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The reaction $p + d \rightarrow p + d + X$ was studied at 0.8-2.0 GeV proton beam energies with the ANKE magnetic spectrometer at the COSY synchrotron storage ring. The proton-deuteron pairs emerging with high momenta, 0.6-1.8 GeV/$c$, were detected at small angles with respect to the proton beam. Distribution over the reaction missing mass $M_x$ reveals a local enhancement near the threshold of the pion pair production specific for the so-called ABC effect. The enhancement has a structure of a narrow bump placed above a smooth continuum. The invariant mass of the $d\pi\pi$ system in this enhancement region exhibits a resonance-like peak at $M_{d\pi\pi} \approx 2.36$ GeV/$c^2$ with the width $\Gamma \approx 0.10$ GeV/$c^2$. A possible interpretation of these features is discussed., Comment: 14 pages, 16 figures, submitted to Eur. Phys. J. A. v2: Added references [42,43] in section IV.A. v3: revised version according to referee remarks v4: revised version according to referee remarks

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.

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 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.

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 → 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.

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.

The d+d->alpha+eta reaction has been investigated near threshold using the ANKE facility at COSY-Juelich. Both total and differential cross sections have been measured at two excess energies, Q=2.6 MeV and 7.7 MeV, with a subthreshold measurement being undertaken at Q=-2.6 MeV to study the physical background. While consistent with isotropy at the lower energy, the angular distribution reveals a pronounced anisotropy at the higher one, indicating the presence of higher partial waves. Options for the decomposition into partial amplitudes and their consequences for determination of the s-wave eta-alpha scattering length are discussed.

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

The transverse spin correlations ${A}_{x,x}$ and ${A}_{y,y}$ have been measured in the $\stackrel{P\vec}{d}\stackrel{P\vec}{p}\ensuremath{\rightarrow}{p}_{\text{spec}}{{pp}}_{s}{\ensuremath{\pi}}^{\ensuremath{-}}$ reaction at COSY-ANKE at 353 MeV per nucleon. Here ${{pp}}_{s}$ denotes a proton-proton pair with low excitation energy, which is dominantly in the ${}^{1}{S}_{0}$ state. By measuring three protons in the final state it was possible to extract events where there was a spectator proton ${p}_{\text{spec}}$ so that the reaction could be interpreted in terms of quasifree $\stackrel{P\vec}{n}\phantom{\rule{0.16em}{0ex}}\stackrel{P\vec}{p}\ensuremath{\rightarrow}{{pp}}_{s}{\ensuremath{\pi}}^{\ensuremath{-}}$. The proton and neutron analyzing powers in this reaction were also deduced from this data set by averaging over the polarizations of the deuteron beam and hydrogen target, respectively. The values of ${A}_{y}$ were shown to be consistent with a refined analysis of our earlier results obtained with a polarized proton incident on a deuterium target. Taking these data in combination with our previous measurements of the differential cross sections and analyzing powers in the $\stackrel{P\vec}{p}p\ensuremath{\rightarrow}{{pp}}_{s\phantom{\rule{0.16em}{0ex}}}{\ensuremath{\pi}}^{0}$ reaction, a more robust partial wave decomposition was achieved. Three different acceptable solutions were found, and the only way of resolving this ambiguity without further theoretical input would be through a measurement of the mixed spin-correlation parameter ${A}_{x,z}$.

The $pp\ensuremath{\rightarrow}pp{K}^{+}{K}^{\ensuremath{-}}$ reaction was measured below the $\ensuremath{\phi}$ threshold at a beam energy of 2.568 GeV using the COSY-ANKE magnetic spectrometer. By assuming that the four-body phase space is distorted only by the product of two-body final-state interactions, fits to a variety of one-dimensional distributions permit the evaluation of differential and total cross sections. The shapes of the distributions in the $Kp$ and $Kpp$ invariant masses are reproduced only if the ${K}^{\ensuremath{-}}p$ interaction is even stronger than that found at higher energy. The cusp effect in the ${K}^{+}{K}^{\ensuremath{-}}$ distribution at the ${K}^{0}{\overline{K}}^{0}$ threshold is much more clear and some evidence is also found for coupling between the ${K}^{\ensuremath{-}}p$ and ${\overline{K}}^{0}n$ channels. However, the energy dependence of the total cross section cannot be reproduced by considering only a simple product of such pairwise final-state interactions.

The production of phi mesons in proton collisions with C, Cu, Ag, and Au targets has been studied via the phi -> K+K- decay at an incident beam energy of 2.83 GeV using the ANKE detector system at COSY. For the first time, the momentum dependence of the nuclear transparency ratio, the in-medium phi width, and the differential cross section for phi meson production at forward angles have been determined for these targets over the momentum range of 0.6 - 1.6 GeV/c. There are indications of a significant momentum dependence in the value of the extracted phi width, which corresponds to an effective phi-N absorption cross section in the range of 14 - 21 mb., 9 pages, 5 figures

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., 8 pages with 2 eps figures

Spin observables in proton deuteron breakup reactions at low energies offer a rich testing ground for the modern theory of nuclear forces, the chiral effective field theory (EFT). In the three-nucleon continuum the experimental data and the theore tical predictions are today at variance. At the PAX facility at COSY we plan to make an extensive study of analyzing powers and spin correlation parameters in pd breakup reactions at low energies between 30 and 50 MeV, an energy range where previous measu rements are scarce and limited while three-nucleon effects are expected to be significant. Furthermore it is an ideal energy for the predictive power of chiral EFT to be tested. The longstanding physics question of the nature of three-nucleon forces will be studied with large coverage provided by an optimized silicon detector barrel, and flexibility utilizing the sampling method, a technique for direct comparison between experiment and theory developed specifically for the complex analysis of three-partic le final states. The proposed experiment will yield an independent determination of the low-energy constants D and E and enable tests of appearing three-nucleon interactions in chiral EFT, with possible implications also for the spectra of light nuclei.

The three big experiments at the Cooler Synchrotron COSY in Juelich (ANKE, WASA and TOF) permanently require an improvement of their data aquisition systems. We will use ANKE as an example for the overall structure of these data aquisition systems und the improvements in the last years.

Measurements of the pd{yields}p{sub sp}dK{sup +}K{sup -} reaction, where p{sub sp} is a spectator proton, have been undertaken at the Cooler Synchrotron COSY-Juelich by detecting a fast deuteron in coincidence with a K{sup +}K{sup -} pair in the ANKE facility. Although the proton beam energy was fixed, the moving target neutron allowed values of the nonresonant quasifree pn{yields}dK{sup +}K{sup -} total cross section to be deduced up to an excess energy {epsilon}{approx_equal}100 MeV. Evidence is found for the effects of K{sup -}d and KK final state interactions. The comparison of these data with those of pp{yields}ppK{sup +}K{sup -} and pp{yields}dK{sup +}K{sup 0} shows that all the total cross sections are very similar in magnitude.

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., 12 two-column pages, 12 figures, 1 table

For future few‐nucleon interactions studies with polarized beams and targets at COSY‐Julich, a polarized internal storage cell gas target was implemented at the magnetic spectrometer ANKE in summer 2005. First commissioning of the polarized Atomic Beam Source (ABS) at ANKE was carried out and some improvements of the system have been done. At the same time, storage‐cell tests to determine the COSY beam dimensions have been performed. In February 2005, a first storage cell prototype was implemented. It was made from an aluminum foil covered by a special PTFE suspension. In November 2005, tests were carried out with a storage cell using a polarized hydrogen beam from the ABS, electron cooling and stacking injection of the COSY beam at different deflection angles of the ANKE spectrometer magnet. An average target polarization of P=0.44±0.03 (November 2005 beamtime) was measured, while we expected about P=0.51–0.55 due to the availability of rf‐transition units in the ABS. The jet target thickness was measured as (1.5±0.1)⋅1011 atoms/cm2. In March 2006, measurements with unpolarized protons at T=831 MeV and an unpolarized H2 beam injected from a gas feeding system into the aluminum storage cell were carried out. The analysis of the pp → ppπ0 and pp → pnπ+ reactions showed that events from the extended target can be clearly identified in the ANKE forward detector system.

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 pp ! ppreaction has been studied at the Cooler Synchrotron COSY-Julich, using the internal beam and ANKE facility. Total cross sections have been determined at three excess energiesnear the production threshold. The differential cross section closest to threshold at � � 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! production, a significant enhancement of the �=! ratio of a factor 8 is found compared to predictions based on the Okubo-Zweig-Iizuka rule.

The pp--ppphi reaction has been studied at the Cooler Synchrotron COSY-Jülich, 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 ppomega 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.

At the ANKE facility of COSY Julich, the reactions pp→ppφ and pn→dφ have been investigated. Data for the total cross section in the pp entrance channel have been obtained at excess energies of 19 MeV, 35 MeV and 76 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 target neutron using a deuterium target. The new φ data combined with the existing data on ω‐meson production provides the φ/ω production ratio in both, the pp‐ and pn‐channels. The ratios of both channels are found to be similar and about eight times larger than the ratio based on Okubo‐Zweig‐Iizuka (OZI) rule.

Vector and tensor analysing powers of the d(pol)p->(pp)n (charge-exchange) and d(pol)p->(pn)p (non-charge-exchange) breakup reactions have been measured with the ANKE spectrometer at the COSY ring at a deuteron beam energy of 1170 MeV for small momentum transfers to the low excitation energy (pp) or (pn) systems. A quantitative understanding of the values of A_xx and A_yy for the charge-exchange reaction is provided by impulse approximation calculations. The data suggest that spin-flip isospin-flip transitions, which dominate the charge-exchange breakup of the deuteron, are also important in the non-charge-exchange reaction., 10 pages, 4 figures

A measurement of the analyzing power A(y) of the p-->d--> (p p) + n reaction was carried out at the ANKE spectrometer at COSY at beam energies of 0.5 and 0.8 GeV by detection of a fast forward proton pair of small excitation energy E(pp) < 3 MeV. The S-wave dominance in the fast diproton is experimentally demonstrated in this reaction. While at T(p) = 0.8 GeV the measured analyzing power almost vanishes, it rises to nearly unity at T(p) = 0.5 GeV for neutrons emitted at theta(c.m.)(n) = 167 degrees. The results are compared with a model taking into account one-nucleon exchange, single scattering, and Delta(1232) excitation in the intermediate state. The model describes fairly well the unpolarized cross section obtained earlier and the analyzing power at 0.8 GeV; it fails to reproduce A(y) at 0.5 GeV.

A measurement of the analyzing power A(y) of the p--d--(p p) + n reaction was carried out at the ANKE spectrometer at COSY at beam energies of 0.5 and 0.8 GeV by detection of a fast forward proton pair of small excitation energy E(pp)3 MeV. The S-wave dominance in the fast diproton is experimentally demonstrated in this reaction. While at T(p) = 0.8 GeV the measured analyzing power almost vanishes, it rises to nearly unity at T(p) = 0.5 GeV for neutrons emitted at theta(c.m.)(n) = 167 degrees. The results are compared with a model taking into account one-nucleon exchange, single scattering, and Delta(1232) excitation in the intermediate state. The model describes fairly well the unpolarized cross section obtained earlier and the analyzing power at 0.8 GeV; it fails to reproduce A(y) at 0.5 GeV.

A kinematically complete study of the pd ? (pp)sn reaction with forward emission of an S-wave proton pair (pp)s has been performed at six beam energies 0.6, 0.7, 0.8, 0.95, 1.35 and 1.9 GeV. The experiment was carried out at the ANKE spectrometer installed at the internal beam of the proton synchrotron COSY (J?lich). The 3-momenta of both final state protons have been measured and events with a relative proton energy less than 3 MeV were selected as 1S0 diprotons. The differential cross sections of such pair production averaged over the c.m. polar angle of the total momentum of the pair in the range 0??8.1? have been obtained. A comparison of the result with a theoretical model based on the mechanism of pd-backward elastic scattering is described as well.

The vector and tensor polarizations of a deuteron beam have been measured using elastic deuteron-carbon scattering at 75.6 MeV and deuteron-proton scattering at 270 MeV. After acceleration to 1170 MeV inside the COSY ring, the polarizations of the deuterons were checked by studying a variety of nuclear reactions using a cluster target at the ANKE magnet spectrometer placed at an internal target position of the storage ring. All these measurements were consistent with the absence of depolarization during acceleration and provide a number of secondary standards that can be used in subsequent experiments at the facility., Comment: 12 pages, 13 figures

Values of the proton analysing power in the $pd\to{}^{3}\textrm{He}\,\pi^0/^{3}\textrm{H}\,\pi^+$ reactions at 350-360~MeV per nucleon were obtained by using a polarised proton beam incident on a deuterium cluster-jet target and with a polarised deuteron beam incident on a target cell filled with polarised hydrogen. These results have a much larger angular coverage than existing data. First measurements are also presented of the deuteron vector analysing power and the deuteron-proton spin correlations. Data were also obtained on the deuteron-proton spin correlation and proton analysing power at small angles at 600~MeV per nucleon, though the angular coverage at this energy was much more restricted even when using a deuteron beam. By combining the extrapolated values of the spin correlations to the forward or backward directions with published measurements of the deuteron tensor analysing powers, the relative phases between the two non-vanishing amplitudes were evaluated., Comment: 5 pages, 5 figures