Teresa Palmer | Searcharxiv

arXiv2013

Form factors for semileptonic D decays

We study the form factors for semileptonic decays of $D$-mesons. That is, we consider the matrix element of the weak left-handed quark current for the transitions $D \rightarrow P$ and $D \rightarrow V$, where $P$ and $V$ are light pseudoscalar or vector mesons, respectively. Our motivation to perform the present study of these form factors are future calculations of non-leptonic decay amplitudes. We consider the form factors within a class of chiral quark models. Especially, we study how the Large Energy Effective Theory (LEET) limit works for $D$-meson decays. Compared to previous work we also introduce light vector mesons $V = ρ, K^*,...$ within chiral quark models. In order to determine some of the parameters in our model, we use existing data and results based on some other methods like lattice calculations, light-cone sum rules, and heavy-light chiral perturbation theory. We also obtain some predictions within our framework.

hep-ph↗

arXiv2010

On the color suppressed contribution to $\bar{B_{d}^0} \rightarrow \, π^0 π^{0}

The decay modes of the type $B \rightarrow π\, π$ are dynamically different. For the case $\bar{B_{d}^0} \rightarrow \, π^+ π^- $ there is a substantial factorized contribution which dominates. In contrast, the decay mode $\bar{B_{d}^0} \rightarrow \, π^0 π^{0} $ has a small factorized contribution, being proportional to a small Wilson coefficient combination. However, for the decay mode $\bar{B_{d}^0} \rightarrow \, π^0 π^{0} $ there is a sizeable nonfactorizable (color suppressed) contribution due to soft (long distance) interactions, which dominate the amplitude. We estimate the branching ratio for the mode $\bar{B_{d}^0} \rightarrow \, π^0 π^{0} $ in the heavy quark limit for the $b$- quark. In order to estimate color suppressed contributions we treat the energetic light ($u,d,s$) quark within a variant of Large Energy Effective Theory combined with a recent extension of chiral quark models in terms of model- dependent gluon condensates. We find that our calculated color suppressed amplitude is suppressed by a factor of order $Λ_{QCD}/m_b$ with respect to the factorizable amplitude, as it should according to QCD-factorization. Further, for reasonable values of the constituent quark mass and the gluon condensate, the calculated nonfactorizable amplitude for $\bar{B_{d}^0} \rightarrow \, π^0 π^{0} $ can easily accomodate the experimental value. Unfortunately, the color suppressed amplitude is very sensitive to the values of these model dependent parameters. Therefore fine-tuning is necessary in order to obtain an amplitude compatible with the experimental result for $\bar{B_{d}^0} \rightarrow \, π^0 π^{0} $. A possible link to the triangle anomaly is discussed.

hep-ph↗