We study the single and double lepton polarization asymmetries in the semileptonic $B$ meson decays $B \to K_1 (1270) \ell^+ \ell^-$ $\ell \equiv e$, $μ$, $τ$), where the strange $P$-wave meson, $K_1(1270)$, is the mixtures of the $K_{1A}$ and $K_{1B}$, which are the $1^3P_1$ and $1^1P_1$ states, respectively. The lepton polarization asymmetries show relatively strong dependency in the various region of dileptonic invariant mass. The lepton polarization asymmetries can also be used for determining the $K_1(1270)$--$K_1(1400)$ mixing angle, $θ_{K_1}$ and new physics effects. Furthermore, it is shown that these asymmetries in $B\to K_1(1270)\ell^+\ell^-$ decay compared with those of $B\to K^*\ell^+\ell^-$ decay are more sensitive to the dileptonic invariant mass.
Lepton polarization asymmetries in $B \to X_s τ^+ τ^-$ in MSSM
B介子的半轻子和轻子衰变是检验SM和超越SM的理论的重要探针，因为它们相对干净，理论不确定性小得多。在基于夸克能级跃迁$b \to s τ^+ τ^-$的半轻子衰变中，除了分支比之外，人们还可以研究与末态轻子相关的许多其他（可能的）可观测量，如轻子对前后不对称性，轻子极化不对称性等。但正如最近提出的，如果我们可以标记B介子，那么我们就可以测量两个轻子的极化不对称性。在这里，我们将研究SM中末态轻子及其最小超对称扩展（MSSM）的极化不对称性。
We study the effects of the identical leptons in the final state of the $B^+\to \ell^+ \ell^- \ell^+\barν_{\ell}$ decay. The amplitude of the process is described by the same form factors as the amplitude of the ${B\to \ell \ell \ell'\barν'_{\ell}}$ decay for non-identical leptons in the final state. However, the differential distributions are strongly different, as the ${B^+\to \ell^+ \ell^- \ell^+\barν_{\ell}}$ amplitude contains both the direct ($M_a$) and the exchange ($M_b$) diagrams. We calculate a number of the differential distirbutions. In particular, we propose an interesting observa…
Double-Lepton Polarization Asymmetries and Polarized Forward Backward Asymmetries in the Rare b \to s \ell^+ \ell^- Decays in a Single Universal Extra Dimension Scenario
研究了在标准模型和Appelquist-Cheng-Dobrescu模型中稀有b \to s \ell^+ \ell^-模式的双轻子极化不对称性和单、双轻子极化前后不对称性.特别地，我们研究了观测量对紧化额外维度半径R的敏感性，这是这个新物理模型中的新参数。
We evaluate the decays $\ell_1^\pm \to \ell_2^\pm γ$, $Z \to \ell_1^+ \ell_2^-$, and $h \to \ell_1^+ \ell_2^-$, where $\ell_1$ and $\ell_2$ are charged leptons with different flavours and $h$ is the scalar particle with mass 125.25 GeV, in a two-Higgs-doublet model where all the Yukawa-coupling matrices conserve the lepton flavours but the Majorana mass terms of the right-handed neutrinos break the flavour lepton numbers. We find that (1) the decays $\ell_1^\pm \to \ell_2^\pm γ$ require large Yukawa couplings and very light right-handed neutrinos in order to be visible, (2) the decays $Z \to \…
Inspired by the recent hints of lepton flavor universality violation in $b\to s\ell\ell$ and $b\to c\ellν$ transitions, we study lepton flavor violating exclusive $Λ_b\toΛ\ell_1^+\ell_2^-$ ($\ell_1\neq \ell_2$) decay, which is forbidden in the Standard Model. Starting from a general effective Hamiltonian for a $b\to s\ell_1^+\ell_2^-$ transition that includes vector and axial-vector operators, and scalar and pseudo-scalar operators, we derive a two-fold decay distribution of $Λ_b\toΛ\ell_1^+\ell_2^-$. The distribution helps us to construct the differential branching ratio and the lepton side f…
We study the effect of non-universal $Z'$ boson on the rare leptonic decay modes of $B_s^*$ mesons, mediated by $b arrow sll$ quark transition. Rare B decays are sensitive to various new physics operators. As B mesons are composite particles, such decay modes of the excited states are ideal for probing new physics beyond the standard model. We have constrained our model parameters from $B_(s,d)-$ {B bar(s,d)}$ mixing data to predict the lepton polarization asymmetry of $B_(s,d)^*$ arrow $μ^+ μ^-$ channel. It is found that this asymmetry deviates from its SM prediction along with the $Z'$effect
The most recent measurements of the observables $R_{D^{(*)}}$ are in tension with the Standard Model offering hints of New Physics in $b\rightarrow c \ell \barν_{\ell}$ transitions. Motivated by these results, in this work we present an analysis on their $b\rightarrow u \ell \barν_{\ell}$ counterparts (for $\ell=e, ~μ, ~τ$). Our study has three main objectives. Firstly, using ratios of branching fractions, we assess the effects of beyond the Standard Model scalar and pseudoscalar particles in leptonic and semileptonic $B$ decays ($B^-\rightarrow \ell^- \barν_{\ell}$, $\bar{B}\rightarrow π\ell …
