878 research outputs found
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
The Renormalization Group Evolution of the CKM Matrix
We compute the renormalization of the complete CKM matrix in the MSbar scheme
and perform a renormalization group analysis of the CKM parameters. The
calculation is simplified by studying only the Higgs sector, which for the
\beta-function of the CKM matrix is at one loop the same as in the full
Standard Model. The renormalization group flow including QCD corrections can be
computed analytically using the hierarchy of the CKM parameters and the large
mass differences between the quarks. While the evolution of the Cabibbo angle
is tiny V_{ub} and V_{cb} increase sizably. We compare our results with the
ones in the full Standard Model.Comment: Latex, 31 pages, extensions amsmath, epsfig required The complete
paper, including figures, is also available via anonymous ftp at
ftp://ttpux2.physik.uni-karlsruhe.de/, or via www at
http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints
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
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
Two body non-leptonic decays in quark model with factorization ansatz
The two body non-leptonic decays are analyzed in factorization
approximation, using quark model, as a free parameter. It is
shown that the experimental branching ratio for restricts and this ratio can be understood for a value
of which lies in the range suggested by two body
B meson decays. The branching ratios for are predicted to be larger than the previous estimates. Finally it
is pointed that CKM-Wolfenstein parameter , where is CP
phase, can be determined from the ratio of widths of and or that of
and
independent of the parameter .Comment: 18 pages, latex, 1 figure available on request, please send any
questions or comments to [email protected]
Plasma-wall-interaction in ECRIS II
In an ECR-discharge, where the plasma is confined inside a copper-resonator by a simple magnetic mirror, it could be shown that sputtering of wall material has an important influence upon the plasma [1]. Spectroscopic measurements in ECRIS II with a copper vessel confirmed this model. Evidence for the presence of copper atoms and ions in the plasma could be found by ion extraction as well as with VUV-spectrometry. In a nitrogen discharge by adding helium as a mixing-gas we found that the extracted current of Cu-ions decreased and measured line intensities of copper emission lines dropped down. [1] D. Meyer, "Einfluss der Plasmainstabilitaet auf die Produktion hochgeladener Ionen in einer ECR-Entladung", Dissertation, Bochum, 199
Light-cone distribution functions for B decays at subleading order in
We construct the higher twist structure functions that describe inclusive b hadron decays in regions of phase space where the hadronic decay products carry high energy but have low invariant mass. We show that, for B meson decays, there are four new non-vanishing matrix elements of non-local operators. We show that to subleading twist these decays are parametrized in terms of four functions. We compute the tree-level matching for a general heavy-to-light current and apply it to B -> X_s gamma. Using a simple model for these functions we estimate the subleading twist contributions to this decay
Coulomb gauge confinement in the heavy quark limit
The relationship between the nonperturbative Green's functions of Yang-Mills
theory and the confinement potential is investigated. By rewriting the
generating functional of quantum chromodynamics in terms of a heavy quark mass
expansion in Coulomb gauge, restricting to leading order in this expansion and
considering only the two-point functions of the Yang-Mills sector, the
rainbow-ladder approximation to the gap and Bethe-Salpeter equations is shown
to be exact in this case and an analytic, nonperturbative solution is
presented. It is found that there is a direct connection between the string
tension and the temporal gluon propagator. Further, it is shown that for the
4-point quark correlation functions, only confined bound states of
color-singlet quark-antiquark (meson) and quark-quark (baryon) pairs exist.Comment: 22 pages, 6 figure
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