6,991 research outputs found
CP Violation in B Decays at the Tevatron
Between 1992 to 1996, the CDF and D0 detectors each collected data samples exceeding 100 pb^{-1} of p\bar{p} collisions at sqrt{s}=1.8 TeV at the Fermilab Tevatron. These data sets led to a large number of precision measurements of the properties of B hadrons including lifetimes, masses, neutral B meson flavor oscillations, and relative branching fractions, and to the discovery of the B_c meson. Perhaps the most exciting result was the first look at the CP violation parameter sin(2beta) using the world's largest sample of fully reconstructed B^0/bar{B}^0 -> J/psi K^0_S decays. A summary of this result is presented here. In the year 2000, the Tevatron will recommence p\bar{p} collisions with an over order of magnitude expected increase in integrated luminosity (1 fb^{-1} per year). The CDF and D0 detectors will have undergone substantial upgrades, particularly in the tracking detectors and the triggers. With these enhancements, the Tevatron B physics program will include precision measurements of sin(2beta) and B^0_s flavor oscillations, as well as studies of rare B decays that are sensitive to new physics. The studies of B^0_s mesons will be particularly interesting as this physics will be unique to the Tevatron during the first half of the next decade
Multi-particle-collision dynamics: Flow around a circular and a square cylinder
A particle-based model for mesoscopic fluid dynamics is used to simulate
steady and unsteady flows around a circular and a square cylinder in a
two-dimensional channel for a range of Reynolds number between 10 and 130.
Numerical results for the recirculation length, the drag coefficient, and the
Strouhal number are reported and compared with previous experimental
measurements and computational fluid dynamics data. The good agreement
demonstrates the potential of this method for the investigation of complex
flows.Comment: 6 pages, separated figures in .jpg format, to be published in
Europhysics Letter
Hard exclusive photoproduction of mesons
We calculate the differential cross section and single-polarization
observables for the reaction within perturbative QCD,
treating the proton as a quark-diquark system. The phenomenological couplings
of gauge bosons to (spatially extended) diquarks and the quark-diquark
distribution amplitude of the proton are adopted from previous investigations
of baryon form factors and two-photon processes. Going beyond leading order, we
take into account hadron-mass effects by means of a systematic expansion in the
small parameter (hadron mass/ photon energy). With the -meson
distribution amplitude taken from the literature our predictions for the
differential cross section at | t | \agt 4 \text{GeV}^2 seem to provide a
reasonable extrapolation of the low-t data and are also comparable in magnitude
with the results of a two-gluon exchange model in which the gluons are
considered as a remnant of the pomeron. For momentum transfers of a few GeV
hadron-mass effects appear still to be sizeable.Comment: 37 pages, 7 figures, uses RevTeX styl
Exclusive Photoproduction of Large Momentum-Transfer K and K* Mesons
The reactions gamma p -> K+ Lambda and gamma p -> K* Lambda are analyzed
within perturbative QCD, allowing for diquarks as quasi-elementary constituents
of baryons. The diquark-model parameters and the quark-diquark distribution
amplitudes of proton and Lambda are taken from previous investigations of
electromagnetic baryon form factors and Compton-scattering off protons.
Unpolarized differential cross sections and polarization observables are
computed for different choices of the K and K* distribution amplitudes. The
asymptotic form of the K distribution amplitude (proportional to x1 x2) is
found to provide a satisfactory description of the K photoproduction data.Comment: 32 pages, 7 figures available as tared, compressed and uuencoded
PS-file
Preserving the gauge invariance of meson production currents in the presence of explicit final-state interactions
A comprehensive formalism is developed to preserve the gauge invariance of
currents describing the photo- or electroproduction of mesons off the nucleon
when the final-state interactions of mesons and nucleons is taken into account
explicitly. Replacing exchange currents by auxiliary currents, it is found that
all contributions due to explicit final-state interactions are purely
transverse and do not contain a Kroll-Ruderman-type contact current. The
relation of the present formulation to tree-level-type prescriptions is shown.Comment: 6 pages, 2 figures; published versio
Radiative Corrections to the Muonium Hyperfine Structure. I. The Correction
This is the first of a series of papers on a systematic application of the
NRQED bound state theory of Caswell and Lepage to higher-order radiative
corrections to the hyperfine structure of the muonium ground state. This paper
describes the calculation of the radiative correction. Our
result for the complete correction is 0.424(4) kHz, which
reduces the theoretical uncertainty significantly. The remaining uncertainty is
dominated by that of the numerical evaluation of the nonlogarithmic part of the
term and logarithmic terms of order .Comment: 56 pages, Rev.tex V3.0 and epsf.tex. 12 postscript files are called
in the text. Version accepted by Phys. Rev. D. A new table is adde
AP180 promotes release site clearance and clathrin-dependent vesicle reformation in mouse cochlear inner hair cells
High-throughput neurotransmission at ribbon synapses of cochlear inner hair cells (IHCs) requires tight coupling of neurotransmitter release and balanced recycling of synaptic vesicles (SVs) as well as rapid restoration of release sites. Here, we examined the role of the adaptor protein AP180 (also known as SNAP91) for IHC synaptic transmission by comparing AP180-knockout (KO) and wild-type mice using high-pressure freezing and electron tomography, confocal microscopy, patch-clamp membrane capacitance measurements and systems physiology. AP180 was found predominantly at the synaptic pole of IHCs. AP180-deficient IHCs had severely reduced SV numbers, slowed endocytic membrane retrieval and accumulated endocytic intermediates near ribbon synapses, indicating that AP180 is required for clathrin-dependent endocytosis and SV reformation in IHCs. Moreover, AP180 deletion led to a high prevalence of SVs in a multi-tethered or docked state after stimulation, a reduced rate of SV replenishment and a hearing impairment. We conclude that, in addition to its role in clathrin recruitment, AP180 contributes to release site clearance in IHCs
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