Search

This letter reports a first quantitative analysis of the contribution of higher partial waves in the charge symmetry breaking reaction dd→4Heπ0 using the WASA-at-COSY detector setup at an excess energy of Q=60MeV. The determined differential cross section can be parametrized as dσ/dΩ=a+bcos2⁡θ⁎, where θ⁎ is the production angle of the pion in the center-of-mass coordinate system, and the results for the parameters are a=(1.55±0.46(stat)+0.32−0.8(syst))pb/sr and b=(13.1±2.1(stat)−2.7+1.0(syst))pb/sr. The data are compatible with vanishing p-waves and a sizable d-wave contribution. This finding should strongly constrain the contribution of the Δ isobar to the dd→4Heπ0 reaction and is, therefore, crucial for a quantitative understanding of quark mass effects in nuclear production reactions.

Exclusive measurements of the quasifree pp→ppπ^{+}π^{-} reaction have been carried out at WASA@COSY by means of pd collisions at T_{p}=1.2 GeV. Total and differential cross sections have been extracted covering the energy region T_{p}=1.08-1.36 GeV, which is the region of N^{*}(1440) and Δ(1232)Δ(1232) resonance excitations. Calculations describing these excitations by t-channel meson exchange are at variance with the measured differential cross sections and underpredict substantially the experimental total cross section. An isotensor ΔN dibaryon resonance with I(J^{P})=2(1^{+}) produced associatedly with a pion is able to overcome these deficiencies.

New data on both total and differential cross sections of the production of η mesons in proton–deuteron fusion to He3η in the excess energy region 13.6MeV≤Qη≤80.9MeV are presented. These data have been obtained with the WASA-at-COSY detector setup located at the Forschungszentrum Jülich, using a proton beam at 15 different beam momenta between pp=1.60GeV/c and pp=1.74GeV/c. While significant structure of the total cross section is observed in the energy region 20MeV≲Qη≲60MeV, a previously reported sharp variation around Qη≈50MeV cannot be confirmed. Angular distributions show the typical forward-peaking that was noted earlier. For the first time, it is possible to study the development of these angular distributions with rising excess energy over a wide interval.

The investigation of the recombination of nuclear polarized hydrogen and deuterium atoms into polarized molecules gives new insights into different fields in physics and chemistry. On the one hand, the measurement of the polarization preservation during the recombination process itself allows one the observation of a new parameter during the chemical processes on different surfaces and enables the production of hyper-polarized molecules. On the other hand, the molecular polarization measured as a function of the imposed external magnetic field delivers the coupling forces of the nuclear spins and the rotational magnetic moments of the molecules as well as the coupling between the two nuclear spins themselves. This knowledge allows one to optimize storage-cell gas targets for coming accelerators experiments or to produce and handle polarized fuel for future fusion reactors.

This letter reports the successful use of feedback from a spin polarization measurement to the revolution frequency of a 0.97 GeV/$c$ bunched and polarized deuteron beam in the Cooler Synchrotron (COSY) storage ring in order to control both the precession rate ($\approx 121$ kHz) and the phase of the horizontal polarization component. Real time synchronization with a radio frequency (rf) solenoid made possible the rotation of the polarization out of the horizontal plane, yielding a demonstration of the feedback method to manipulate the polarization. In particular, the rotation rate shows a sinusoidal function of the horizontal polarization phase (relative to the rf solenoid), which was controlled to within a one standard deviation range of $\sigma = 0.21$ rad. The minimum possible adjustment was 3.7 mHz out of a revolution frequency of 753 kHz, which changes the precession rate by 26 mrad/s. Such a capability meets a requirement for the use of storage rings to look for an intrinsic electric dipole moment of charged particles.

In this paper, we demonstrate the connection between a magnetic storage ring with additional sextupole fields set so that the x and y chromaticities vanish and the maximizing of the lifetime of in-plane polarization (IPP) for a 0.97-GeV/c deuteron beam. The IPP magnitude was measured by continuously monitoring the down-up scattering asymmetry (sensitive to sideways polarization) in an in-beam, carbon-target polarimeter and unfolding the precession of the IPP due to the magnetic anomaly of the deuteron. The optimum operating conditions for a long IPP lifetime were made by scanning the field of the storage ring sextupole magnet families while observing the rate of IPP loss during storage of the beam. The beam was bunched and electron cooled. The IPP losses appear to arise from the change of the orbit circumference, and consequently the particle speed and spin tune, due to the transverse betatron oscillations of individual particles in the beam. The effects of these changes are canceled by an appropriate sextupole field setting., Comment: 18 pages, 18 figures, prepared for Phys. Rev. Accel. Beams

Charge symmetry breaking (CSB) observables are a suitable experimental tool to examine effects induced by quark masses on the nuclear level. Previous high precision data from TRIUMF and IUCF are cu ...

The deuteron tensor analysing power t_{20} of the d(pol) p --> 3He eta reaction has been measured at the COSY-ANKE facility in small steps in excess energy Q up to Q = 11 MeV. Despite the square of the production amplitude varying by over a factor of five through this range, t_{20} shows little or no energy dependence. This is evidence that the final state interaction causing the energy variation is not influenced by the spin configuration in the entrance channel. The weak angular dependence observed for t_{20} provides useful insight into the amplitude structure near threshold.

The transverse spin correlations A x , x and A y , y in the n → p → → d π 0 reaction have been measured for the first time in quasi-free kinematics at the COSY-ANKE facility using a polarised deuteron beam incident on a polarised hydrogen cell target. The results obtained for neutron energies close to 353 MeV and 600 MeV are in good agreement with the partial wave analysis of data on the isospin-related p p → d π + reaction, though the present results cover kinematic regions that are largely absent from existing data sets.

The charge-exchange break-up of polarised deuterons d → p → { p p } s n , where the final { p p } s diproton system has a very low excitation energy and hence is mainly in the S 0 1 state, is a powerful tool to probe the spin-flip terms in the proton–neutron charge-exchange scattering. Recent measurements with the ANKE spectrometer at the COSY storage ring at 1.6, 1.8, and 2.27 GeV have extended these studies into the pion-production regime in order to investigate the mechanism for the excitation of the Δ ( 1232 ) isobar in the d → p → { p p } s X reaction. Values of the differential cross section and two deuteron tensor analysing powers, A x x and A y y , have been extracted as functions of the momentum transfer to the diproton or the invariant mass M X of the unobserved system X. The unpolarised cross section in the high M X region is well described in a model that includes only direct excitation of the Δ isobar through undistorted one pion exchange. However, the cross section is grossly underestimated for low M X , even when Δ excitation in the projectile deuteron is included in the calculation. Furthermore, direct Δ production through one pion exchange only reproduces the angular dependence of the difference between the two tensor analysing powers.

The presently world largest data sample for π 0 → γ e + e − decays studies containing nearly 5 × 10 5 events was collected using the WASA detector at COSY. A search for a dark photon U produced in the π 0 → γ U → γ e + e − decay from the p p → p p π 0 reaction was carried out. An upper limit on the square of the U − γ mixing strength parameter ϵ 2 of 5 × 10 − 6 at 90% CL was obtained for the mass range 20 MeV M U 100 MeV . This result together with other recent experimental limits significantly reduces the M U vs. ϵ 2 parameter space which could explain the presently seen deviation between the Standard Model prediction and the direct measurement of the anomalous magnetic moment of the muon.

The WASA-at-COSY experiment has collected $3\ifmmode\times\else\texttimes\fi{}{10}^{7}$ events with $\ensuremath{\eta}$ mesons produced via the reaction $pd\ensuremath{\rightarrow}^{3}\mathrm{He}\phantom{\rule{0.16em}{0ex}}\ensuremath{\eta}$ at $\mathrm{T}=1.0\phantom{\rule{4pt}{0ex}}\mathrm{GeV}$. Using this data set, we evaluate the branching ratios of the decays $\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{\gamma}$, $\ensuremath{\eta}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}\ensuremath{\gamma}$, $\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{e}^{+}{e}^{\ensuremath{-}}$, and $\ensuremath{\eta}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}{e}^{+}{e}^{\ensuremath{-}}$. The branching ratios are normalized to the $\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ decay. In addition an upper limit on a $CP$-violating asymmetry in $\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{e}^{+}{e}^{\ensuremath{-}}$ is extracted.

We report on measurements of the differential cross section $d\ensuremath{\sigma}/d\mathrm{\ensuremath{\Omega}}$ and the first measurement of the analyzing power ${A}_{y}$ in the $\mathrm{\ensuremath{\Delta}}(1232)$ excitation energy region of the reaction $pp\ensuremath{\rightarrow}{{pp}}_{s}{\ensuremath{\pi}}^{0}$ where ${{pp}}_{s}$ is a $^{1}S_{0}$ proton pair. The experiment has been performed with the ANKE spectrometer at COSY-J\"ulich. The data reveal a peak in the energy dependence of the forward ${{pp}}_{s}$ differential cross section, a minimum at zero degrees of its angular distribution, and a large analyzing power. The results present a direct manifestation of two two-baryon resonance-like states with ${J}^{P}={2}^{\ensuremath{-}}$ and ${0}^{\ensuremath{-}}$ and an invariant mass of $2.2\phantom{\rule{0.16em}{0ex}}\mathrm{GeV}/{c}^{2}$.

The use of nuclear-polarized particles is an interesting option to increase the energy output of future fusion reactors or to decrease their costs. However, before polarized particles can be used as polarized fuel studies on production and handling of sufficient amounts of polarized fuels are necessary. This should not be a problem \(\mathrm{for}\ {}{^3}\mathrm{He}\) and T, because both can be polarized by so called “optical-pumping”. Unfortunately, this method has not been very successful in producing polarized deuterium yet. For the use of polarized fuel in magnetic-confinement fusion devices (e.g. in tokamaks) the production of polarized deuterium molecules by recombination of polarized deuterium atoms from a polarized atomic beam source is another option. In first experiments with hydrogen, the initial nuclear polarization of about 0.9 has mostly been preserved during the recombination process on a Fomblin surface. For deuterium polarization losses due to wall collisions are expected to be substantially reduced when the temperature of the deuterium gas is lowered to near liquefaction temperatures. Therefore, storing of polarized deuterium molecules seems to be possible, either as very cold gas in strong magnetic fields, or by freezing out as polarized deuterium ice.

The PAX Collaboration has successfully performed a spin-filtering experiment with protons at the COSY-ring. The measurement allowed the determination of the spin-dependent polarizing cross section, that compares well with the theoretical prediction from the nucleon-nucleon potential. The test confirms that spin-filtering can be adopted as a method to polarize a stored beam and that the present interpretation of the mechanism in terms of the proton-proton interaction is correct. The outcome of the experiment is of utmost importance in view of the possible application of the method to polarize a beam of stored antiprotons. (C) 2012 Elsevier B.V. All rights reserved.

The differential cross section d σ / d Ω and analysing power A y of the p → p → { p p } s π 0 reaction have been measured at COSY-ANKE at 353 MeV. The final proton pair was detected at very low excitation energy, leading to an S -wave diproton, denoted here as { p p } s . The angular dependence of both d σ / d Ω and A y can be described in terms of s - and d -wave pion production. By using phase information from elastic pp scattering, unique solutions are derived for the corresponding amplitudes only as a result of the combined analysis of both experimental observables. The large d -wave term thus obtained is important for the tests of the current state-of-the-art chiral perturbation theory approach. The amplitudes will also help towards determining the isospin dependence of pion production in nucleon–nucleon collisions with diproton formation.

In order to test chiral perturbation theory and establish links between p-wave pion production in nucleon–nucleon collisions and low energy three-nucleon scattering, an extensive programme of experiments on pion production is currently underway at COSY-ANKE. The final proton pair is measured at very low excitation energy, leading to an S-wave diproton, denoted here as {pp}s. By using a deuterium target we have obtained data on the differential cross section and analysing power of the quasi-free p→n→{pp}sπ− reaction at 353 MeV. The spectator proton psp was either measured directly in silicon tracking telescopes or reconstructed using the momentum of a detected π−. Both observables can be described in terms of s-, p-, and d-wave pion production amplitudes. Taken together with the analogous data on the p→p→{pp}sπ0 reaction, full partial wave decompositions of both processes were carried out.

The ratios of the cross sections for ϕ-meson production induced by 2.83-GeV protons on Cu, Ag, and Au nuclei to the respective cross section for C nuclei were measured at the ANKE-COSY facility in the momentum range of 0.6–1.6 GeV/c and the angular range of 0°–8°. The product ϕ mesons were identified by their decay ϕ → K+K−. The procedure used to separate kaon pairs was described in detail, and all sources of the background and their contribution to the resulting error in the values found for the above cross-section ratios were analyzed. The A dependence of the cross section for ϕ-meson production was shown to obey the A0.56±0.03 law. The total width of the ϕ meson at a normal nuclear density was extracted from a comparison of the measured cross-section ratios with the results of calculations based on two theoretical models. The resulting width value exceeds substantially both the vacuum width and the width expected in the absence of the nuclear-matter effect on the properties of the ϕ meson.

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 -> He-3 X at a proton be ...

COSY has a history of highly successful operation of cooled beams and internal targets both with and without polarization and as such it constitutes a unique facility for hadronic probes on a world-wide scale. Starting from meson production and nucleon-nucleon scattering more and more experience in polarized beam/target manipulation and polarimetry is gained. Extending polarization physics to antiprotons requires pre-studies at COSY to be continued at the antiproton decelerator AD at CERN. As a long-term perspective, the search for electric dipole moments of the proton, deuteron, and 3He in a dedicated storage ring could provide a new method to push the limits in the quest for CP violation searches beyond the Standard Model.

A spinfilter, the most important component of a Lamb-shift polarimeter, can be used to produce a beam of metastable hydrogen (deuterium) atoms in one hyperfine state (α1, α2 and together with the Sona transition β3). As function of a magnetic field separated transitions between the 2S1/2 metastable hyperfine states seem to be observable as well as single transitions into the short-lived 2P1/2 and 2P3/2 states. The Breit-Rabi diagrams for these states can be measured with good precision. Furthermore, the hyperfine splittings and the Lamb shift can be observed as well. Application of this method to anti-hydrogen atoms are suggested.

The differential cross section and deuteron analysing powers of the $$ \vec d $$ p → {pp}n charge-exchange reaction have been measured with the ANKE spectrometer at the COSY storage ring. Using a deuteron beam of energy 1170MeV, data were obtained for small momentum transfers to a {pp} system with low excitation energy. A good quantitative understanding of all the measured observables is provided by the impulse approximation using known neutron-proton amplitudes. The proof of principle achieved here for the method suggests that measurements at higher energies will provide useful information in regions where the existing np database is far less reliable.

A first storage cell for the Polarized Internal gas Target (PIT) of the ANKE facility at COSY was produced from a Teflon-coated pure Aluminum foil and successfully used in the double polarized experiment with a 1.2 GeV polarized deuteron beam carried out at the COSY accelerator in January 2007. Prior to this experiment, the minimum possible cross section of the storage-cell beam tube at the interaction point at ANKE was determined, based on the COSY beam profile at different beam formation stages. Electron cooling combined with stacking and stochastic cooling have been studied as well. Experiments with N2 gas in the storage cell to simulate the background produced by beam interaction with the aluminum cell walls were performed. The analysis of the [Formula: see text] and [Formula: see text] reactions showed that events from the extended target can be clearly identified in the ANKE detector system. Taking into account the known intensity of the Atomic Beam Source (ABS), the expected target density in the experiment with a storage-cell beam tube of 15hor × 20vert × 390long mm3 and a 130 mm long feeding tube with 15 mm diameter reach values of 3.2 × 1013 at/cm2. The polarization, measured by the np → dπ0 reaction with the storage-cell, was 0.75 ± 0.06.

The cross sections for the p p → p p K + 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 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 K 0 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 K 0 K ¯ 0 threshold, the low mass behaviour suggests that isospin-zero production is dominant.

The p p → { p p } s π 0 differential cross section has been measured with the ANKE spectrometer at COSY-Julich for seven proton beam energies T p between 0.51 and 1.97 GeV. By selecting proton pairs with an excitation energy of less than 3 MeV it is ensured that the final { p p } s system is in the S 0 1 state. In the measured region of θ p p cm ≲ 18 ° , 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 Δ ( 1232 ) excitation, and a minimum at 1.4 GeV. Some of these features are similar to those observed for the spin–isospin partner reaction, p p → d π + . 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.

The pp ! pK + Y 0 reaction has been studied for hyperon masses m(Y 0 ) � 1540MeV/c 2 at COSY-Julich by using a 3.65GeV/c circulating proton beam incident on an in- ternal hydrogen target. Final states comprising two protons, one positively charged kaon and one negatively charged pion have been identified with the ANKE spectrom- eter. Such configurations are sensitive to the production of the ground stateand � 0 hyperons as well as the � 0 (1385) and �(1405) resonances. Applying invariant- and missing-mass techniques, the two overlapping excited states could be well sep- arated, though with limited statistics. The shape and position of the �(1405) distri- bution, reconstructed cleanly in the � 0 � 0 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 �(1405) to be a two-state resonance.

The observed variation of the total cross section for the dp -> He-3 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 He-3 state. The interpretation can be investigated further through measurements of the deuteron or proton analysing powers and/or spin-correlations. (C) 2007 Elsevier B.V. All rights reserved.

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 + π + correlated pairs, can all be well described using consistent values of the total cross sections for the p p → K + p Λ , p p → K + p Σ 0 , and p p → K + n Σ + reactions. While the resulting values for Λ and Σ 0 production are in good agreement with world data, our value for the total Σ + production cross section, σ ( p p → K + n Σ + ) = ( 2.5 ± 0.6 stat ± 0.4 syst ) μb at an excess energy of e = 129 MeV , could only be reconciled with other recently published data if there were a highly unusual near threshold behaviour.

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 pp → ppϕ and quasi–free pn → dϕ reactions have been studied at the Cooler Synchrotron COSY–Jülich, using the internal beam and the ANKE facility. Total cross sections in the pp entrance channel have been determined at three excess energies ∊ in the range of 18.5–75.9 MeV. In case of the pn entrance channel the energy dependence of the cross section up to 80 MeV has been extracted by exploiting the intrinsic momentum of the neutron inside a deuterium target. Taken together with data for ω–production, a significant enhancement of the ϕ/ω ratio for both entrance channels of a factor 8 is found compared to predictions based on the Okubo–Zweig–Iizuka rule.

Kℓ4 decays have several features of interest: they allow an accurate measurement of ππ -scattering lengths; they provide the best source for the determination of some low-energy constants of χ PT; one form factor is directly related to the chiral anomaly, which can be measured here. We present a dispersive treatment of Kℓ4 decays that provides a resummation of ππ - and Kπ -rescattering effects. The free parameters of the dispersion relation are fitted to the data of the high-statistics experiments E865 and NA48/2. The matching to χ PT at NLO and NNLO enables us to determine the LECs L1r , L2r and L3r . With recently published data from NA48/2, the LEC L9r can be determined as well. In contrast to a pure chiral treatment, the dispersion relation describes the observed curvature of one of the form factors, which we understand as a rescattering effect beyond NNLO.

The preservation of the nuclear polarization of hydrogen atoms during the recombination to molecules was observed on different surface materials in the temperature range from 45 to 100 K and for magnetic fields up to 1 T. On a gold and a fused quartz surface, the expected molecular polarization of about 50% or lower of the atomic polarization was measured, while a surface layer of perfluoropolyether (Fomblin) shows a nearly complete preservation (at least 97%) of the atomic polarization during the recombination process. Further experiments have the possibility of storing polarized deuterium molecules and to use them in nuclear-fusion installations. Another application might be the production of polarized substances for enhanced NMR techniques.

The preservation of the nuclear polarization of hydrogen atoms during the recombination to molecules was observed on different surface materials in the temperature range from 45 to 100 K and for magnetic fields up to 1 T. On a gold and a fused quartz surface, the expected molecular polarization of about 50% or lower of the atomic polarization was measured, while a surface layer of perfluoropolyether (Fomblin) shows a nearly complete preservation (at least 97%) of the atomic polarization during the recombination process. Further experiments have the possibility of storing polarized deuterium molecules and to use them in nuclear-fusion installations. Another application might be the production of polarized substances for enhanced NMR techniques.

The charge exchange of vector polarised deuterons on a polarised hydrogen target has been studied in a high statistics experiment at the COSY-ANKE facility at a deuteron beam energy of T d = 726 MeV . By selecting two fast protons at low relative energy E p p , the measured analysing powers and spin correlations are sensitive to interference terms between specific neutron–proton charge-exchange amplitudes at a neutron kinetic energy of T n ≈ 1 2 T d = 363 MeV . An impulse approximation calculation, which takes into account corrections due to the angular distribution in the diproton, describes reasonably the dependence of the data on both E p p and the momentum transfer. This lends broad support to the current neutron–proton partial wave solution that was used in the estimation.

A new method to determine the spin tune is described and tested. In an ideal planar magnetic ring, the spin tune - defined as the number of spin precessions per turn - is given by $\nu_s = \gamma G$ (gamma is the Lorentz factor, $G$ the magnetic anomaly). For 970 MeV/c deuterons coherently precessing with a frequency of ~120 kHz in the Cooler Synchrotron COSY, the spin tune is deduced from the up-down asymmetry of deuteron carbon scattering. In a time interval of 2.6 s, the spin tune was determined with a precision of the order $10^{-8}$, and to $1 \cdot 10^{-10}$ for a continuous 100 s accelerator cycle. This renders the presented method a new precision tool for accelerator physics: controlling the spin motion of particles to high precision is mandatory, in particular, for the measurement of electric dipole moments of charged particles in a storage ring., Comment: 6 pages, 6 figures

Exclusive and kinematically complete measurements of the double pionic fusion to He-3 have been performed in the energy region of the so-called ABC effect, which denotes a pronounced low-mass enhan ...

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 table

The pp → ppπ 0 differential cross section has been measured with the ANKE spectrometer at COSY–Julich for pion cms angles between 0 ◦ and 15.4 ◦ at a proton beam energy of 0.8 GeV. The selection of diproton pairs with an excitation energy Epp < 3 MeV ensures that the final pp system is dominantly in the spin-singlet 1 S0 state. The kinematics are therefore very similar to those of pp → dπ + but with different spin and isospin transitions. The cross sections are over two orders of magnitude smaller than those of pp → dπ + and show a forward dip that is even stronger than that seen at lower energies. The results should provide a crucial extra test of pion production models in nucleon–nucleon collisions.

New data on ϕ -meson production in pp collisions have been obtained at the ANKE facility of COSY-Julich. These data will provide the energy dependence of the total cross section down to an excess energy of 19 MeV above threshold. In combination with the existing SPES-III and COSY-TOF results on ω -meson production the ϕ / ω production ratio at this low excess energy will be extracted. As an exciting new aspect an enhancement in the invariant ϕp mass spectrum is observed at a mass around 1.965 GeV / c 2 .

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., Baryons2004 Proceedings, 4 pages, 6 figures

The first measurement of the $pn\rightarrow d\omega$ total cross-section has been achieved at mean excess energies $Q\approx 28$ and 57 MeV by using a deuterium cluster-jet target. The momentum of the fast deuteron was measured in the ANKE spectrometer at COSY-Julich and that of the slow “spectator” proton $(p_{\rm {sp}})$ from the $pd\rightarrow p_{\rm {sp}}d\omega$ reaction in a silicon telescope placed close to the target. The cross-sections lie above those measured for $pp\rightarrow pp\omega$ but seem to be below theoretical predictions.

Results of a first experiment on (K+p) and (K+d) correlations from proton-carbon (pC) and proton-deuteron (pd) interactions at beam energies above and much below the threshold for elementary kaon production in nucleon-nucleon reactions ( TNN = 1580 MeV) are discussed. These data, obtained with the ANKE spectrometer at COSY-Julich, provide first direct evidence for K+ production via the two-step mechanism and an indication for a cluster mechanism. It is shown that both processes contribute significantly in pC collisions at 1200 MeV, while they are strongly suppressed at 2300 MeV and also in pd-interactions at 1344 MeV. It is emphasized that the underlying kinematics can be exploited to distinguish between these reaction mechanisms.

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}, 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

Quasi-free photoproduction of eta-mesons from the deuteron has been measured at the tagged photon facility of the Mainz microtron MAMI with the photon spectrometer TAPS for incident photon energies from the production threshold at 630 MeV up to 820 MeV. In a fully exclusive measurement eta-mesons and recoil nucleons were detected in coincidence. At incident photon energies above the production threshold on the free nucleon, where final state interaction effects are negligible, an almost constant ratio of sigma(n)/sigma(p)=0.66+/-0.10 was found. At lower incident photon energies the ratio rises due to re-scattering effects. The average ratio agrees with the value extracted from a comparison of the inclusive d(gamma,eta)X cross section to the free proton cross section via a participant - spectator model for the deuteron cross section (sigma(n)/sigma(p)=0.67+/-0.07). The angular dependence of the ratio agrees with the expected small deviation of neutron and proton cross section from isotropy due to the influence of the D13(1520) resonance. The energy dependence of the ratio in the excitation energy range of the S11(1535) resonance disfavors model predictions which try to explain this resonance as K-Sigma bound state., Comment: 10 pages, 9 figures, Eur. Phys. Journal A, accepted

The nonmesonic decay of Λ hyperons has been investigated by the observation of delayed fission of heavy hypernuclei produced in proton–U collisions at Tp = 1.9 GeV. The lifetime of heavy hypernuclei with masses A ≈ 220 of the present work, τΛ = (138 ± 6 (stat) ± 17 (syst)) ps, is the most accurate result obtained in proton and antiproton induced collisions on a U target so far. This result together with the values of the lifetime measured previously by the COSY-13 collaboration, for p+Bi (161 ± 7(stat) ± 14(syst)) ps and p+Au (130 ± 13(stat) ± 15(syst)) ps, gives an average value for the lifetime of heavy hypernuclei with masses A > 180: τΛ = (145 ± 11) ps. This value was obtained by averaging the above lifetimes with weights taken as reciprocals of the sum of squares of statistical and systematic errors. By comparing the lifetimes of light and heavy hypernuclei we found—on the confidence level of 0.98—a violation of the phenomenological ΔI = 1/2 rule known from the weak mesonic decays of strange particles.

The photoproduction of eta-mesons from H-2 and He-4 has been studied for energies close to the production thresholds. The experiments were carried out with the tagged photon beam of the Mainz MAMI accelerator. The eta-mesons were detected via their two photon decays with the electromagnetic calorimeter TAPS. Total cross-sections, angular and momentum distributions of the eta-mesons have been determined for both reactions. The total cross-sections in the threshold region show a large enhancement over the predictions of a participant-spectator model, indicating significant final-state interaction effects. The results are compared to recent model calculations taking into account nucleon-nucleon and nucleon-eta final-state interaction effects on different levels of sophistication

The photoproduction of η-mesons from 2H and 4He has been studied for energies close to the production thresholds. The experiments were carried out with the tagged photon beam of the Mainz MAMI accelerator. The η-mesons were detected via their two photon decays with the electromagnetic calorimeter TAPS. Total cross-sections, angular and momentum distributions of the η-mesons have been determined for both reactions. The total cross-sections in the threshold region show a large enhancement over the predictions of a participant-spectator model, indicating significant final-state interaction effects. The results are compared to recent model calculations taking into account nucleon-nucleon and nucleon-η final-state interaction effects on different levels of sophistication.

The spectrometer ANKE has been put into operation at the accelerator COSY of the Forschungszentrum Julich in spring 1998. An initial scientific goal is to study K + -production in pA collisions at subthreshold energies far below the free NN-threshold at T p =1.58 GeV. This requires the identification of K + -mesons in a background of pions and protons, about 10 6 times more intense. In this paper the sophisticated detection system and the software procedures for kaon identification are described. With the help of TOF, energy-loss and range measurements as well as the track information from wire chambers, it is possible to measure d 2 σ/ d Ω d p for deep subthreshold K + production at beam energies down to T p =1.0 GeV.

In order to provide the experimental tools necessary to carry out few-nucleon reaction studies with polarized beams and targets at the medium energy storage ring COSY at Julich, our group is currently developing a polarized internal storage-cell gas target for first use at the magnetic spectrometer ANKE. In this paper we give an overview about currently relevant aspects of the polarized deuteron breakup experiment.