3,963 research outputs found
Calculation of Infrared-Divergent Feynman Diagrams with Zero Mass Threshold
Two-loop vertex Feynman diagrams with infrared and collinear divergences are
investigated by two independent methods. On the one hand, a method of
calculating Feynman diagrams from their small momentum expansion extended to
diagrams with zero mass thresholds is applied. On the other hand, a numerical
method based on a two-fold integral representation is used. The application of
the latter method is possible by using lightcone coordinates in the parallel
space. The numerical data obtained with the two methods are in impressive
agreement.Comment: 20 pages, Latex with epsf-figures, References updated, to appear in
Z.Phys.
Weak Phase From Ratio of Rates
The ratio of partial decay rates for charged and neutral mesons to final states provides information on the weak phase when augmented with information on the CP-violating asymmetry
in the mode. The requirements for a useful determination of
are examined in the light of present information about the decays , , and the corresponding charge-conjugate
modes. The effects of electroweak penguins and rescattering corrections are
noted, and proposals are made for estimating and measuring their importance.Comment: 16 pages, latex, 3 figures, revised version sent to Phys. Rev.
Relativistic description of electron scattering on the deuteron
Within a quasipotential framework a relativistic analysis is presented of the
deuteron current. Assuming that the singularities from the nucleon propagators
are important, a so-called equal time approximation of the current is
constructed. This is applied to both elastic and inelastic electron scattering.
As dynamical model the relativistic one boson exchange model is used.
Reasonable agreement is found with a previous relativistic calculation of the
elastic electromagnetic form factors of the deuteron. For the unpolarized
inelastic electron scattering effects of final state interactions and
relativistic corrections to the structure functions are considered in the
impulse approximation. Two specific kinematic situations are studied as
examples.Comment: (19 pages in revtex + 15 figures not included, available upon
request.) report THU-93-10
A Critical Study of B Decays to Light Pseudoscalar
Motivated by the large branching ratios observed for the process
, we examine critically all the ingredients that go into
estimates of B decays into two light pseudoscalars. Within factorization
approximation, we examine several assumptions on the input parameters that
could have a strong bearing on the predictions. Among these are (i) the QCD
scale (ii) value of the form factors (iii) value of the light quark
masses, and in particular (iv) the value , (v) charm content
of . It is possible to account for all the data without invoking
new physics, though future experiments will provide tighter constraints on the
parameter space. We fin that CP violating asymmetries are in the observable
range for some modes.Comment: 29 pages(Latex), 17 figures, a few changes have been made, version to
appear in Phys.Rev.
Exploring CP Violation through Correlations in B --> pi K, B_d --> pi^+pi^-, B_s --> K^+K^- Observable Space
We investigate allowed regions in observable space of B --> pi K, B_d -->
pi^+pi^- and B_s --> K^+K^- decays, characterizing these modes in the Standard
Model. After a discussion of a new kind of contour plots for the
system, we focus on the mixing- induced and direct CP asymmetries of the decays
B_d --> pi^+pi^- and B_s--> K^+K^-. Using experimental information on the
CP-averaged B_d --> pi^{+/-}K^{+/-} and B_d --> pi^+pi^- branching ratios, the
relevant hadronic penguin parameters can be constrained,implying certain
allowed regions in observable space. In the case of B_d --> pi^+pi^-, an
interesting situation arises now in view of the recent B-factory measurements
of CP violation in this channel, allowing us to obtain new constraints on the
CKM angle gamma as a function of the B^0_d--\bar{B^0_d} mixing phase
phi_d=2beta, which is fixed through A_{CP}^{mix}(B_d --> J/psi K_S) up to a
twofold ambiguity. If we assume that A_{CP}^{mix}(B_d --> pi^+pi^-) is
positive, as indicated by recent Belle data, and that phi_d is in agreement
with the ``indirect'' fits of the unitarity triangle, also the corresponding
values for gamma around 60 degrees can be accommodated. On the other hand, for
the second solution of phi_d, we obtain a gap around gamma ~ 60 degrees. The
allowed region in the space of A_{CP}^{mix}(B_s --> K^+K^-) and
A_{CP}^{dir}(B_s --> K^+K^-) is very constrained in the Standard Model, thereby
providing a narrow target range for run II of the Tevatron and the experiments
of the LHC era.Comment: 34 pages, LaTeX, 12 figures. More detailed introduction and a few
Comments added, conclusions unchanged. To appear in Phys. Rev.
Exploring CP Violation with Decays
We point out that the pure ``tree'' decays are
particularly well suited to extract the CKM angle through amplitude
relations. In contrast to conceptually similar strategies using or decays, the advantage of the approach is that
the corresponding triangles have three sides of comparable length and do not
involve small amplitudes. Decays of the type -- the
-spin counterparts of -- can be added to the
analysis, as well as channels, where the - and -mesons are
replaced by higher resonances.Comment: 9 pages, LaTeX, 3 figures, reference adde
Rescattering Information from Decays
Rescattering effects can modify the dependence on the weak phase of the ratio of rates for and . A test for these effects based on the
processes has been suggested. It is pointed out that the
rates for the processes , which are expected to be {\it
dominated} by rescattering and for which considerably better experimental
bounds exist, are likely to provide a more stringent constraint on these
effects.Comment: 22 pages, latex, 7 figures, to be published in Phys. Rev. D. Minor
corrections and addition
Vibration analysis of moving machine tool axes based on phase information in video data
Vibrations of machine tools limit quality and productivity and therefore need to be analyzed. Video based vibration analysis using spatial phase information could in principle reduce measuring effort significantly. However, feasibility of these approaches for moving machine tool axes and relative movement between camera and object is yet to be shown. This paper investigates an approach for stabilizing linear axis movement to analyze vibration. It is shown that shaker induced vibration on a linearly moving clamping tower can be derived for low frequencies. However, influences of actual cutting processes as well as compensation of unwanted camera vibration needs further investigation
Taming the Penguin in the B0(t) -> Pi+Pi- CP-asymmetry: Observables and Minimal Theoretical Input
Penguin contributions, being not negligible in general, can hide the
information on the CKM angle alpha coming from the measurement of the
time-dependent B0(t) -> pi+pi- CP-asymmetry. Nevertheless, we show that this
information can be summarized in a set of simple equations, expressing alpha as
a multi-valued function of a single theoretically unknown parameter, which
conveniently can be chosen as a well-defined ratio of penguin to tree
amplitudes. Using these exact analytic expressions, free of any assumption
besides the Standard Model, and some reasonable hypotheses to constrain the
modulus of the penguin amplitude, we derive several new upper bounds on the
penguin-induced shift |2alpha-2alpha_eff|, generalizing the recent result of
Grossman and Quinn. These bounds depend on the averaged branching ratios of
some decays (pi0pi0, K0K0bar, K+-pi-+) particularly sensitive to the penguin.
On the other hand, with further and less conservative approximations, we show
that the knowledge of the B+- -> Kpi+- branching ratio alone gives sufficient
information to extract the free parameter without the need of other
measurements, and without knowing |V_td| or |V_ub|. More generally, knowing the
modulus of the penguin amplitude with an accuracy of ~30% might result in an
extraction of alpha competitive with the experimentally more difficult isospin
analysis. We also show that our framework allows to recover most of the
previous approaches in a transparent and simple way, and in some cases to
improve them. In addition we discuss in detail the problem of the various kinds
of discrete ambiguities.Comment: LaTeX2e, 44 pages, 9 figures (from 18 postscript files) included with
epsf. Minor changes, references updated. New CLEO results from ICHEP'98 are
taken into account. To appear in Phys. Rev.
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