1,792 research outputs found
Summary on tau Leptonic Branching Ratios and Universality
The large samples of tau decays available from CLEO and the four LEP
experiment have resulted in new, precise measurements of the leptonic branching
ratios of the . The experimental techniques to obtain these results are
reviewed with special emphasis on the DELPHI measurement. World averages are
found to be Be = (17.81 +/- 0.06) % and Bmu = (17.36 +/- 0.06) %. These results
are consistent with universality in the charged current couplings to a
precision of about 0.25 %. The branching ratio measurements can also be used to
constrain the "low energy parameter" eta. It is shown that the sensitivity to
eta depends on details of the momentum acceptance for muon identification in
the different experiments. Assuming universality in the couplings, the estimate
eta = 0.012 +/- 0.024 is obtained.Comment: 10 pages, LaTeX, including 9 figures, uses epsf and espcrc2. Invited
talk at the Fifth Intl. Workshop on Tau Lepton Physics, 14-17 September 1998,
Santander (Spain
Measurement and Compensation of Horizontal Crabbing at the Cornell Electron Storage Ring Test Accelerator
In storage rings, horizontal dispersion in the rf cavities introduces
horizontal-longitudinal (xz) coupling, contributing to beam tilt in the xz
plane. This coupling can be characterized by a "crabbing" dispersion term
{\zeta}a that appears in the normal mode decomposition of the 1-turn transfer
matrix. {\zeta}a is proportional to the rf cavity voltage and the horizontal
dispersion in the cavity. We report experiments at the Cornell Electron Storage
Ring Test Accelerator (CesrTA) where xz coupling was explored using three
lattices with distinct crabbing properties. We characterize the xz coupling for
each case by measuring the horizontal projection of the beam with a beam size
monitor. The three lattice configurations correspond to a) 16 mrad xz tilt at
the beam size monitor source point, b) compensation of the {\zeta}a introduced
by one of two pairs of RF cavities with the second, and c) zero dispersion in
RF cavities, eliminating {\zeta}a entirely. Additionally, intrabeam scattering
(IBS) is evident in our measurements of beam size vs. rf voltage.Comment: 5 figures, 10 page
New Results From CLEO and BES
Latest experimental results from BES in the charmonium mass region, and those
from CLEO in the bottomonium and charmonium spectroscopy are reviewed.Comment: 12 pages, 12 figures, Presented at First Meeting of the APS Topical
Group on Hadron Physics, Fermilab, Batavia, Illinois, Oct 24-26, 200
Intrabeam Scattering Studies at CesrTA
Intrabeam scattering (IBS) limits the emittance and single-bunch current that
can be achieved in electron or positron storage ring colliders, damping rings,
and light sources. Much theoretical work on IBS exists, and while the theories
have been validated in hadron and ion machines, the presence of strong damping
makes IBS in lepton machines a different phenomenon. We present the results of
measurements at CesrTA of IBS dominated beams, and compare the data with
theory. The beams we study have parameters typical of those specified for the
next generation of wiggler dominated storage rings: low emittance, small bunch
length, and few GeV energy. Our measurements are in good agreement with IBS
theory, provided a tail-cut procedure is applied.Comment: 14 pages, 15 figure
Properties of the a1 Meson from Lattice QCD
We determine the mass and decay constant of the meson using Monte Carlo
simulation of lattice QCD. We find MeV and , in good agreement with experiment.Comment: 9 page uu-encoded compressed postscript file. version appearing in
Phys. Rev. Lett. 74 (1995) 459
Axial Vector Charmonium and Bottomonium Hybrid Mass Predictions with QCD Sum-Rules
Axial vector charmonium and bottomonium hybrid masses are
determined via QCD Laplace sum-rules. Previous sum-rule studies in this channel
did not incorporate the dimension-six gluon condensate, which has been shown to
be important for and heavy quark hybrids. An updated analysis
of axial vector charmonium and bottomonium hybrids is presented, including the
effects of the dimension-six gluon condensate. The axial vector charmonium and
bottomonium hybrid masses are predicted to be 5.13 GeV and 11.32 GeV,
respectively. We discuss the implications of this result for the
charmonium-like XYZ states and the charmonium hybrid multiplet structure
observed in recent lattice calculations.Comment: 10 pages, 7 figures. Updated to match published versio
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