242 research outputs found
Search for the Photoexcitation of Exotic Mesons in the \u3ci\u3eπ\u3c/i\u3e\u3csup\u3e+\u3c/sup\u3e\u3ci\u3eπ\u3c/i\u3e\u3csup\u3e+\u3c/sup\u3e\u3ci\u3eπ\u3c/i\u3e\u3csup\u3e-\u3c/sup\u3e System
A search for exotic mesons in the π+π+π- system photoproduced by the charge exchange reaction γp → π+π+π- was carried out by the CLAS Collaboration at Jefferson Lab. A tagged-photon beam with energies in the 4.8 to 5.4 GeV range, produced through bremsstrahlung from a 5.744 GeV electron beam, was incident on a liquid-hydrogen target. A partial wave analysis was performed on a sample of 83 000 events, the highest such statistics to date in this reaction at these energies. The main objective of this study was to look for the photoproduction of an exotic JPC = 1-+ resonant state in the 1 to 2 GeV mass range. Our partial wave analysis shows production of the a2(1320) and the π2(1670) mesons, but no evidence for the a1(1260), nor the π1(1600) exotic state at the expected levels. An upper limit of 13.5 nb is determined for the exotic π1(1600) cross section, less than 2% of the a2(1320) production
Dissipation in a weak-link-limited superconductor as a problem of percolation theory
Broadening of the resistive transition of sintered GdBa2Cu3O7-x superconductor has been studied varying the measuring current over the range of five orders of magnitude. The observed well-defined branching points in the resistive transition coincide with the quasi-Ohmic saturation of V-I curves and scale with the average grain size. The results suggest the validity of a simple percolation model for dissipation in systems whose global superconductivity is realized by Josephson coupling of the superconducting grains. A common origin of structured resistive transition, observed in many superconducting systems, has been also discussed
Magnetic fluctuations in frustrated Laves hydrides R(Mn_{1-x}Al_{x})_{2}H_{y}
By neutron scattering, we have studied the spin correlations and spin
fluctuations in frustrated Laves hydrides, where magnetic disorder sets in the
topologically frustrated Mn lattice. Below the transition towards short range
magnetic order, static spin clusters coexist with fluctuating and alsmost
uncorrelated spins. The magnetic response shows a complexe lineshape, connected
with the presence of the magnetic inhomogeneities. Its analysis shows the
existence of two different processes, relaxation and local excitations, for the
spin fluctuations below the transition. The paramagnetic fluctuations are
discussed in comparison with classical spin glasses, cluster glasses, and non
Fermi liquid itinerant magnets
Measurement of the Muon Decay Parameter delta
The muon decay parameter delta has been measured by the TWIST collaboration.
We find delta = 0.74964 +- 0.00066(stat.) +- 0.00112(syst.), consistent with
the Standard Model value of 3/4. This result implies that the product Pmuxi of
the muon polarization in pion decay, Pmu, and the muon decay parameter xi falls
within the 90% confidence interval 0.9960 < Pmuxi < xi < 1.0040. It also has
implications for left-right-symmetric and other extensions of the Standard
Model.Comment: Extended to 5 pages. Referee's comments answere
A partial wave analysis of the system produced in charge exchange collisions
A partial wave analysis of the of the system produced in the
charge exchange reaction: at an incident momentum of
is presented as a function of invariant mass,
, and momentum transfer squared, , from the incident
to the outgoing system.Comment: 24 pages total,8 pages text, 14 figures, 1 table. Submitted to Phys
Rev
Observation of exotic meson production in the reaction at 18 GeV/c
An amplitude analysis of an exclusive sample of 5765 events from the reaction
at 18 GeV/c is described. The
production is dominated by natural parity exchange and by
three partial waves: those with and . A
mass-dependent analysis of the partial-wave amplitudes indicates the production
of the meson as well as the meson, observed for the
first time decaying to . The dominant, exotic
(non- partial wave is shown to be resonant with a mass of
GeV/c^2 and a width of GeV/c^2 . This exotic state, the , is produced with a
dependence which is different from that of the meson, indicating
differences between the production mechanisms for the two states.Comment: 5 pages with 4 figure
5f-Ligand Hybridization and Magnetism in UTX Compounds
Investigations of magnetic and related electronic properties of UTX compounds have revealed a variety of magnetic phenomena ranging from weak paramagnetism to various types of magnetic ordering. The observed systematics of ground-state properties is discussed with respect to the development of the electronic structure related to the expected variations of the 5f-ligand hybridization. The huge magnetic anisotropy observed in all studied materials is tentatively attributed mainly to the hybridization-mediated anisotropic two-ion interaction. © 1990
- …