1,006 research outputs found
Implications of Results from Z- and WW-Threshold Running
One year of Z- and WW-Threshold running of TESLA can provide the possibility
to measure electroweak precision observables to an extremely high accuracy. At
the Z peak O(10^9) Z bosons and about 6 10^8 b quarks can be collected. We
employ the expected uncertainties \Delta MW = 6 MeV and \Delta sin(theta_W,eff)
= 0.00001 and demonstrate in this way that very stringent consistency tests of
the Standard Model and the Minimal Supersymmetric Standard Model will be
possible. The indirect determination of the Higgs-boson mass within the
Standard Model can reach an accuracy of about 5 %. The 6 10^8 b quarks can be
used to investigate various b physics topics.Comment: 7 pages, 2 figures, talk given at LCWS99, Sitges, Spain. Two
clarifications, one reference adde
Shape Function Effects in B -> X_c l \nu_l
Owing to the fact that m_c^2 ~ m_b \Lambda_QCD, the endpoint region of the
charged lepton energy spectrum in the inclusive decay B -> X_c l \nu_l is
affected by the Fermi motion of the initial-state b quark bound in the B meson.
This effect is described in QCD by shape functions. Including the mass of the
final-state quark, we find that a different set of operators as employed in
Ref. hep-ph/0205150 is needed for a consistent matching, when incorporating the
subleading contributions in B -> X_q l \nu_l for both q = u and q = c. In
addition, we modify the usual twist expansion in such a way that it yields a
description of the lepton energy spectrum which is not just valid in the
endpoint region, but over the entire phase space.Comment: 8 Pages, LaTeX, 2 figures; a few typos corrected and some
clarifications added, final journal versio
Role of "Intrinsic Charm" in Semi-Leptonic B-Meson Decays
We discuss the role of so-called "intrinsic-charm" operators in semi-leptonic
B-meson decays, which appear first at order 1/m_b^3 in the heavy quark
expansion. We show by explicit calculation that -- at scales mu <= m_c -- the
contributions from "intrinsic-charm" effects can be absorbed into
short-distance coefficient functions multiplying, for instance, the Darwin
term. Then, the only remnant of "intrinsic charm" are logarithms of the form
ln(m_c^2/m_b^2), which can be resummed by using renormalization-group
techniques. As long as the dynamics at the charm-quark scale is perturbative,
alpha_s(m_c) << 1, this implies that no additional non-perturbative matrix
elements aside from the Darwin and the spin-orbit term have to be introduced at
order 1/m_b^3. Hence, no sources for additional hadronic uncertainties have to
be taken into account. Similar arguments may be made for higher orders in the
1/m_b expansion.Comment: 14 pages, 1 figure, uses slashed.sty, slight modifications to match
published versio
Non-perturbative effects in semi-leptonic B_c decays
We discuss the impact of the soft degrees of freedom inside the B_c meson on
its rate in the semi-leptonic decay B_c -> X l nu_l where X denotes light
hadrons below the D^0 threshold. In particular we identify contributions
involving soft hadrons which are non-vanishing in the limit of massless
leptons. These contributions become relevant for a measurement of the purely
leptonic B_c decay rate, which due to helicity suppression involves a factor
m_l^2 and thus is much smaller than the contributions involving soft hadrons.Comment: LaTeX, 22 pages, 1 figur
Radiatively corrected shape function for inclusive heavy hadron decays
We discuss the non-perturbative and the radiative corrections to inclusive B
decays from the point of view known from QED corrections to high energy e^+ e^-
processes. Here the leading contributions can be implemented through the so
called ``radiator function'' which corresponds to the shape function known in
heavy hadron decays. In this way some new insight into the origin of the shape
function is obtained. As a byproduct, a parameterization of the radiatively
corrected shape function is suggested which can be implemented in Monte Carlo
studies of inclusive heavy hadron decays.Comment: LaTeX, uses a4, graphicx and psfrag, 10 pages. The complete paper is
also available at http://www-ttp.physik.uni-karlsruhe.de/Preprints
Perturbative and Non-perturbative Corrections to
It is shown that certain double ratios introduced for computing semileptonic
form factors are accurate to order , even when the action and current
are accurate to order .Comment: Lattice99(heavyquarks); 3 + epsilon pp. LaTe
Sequential Flavour Symmetry Breaking
The gauge sector of the Standard Model (SM) exhibits a flavour symmetry which
allows for independent unitary transformations of the fermion multiplets. In
the SM the flavour symmetry is broken by the Yukawa couplings to the Higgs
boson, and the resulting fermion masses and mixing angles show a pronounced
hierarchy. In this work we connect the observed hierarchy to a sequence of
intermediate effective theories, where the flavour symmetries are broken in a
step-wise fashion by vacuum expectation values of suitably constructed spurion
fields. We identify the possible scenarios in the quark sector and discuss some
implications of this approach.Comment: 22 pages latex, no figure
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