Search

The momentum spectra of K+ produced at small angles in proton-proton and proton-deuteron collisions have been measured at four beam energies, 1.826, 1.920, 2.020, and 2.650 GeV, using the ANKE spectrometer at COSY-Juelich. After making corrections for Fermi motion and shadowing, the data indicate that K+ production near threshold is stronger in pp- than in pn-induced reactions. However, most of this difference could be made up by the unobserved K0 production in the pn case., Comment: 6 pages, 4 figures, Submitted to PRC

An exclusive measurement of the decay eta --> pi+ pi- gamma has been performed at the WASA facility at COSY. The eta mesons were produced in the fusion reaction pd --> 3He X at a proton beam momentum of 1.7 GeV/c. Efficiency corrected differential distributions have been extracted based on 13340\pm140 events after background subtraction. The measured pion angular distribution is consistent with a relative p-wave of the two-pion system, whereas the measured photon energy spectrum was found at variance with the simplest gauge invariant matrix element of eta --> pi+ pi- gamma. A parameterization of the data can be achieved by the additional inclusion of the empirical pion vector form factor multiplied by a first-order polynomial in the squared invariant mass of the pi+ pi- system., Comment: 7 pages, 10 figures, submitted to Phys.Lett.B

The reaction pp->pppi0pi0 has been investigated at a beam energy of 1.4 GeV using the WASA-at-COSY facility. The total cross section is found to be (324 +- 21_systematic +- 58_normalization) mub. In order to to study the production mechanism, differential kinematical distributions have been evaluated. The differential distributions indicate that both initial state protons are excited into intermediate Delta(1232) resonances, each decaying into a proton and a single pion, thereby producing the pion pair in the final state. No significant contribution of the Roper resonance N*(1440) via its decay into a proton and two pions is found, Comment: Submitted to PLB

We report on a high-statistics measurement of the basic double pionic fusion reaction $pn \to d\pi^0\pi^0$ over the energy region of the so-called ABC effect, a pronounced low-mass enhancement in the $\pi\pi$-invariant mass spectrum. The measurements were performed with the WASA detector setup at COSY. The data reveal the ABC effect to be associated with a Lorentzian shaped energy dependence in the integral cross section. The observables are consistent with a resonance with $I(J^P) =0(3^+)$ in both $pn$ and $\Delta\Delta$ systems. Necessary further tests of the resonance interpretation are discussed.

The production of phi mesons in the collisions of 2.83 GeV protons with C, Cu, Ag, and Au at forward angles has been measured via the phi -> K+K- decay using the COSY-ANKE magnetic spectrometer. The phi meson production cross section follows a target mass dependence of A^0.56+/-0.02 in the momentum region of 0.6-1.6 GeV/c. The comparison of the data with model calculations suggests that the in-medium phi width is about an order of magnitude larger than its free value., Comment: 8 pages with 2 eps figures

Selected results from experiments at COSY-Juelich are presented: an attempt to measure the mass of the eta meson with high precision (ANKE facility), first steps towards the detection of rare eta decays (WASA), and several measurements of KKbar-pair production (ANKE, COSY-11, MOMO)., Comment: Proceedings of QNP2009, Beijing, Sept. 2009; to be published in Chinese Physics C. 6 pages, 5 figures

The production of the Sigma+ hyperon through the pp->K+nSigma+ reaction has been investigated at four energies close to threshold, 1.826, 1.920, 1.958, and 2.020 GeV. At low energies, correlated K+pi+ pairs can only originate from Sigma+ production so that their measurement allows the total cross section for the reaction to be determined. The results obtained are completely consistent with the values extracted from the study of the K+-proton correlation spectra obtained in the same experiment. These spectra, as well as the inclusive K+ momentum distributions, also provide conservative upper limits on the Sigma+ production rates. The measurements show a Sigma+ production cross section that varies roughly like phase space and, in particular, none of the three experimental approaches used supports the anomalously high near-threshold pp->K+ nSigma+ total cross section previously reported [T. Rozek et al., Phys. Lett. B 643, 251 (2006)]., Comment: Submitted to PRC

This document is the Technical Design Report covering the two large spectrometer magnets of the PANDA detector set-up. It shows the conceptual design of the magnets and their anticipated performance. It precedes the tender and procurement of the magnets and, hence, is subject to possible modifications arising during this process., Comment: 10 pages, 14MB, accepted by FAIR STI in May 2009, editors: Inti Lehmann (chair), Andrea Bersani, Yuri Lobanov, Jost Luehning, Jerzy Smyrski, Technical Coordiantor: Lars Schmitt, Bernd Lewandowski (deputy), Spokespersons: Ulrich Wiedner, Paola Gianotti (deputy)

The differential and total cross sections for the d+p->3He+eta reaction have been measured at COSY-ANKE at excess energies of 19.5, 39.4, and 59.4 MeV over the full angular range. The results are in line with trends apparent from the detailed near-threshold studies and also agree with those from CELSIUS, though the present data have higher precision. While at 19.5 MeV the results can be described in terms of s- and p-wave production, by 59.4 MeV higher partial waves are required. Including the 19.5 MeV point together with the near-threshold data in a global s- and p-wave fit gives a poorer overall description of the data though the position of the pole in the 3He scattering amplitude, corresponding to the quasi-bound or virtual state, is hardly changed., Comment: 4 pages, 4 figures, 1 table

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 figures

To study fundamental questions of hadron and nuclear physics in interactions of antiprotons with nucleons and nuclei, the universal PANDA detector will be built. Gluonic excitations, the physics of strange and charm quarks and nucleon structure studies will be performed with unprecedented accuracy thereby allowing high-precision tests of the strong interaction. The proposed PANDA detector is a state-of-the art internal target detector at the HESR at FAIR allowing the detection and identification of neutral and charged particles generated within the relevant angular and energy range. This report presents a summary of the physics accessible at PANDA and what performance can be expected., Comment: 216 pages

Measurements of the pn -> p_spec dK^+K^- reaction, where p_spec is a spectator proton, have been undertaken at the Cooler Synchrotron COSY-Juelich by detecting a fast deuteron in coincidence with a K^+K^- pair in the ANKE facility. Although the proton beam energy was fixed, the moving target neutron allowed values of the non-resonant quasi-free pn -> dK^+K^- total cross section to be deduced up to an excess energy epsilon ~ 100 MeV. Evidence is found for the effects of K^-d and KKbar final state interactions. The comparison of these data with those of pp -> ppK^+K^- and pp -> dK^+Kbar shows that all the total cross sections are very similar in magnitude., Comment: 4 pages, 4 figures, 1 table; submitted to PRC (rapid communication)

This document presents the technical layout and the envisaged performance of the Electromagnetic Calorimeter (EMC) for the PANDA target spectrometer. The EMC has been designed to meet the physics goals of the PANDA experiment, which is being developed for the Facility for Antiproton and Ion Research (FAIR) at Darmstadt, Germany. The performance figures are based on extensive prototype tests and radiation hardness studies. The document shows that the EMC is ready for construction up to the front-end electronics interface., Comment: 199 pages, submitted to FAIR STI on July 1st 2008, Editors: Fritz-Herbert Heinsius, Bertram Kopf, Bernd Lewandowski (Deputy Technical Coordinator), Herbert L\"ohner, Rainer Novotny (Project Coordinator), Klaus Peters, Philippe Rosier, Lars Schmitt (Technical Coordinator), Alexander Vasiliev; Spokespersons: Ulrich Wiedner, Paola Gianotti (deputy)

The cross sections for the pp -> ppK+K- reaction were measured at three beam energies 2.65, 2.70, and 2.83 GeV at the COSY-ANKE facility. The shape of the K+K- spectrum at low invariant masses largely reflects the importance of K\bar{K} final state interactions. It is shown that these data can be understood in terms of an elastic K+K- rescattering plus a contribution coming from the production of a K0\bar{K}0 pair followed by a charge-exchange rescattering. Though the data are not yet sufficient to establish the size of the cusp at the K0\bar{K}0 threshold, the low mass behaviour suggests that isospin-zero production is dominant., Comment: 9 pages with 4 figures

A combined analysis of the published data on the pp -> dK+K0bar reaction at excess energies of 47.4 MeV and 104.7 MeV is presented. Evidence is found for both the production of the a0+(980)scalar resonance and for a strong K0bar:d final state interaction., Comment: 7 pages + 8 figures

The light scalar mesons a_0/f_0(980) are being investigated at COSY-Juelich by detecting the strong decays into K-K-bar and pi-eta/pi-pi as well as radiative decays into vector mesons. Selected results are discussed with emphasis on recent measurements at the ANKE and WASA spectrometers., Comment: 6 pages, 3 figures; Invited talk presented at SCADRON 70: Workshop on "Scalar Mesons and Related Topics", Lisbon, Portugal, 11-16 February 2008

We report development of generators for periodic, satellite-free fluxes of mono-disperse drops with diameters down to 10 mikrometers from cryogenic liquids like H_2, N_2, Ar and Xe (and, as reference fluid, water). While the breakup of water jets can well be described by Rayleigh's linear theory, we find jet regimes for H_2 and N_2 which reveal deviations from this behavior. Thus, Rayleigh's theory is inappropriate for thin jets that exchange energy and/or mass with the surrounding medium. Moreover, at high evaporation rates, axial symmetry of the dynamics is lost. When the drops pass into vacuum, frozen pellets form due to surface evaporation. The narrow width of the pellet flux paves the way towards various industrial and scientific applications., Comment: 4 pages, 4 figures, 1 table; final version to appear in Phys.Rev.Lett (minor changes with respect to v1)

The pp -> {pp}_s pi0 differential cross section has been measured with the ANKE spectrometer at COSY-Juelich for seven proton beam energies T_p between 0.5 and 1.97 GeV. By selecting proton pairs with an excitation energy of less than 3 MeV it is ensured that the final {pp}_s system is in the 1S0 state. In the measured region of theta_{pp}^{cm} < 18 deg, the data reveal a forward dip for T_p =< 1.4 GeV whereas a forward peaking is seen at 1.97 GeV. The energy dependence of the forward cross section shows a broad peak in the 0.6-0.8 GeV region, probably associated with Delta(1232) excitation, and a minimum at 1.4 GeV. Some of these features are similar to those observed for the spin-isospin partner reaction, pp -> d pi+. However, the ratio of the forward differential cross sections of the two reactions shows a significant suppression of single pion production associated with a spin--singlet final nucleon pair., Comment: 12 pages, 4 figures

The differential and total cross sections for kaon pair production in the pp->ppK+K- reaction have been measured at three beam energies of 2.65, 2.70, and 2.83 GeV using the ANKE magnetic spectrometer at the COSY-Juelich accelerator. These near-threshold data are separated into pairs arising from the decay of the phi-meson and the remainder. For the non-phi selection, the ratio of the differential cross sections in terms of the K-p and K+p invariant masses is strongly peaked towards low masses. This effect can be described quantitatively by using a simple ansatz for the K-p final state interaction, where it is seen that the data are sensitive to the magnitude of an effective K-p scattering length. When allowance is made for a small number of phi events where the K- rescatters from the proton, the phi region is equally well described at all three energies. A very similar phenomenon is discovered in the ratio of the cross sections as functions of the K-pp and K+pp invariant masses and the identical final state interaction model is also very successful here. The world data on the energy dependence of the non-phi total cross section is also reproduced, except possibly for the results closest to threshold., Comment: 12 two-column pages, 12 figures, 1 table

The observed variation of the total cross section for the dp -> 3He eta reaction near threshold means that the magnitude of the s--wave amplitude falls very rapidly with the eta centre--of--mass momentum. It is shown here that recent measurements of the momentum dependence of the angular distribution imply a strong variation also in the phase of this amplitude. Such a behaviour is that expected from a quasi--bound or virtual eta-3He state. The interpretation can be investigated further through measurements of the deuteron or proton analysing powers and/or spin--correlations., Comment: 10 pages with two eps figures

The pp -> p K+ Y0 reaction has been studied for hyperon masses m(Y0)<1540 MeV/c2 at COSY-Juelich by using a 3.65 GeV/c circulating proton beam incident on an internal hydrogen target. Final states comprising two protons, one positively charged kaon and one negatively charged pion have been identified with the ANKE spectrometer. Such configurations are sensitive to the production of the ground state Lambda and Sigma0 hyperons as well as the Sigma0(1385) and Lambda(1405) resonances. Applying invariant- and missing-mass techniques, the two overlapping excited states could be well separated, though with limited statistics. The shape and position of the Lambda(1405) distribution, reconstructed cleanly in the Sigma0 pion0 channel, are similar to those found from other decay modes and there is no obvious mass shift. This finding constitutes a challenging test for models that predict Lambda(1405) to be a two-state resonance., Comment: 10 pages, 4 figures, accepted for publication in Phys. Lett. B

Inclusive K+ production in proton-proton collisions has been measured at a beam energy of 2.16 GeV using the COSY-ANKE magnetic spectrometer. The resulting spectrum, as well as those corresponding to K+ p and K+ pi+ correlated pairs, can all be well described using consistent values of the total cross sections for the pp->K+ p Lambda, pp->K+ p Sigma0, and pp->K+ n Sigma+ reactions. While the resulting values for Lambda and Sigma0 production are in good agreement with world data, our value for the total Sigma+ production cross section, sigma(pp->K+ n Sigma+) = 2.5+/-0.6(stat)+/-0.4(syst) mkb at an excess energy of epsilon=129 MeV, could only be reconciled with other recently published data if there were a highly unusual near--threshold behaviour., Comment: 9 pages, 5 figures

The differential and total cross sections for the d+p->3He+eta reaction have been measured in a high precision high statistics COSY-ANKE experiment near threshold using a continuous beam energy ramp up to an excess energy Q of 11.3 MeV with essentially 100% acceptance. The kinematics allowed the mean value of Q to be determined to about 9 keV. Evidence is found for the effects of higher partial waves for Q>4 MeV. The very rapid rise of the total cross section to its maximum value within 0.5 MeV of threshold implies a very large eta-3He scattering length and hence the presence of a quasi-bound state extremely close to threshold., Comment: 4 pages, 4 figures, 1 table, submitted to Phys. Rev. Lett

The reaction pp->p K0 pi+ Lambda has been studied with the ANKE spectrometer at COSY-Juelich at a beam momentum of 3.65 GeV/c in order to search for a possible signal of the pentaquark Theta+(1540), decaying into the p K0 system. By detecting four charged particles in the final state, the K0 and the Lambda have been reconstructed to tag strangeness production. It has been found that the pi+ Lambda missing-mass spectrum displays no significant signal expected from the Theta+(1540) excitation. The total cross section for the reaction pp->p K0 pi+ Lambda has been deduced, as well as an upper limit for the Theta+ production cross section. The intermediate Delta++ K0 Lambda state is found to provide a significant contribution to the reaction., Comment: 10 pages, 7 figures; text changed, references added, style file changed

The production of omega-mesons in the pp->pp omega reaction has been investigated with the COSY-ANKE spectrometer for excess energies of 60 and 92MeV by detecting the two final protons and reconstructing their missing mass. The large multipion background was subtracted using an event-by-event transformation of the proton momenta between the two energies. Differential distributions and total cross sections were obtained after careful studies of possible systematic uncertainties in the overall ANKE acceptance. The results are compared with the predictions of theoretical models. Combined with data on the phi-meson, a more refined estimate is made of the Okubo-Zweig-Iizuka rule violation in the phi/omega production ratio., Comment: 10 pages, 9 figures, version 1, submitted to EPJ-A

We investigate the K^- ^3He and K^+ K^- interactions in the reaction pd -> ^3He K^+ K^- near threshold and compare our model calculations with data from the MOMO experiment at COSY-Juelich. A large attractive effective K^- p amplitude would give a significant K^- ^3He final-state interaction effect which is not supported by the experimental data. We also estimate upper limits for the a_0(980) and f_0(980) contributions to the produced K^+ K^- pairs., Comment: 5 pages, 2 figures, accepted for publication in PRC

The quasi-free pn->dphi reaction has been studied at the Cooler Synchrotron COSY-Juelich, using the internal proton beam incident on a deuterium cluster-jet target and detecting a fast deuteron in coincidence with the K+K- decay of the phi-meson. The energy dependence of the total and differential cross sections are extracted for excess energies up to 80 MeV by determining the Fermi momentum of the target neutron on an event-by-event basis. Though these cross sections are consistent with s-wave production, the kaon angular distributions show the presence of p waves at quite low energy. Production on the neutron is found to be stronger than on the proton but not by as much as for the eta-meson., Comment: 4 Pages, 3 Figures, version 2, resubmitted to Phys. Rev. Lett

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., Comment: 7 pages, 6 figures; accepted for publication in Eur.Phys.J. A

The pp->pp phi reaction has been studied at the Cooler Synchrotron COSY-Juelich, using the internal beam and ANKE facility. Total cross sections have been determined at three excess energies epsilon near the production threshold. The differential cross section closest to threshold at epsilon=18.5 MeV exhibits a clear S-wave dominance as well as a noticeable effect due to the proton-proton final state interaction. Taken together with data for pp omega-production, a significant enhancement of the phi/omega ratio of a factor 8 is found compared to predictions based on the Okubo-Zweig-Iizuka rule., Comment: 4 Pages, 3 Figures, 1 Table, submitted to Phys. Rev. Lett

We calculate the scattering lenths A(K-,3He) and A(K-,4He) using the multiple scattering approach and different parameters sets for the elementary a(Kbar,N). Within the zero-range approximation, we find for both systems loosely bound states with binding energies in the range 2-7 MeV and widths 11-18 MeV. It is demonstrated that the existence of deeply bound K-,4He states, which have been predicted in literature, can be tested by measuring the reaction dd -> 4He K-K+ at COSY., Comment: 4 pages, 1 figure, 1 table; prepared for the proceedings of STORI2005

Indications for the production of a neutral excited hyperon in the reaction pp -> p K^+ Y^{0*} are observed in an experiment performed with the ANKE spectrometer at COSY-J\"ulich at a beam momentum of 3.65 GeV/c. Two final states were investigated simultaneously, viz. Y^{0*} -> pi^+X^- and pi^-X^+, and consistent results were obtained in spite of the quite different experimental conditions. The parameters of the hyperon state are M(Y^{0*})= (1480 +/- 15) MeV/c^2 and Gamma(Y^{0*})= (60 +/- 15) MeV/c^2. The production cross section is of the order of few hundred nanobarns. Since the isospin of the Y^{0*} has not been determined here, it could either be an observation of the Sigma(1480), a one-star resonance of the PDG tables, or alternatively a Lambda hyperon. Relativistic quark models for the baryon spectrum do not predict any excited hyperon in this mass range and so the Y^{0*} may be of exotic nature., Comment: 4 pages, 3 figures, accepted for publication in Phys.Rev.Lett

We present predictions for the the K^- \alpha scattering length obtained within the framework of the multiple scattering approach. Evaluating the pole position of the K^- \alpha scattering amplitude within the zero range approximation, we find a loosely bound K^- \alpha state with a binding energy of E_R = -2 ... -7 MeV and a width \Gamma_R = 11 ... 18 MeV. We propose to measure the K^- \alpha scattering length through the final state interaction between the \alpha and K^- meson produced in the reaction dd \to \alpha K^+ K^-. It is found that the K^-\alpha invariant mass distribution from this reaction at energies near the threshold provides a new tool to determine the s-wave K^- \alpha scattering length., Comment: 6 pages, 3 PS figures

The reaction pp->pK+Y has been studied with the ANKE spectrometer at COSY-Juelich in order to investigate heavy hyperon production. The missing mass spectra MM(pK+) have been analyzed and compared with Monte Carlo simulations. Indications for a hyperon resonance Y0*(1480) have been found., Comment: Baryons2004 Proceedings, 4 pages, 6 figures

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., Comment: 5 pages, 8 figures, 1 table

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 J\"ulich. 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., Comment: 6 pages, 3 PS figures, uses espcrc2.sty

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 A

The production of K^+ mesons in pA (A = D, C, Cu, Ag, Au) collisions has been investigated at the COoler SYnchrotron COSY-J\"ulich for beam energies T_p = 1.0 - 2.3 GeV. Double differential inclusive pC cross sections at forward angles theta < 12 degrees as well as the target-mass dependence of the K^+ momentum spectra have been measured with the ANKE spectrometer. Far below the free NN threshold at T_{NN}=1.58 GeV the spectra reveal a high degree of collectivity in the target nucleus. From the target-mass dependence of the cross sections at higher energies, the repulsive in-medium potential of K^+ mesons can be deduced. Using pN cross-section parameterisations from literature and our measured pD data we derive a cross-section ratio of sigma(pn -> K^+ X) / sigma(pp -> K^+ X) ~ (3-4)., Comment: Accepted for publication in EPJ A; 17 pages, 10 figures, 11 tables

The COoler SYnchrotron COSY-J\"ulich delivers phase-space cooled, polarized proton and deuteron beams with momenta up to p=3.65 GeV/c. Various experiments on hadron-induced strangeness production on proton, neutron and nuclear targets have been carried out. Here we report about recent results on associated strangeness production in pp -> KYN (Y= Lambda,Sigma) reactions, on K^+ production in pn collisions, and on K K-bar pair production in pp interactions. We also briefly discuss possible measurements to disentangle the parity of the recently discovered pentaquark state Theta^+, the spin dependence of the YN interaction, as well as planned experiments which aim at the determination of the a_0-f_0 mixing matrix element, a quantity which is believed to be sensitive to the nature of the light scalar mesons a_0/f_0(980)., Comment: 10 pages, 3 figures; Proc. VIII Int. Conf. on Hypernuclear and Strange Particle Physics, JLab, Oct. 14 - 18, 2003

Triggered by a recent paper by Thomas, Hicks and Hosaka, we investigate which observables can be used to determine the parity of the $\Theta^+$ from the reaction $\vec p\vec p \to \Sigma^+\Theta^+$ near its production threshold. In particular, we show that the sign of the spin correlation coefficient $A_{xx}$ for small excess energies yields the negative of the parity of the $\Theta^+$. The argument relies solely on the Pauli principle and parity conservation and is therefore model--independent., Comment: References completed, discussion on possible influence of background added; conclusions unchanged

ANKE is a magnetic spectrometer and detection system at an internal target position of COSY-Juelich optimized for charged kaon detection. Recent results from ANKE on kaon production in pp and pD interactions are reported. From the pp data first absolutely normalized angular and invariant-mass spectra for the reaction pp -> dK+ K0-bar have been obtained. A partial-wave decomposition reveals a strong contribution of S-wave KK-bar pairs with low relative energy, suggesting dominance of resonant kaon production via the a0+(980). This indicates that systematic studies of the light scalar resonances a0/f0(980) are possible at COSY. Final goal of these measurements -- requiring a neutral-particle detector which is not yet available -- is to obtain information about the charge-symmetry breaking a0-f0 mixing. From the analysis of the pD data it is concluded that the K+ production cross section on the neutron is significantly larger as compared to the proton. A cross-section ratio of sigma(n)/sigma(p) ~ 4 is deduced., Comment: 11 pages, contribution to XXVIII Mazurian Lakes Conference on Physics, August 31--September 7, 2003, Krzyze, Poland

The first measurement of the p n -> d omega total cross section has been achieved at mean excess energies of Q = 28 and 57 MeV by using a deuterium cluster-jet target. The momentum of the fast deuteron was measured in the ANKE spectrometer at COSY-Juelich and that of the slow "spectator" proton p(sp) from the p d -> p(sp) d omega reaction in a silicon telescope placed close to the target. The cross sections lie above those measured for p p -> p p omega but seem to be below theoretical predictions., Comment: 7 pages, 8 figures; second approach to describe the background has been added; results changed insignificantly, EPJ in press

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., Comment: 4 pages, 4 figures; accepted by Phys. Rev. Lett

The $a_0$(980) and $f_0$(980) resonances are two well established states in the excited meson spectrum. We review the most prominent theoretical models which try to explain the structure of these states. It is discussed whether data from COSY on $a_0$ and $f_0$ production in $pp$, $pn$, $pd$ and $dd$ collisions allow to distinguish between the different approaches. Very promising in this respect seems to be the measurement of the reaction $dd \to (\mathrm{^4He} a_0^0 \to) \mathrm{^4He} \pi^0\eta$ which violates isospin conservation and can be related to $a_0$-$f_0$ mixing., Comment: Contribution to the workshop on the future physics program at COSY-Juelich, CSS2002 (8 pages, no figures)

A study of the deuteron breakup reaction $pd \to (pp)n$ with forward emission of a fast proton pair with small excitation energy $E_{pp}<$ 3 MeV has been performed at the ANKE spectrometer at COSY--J\"ulich. An exclusive measurement was carried out at six proton--beam energies $T_p=$~0.6,~0.7,~0.8,~0.95,~1.35, and 1.9 GeV by reconstructing the momenta of the two protons. The differential cross section of the breakup reaction, averaged up to $8^{\circ}$ over the cm polar angle of the total momentum of the $pp$ pairs, has been obtained. Since the kinematics of this process is quite similar to that of backward elastic $pd \to dp$ scattering, the results are compared to calculations based on a theoretical model previously applied to the $pd \to dp$ process., Comment: 17 pages including 6 figures and 1 table v2: minor changes; v3: minor change of author list; v4: changes in accordance with referee remarks

We consider near-threshold $a_0(980)$-meson production in $\pi N$ and $NN$ collisions. An effective Lagrangian approach with one-pion exchange is applied to analyze different contributions to the cross section for different isospin channels. The Reggeon exchange mechanism is also evaluated for comparison. The results from $\pi N$ reactions are used to calculate the contribution of the $a_0$ meson to the cross sections and invariant $K \bar K$ mass distributions of the reactions $pp\to pn K^+\bar K^0$ and $pp\to pp K^+K^-$. It is found that the experimental observation of $a_0^+$ mesons in the reaction $pp\to pn K^+\bar K^0$ is much more promising than the observation of $a_0^0$ mesons in the reaction $pp\to pp K^+K^-$. Effects of isospin violation in the reactions $pN \to d a_0$, $pd \to \mathrm{^3He/^3H} a_0$, and $ dd \to \mathrm{^4He} a_0$, which are induced by $a_0(980)$--$f_0(980)$ mixing, are also analyzed., Comment: 43 pages, including 16 eps figures, to be bublished in Phys. Atom. Nucl. (Yad. Fiz.) vol. 65, No. 11 (2002)

The production of K+ mesons in pA (A= C, Cu, Ag, Au) collisions has been investigated at the COoler SYnchrotron COSY-Juelich at beam energies T=1.0 ... 2.3 GeV using the ANKE spectrometer. ANKE allows to measure double differential cross sections for K+ production at forward angles theta< 12 degr. in a wide momentum range. The cross sections obtained in these experiments together with those from literature show a uniform behavior as functions of momentum transfer and excitation energy of the residual nucleus. At the lowest measured beam energy, far below the free NN-threshold (T_NN=1.58 GeV), the data reveal a high degree of collectivity in the target nucleus. The spectra obtained above threshold should allow one to extract the nuclear K+ potential with an accuracy of better than +/-3 MeV. Information about the mechanisms leading to K+ production can be obtained from K+p and K+d coincidence measurements., Comment: 12 pages, 6 figures; contribution to MESON 2002 Workshop, Crakow 24-28 May 2002

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 content

We investigate the cross section for the reaction $NN \to NNa_0$ near threshold and at medium energies. An effective Lagrangian approach with one-pion exchange is applied to analyze different contributions to the cross section for different isospin channels. The Reggeon exchange mechanism is also considered. The results are used to calculate the contribution of the $a_0$ meson to the cross sections and invariant $K \bar K$ mass distributions of the reactions $pp\to pn K^+\bar K^0$ and $pp\to pp K^+K^-$. It is found that the experimental observation of $a_0^+$ mesons in the reaction $pp\to pn K^+\bar K^0$ is much more promising than the observation of $a_0^0$ mesons in the reaction $pp\to pp K^+K^-$., Comment: 26 pages, including 11 eps figures, to be bublished in J. Phys. G