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J. Vandermeulen 《Zeitschrift fur Physik C Particles and Fields》1988,37(4):563-567
N \(\bar N\) annihilation is assumed to occur exclusively via two-meson production, with nearest threshold dominance. A phenomenological expression for the branching ratios, implementing the rule, contains two parameters. The set ofs- andp-wave (q \(\bar q\) ) mesons is used. Reasonable results are obtained for rates measured inp \(\bar p\) annihilation at rest. The numerous channels are projected into the multipion and kaon final states for comparison with in-flight experiments. A good overall agreement is reached up top lab~3 GeV/c; beyond, more mesons should be included to provide new thresholds. 相似文献
2.
Guido W Vandermeulen Dariush Hinderberger Hui Xu Sergei S Sheiko Gunnar Jeschke Harm-Anton Klok 《Chemphyschem》2004,5(4):488-494
Herein we describe the structure and dynamics of self-assembled nano-objects generated from poly(ethylene glycol) based (PEG-ylated) coiled-coil hybrid block copolymers. Electron paramagnetic resonance (EPR) experiments on spin-labeled samples provided a strong indication for a parallel alignment of the peptide helices in at least the dimeric coiled-coil nano-object and indicated that the PEG chains are folded rather closely around the peptide core of the nano-objects. The EPR results were supported by AFM studies, which revealed the presence of discrete nanosized objects in thin, spin cast films of the block copolymers on mica substrates. Since their size and structure may be engineered via directed mutations in the amino acid sequence, these nano-objects may be interesting building blocks for the development of supramolecular materials with various potential applications. 相似文献
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The relation between the amount ofp-wave in antineutron-proton annihilation into pions at very low momenta (≦ 0.3 GeV/c) and the even or odd character of the produced pion number is underlined. A simple calculation of the magnitude of the effect suggests the possible interest of measurements. 相似文献
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A model for pion production is studied in the context of a cascade calculation. The pions are produced through Δ-resonances which are allowed to decay. The emitted pions are assumed to interact with the other nucleons by forming new Δ -resonances. The time evolution of the pion and Δ-population is studied; it is found that Δs are always more numerous than pions during the sequence of baryon-baryon collisions. The spectrum of the pions is in considerably better agreement with experiment than the one obtained with frozen Δ-isobars. The presence of Δ-resonances appears to be important for the cooling of the pion system. The pion multiplicity is found to deviate from a Poisson distribution. The pion yield is overestimated by at least 25%; this result is discussed within the framework of conventional dynamics. 相似文献
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The annihilation of 100 MeV antiprotons in atomic nuclei is studied in the frame of an intranuclear cascade model. It is found that the antiproton is annihilated about 1 fm inside the nucleus on the average. The energy released by the annihilation is carried by an average of 5 pions, which cascade throughout the nucleus. About 5% (10%) of the primordial pions are absorbed by the 40Ca (108Ag) target. The pions transfer around 5̃50 MeV (7̃00 MeV) to the nucleons and eject about one-fifth of the nucleons. The pion and proton cross sections are calculated. In particular, the relative transparency of the nucleus to high-energy pions (and not to pions in the Δ-resonance region) gives rise to a peculiar pion emission pattern. The time evolution of the baryon density and of the spectrum of the participant nucleons is investigated. It turns out that the cascade does not generate high energy density. 相似文献
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M. Trzaska D. Pelte M. -C. Lemaire J. P. Alard J. Augerat D. Bachelier N. Bastid J. -L. Boyard C. Cavata P. Charmensat J. Cugnon P. Dupieux P. Gorodetzky J. Gosset T. Hennino J. -C. Jourdain A. LeMerdy D. L'Hôte B. Lucas J. Marroncle G. Montarou M. -J. Parizet J. Poitou D. Quassoud P. Radvanyi B. Ramstein A. Rahmani M. Roy-Stephan O. Valette J. Vandermeulen P. Zupranski 《Zeitschrift für Physik A Hadrons and Nuclei》1991,340(3):325-331
The excitation of theΔ resonance is observed in proton collisions on C, Nb and Pb targets at 0.8 and 1.6 GeV incident energies. The mass E0 and widthΓ of the resonance are determined from the invariant mass spectra of correlated (p, π±)-pairs in the final state of the collision: The mass E0 is smaller than that of the free resonance, however by comparing to intra-nuclear cascade calculations, this reduction is traced back to the effects of Fermi motion, NN scattering and pion reabsorption in nuclear matter. 相似文献
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The measurement of fast protons and neutrons emitted after antiproton annihilation at rest on238U and63Cu reveals a large neutron/proton ratioR. Its value for63Cu is larger than expected from the conventional model of intranuclear pion rescattering. A value ofR essentially constant over the whole range of mass number, from12C up to238U, is also announced by the experimentalists. It is shown that, on the contrary, the conventional scheme predicts a regular increase ofR with mass number. Alternative explanations of the effect are looked for. Within the usual scheme, an excess of negative pions, leading to more emitted neutrons, is not compatible with final pion multiplicities. The influence of meson resonances on the neutron/proton ratio is considered, as well as the possible occurrence of annihilations on two nucleons. They cannot warrant an increase ofR at low mass targets sufficient to explain a constant value over the whole range of target masses. 相似文献
10.
L'Hôte D Alard JP Augerat J Babinet R Brochard F Fodor Z Fraysse L Girard J Gorodetzky P Gosset J Laspalles C Lemaire MC Lucas B Montarou G Parizet MJ Poitou J Racca C Schimmerling W Tamain JC Terrien Y Valero J Cugnon J Vandermeulen J 《Physics letters. [Part B]》1987,198(2):139-142
Mean multiplicities of pi+ and pi- in 4He collisions with C, Cu, and Pb at 200, 600, and 800 MeV/u, and with C and Pb at 400 MeV/u have been measured using the large solid angle detector Diogene. The independence of pion multiplicity on projectile incident energy, target mass and proton multiplicity is studied in comparison with intra-nuclear cascade predictions. The discrepancy between experimental results and theory is pointed out and discussed. 相似文献