4,337 research outputs found
QCD Approach to B->D \pi Decays and CP Violation
The branching ratios and CP violations of the decays, including
both the color-allowed and the color-suppressed modes, are investigated in
detail within QCD framework by considering all diagrams which lead to three
effective currents of two quarks. An intrinsic mass scale as a dynamical gluon
mass is introduced to treat the infrared divergence caused by the soft
collinear approximation in the endpoint regions, and the Cutkosky rule is
adopted to deal with a physical-region singularity of the on mass-shell quark
propagators. When the dynamical gluon mass is regarded as a universal
scale, it is extracted to be around MeV from one of the
well-measured decay modes. The resulting predictions for all
branching ratios are in agreement with the current experimental measurements.
As these decays have no penguin contributions, there are no direct
asymmetries. Due to interference between the Cabibbo-suppressed and the
Cabibbo-favored amplitudes, mixing-induced CP violations are predicted in the
decays to be consistent with the experimental data at
1- level. More precise measurements will be helpful to extract weak
angle .Comment: 21pages,5 figures,3 tables, typos corrected and numerical result for
one of decay channels is improve
Two Photon Radiation in W and Z Boson Production at the Tevatron Collider
We present a calculation of two photon radiation in W and Z boson production
in hadronic collisions, based on the complete matrix elements for the processes
q\bar q'\to\ell^\pm\nu\gamma\gamma and q\bar q\to\ell^+\ell^-\gamma\gamma,
including finite charged lepton masses. In order to achieve stable numerical
results over the full phase space, multiconfiguration Monte Carlo techniques
are used to map the peaks in the differential cross section. Numerical results
are presented for the Fermilab Tevatron.Comment: Revtex, 28 pages, 3 figure
Role of electromagnetic dipole operator in the electroweak penguin dominated vector meson decays of meson
The pure annihilation type decays and
receive only color suppressed penguin contributions with a very small branching
ratio in the standard model. When we include the previously neglected
electromagnetic dipole operator, the branching ratios can be enhanced one order
magnitude larger than previous study using QCD factorization approach. That is
and . The new effect can also give
a large contribution, of order , to transverse polarization of
and which is comparable to the longitudinal
part. These effects can be detected in the LHCb experiment and the Super-B
factories.Comment: Revised extensively. 8 pages, 4 figure
Charmless hadronic decays in the perturbative QCD approach
In this work, we calculate the branching ratios (BRs) and the polarization
fractions of sixty two charmless two-body meson decays into final states
involving one vector and one axial-vector meson () or two axial-vector
mesons() within the framework of perturbative QCD (pQCD) approach
systematically, where is either a or axial-vector meson.
All considered decay channels can only occur through the annihilation
topologies in the standard model. Based on the perturbative calculations and
phenomenological analysis, we find the following results: (i) the CP-averaged
BRs of the considered sixty two decays are in the range of to
; (ii) since the behavior for meson is much different from
that of meson, the BRs of decays are
generally larger than that of decays in the
pQCD approach; (iii) many considered decays modes, such as , , etc, have sizable BRs within the reach of the LHCb
experiments; (iv) the longitudinal polarization fractions of most considered
decays are large and play the dominant role; (v) the pQCD predictions for
several decays involving mixtures of and/or mesons are highly
sensitive to the values of the mixing angles, which will be tested by the
ongoing LHC and forthcoming Super-B experiments; (vi) the CP-violating
asymmetries of these considered decays are absent in the standard model
because only one type tree operator is involved.Comment: 31 pages, 1 figur
Recent developments in radiative B decays
We report on recent theoretical progress in radiative B decays. We focus on a
calculation of logarithmically enhanced QED corrections to the branching ratio
and forward-backward asymmetry in the inclusive rare decay anti-B --> X(s) l+
l-, and present the results of a detailed phenomenological analysis. We also
report on the calculation of NNLO QCD corrections to the inclusive decay anti-B
--> X(s) gamma. As far as exclusive modes are concerned we consider
transversity amplitudes and the impact of right-handed currents in the
exclusive anti-B --> K^* l+ l- decay. Finally, we state results for exclusive B
--> V gamma decays, notably the time-dependent CP-asymmetry in the exclusive B
--> K^* gamma decay and its potential to serve as a so-called ``null test'' of
the Standard Model, and the extraction of CKM and unitarity triangle parameters
from B --> (rho,omega) gamma and B --> K^* gamma decays.Comment: 5 pages, 2 figures. Accepted for publication in the proceedings of
International Europhysics Conference on High Energy Physics (EPS-HEP2007),
Manchester, England, 19-25 Jul 200
Fast shower simulation in the ATLAS calorimeter
The time to simulate pp collisions in the ATLAS detector is largely dominated by the showering of electromagnetic particles in the heavy parts of the detector, especially the electromagnetic barrel and endcap calorimeters. Two procedures have been developed to accelerate the processing time of electromagnetic particles in these regions: (1) a fast shower parameterisation and (2) a frozen shower library. Both work by generating the response of the calorimeter to electrons and positrons with Geant 4, and then reintroduce the response into the simulation at runtime.
In the fast shower parameterisation technique, a parameterisation is tuned to single electrons and used later by simulation. In the frozen shower technique, actual showers from low-energy particles are used in the simulation. Full Geant 4 simulation is used to develop showers down to ~1 GeV, at which point the shower is terminated by substituting a frozen shower. Judicious use of both techniques over the entire electromagnetic portion of the ATLAS calorimeter produces an important improvement of CPU time. We discuss the algorithms and their performance in this paper
The Semileptonic to Decays in QCD Sum Rules
We analyze the semileptonic rare decays of meson to and
axial vector mesons. The
decays are significant flavor changing neutral current decays of the meson.
These decays are sensitive to the new physics beyond SM, since these processes
are forbidden at tree level at SM. These decays occurring at the quark level
via transition, also provide new opportunities for
calculating the CKM matrix elements and . In this study, the
transition form factors of the decays
are calculated using three-point QCD sum rules approach. The resulting form
factors are used to estimate the branching fractions of these decays.Comment: 18 pages, 7 figures, version to appear in JP
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