23 research outputs found
Soft Wilson lines in soft-collinear effective theory
The effects of the soft gluon emission in hard scattering processes at the
phase boundary are resummed in the soft-collinear effective theory (SCET). In
SCET, the soft gluon emission is decoupled from the energetic collinear part,
and is obtained by the vacuum expectation value of the soft Wilson-line
operator. The form of the soft Wilson lines is universal in deep inelastic
scattering, in the Drell-Yan process, in the jet production from e+e-
collisions, and in the gamma* gamma* -> pi0 process, but its analytic structure
is slightly different in each process. The anomalous dimensions of the soft
Wilson-line operators for these processes are computed along the light-like
path at leading order in SCET and to first order in alpha_s, and the
renormalization group behavior of the soft Wilson lines is discussed.Comment: 36 pages, 10 figures, 3 table
Radiative B decays to the axial mesons at next-to-leading order
We calculate the branching ratios of at next-to-leading
order (NLO) of where is the orbitally excited axial vector
meson. The NLO decay amplitude is divided into the vertex correction and the
hard spectator interaction part. The one is proportional to the weak form
factor of transition while the other is a convolution between
light-cone distribution amplitudes and hard scattering kernel. Using the
light-cone sum rule results for the form factor, we have \calB(B^0\to
K_1^0(1270)\gamma)=(0.828\pm0.335)\times 10^{-5} and \calB(B^0\to
K_1^0(1400)\gamma)=(0.393\pm0.151)\times 10^{-5}.Comment: 17pages, 4 figures. Minor changes, typos corrected. PRD accepted
versio
Exclusive B-> M \nu \bar{\nu} (M= \pi, K, \rho, K^*) Decays and Leptophobic Z^\prime Model
We consider the exclusive flavor changing neutral current processes B -> M
\nu \bar{\nu} (M= \pi, K, \rho, K^*) in the leptophobic Z^\prime model, in
which the charged leptons do not couple to the extra Z^\prime boson. We find
that these exclusive modes are very effective to constrain the leptophobic
Z^\prime model. In the leptophobic Z^\prime model, additional right-handed
neutrinos are introduced and they can contribute to the missing energy signal
in B -> M + E_missing decays. Through the explicit calculations, we obtain
quite stringent bounds on the model parameters, |U_{sb}^{Z^\prime}| \leq 0.29
and |U_{db}^{Z^\prime}| \leq 0.61, from the already existing experimental data.
We also briefly discuss an interesting subject of massive right-handed
neutrinos, which might be connected with the dark matter problem.Comment: 17 pages, 3 figures, minor corrections, version to appear in PL
from the Hadron Energy Spectrum in Inclusive Semileptonic B Decays
A measurement of the hadron energy spectrum in inclusive semileptonic
decays is proposed as a viable method for extracting . Compared to
the traditional energy spectrum of the charged lepton, the hadron energy
spectrum exhibits kinematical advantages such as a wider energy window and a
larger signal branching fraction. It is emphasized that the hadron energy
spectrum method is most suited for symmetric factories, such as CLEO. The
hadron energy distribution is calculated in the approach of the Altarelli et
al. model and of the heavy-quark effective field theory. In both methods,
perturbative QCD corrections, the Fermi motion of the -quark in the
-meson, and the recoil momentum of the -meson (stemming from the
resonance) are taken into account. We have found excellent
agreement between the spectra calculated in both methods, especially in the
relevant kinematical region below the charmed meson threshold. The theoretical
error to , which is dominated by the uncertainty of the -quark
mass, is estimated to be at the level.Comment: 16 pages, 4 Figures included in the text (uses epsfig.sty), 1 tabl