26,918 research outputs found
IUE observations of blue halo high luminosity stars
Two high luminosity population II blue stars of high galactic latitude, BD+33 deg 2642 and HD 137569 were observed at high resolution. The stellar spectra show the effect of mass loss in BD+33 deg 2642 and abnormally weak metallic lines in HD 137569. The interstellar lines in the direction of BD+33 deg 2642, which lies at a height z greater than or equal to 6.2 kpc from the galactic plane, are split into two components. No high ionization stages are found at the low velocity component; nor can they be detected in the higher velocity clouds because of mixing with the corresponding stellar/circumstellar lines
Scheme Independence of the Effective Hamiltonian for and Decays
We present a calculation of the effective weak Hamiltonian which governs and transitions in two different
renormalization schemes (NDR and HV). In the leading logarithmic approximation,
we show that the coefficients of the effective Hamiltonian are scheme
independent only when one takes correctly into account the scheme dependence of
one- and two- loop diagrams. We demonstrate that in NDR there are contributions
which were missed in previous calculations. These contributions are necessary
to obtain scheme independent coefficients in the final results.Comment: 16 pp + 5 figures not included (available by anonymous ftp at
amisan.iss.infn.it (141.108.15.215), directory /ftp/bsgamma), LaTeX, LPTENS
93/28, ROME 93/958, ULB-TH 93/0
Penguin Contractions and Factorization in B -> K pi Decays
We study Lambda_{QCD}/m_B corrections to factorization in B -> K pi decays.
First, we analyze these decay channels within factorization, showing that,
irrespectively of the value of gamma, it is not possible to reproduce the
experimental data. Then, we discuss Lambda_{QCD}/m_B corrections to these
processes, and argue that there is a class of doubly Cabibbo enhanced
non-factorizable contributions, usually called charming penguins, that cannot
be neglected. Including these corrections, we obtain an excellent agreement
with experimental data. Furthermore, contrary to what is obtained with
factorization, we predict sizable rate asymmetries in B^\pm -> K^\pm \pi^0 and
B -> K^\pm pi^\mp.Comment: 4 pages, 3 figures. Talk given by L. Silvestrini at BCP4, Ise-Shima,
Japan, 18-23 Feb 200
Charming Penguins in B decays
Full expressions of the and
amplitudes, given in terms of matrix elements of operators of the effective
weak Hamiltonian, are used to study the dependence of the relevant branching
ratios on the different contributions. The uncertainty in the extraction of the
weak phase from the measurement of the time-dependent asymmetry in
decays is also analyzed. We find that, among several
effects which may enhance the branching ratio, the most
important is due to ``charming penguin" diagrams that have never been studied
before. These diagrams easily increase up to a
value of . The same effect produces, however, a large error
in the extraction of from the measurement of the time-dependent asymmetry. We show that it is possible to determine
charming-penguin amplitudes from the experimental measurement of many decay
rates. Their effect is impressive in and decays, where charming-penguin contributions easily give values of
and of about . Among other possibilities, we also suggest to use , the BR of which can be as large as , to determine the
size of charming-penguin amplitudes.Comment: LaTeX, 28 pages, 8 figure
Two Body B Decays, Factorization and LambdaQCD/mb Corrections
By using the recent experimental measurements of B -> pi pi and B -> K pi
branching ratios, we find that the amplitudes computed at the leading order of
the LambdaQCD/mb expansion disagree with the observed BRs, even taking into
account the uncertainties of the input parameters. Beyond the leading order,
Charming and GIM penguins allow to reconcile the theoretical predictions with
the data. Because of these large effects, we conclude, however, that it is not
possible, with the present theoretical and experimental accuracy, to determine
the CP violation angle gamma from these decays. We compare our results with
those obtained with the parametrization of the chirally enhanced
non-perturbative contributions by BBNS. We also predict large asymmetries for
several of the particle--antiparticle BRs, in particular BR(B+ -> K+ pi0),
BR(Bd -> K+ pi-) and BR(Bd -> pi+ pi-).Comment: 14 pages 3 figures uses aippro
- …