arXiv subjects
Publications and source records attributed to Cai-Dian Lu.
Using the generalized factorization approach, we calculate the CP asymmetries of charmless B decays. A number of decay channels has large CP asymmetries, which can be measured in the B factories.
The radiative corrections to the pure leptonic decay $B_c \to \ellν_{\ell}$ up-to one-loop order is presented. How to cancel the infrared divergences appearing in the loop calculations, and the radiative decay $B_c \to \ellν_{\ell}γ$ is shown precisely. It is emphasized that the radiative decay may be separated properly and may compare with measurements directly as long as the theoretical `softness' of the photon corresponds to the experimental resolutions. Furthermore with a kind of non-relativistic constituent quark model, a kind of typical long distance contributions to the radiative decays is estimated, and it is shown that the contributions are negligible in comparison with the accuracy of one-loop corrections and the expected experimental measurements.
We calculate the two-body nonleptonic B decays using the factorization method. The recent measured decays by CLEO Collaboration can be explained in the factorization approach. We propose a number of ratios of branching ratios to determine the effective coefficients and the form factors.
To the leading order, the radiative leptonic decays $B_c \to γ\ell \bar ν$ ($ \ell=e, μ$) are studied carefully. In the study, a non-relativistic constituent quark model and the effective Lagrangian for the heavy flavour decays are used. As a result, the branching ratios turn out to be of the orders of $10^{-5}$ for $B_c \to γμ\bar ν$ or for $B_c \to γe \bar ν$. Based on this study, we point out the decays being accessible experimentally at the future LHC, and the possibility to determine the decay constant $f_{B_c}$ through the radiative decays.
Non-leptonic decays of B mesons into two mesons or meson resonances are studied on the basis of two versions of simple pole-dominance models involving scalar, vector, pseudoscalar and axial-vector poles. The results are compared with those obtained from the usual factorization model and used to obtain information on strong coupling constants between B meson and one light or one charmed meson, respectively. These coupling constants are compared to results from various QCD sum rule calculations.
We analyze the effects of the space-like penguin diagrams in two body B decays $B^-\to K^-{\bar K}^0$ and $B^-\to π^-{\bar K}^0$. Special attention is paid to the operator $Q_6$, whose contribution is large in the BSW model, but vanishes in the PQCD method in the approximation of neglecting the masses in the final states. Suppressions of the space-like penguin diagrams are found in the PQCD method, which implies that the contributions of the space-like penguins are small compared to those of the time-like penguins.
We re-analyse the long distance contributions to the process $b \to s l^+ l^-$. Full $q^2$-behavior of the vector meson dominance amplitude is used together with the effect of Terasaki suppression, and comparisons with the previous results are given. We show that the interference between short- and long- distance contributions makes it difficult to extract the short distance information from the dominant long distance background, either in the dilepton invariant mass distribution or in the single lepton energy spectrum.
The effective Hamiltonian for the R-parity violating couplings induced nonleptonic decay $B^-\to K^-K^0$ is calculated including leading log QCD corrections running from $m_{\tilde q}$, the mass of the up-type squark, to $m_b$. Experimental upper limit of this decay is used to give the bound on the R-parity violating couplings $λ''$.
We give a more complete calculation of $b \to s e^+e^- $ decay including leading log QCD corrections from $m_{top}$ to $M_W$ in addition to corrections from $M_{W}$ to $m_b$. The differential decay rate is found to be slightly suppressed for a large invariant mass of the $e^+e^- $ pair; while the integrated width is slightly enhanced comparing with the results without the QCD running from $m_{top}$ to $M_W$.
We investigate the radiative dileptonic decays $B_s(B_d)\toγl^+l^-$ within the standard model. Using the constituent quark model, the branching ratios turn out to be around $5\times 10^{-9}$ for $B_s\to γμ^+μ^- $ and around $6\times 10^{-10}$ for $B_d \to γμ^+μ^- $, with slightly larger values for $B_s(B_d) \to γe^+e^- $. The differential rate as a function of the dilepton invariant mass is given. The possibility of using these processes to determine the decay constants of $B_s$ or $B_d$ is discussed.
We study the loop induced rare decays $B_s(B_d)\toγν\barν$ within the standard model. Both constituent quark model and pole model are used and the branching ratios turn out to be of the orders of $10^{-8}$ for $B_s\to γν\bar ν$ and $10^{-9}$ for $B_d \to γν\bar ν$. These processes can be served to determine the decay constants of $B_s$ and $B_d$.
We study the influence of messenger Yukawa couplings and top, bottom and $τ$ Yukawa couplings on the proton lifetime in SU(5) Supersymmetric GUT with dynamical supersymmetry breaking mechanism due to Dine and Nelson.
In this paper we calculate the contributions to the branching ratio of $B\to X_s γ$ from the charged Pseudo-Goldstone bosons appeared in one generation Technicolor model. The current $CLEO$ experimental results can eliminate large part of the parameter space in the $m(P^\pm) - m(P_8^\pm)$ plane, and specifically, one can put a strong lower bound on the masses of color octet charged PGBs $P_8^\pm$: $m(P^{\pm}_8) > 400\;GeV$ at $90\%C.L$ for free $m(P^{\pm})$.
QCD corrections to $b \to s γ$ decay in the two Higgs doublet model are calculated from the energy scale of top quark to that of bottom. The constraints on the two Higgs doublet model from the new experimental bounds of $b\to sγ$ by CLEO and the latest top quark mass by CDF and D0 are reanalyzed. It shows that the constraints become more stringent than that of the earlier analysis, i.e. a bigger region of the parameter space of the model is ruled out.
We give a more complete calculation of $b \to sγ$ decay, including leading log QCD corrections from $m_{top}$ to $M_W$ in addition to corrections from $M_{W}$ to $m_b$. We have included the full set of dimension-6 operators and corrected numerical mistakes of anomalous dimensions in a previous paper\cite{Cho}. Comparing with the calculations without QCD running from $m_{top}$ to $M_W$\cite{Mis}, the inclusive decay rate is found to be enhanced. At $m_t=150$GeV, it results in 12\% enhancement, and for $m_t=250$GeV, 15\% is found. The total QCD effect makes an enhanced factor of 4.2 at $m_t=150$GeV, and 3.2 for $m_t=250$GeV.
QCD corrections to the penguin induced charmless inclusive $B$ decays are performed to an improved leading-log approximation. For process $b \to s q\overline{q} $ (q=uds) and $ b \overline{q} \to s \overline{q} $, four previous missed 4-quark operators are included to make a complete leading log QCD corrected result. Furthermore, part of the next-leading log effect was also given for the above processes and process $b \to s g$. In comparison to previous QCD corrected calculations by Grigjanis et al., the inclusive decay rates for process $b \to s q\overline{q} $ (q=ud), $b\to s s\overline{s}$ and $ b \overline{q} \to s \overline{q} $ are suppressed 10\%, 14\% and 18\% respectively. The branching ratio of process $b \to s g$ is enhanced by 2-3 orders, the result for this process is in agreement with the result of Ciuchini et al.
We give a more complete calculation of $b \to sγ$ decay in 2-Higgs doublet model, including leading log QCD corrections from $m_{top}$ to $M_W$ in addition to corrections from $M_{W}$ to $m_b$. The inclusive decay rate in the first model is found to be suppressed 23\% comparing with the calculations without the QCD running from $m_{top}$ to $M_W$. And the enhancement up to 5\% is found in calculations of the second model. More strict restrictions to parameters of 2-Higgs doublet model II are found.
We introduce an anomalous top quark coupling (right-handed current) into Standard Model Lagrangian. Based on this, a more complete calculation of $b \to sγ$ decay including leading log QCD corrections from $m_{top}$ to $M_W$ in addition to corrections from $M_{W}$ to $m_b$ is given. The inclusive decay rate is found to be suppressed comparing with the case without QCD running from $m_t$ to $M_W$ except at the time of small values of $|f_R^{tb}|$. e.g. when $f_R^{tb}=-0.08$, it is only $1/10$ of the value given before. As $|f_R^{tb}|$ goes smaller, this contribution is an enhancement like standard model case. From the newly experiment of CLEO Collaboration, strict restrictions to parameters of this top-bottom quark coupling are found.