2,654 research outputs found
A radiometer for stochastic gravitational waves
The LIGO Scientific Collaboration recently reported a new upper limit on an
isotropic stochastic background of gravitational waves obtained based on the
data from the 3rd LIGO science Run (S3). Now I present a new method for
obtaining directional upper limits that the LIGO Scientific Collaboration
intends to use for future LIGO science runs and that essentially implements a
gravitational wave radiometer.Comment: 6 pages, 2 figure
Detecting a stochastic background of gravitational waves in the presence of non-Gaussian noise: A performance of generalized cross-correlation statistic
We discuss a robust data analysis method to detect a stochastic background of
gravitational waves in the presence of non-Gaussian noise. In contrast to the
standard cross-correlation (SCC) statistic frequently used in the stochastic
background searches, we consider a {\it generalized cross-correlation} (GCC)
statistic, which is nearly optimal even in the presence of non-Gaussian noise.
The detection efficiency of the GCC statistic is investigated analytically,
particularly focusing on the statistical relation between the false-alarm and
the false-dismissal probabilities, and the minimum detectable amplitude of
gravitational-wave signals. We derive simple analytic formulae for these
statistical quantities. The robustness of the GCC statistic is clarified based
on these formulae, and one finds that the detection efficiency of the GCC
statistic roughly corresponds to the one of the SCC statistic neglecting the
contribution of non-Gaussian tails. This remarkable property is checked by
performing the Monte Carlo simulations and successful agreement between
analytic and simulation results was found.Comment: 15 pages, 8 figures, presentation and some figures modified, final
version to be published in PR
Negatively Charged Strangelet Search using the E864 Spectrometer at the AGS
We provide a status report on the progress of searching for negatively
charged strangelets using the E864 spectrometer at the AGS. About 200 million
recorded events representing approximately 14 billion 10% central interactions
of Au + Pt at 11.5 GeV/c taken during the 1996-1997 run of the experiment are
used in the analysis. No strangelet candidates are seen for charges Z=-1 and
Z=-2, corresponding to a 90% confidence level for upper limits of strangelet
production of ~1 x 10^{-8} and ~4 x 10^{-9} per central collision respectively.
The limits are nearly uniform over a wide range of masses and are valid only
for strangelets which are stable or have lifetimes greater than ~50 ns.Comment: 6 pages, 4 figures; Talk at SQM'98, Padova, Italy (July 20-24, 1998
Model-Independent Semileptonic Form Factors Using Dispersion Relations
We present a method for parametrizing heavy meson semileptonic form factors
using dispersion relations, and from it produce a two-parameter description of
the B -> B elastic form factor. We use heavy quark symmetry to relate this
function to B -> D* l nu form factors, and extract
|V_cb|=0.0355^{+0.0029}_{-0.0025} from experimental data with a least squares
fit. Our method eliminates model-dependent uncertainties inherent in choosing a
parametrization for the extrapolation of the differential decay rate to
threshold.Comment: uses lanlmac(harvmac) and epsf, 12 pages, 1 eps figure included (Talk
by BG at the 6-th International Symposium on Heavy Flavour Physics, Pisa,
Italy, 6--10 June, 1995
Low--Energy Theorems for Weak Pion Production
We derive novel low--energy theorems for single pion production off nucleons
through the isovector axial current. We find that the -dependence of the
multipole at threshold is given by the nucleon scalar form
factor, namely . The relation to
PCAC results for soft pions including electroweak form factors is also
clarified.Comment: 9 pp, TeX, 2 figures available as ps files, CRN 93-5
Factorization theorems, effective field theory, and nonleptonic heavy meson decays
The nonleptonic heavy meson decays
and are studied based on the three-scale perturbative QCD
factorization theorem developed recently. In this formalism the
Bauer-Stech-Wirbel parameters a_1 and a_2 are treated as the Wilson
coefficients, whose evolution from the W boson mass down to the characteristic
scale of the decay processes is determined by effective field theory. The
evolution from the characteristic scale to a lower hadronic scale is formulated
by the Sudakov resummation. The scale-setting ambiguity, which exists in the
conventional approach to nonleptonic heavy meson decays, is moderated.
Nonfactorizable and nonspectator contributions are taken into account as part
of the hard decay subamplitudes. Our formalism is applicable to both bottom and
charm decays, and predictions, including those for the ratios R and R_L
associated with the decays, are consistent with
experimental data.Comment: 39 pages, latex, 5 figures, revised version with some correction
Semileptonic B and Lambda_b Decays and Local Duality in QCD
The inclusive and exclusive semileptonic decay distributions for b -> c decay
are computed in the Shifman-Voloshin limit. The inclusive decay distributions
(computed using an operator product expansion) depend on quark masses, and the
exclusive decay distributions depend on hadron masses. Nevertheless, we show
explicitly how the first two terms in the 1/m expansion match between the
inclusive and exclusive decays. Agreement between the inclusive and exclusive
decay rates requires a minimum smearing region of size Lambda_QCD before local
duality holds in QCD. The alpha_s corrections to the inclusive and exclusive
decay rates are also shown to agree to order (log m)/m^2. The alpha_s/m^2
corrections are used to obtain the alpha_s correction to Bjorken's inequality
on the slope of the Isgur-Wise function.Comment: 22 pages, 3 eps figures, uses revtex (Revision: a discussion of
radiative corrections to the bound K>0 of Section 7.B has been added; some
typos, including labels in fig 2
The Isgur-Wise function in a relativistic model for system
We use the Dirac equation with a ``(asymptotically free) Coulomb + (Lorentz
scalar) linear '' potential to estimate the light quark wavefunction for mesons in the limit . We use these wavefunctions to
calculate the Isgur-Wise function for orbital and radial
ground states in the phenomenologically interesting range . We find a simple expression for the zero-recoil slope, , where is the energy eigenvalue
of the light quark, which can be identified with the parameter
of the Heavy Quark Effective Theory. This result implies an upper bound of
for the slope . Also, because for a very light quark the size of the meson is determined mainly by the
``confining'' term in the potential , the shape of
is seen to be mostly sensitive to the dimensionless
ratio . We present results for the ranges of
parameters , and
light quark masses and compare to existing
experimental data and other theoretical estimates. Fits to the data give:
,
and [ARGUS
'93]; , and
[CLEO '93]; ${\bar\Lambda_{u,d}}^2/Comment: 22 pages, Latex, 4 figures (not included) available by fax or via
email upon reques
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