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Search Results: 1 - 10 of 149750 matches for " H. Stroeher "
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Nonmesonic decay of the Lambda-hyperon in hypernuclei produced by p+Au collisions
B. Kamys,P. Kulessa,H. Ohm,K. Pysz,Z. Rudy,H. Stroeher,W. Cassing
Physics , 2000, DOI: 10.1007/s100500170089
Abstract: The lifetime of the Lambda-hyperon for the nonmesonic decay Lambda N ---> N N has been determined by a measurement at COSY Juelich of the delayed fission of heavy hypernuclei produced in proton - Au collisions at T_p=1.9 GeV. It is found that heavy hypernuclei with mass numbers A= 180 +- 5 and atomic numbers Z= 74 +-2 fission with a lifetime 130ps +- 13ps (stat.) +- 15ps (syst.) . This value together with the results obtained for other heavy hypernuclei in previous investigations indicates (on the confidence level of 0.9) a violation of the phenomenological Delta I = 1/2 rule for Lambda N ---> NN transitions as known from the weak mesonic decays of kaons and hyperons. PACS: {13.30.-a}{Decays of baryons} {13.75.Ev}{Hyperon-nucleon interaction} {21.80}{Hypernuclei} {25.80.Pw}{Hyperon-induced reactions}
The lifetime of the Lambda hyperon bound in hypernuclei produced by p+U collisions
P. Kulessa,W. Cassing,L. Jarczyk,B. Kamys,H. Ohm,K. Pysz,Z. Rudy,H. Stroeher
Physics , 2001,
Abstract: The nonmesonic decay of the Lambda hyperon has been investigated by observation of delayed fission from heavy hypernuclei produced in proton-U collisions at Tp = 1.9 GeV. The lifetime of heavy hypernuclei with masses A approximately 220 obtained in the present work, i.e. tau = 138 +- 6 (stat.) +-m 17 (syst.) ps, is the most accurate result for heavy hypernuclei produced in proton and antiproton induced collisions on a U target so far. PACS: {13.30.-a}{Decays of baryons} {13.75.Ev}{Hyperon-nucleon interaction} {21.80}{Hypernuclei} {25.80.Pw}{Hyperon-induced reactions}
Luminosity determination for the pd reaction at 2.14 GeV with WASA-at-COSY
C. Zheng,M. Buescher,P. Fedorets,V. Hejny,H. Stroeher,H. Xu,X. Yuan
Statistics , 2011, DOI: 10.1088/1674-1137/36/7/007
Abstract: The luminosity for a WASA-at-COSY experiment involving the pd reaction at 2.14 GeV proton-beam energy is determined by the forward pd elastic scattering, which yields an average beam-on-target value of [5.2\pm0.3(stat)\pm0.3(syst)]*10^{30} s^{-1}cm^{-2}. In addition, the forward pd elastic-scattering angular distribution is obtained with four-momentum transfer squared -t between 0.16 (GeV/c)^{2} and 0.78 (GeV/c)^{2} at this beam energy, which is compared with other experimental data and the pd double scattering model.
Contribution of a Genomic Accessory Region Encoding a Putative Cellobiose Phosphotransferase System to Virulence of Streptococcus pneumoniae
Lauren J. McAllister, Abiodun D. Ogunniyi, Uwe H. Stroeher, James C. Paton
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0032385
Abstract: Streptococcus pneumoniae (the pneumococcus) is a formidable human pathogen, responsible for massive global morbidity and mortality. The ability to utilize carbohydrates in a variety of host niches appears to be integral to pneumococcal pathogenesis. In this study we investigated a genomic island, which includes a ROK family protein, a putative cellobiose phosphotransferase system (PTS) and a putative sulfatase. This accessory region is widespread in the pneumococcus in strains of various serotypes and levels of virulence. We have performed simple bioinformatic analysis of the region and investigated its role in vivo in 2 strains with markedly different virulence profiles (WCH206 of serotype 3, ST180; Menzies5 of serotype 11A, ST662). Deleting and replacing the entire island with an antibiotic resistance cassette caused the virulent serotype 3 strain to become attenuated in a murine pneumonia/sepsis model. Further mutants were constructed and used to show that various components of the island contribute significantly to the fitness of WCH206 in a variety of niches of this model, including the nasopharynx, ears and blood, but especially in the lungs. In addition, the island conferred a competitive advantage in nasopharyngeal colonization for the serotype 11A strain, which was essentially avirulent in the pneumonia/sepsis model. The contribution of this island to both pathogenesis and colonization may explain why this accessory region is widespread in the pneumococcus.
Interpretation of K+K0bar pair production in pp collisions
A. Dzyuba,M. Buescher,C. Hanhart,V. Kleber,V. Koptev,H. Stroeher,C. Wilkin
Physics , 2008, DOI: 10.1140/epja/i2008-10647-9
Abstract: 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.
Coherent pi0-photoproduction from atomic nuclei
B. Krusche,J. Ahrens,R. Beck,S. Kamalov,V. Metag,R. O. Owens,H. Stroeher
Physics , 2003, DOI: 10.1016/S0370-2693(01)01503-9
Abstract: Differential and total cross sections for coherent pi0-photoproduction from 12C, 40Ca, 93Nb and Pb targets have been measured throughout the region of the Delta(1232)-resonance. The experiments were performed with the TAPS-detector at the Mainz accelerator MAMI. The characteristic proportionality of the cross section to the square of the atomic mass number and to the nuclear mass form factor is clearly demonstrated. The data allow for the first time detailed tests of model predictions for this reaction. The comparison of the data to model predictions shows that the Delta-nucleus interaction saturates: it is described for heavy nuclei with the same potential parameters as for 4He.
Near-threshold production of $a_0(980)$-mesons in $πN$ and NN collisions and $a_0/f_0$-mixing
L. A. Kondratyuk,E. L. Bratkovskaya,V. Yu. Grishina,M. Buescher,W. Cassing,H. Stroeher
Physics , 2002, DOI: 10.1134/1.1540670
Abstract: 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.
a0(980)-f0(980) mixing and isospin violation in the reactions pN -> d a0, pd -> 3He/3H a0 and dd -> 4He a0
V. Yu. Grishina,L. A. Kondratyuk,M. Buescher,W. Cassing,H. Stroeher
Physics , 2001, DOI: 10.1016/S0370-2693(01)01210-2
Abstract: It is demonstrated that f_0-a_0 mixing can lead to a comparatively large isospin violation in the reactions pN -> da_0, pd -> ^3He/^3H a_0 and dd -> ^4He a_0 close to the corresponding production thresholds. The observation of such mixing effects is possible, e.g., by measuring the forward-backward asymmetry in the reaction pn -> d a_0^0 -> d eta pi^0.
Medium effects in the production and pi0 gamma decay of omega-mesons in pA collisions in the GeV region
Ye. S. Golubeva,L. A. Kondratyuk,M. Buescher,W. Cassing,V. Hejny,H. Stroeher
Physics , 2001, DOI: 10.1007/s100500170088
Abstract: The omega-resonance production and its pi0 gamma decay in p-A reactions close to threshold is considered within the Intranuclear Cascade (INC) Model. The pi0 gamma invariant mass distribution shows two components which correspond to the omega decay 'inside' and 'outside' the nucleus, respectively. The 'inside' component is distorted by medium effects, which introduce a mass shift as well as collisional broadening for the omega-meson and its decaying pion. The relative contribution of the 'inside' component is analyzed in detail for different kinematical conditions and nuclear targets. It is demonstrated that a measurement of the correlation in azimuthal angle between the pi0 and gamma momenta allows to separate events related to the 'inside' omega decay from different sources of background when uncorrelated pi0's and gamma's are produced.
Nonmesonic decay of the Lambda hyperon in nuclear matter - implications on the weak Lambda-N interaction
W. Cassing,L. Jarczyk,B. Kamys,P. Kulessa,H. Ohm,K. Pysz,Z. Rudy,O. W. B. Schult,H. Stroeher
Physics , 2001, DOI: 10.1140/epja/i2002-10131-8
Abstract: The lifetime of the Lambda hyperon in heavy hypernuclei as measured by the COSY-13 Collaboration in proton - Au, Bi and U collisions has been analysed to yield tau(Lambda) = (145 +- 11) ps. This value for tau(Lambda) is compatible with the lifetime extracted from antiproton annihilation on Bi and U targets, however, much more accurate. We find that the dependence of the lifetime tau(Lambda) on the mass of hypernuclei indicates a violation of the phenomenological Delta I = 1/2 rule known from the weak mesonic decays of strange particles. PACS: {13.30.-a}{Decays of baryons} {13.75.Ev}{Hyperon-nucleon interaction} {21.80}{Hypernuclei} {25.80.Pw}{Hyperon-induced reactions}
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