -> ^4He a_0 close to the corresponding production thresholds. The observation of such mixing effects is possible, e.g., by measuring the forward-backward asymmetry in the reaction pn -> d a_0^0 -> d eta pi^0.Comment: 14 pages, 5 figure

Production of a0a_0-mesons in the reactions πN→a0N\pi N \to a_0 N and pp→da0+p p \to d a_0^+ at GeV energies

We investigate the reactions $\pi N \to a_0 N$ and $p p \to d a_0^+$ near threshold and at medium energies. An effective Lagragian approach and the Regge pole model are applied to analyze different contributions to the cross section of the reaction $\pi N \to a_0 N$. These results are used to calculate the differential and total cross sections of the reaction $p p \to d a_0^+$ within the framework of the two-step model in which two nucleons produce an $a_0$-meson via $\pi$ -meson exchange and fuse to a deuteron. The necessity of new measurements on $a_0$ production and branching fractions (of its decay to the $K\bar K$ and $\pi\eta$ channels) is emphasized for clarifying the $a_0$ structure. Detailed predictions for the reaction $pp \to d a_0^+$ are presented for the energy regime of the proton synchrotron COSY-J\"ulich.Comment: 9 pages, including 6 eps figure

Measurement of the isospin-filtering dd -> 4He K+ K- reaction at Q=39 MeV

The total cross section for the dd -> 4He K+ K- reaction has been measured at a beam momentum of 3.7 GeV/c, corresponding to an excess energy of 39 MeV, which is the maximum possible at the Cooler Synchrotron COSY-J\"{u}lich. A deuterium cluster-jet target and the ANKE forward magnetic spectrometer, placed inside the storage ring, have been employed in this investigation. We find a total cross section of sigma(tot) < 14 pb, which brings into question the viability of investigating the dd -> 4He a0(980) reaction as a means of studying isospin violation.Comment: Five pages with three eps figure

Medium effects in the production and pi0 gamma decay of omega-mesons in pA collisions in the GeV region

The omega-resonance production and its pi0 gamma decay in p-A reactions close to threshold is considered within the Intranuclear Cascade (INC) Model. The pi0 gamma invariant mass distribution shows two components which correspond to the omega decay 'inside' and 'outside' the nucleus, respectively. The 'inside' component is distorted by medium effects, which introduce a mass shift as well as collisional broadening for the omega-meson and its decaying pion. The relative contribution of the 'inside' component is analyzed in detail for different kinematical conditions and nuclear targets. It is demonstrated that a measurement of the correlation in azimuthal angle between the pi0 and gamma momenta allows to separate events related to the 'inside' omega decay from different sources of background when uncorrelated pi0's and gamma's are produced.Comment: 24 pages, 11 figure

Kaon pair production in proton-nucleus collisions at 2.83 GeV kinetic energy

The production of non-phi K+K- pairs by protons of 2.83 GeV kinetic energy on C, Cu, Ag, and Au targets has been investigated using the COSY-ANKE magnetic spectrometer. The K- momentum dependence of the differential cross section has been measured at small angles over the 0.2--0.9 GeV/c range. The comparison of the data with detailed model calculations indicates an attractive K- -nucleus potential of about -60 MeV at normal nuclear matter density at a mean momentum of 0.5 GeV/c. However, this approach has difficulty in reproducing the smallness of the observed cross sections at low K- momenta.Comment: 7 pages, 5 figures, 1 tabl

Evidence of kaon nuclear and Coulomb potential effects on soft K+ production from nuclei

The ratio of forward K+ production on copper, silver and gold targets to that on carbon has been measured at proton beam energies between 1.5 and 2.3 GeV as a function of the kaon momentum p_K using the ANKE spectrometer at COSY-Juelich. The strong suppression in the ratios observed for p_K<200-250 MeV/c can be ascribed to a combination of Coulomb and nuclear repulsion in the K+A system. This opens a new way to investigate the interaction of K+-mesons in the nuclear medium. Our data are consistent with a K+A nuclear potential of V_K~20 MeV at low kaon momenta and normal nuclear density. Given the sensitivity of the data to the kaon potential, the current experimental precision might allow one to determine V_K to better than 3 MeV.Comment: 9 pages, 3 figures; changed conten

The Fourth Standard Model Family and the Competition in Standart Model Higgs Boson Search at Tevatron and LHC

The impact of the fourth Standard Model family on Higgs boson search at Tevatron and LHC is reviewed.Comment: 7 pages, 13 figure