1,273 research outputs found
Semileptonic decays of baryons in a relativistic quark model
We calculate semileptonic decays of light and heavy baryons in a
relativistically covariant constituent quark model. The model is based on the
Bethe-Salpeter-equation in instantaneous approximation. It generates
satisfactory mass spectra for mesons and baryons up to the highest observable
energies. Without introducing additional free parameters we compute on this
basis helicity amplitudes of electronic and muonic semileptonic decays of
baryons. We thus obtain form factor ratios and decay rates in good agreement
with experiment.Comment: 8 pages, 10 figures, 2 tables, typos remove
Strong Two--Body Decays of Light Mesons
In this paper, we present results on strong two-body decay widths of light
mesons calculated in a covariant quark model. The model is based on
the Bethe-Salpeter equation in its instantaneous approximation and has already
been used for computing the complete meson mass spectrum and many electroweak
decay observables. Our approach relies on the use of a phenomenological
confinement potential with an appropriate spinorial Dirac structure and 't
Hooft's instanton--induced interaction as a residual force for pseudoscalar and
scalar mesons. The transition matrix element for the decay of one initial meson
into two final mesons is evaluated in lowest order by considering conventional
decays via quark loops as well as Zweig rule violating instanton--induced
decays generated by the six--quark vertex of 't Hooft's interaction; the latter
mechanism only contributes if all mesons in the decay have zero total angular
momentum. We show that the interference of both decay mechanisms plays an
important role in the description of the partial widths of scalar and
pseudoscalar mesons.Comment: 35 pages, 7 figure
Substitutional disorder in the substituted nixantphos ligand C39H32Br0.27Cl0.73NOP2
The structure of 10-(3-bromo/chloropropyl)-4,6-bis(diphenylphosphino)-10H-phenoxazine, C39H32Br0.27Cl0.73NOP2, shows chloro/bromo substitutional disorder in a 3:1 ratio. For application as a ligand in catalysis, the intramolecular P⋯P distance of 4.263 (2) Å is relevant. The phenoxazine ring system is essentially planar
A photoemission study of the surface carbonate species on Ag{110}
The electronic structure of the surface carbonate species adsorbed on Ag{110} has been studied with angle‐resolved photoemission using synchrotron radiation. Despite the low symmetry of the surface complex (Cs) and more than one azimuthal orientation of the vertical symmetry plane, it has been possible to assign the adsorbate‐induced levels. Recent semiempirical quantum chemical calculations have proved to be of considerable assistance in this process. The resonant behavior observed for the 3a‘ level is discussed in the context of photoelectron data for the free BF3 molecule, which is isoelectronic with CO2−3. The Cs symmetry pertaining in the present experiment is compared with the effective D3h symmetry observed in x‐ray‐absorption spectroscopy of the same system
L1599B: Cloud Envelope and C+ Emission in a Region of Moderately Enhanced Radiation Field
We study the effects of an asymmetric radiation field on the properties of a
molecular cloud envelope. We employ observations of carbon monoxide (12CO and
13CO), atomic carbon, ionized carbon, and atomic hydrogen to analyze the
chemical and physical properties of the core and envelope of L1599B, a
molecular cloud forming a portion of the ring at approximately 27 pc from the
star Lambda Ori. The O III star provides an asymmetric radiation field that
produces a moderate enhancement of the external radiation field. Observations
of the [CII] fine structure line with the GREAT instrument on SOFIA indicate a
significant enhanced emission on the side of the cloud facing the star, while
the [Ci], 12CO and 13CO J = 1-0 and 2-1, and 12CO J = 3-2 data from the PMO and
APEX telescopes suggest a relatively typical cloud interior. The atomic, ionic,
and molecular line centroid velocities track each other very closely, and
indicate that the cloud may be undergoing differential radial motion. The HI
data from the Arecibo GALFA survey and the SOFIA/GREAT [CII] data do not
suggest any systematic motion of the halo gas, relative to the dense central
portion of the cloud traced by 12CO and 13CO.Comment: 9 Figure
The structure of Cu(110) (2×3)–N; pseudo‐square reconstruction of a rectangular mesh substrate
The structure of the Cu(110)(2×3)–N phase has been investigated by parallel studies using 3‐keV Li+ and 2‐keV He+ion scattering and scanned energy mode normal emission N 1s photoelectron diffraction. The Li+ion scattering results provide clear evidence for anadsorbate‐induced reconstruction of the Cu surface and, in particular, indicate a shortening of the Cu–Cu atomic spacing along the 〈100〉 azimuth to a value of 2.7±0.1 Å, similar to the 〈110〉 spacing of 2.55 Å. A model of the surface consistent with this result involves a pseudo‐square Cu top atom layer with N atoms occupying alternate hollow sites leading to a local structure which is a 6% distorted Cu(100)c(2×2)–N phase. He+ion scattering data provides support for the N hollow adsorption sites. Scanned energy mode photoelectron diffraction is insensitive to the nature of the reconstruction but provides information on the local adsorption sites and, hence, on the lateral registry of the reconstructed overlayer and the underlying substrate
Quark-antiquark composite systems: the Bethe-Salpeter equation in the spectral-integration technique
The Bethe-Salpeter equations for the light-quark composite systems, q q-bar,
are written in terms of spectral integrals. For the q q-bar -mesons
characterized by the mass M, spin J and radial quantum number n, the equations
are presented for the following (n,M^2)-trajectories: pi_J, eta_J, a_J, f_J,
rho_J, omega_J, h_J and b_J.Comment: 42 pages, 5 figures, typos correcte
Splitting of the pi - rho spectrum in a renormalized light-cone QCD-inspired model
We show that the splitting between the light pseudo-scalar and vector meson
states is due to the strong short-range attraction in the ^1S_0 sector which
makes the pion and the kaon light particles. We use a light-cone QCD-inspired
model of the mass squared operator with harmonic confinement and a Dirac-delta
interaction. We apply a renormalization method to define the model, in which
the pseudo-scalar ground state mass fixes the renormalized strength of the
Dirac-delta interaction.Comment: 9 pages, 2 figures, revtex, accepted by Phys. Rev. D; Corrected typo
Highly multimode memory in a crystal
We experimentally demonstrate the storage of 1060 temporal modes onto a
thulium-doped crystal using an atomic frequency comb (AFC). The comb covers
0.93 GHz defining the storage bandwidth. As compared to previous AFC
preparation methods (pulse sequences i.e. amplitude modulation), we only use
frequency modulation to produce the desired optical pumping spectrum. To ensure
an accurate spectrally selective optical pumping, the frequency modulated laser
is self-locked on the atomic comb. Our approach is general and should be
applicable to a wide range of rare-earth doped material in the context of
multimode quantum memory
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