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The strong-interaction effects both in pionic hydrogen and deuterium atoms have been re-determined with improved precision. The hadronic shift and width in pionic hydrogen together with the hadronic shift in pionic deuterium constitute a one-fold constraint for the two independent pion-nucleon scattering lengths. Furthermore, the hadronic width in pionic deuterium measures the transition strength of s-wave pions on an isoscalar nucleon-nucleon pair which is an independent quantity not related to the pion-nucleon scattering lengths. The experiment was performed at the Paul Scherrer Institute by stopping a high-intensity low-energy pion beam in gaseous targets using the cyclotron trap. The X-rays emitted by the πH and πD atoms were analysed with a high resolution Bragg spectrometer equipped with spherically bent crystals. The pion-nucleon scattering lengths and other physical quantities extracted from the atom data are in good agreement with the results obtained from pionnucleon and nucleon-nucleon scattering experiments and confirm that a consistent picture is achieved for the low-energy pion-nucleon sector with respect to the expectations of chiral perturbation theory.

The strong interaction shift ε1sπD and broadening Γ1sπD in pionic deuterium have been remeasured with high statistics by means of the πD(3p − 1s) X-ray transition using the cyclotron trap and a high-resolution crystal πD πD spectrometer. Preliminary results are ε1sπD = (−2325 ± 31) meV (repulsive) and Γ1sπD(1171+23-49) meV which yields for the πD scattering length aπD = [−(24.8 ± 0.3) + i (6.3-0.3+0.1)] · 10−3 mπ−1. From the imaginary part the threshold parameter for pion production is determined to be α = (252−11+15) µb.

Abstract: K X-rays from pionic hydrogen and deuterium as well as muonic hydrogen have been measured using a highresolution crystal spectrometer at the _E5 beam line of the Paul Scherrer Institut. From the ground-state level shifts and broadenings of the hydrogen isotopes, caused by the strong interaction, low-energy parameters of QCD become accessible as are the pion-nucleon scattering lengths and the threshold production strength of pions in nucleon-nucleon collisions. Muonic hydrogen allows important insights in the de-excitation cascade of such exotic atoms, the understanding of which is essential for a precision determination of the above-mentioned quantities. First experimental results are discussed in the context of recent results from theoretical e_orts within the approach of chiral pertubation theory and atomic cascade calculations. [Copyright &y& Elsevier]

The total cross-section for the dd $ \rightarrow$ 4He K+ K- reaction has been measured at a beam momentum of 3.7GeV/ c, corresponding to an excess energy of 39MeV, which is the maximum possible at the Cooler Synchrotron COSY-Jülich. 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_{{{\rm tot}}}^{}$ < 14 pb, which brings into question the viability of investigating the dd $ \rightarrow$ 4He a0(980) reaction as a means of studying isospin violation. [ABSTRACT FROM AUTHOR]

The line shape of the (3 p − 1 s) X-ray transition in muonic hydrogen was measured for the first time with a high-resolution crystal spectrometer. The assumption of a statistical population of the hyperfine levels was directly confirmed by experiment, and a measured value for the hyperfine splitting is reported. An X-ray line broadening due to Doppler effect could be clearly identified and attributed to different Coulomb de-excitation transitions which precede the measured radiative transition. The results allow a decisive test of advanced cascade model calculations and establish an alternative and “model free” method to extract the strong-interaction parameters from pionic hydrogen data. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The reaction pp → dπ + η has been measured at a beam energy of T p = 2.65 GeV ( p p = 3.46 GeV/ c) using the ANKE spectrometer at COSY-Julich. The missing-mass distribution of the detected dπ + pairs exhibits a peak around the η mass on top of a strong background of multipion pp → dπ +( nπ) events. The differential cross section d 4 σ/ dΩd dΩ π + dp d dp π + for the reaction pp → dπ + η has been determined model independently for two regions of phase space. Employing a dynamical model for the a production allows one then to deduce a total cross section of σ( pp → da → dπ + η) = 1.1 ± 0.3stat ± 0.7syst µb for the production of π + η via the scalar a (980) resonance and σ( pp → dπ + η) = 3.5 ± 0.3stat ± 1.0syst µb for the nonresonant production. Using the same model as for the interpretation of recent results from ANKE for the reaction $$pp \to dK^ + \bar K^0 $$ , the ratio of the total cross sections is $$\sigma (pp \to d(K^ + \bar K^0 )_{L = 0} )/\sigma (pp \to da_0^ + \to d\pi ^ + \eta ) = 0.029 \pm 0.008_{stat} \pm 0.009_{syst} $$ , which is in agreement with branching ratios in the literature. [ABSTRACT FROM AUTHOR]

The production of K+-mesons inpA(A= D, C, Cu, Ag, Au) collisions has been investigated at the COoler SYnchrotron COSY-Jülich for beam energiesTp = 1.0-2.3 GeV. Double differential inclusivepC cross-sections at forward angles ?{K^+}<12° as well as the target mass dependence of the K+ momentum spectra have been measured with the ANKE spectrometer. Far below the freeNNthreshold atTNN = 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 the K+-mesons can be deduced. UsingpNcross-section parameterisations from the literature and our measuredpD data we derive a cross-section ratio s(pn?K+ X)/s(pp?K+ X) ~ (3-4). [ABSTRACT FROM AUTHOR]

: 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-Jülich, 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. [ABSTRACT FROM AUTHOR]

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 pK using the ANKE spectrometer at COSY-Ju¨lich. The strong suppression in the ratios observed for pK<200–250 MeV/c may 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 VK0&ap;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 VK0 to better than 3 MeV. [Copyright &y& Elsevier]

We report on the design, construction, and magnetic field measurements of a system of high field sextupole magnets made from NdFeB compounds. The magnets are utilized as a focusing system for neutral hydrogen (or deuterium) atoms in a polarized atomic beam source based on Stern-Gerlach spin separation. Each magnet consists of 24 segments of permanently magnetized material differing in remanence and coercivity to reduce demagnetization. According to quadratic extrapolation to the pole tip the magnetic flux density reaches values of up to B[sub 0]=1.69 T. Three-dimensional field calculations using the MAFIA code were carried out to optimize the magnet performance and to avoid demagnetization by selecting appropriate materials for the individual segments. Measurements of the radial, azimuthal, and longitudinal magnetic flux density distributions were carried out by means of a small Hall probe (100x200x15 μm[sup 3]). The measurements with the small probe permitted to extract experimentally higher order multipole components very close (∼100 μm) to the inner surface. Experimental values obtained are compared to predictions based on MAFIA calculations and on the Halbach formalism. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: A polarized atomic beam source was developed for the polarized internal storage-cell gas target at the magnet spectrometer ANKE of COSY-Jülich. The intensities of the beams injected into the storage cell, measured with a compression tube, are hydrogen atoms/s (two hyperfine states) and deuterium atoms/s (three hyperfine states). For the hydrogen beam the achieved vector polarizations are . For the deuterium beam, the obtained combinations of vector and tensor ( ) polarizations are (with a constant ), and or (both with vanishing ). The paper includes a detailed technical description of the apparatus and of the investigations performed during the development. This source has been very successfully used for single and double polarization measurements at ANKE as well as for studies of the polarization of recombining hydrogen molecules. [Copyright &y& Elsevier]

The production of cp mesons in proton collisions with C, Cu, Ag, and Au targets has been studied via the φ → 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 &pji; width, and the differential cross section for φ-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 φ width, which corresponds to an effective φN absorption cross section in the range of 14-21 mb. [ABSTRACT FROM AUTHOR]

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, 2.650 GeV, using the ANKE spectrometer at COSY-Jülich. 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. [ABSTRACT FROM AUTHOR]

The spectrometer ANKE has been put into operation at the accelerator COSY of the Forschungszentrum Ju¨lich 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 Tp=1.58 GeV. This requires the identification of K+-mesons in a background of pions and protons, about 106 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 d2σ/dΩ dp for deep subthreshold K+ production at beam energies down to Tp=1.0 GeV. [Copyright &y& Elsevier]

An unusual but effective way to determine at threshold the dpi<-->NN transition strength alpha is to exploit the hadronic ground-state broadening Gamma(1s) in pionic deuterium, accessible by x-ray spectroscopy. The broadening is dominated by the true absorption channel dpi(-)-->nn, which is related to s-wave pion production pp-->dpi(+) by charge symmetry and detailed balance. Using the exotic atom circumvents the problem of Coulomb corrections to the cross section as necessary in the production experiments. Our dedicated measurement finds Gamma(1s)=(1171(-49)(+23)) meV yielding alpha=(252(-11)(+5)) microb.

The cross section for inclusive multipion production in the pp-->ppX reaction was measured at COSY-ANKE at four beam energies, 0.8, 1.1, 1.4, and 2.0 GeV, for low excitation energy in the final pp system, such that the diproton quasiparticle is in the 1S0 state. At the three higher energies, the missing-mass M&#95;{X} spectra show a strong enhancement at low M&#95;{X}, corresponding to an Abashian-Booth-Crowe effect that moves steadily to larger values as the energy is increased. Despite the missing-mass structure looking very different at 0.8 GeV, the variation with M&#95;{X} and beam energy are consistent with two-pion production being mediated through the excitation of two Delta(1232) isobars, coupled to S and D states of the initial pp system. There is no sign of any resonancelike structure in the energy dependence of the type recently observed for the pn-->dpi;{0}pi;{0} total cross section.

The (3p-1s) x-ray transition to the muonic hydrogen ground state was measured with a high-resolution crystal spectrometer. A Doppler effect broadening of the x-ray line was established which could be attributed to different Coulomb deexcitation steps preceding the measured transition. The assumption of a statistical population of the hyperfine levels of the muonic hydrogen ground state was directly confirmed by the experiment, and measured values for the hyperfine splitting can be reported. The results allow a decisive test of advanced cascade model calculations and establish a method to extract fundamental strong-interaction parameters from pionic hydrogen experiments.

The fundamental reaction pp-->{pp}&#95;{s}gamma, where {pp}&#95;{s} is a proton pair with low excitation energy, has been observed with the ANKE spectrometer at COSY-Jülich for proton beam energies of T&#95;{p}=0.353, 0.500, and 0.550 GeV. This is equivalent to photodisintegration of a free 1S0 diproton for photon energies E&#95;{gamma} approximately T&#95;{p}/2. The differential cross sections measured for c.m. angles 0 degrees gammad is on the 10;{-3}-10;{-2} level. The increase of the pp-->{pp}&#95;{s}gamma cross section with T&#95;{p} might reflect the influence of the Delta(1232) excitation.

The quasifree pn-->dvarphi reaction has been studied at the Cooler Synchrotron COSY-Jülich, 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 varphi 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 a 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.

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.

Indications for the production of a neutral excited hyperon in the reaction pp --> pK+Y0* are observed in an experiment performed with the ANKE spectrometer at COSY-Jülich at p(beam) = 3.65 GeV/c. Two final states were investigated simultaneously, viz. Y0* --> 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(Y0*) = (1480 +/-15) MeV/c2 and gamma(Y0*) = (60 +/- 15) MeV/c2. The production cross section for Y0* decaying through these channels is of the order of few hundred nanobarns. Since the isospin of the Y0* has not been determined here, it could either be an observation of the sigma(1480), a one-star resonance of the Particle Data Group 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 Y0* may be of exotic nature.

The reaction pp-->dK+K(-)0 has been investigated at an excess energy of Q=46 MeV above the K+K(-)0 threshold with ANKE at the cooler synchrotron COSY-Jülich. From the detected coincident dK(+) pairs, about 1000 events with a missing K(-)0 were identified, corresponding to a total cross section of sigma(pp-->dK+K(-)0)=[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 a(+)0 (980)-resonance production.

The Irkutsk province and the Republic of Buryatia which are a part of the Baikal Region (Siberia) were studied for environmental iodine balance. The water and local foodstuffs were found to show low iodine levels (they being 0.2 to 6.9 micrograms/l). In children, iodine deficiency was detected in 60-87% of the total number examined. There was a relationship between of the severity of neurological symptoms, the onset of thyroid diseases, general morbidity, physical development, iodine levels in the body. It is concluded that iodine deficiency has a great impact on the development of the regional pathology in children.