1,954 research outputs found

### Factorization of Radiative Leptonic Decays of $B^-$ and $D^-$ Mesons Including the Soft Photon Region

In this work, we study the radiative leptonic decays of $B^-$ and $D^-$
mesons using factorization approach. Factorization is proved to be valid
explicitly at 1-loop level at any order of $O(\Lambda_{\rm
QCD}\left/m_Q\right.)$. We consider the contribution in the soft photon region
that $E_{\gamma} \sim \left. \Lambda^2_{\rm QCD} /\right. m_Q$. The numerical
results shows that, the soft photon region is very important for both the $B$
and $D$ mesons. The branching ratios of $B\to \gamma e\nu_e$ is $5.21\times
10^{-6}$, which is about $3$ times of the result obtained by only considering
the hard photon region $E_{\gamma}\sim m_Q$. And for the case of $D\to \gamma
e\nu_e$, the result of the branching ratio is $1.92\times 10^{-5}$.Comment: arXiv admin note: text overlap with arXiv:1409.035

### B to light meson transition form factors calculated in perturbative QCD approach

We calculate the $B\to P$, $B\to V$ (P: light pseudoscalar meson, V light
vector meson) form factors in the large-recoil limit in perturbative QCD
approach, including both the vector (axial vector) and tensor operators. In
general there are two leading components $\phi_B$ and $\bar{\phi}_B$ for $B$
meson wave functions. We consider both contributions of them. Sudakov effects
($k_{\perp}$ and threshold resummation) are included to regulate the soft
end-point singularity. By choosing the hard scale as the maximum virtualities
of internal particles in the hard $b$-quark decay amplitudes, Sudakov factors
can effectively suppress the long-distance soft contribution. Hard contribution
can be dominant in these approaches.Comment: 21 pages, with 2 figure

### Radiative and leptonic decays of the pseudoscalar charmonium state $\eta_c$

The radiative and leptonic decays of $\eta_c\to \gamma\gamma$ and $\eta_c\to
l^+l^-$ are studied. For $\eta_c\to \gamma\gamma$ decay, the second-order
electromagnetic tree-level diagram gives the leading contribution. The decay
rate of $\eta_c\to \gamma\gamma$ is calculated, the prediction is in good
agreement with the experimental data. For \eta_c\to l^+\l^-, both the tree
and loop diagrams are calculated. The analysis shows that the loop contribution
dominates, the contribution of tree diagram with $Z^0$ intermediate state can
only modifies the decay rate by less than 1%. The prediction of the branching
ratios of $\eta_c\to e^+e^-$ and $\mu^+\mu^-$ are very tiny within the standard
model. The smallness of these predictions within the standard model makes the
leptonic decays of $\eta_c$ sensitive to physics beyond the standard model.
Measurement of the leptonic decay may give information of new physics.Comment: 9 pages, 4 figures, RevTex, small change, version to appear in Phys.
Rev.

### Spectrum of the charmed and b-flavored mesons in the relativistic potential model

We study the bound states of heavy-light quark-antiquark system in the
relativistic potential model, where the potential includes the long-distance
confinement term, the short-distance Coulomb term and spin-dependent term. The
spectrum of $B$, $B^*$, $D$, $D^*$ and states with higher orbital quantum
numbers are obtained. Compared with previous results predicted in the
relativistic potential model, the predictions are improved and extended in this
work, more theoretical masses are predicted which can be tested in experiment
in the future.Comment: 10 pages, no figure, 2 tables, more discussion is added. Version to
appear in JHE

### D^0-D^0bar mixing in \Upsilon(1S) \to D^0 D^0bar decay at Super-B

\Dz-\Dzb mixing and significant CP violation in the charm system may
indicate the signature of new physics. In this study, we suggest that the
coherent \DzDzb events from the decay of \Upsilon(1S) \to \Dz \Dzb can be
used to measure both mixing parameters and CP violation in charm decays. The
neutral $D$ mesons from $\Upsilon(1S)$ decay are strongly boosted, so that it
will offer the possibility to measure the proper-time interval, $\Delta t$,
between the fully-reconstructed \Dz and \Dzb. Both coherent and
time-dependent information can be used to extract \Dz-\Dzb mixing parameters.
The sensitivity of the measurement should be improved at B factories or
super-B.Comment: 6 pages, 1 figure, this is the last version to appear in Phys. Rev.

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