74 research outputs found
Interdigital Resonators in Wideband Ridged-Waveguide Filters
An interdigital resonator approach for wideband filter applications in ridged-waveguide technology is presented. The interdigital arrangement of the ridged-waveguide resonators ensures stronger coupling between the resonators. As the coupling sections are consequently enlarged by the interdigital arrangement of the resonators, more feasible filter structures are possible at increasing frequencies.
The approach itself can be easily implemented with conventional filter synthesis formulas, which is demonstrated by two 20 GHz examples with a bandwidth of 2 GHz and 100 MHz, respectively. The designed filters are subsequently compared to the standard implementation of ridged-waveguide filters.</p
Towards a Lattice Calculation of the Nucleon Structure Functions
We have initiated a programme to compute the lower moments of the unpolarised
and polarised deep inelastic structure functions of the nucleon in the quenched
approximation. We review our progress to date.Comment: One author missed out in heplat title. Paper unchanged. 9 pages,
uuencoded compress postscript, contributed talk to LAT9
SU(3) Breaking in Hyperon Beta Decays: a Prediction for Xi^0 -> Sigma^+ e nu-bar
On the basis of a previous analysis of hyperon semi-leptonic decay data, a
prediction is presented for g_1/f_1 in the Xi^0 -> Sigma^+ e nu-bar beta-decay.
The analysis takes into account SU(3) breaking in this sector via the inclusion
of mass-driven corrections. A rather precise measurement of the above channel
by the KTeV experiment at Fermilab will shortly be available. Since the
dependence on the SU(3) parameters, F and D, is identical to that of the
neutron beta-decay, such a measurement will provide a rather stringent test of
SU(3) and the models used to describe its violation in these decays. The
prediction given here for the above decay is g_1/f_1=1.17, which leads to a
rate of 0.80 x 10^6 s^-1 and thus a branching fraction of 2.3 x 10^-4.Comment: LaTeX, 7 pages, uses acromake, cite and topcapt packages.
Non-printing extended ascii characters replaced plus minor correction
An Alternative Method to Obtain the Quark Polarization of the Nucleon
An alternate method is described to extract the quark contribution to the
spin of the nucleon directly from the first moment of the deuteron structure
function, . It is obtained without recourse to the use of input on the
nucleon wave function from hyperon decays involving the flavor symmetry
parameters, F and D. The result for the quark polarization of the nucleon,
is in good agreement with the values of the singlet axial
current matrix element, , obtained from recent next-to-leading order
analyses of current proton, neutron and deuteron data.Comment: 7 pages, 1 figur
Spin-Dependent Twist-Four Matrix Elements from g_1 Data in the Resonance Region
Matrix elements of spin-dependent twist-four operators are extracted from
recent data on the spin-dependent g_1 structure function of the proton and
deuteron in the resonance region. We emphasize the need to include the elastic
contributions to the first moments of the structure functions at Q^2 < 2 GeV^2.
The coefficients of the 1/Q^2 corrections to the Ellis-Jaffe sum rules are
found to be 0.04 \pm 0.02 and 0.03 \pm 0.04 GeV^2 for the proton and neutron,
respectively.Comment: 10 pages REVTeX, 4 figure
A model for the dependence of polarized structure functions
We present an update of a phenomenological model for the spin dependent
structure functions of the proton and neutron. This model is based
on a broken SU(6) wavefunction parametrized by the unpolarized structure
functions. The two free parameters of the model are choosen to fulfill the
Bjorken and Ellis--Jaffe sum rules. The model respects isospin symmetry and has
zero strange sea polarization. Using new values for from hyperon beta
decay the resulting dependent asymmetries are in perfect agreement
with the existing data. Therefore we do not see any evidence for a ``spin
crisis''. With two choices for the dependence of and
is predicted and shown to be small for both cases.Comment: 18 pages and 11 figures as uudecoded ps file
What We Can Learn About Nucleon Spin Structure From Recent Data
We have used recent polarized deep-inelastic scattering data from CERN and
SLAC to extract information about nucleon spin structure. We find that the SMC
proton data, the E142 neutron data and the deuteron data from SMC and E143 give
different results for fractions of the spin carried by each of the
constituents. These appear to lead to two different and incompatible models for
the polarized strange sea. The polarized gluon distribution occuring in the
gluon anomaly does not have to be large in order to be consistent with either
set of experimental data. However, it appears that the discrepancies in the
implications of these data cannot be resolved with any simple theoretical
arguments. We conclude that more experiments must be performed in order to
adequately determine the fraction of spin carried by each of the nucleon
constituents.Comment: 23 page
Renormalization-Scheme Dependence of Pade Summation in QCD
We study the renormalization-scheme (RS) dependence of Pade Approximants
(PA's), and compare them with the Principle of Minimal Sensitivity (PMS) and
the Effective Charge (ECH) approaches. Although the formulae provided by the
PA, PMS and ECH predictions for higher-order terms in a QCD perturbation
expansion differ in general, their predictions can be very close numerically
for a wide range of renormalization schemes. Using the Bjorken sum rule as a
test case, we find that Pade Summation (PS) reduces drastically the RS
dependence of the Bjorken effective charge. We use these results to estimate
the theoretical error due to the choice of RS in the extraction of
from the Bjorken sum rule, and use the available data at to
estimate , where the first
error is experimental, and the second is theoretical.Comment: 12 pages (latex), including 6 embedded figures; uses epsfig.st
Measurement of the Proton and Deuteron Spin Structure Functions g2 and Asymmetry A2
We have measured the spin structure functions g2p and g2d and the virtual
photon asymmetries A2p and A2d over the kinematic range 0.02 < x < 0.8 and 1.0
< Q^2 < 30(GeV/c)^2 by scattering 38.8 GeV longitudinally polarized electrons
from transversely polarized NH3 and 6LiD targets.The absolute value of A2 is
significantly smaller than the sqrt{R} positivity limit over the measured
range, while g2 is consistent with the twist-2 Wandzura-Wilczek calculation. We
obtain results for the twist-3 reduced matrix elements d2p, d2d and d2n. The
Burkhardt-Cottingham sum rule integral - int(g2(x)dx) is reported for the range
0.02 < x < 0.8.Comment: 12 pages, 4 figures, 1 tabl
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