In this paper, we investigate the effects of the fourth generation of quarks on the double-lepton polarization asymmetries in the $B_s \rar ϕ\ell^+ \ell^-$ decay. It is shown that these asymmetries in $B_s \rar ϕ\ell^+ \ell^-$ decay compared with those of $B \rar K \ell^+ \ell^-$ decay are more sensitive to the fourth-generation parameters. We conclude that an efficient way to establish the existence of the fourth generation of quarks could be the study of these asymmetries in the $B_s \rar ϕ\ell^+ \ell^-$ decay.
Analysis of Various Polarization Asymmetries In The Inclusive $b\to s \ell^+ \ell^-$ Decay In The Fourth-Generation Standard Model
本文系统地分析了四代夸克标准模型中包含$b \rar s \ell^+ \ell^-$衰变的各种极化不对称性。我们发现,对于$μ$和$τ$通道,各种不对称性对新的混合和夸克质量都很敏感。从SM值的大的偏差。因此,$b \rar s \ell^+ \ell^-$衰变是一个有价值的工具,用于搜索SM以外的物理,特别是在间接搜索第四代夸克($t', b')$)。
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 consider measurements of exclusive rare semi-tauonic $b$-hadron decays, mediated by the $b \rightarrow s τ^+ τ^-$ transition, at a future high energy circular electron-positron collider (FCC-$ee$). We argue that the high boosts of $b$-hadrons originating from on-shell $Z$ boson decays allow for a full reconstruction of the decay kinematics in hadronic $τ$ decay modes (up to discrete ambiguities). This, together with the potentially large statistics of $Z\to b\bar b$, opens the door for the experimental determination of $τ$ polarizations in these rare $b$-hadron decays. In light of the curre…
Tree-level FCNC in the B system: from CP asymmetries to rare decays
树级变味中性流(FCNC)是具有额外矢量夸克的模型的特征。这些新的耦合可以强烈地改变B^0 CP不对称性,而不会与低能约束相冲突。鉴于低CP不对称性在B --> J/K_{S} K_{S},我们讨论了这些贡献的影响。我们发现,即使这些低的值可以很容易地容纳在这些模型。此外,我们表明,从B工厂的新数据往往有利于O(20)的增强的b --> d l \bar{l}过渡超过SM的期望。
The rare radiative flavour changing top decays $t\to cγ$ and $t\to cg$ (and the even rarer $t\to uγ$ and $t\to ug$) have been processes of interest for decades as they offer a key probe for studying top quark properties. However an explicit analytical study of the branching ratios and $CP$ asymmetries resulting from these loop level processes has thus far evaded attention. In this work, we provide the formulation for the $CP$ asymmetry resulting from the total kinetic contribution of the loop integrals and their imaginary parts, as well as an updated numerical computation of the predicted Stan…
We investigate the rare baryonic $Λ_b\rightarrowΛl^+ l^-$ decays in a non-universal $Z'$ model, which is one of the well-motivated extensions of the standard model (SM). Considering the effects of $Z'$-mediated flavour-changing neutral currents (FCNCs) we analyse the differential decay rate, forward-backward asymmetries and lepton polarisation asymmetries for the $Λ_b\rightarrowΛl^+ l^-$ decays. We find significant deviations from their SM predictions, which could indicate new physics arising from the $Z'$ gauge boson.
$B \to K \etap$ decays in the SM with fourth generation fermions
利用微扰QCD(pQCD)因子分解方法,计算了含有第四代费米子(SM 4)的标准模型(SM)中由包含$\tp$夸克的圈图引起的四个$B \to K \etap$衰变的新物理贡献.在所考虑的SM 4参数空间内,我们发现:(a)SM和SM 4的次领先阶(next-to-leading分支比,NLO)pQCD预言与实验数据在一个标准差内基本一致;(b)对于$Br(B \to K η)$,第四代贡献的加入可以有效地改善理论预言与实验数据的一致性;(c)对于$Br(B \to K \etar)$,由于$\tp$环引起的衰减与数据不符;(d)对所考虑衰变的CP破坏不对称性的新物理修正仅为10%左右。
We analyze patterns from CP-violating new physics (NP) in hadronic and semileptonic rare charm $\vert Δc \vert=\vert Δu\vert=1$ transitions. Observation of direct CP-violation in hadronic decays, as in $ΔA_{\text{CP}}$, provides opportunities for $c \to u \,\ell^+ \ell^-$, $\ell=e,μ$ transitions, and vice versa. For the concrete case of flavorful, anomaly-free $Z^\prime$-models a NP-interpretation of $ΔA_{\text{CP}}$ suggests measurable CP-asymmetries in semileptonic decays such as $D \to π\, \ell^+ \ell^-$ or $D \to ππ\, \ell^+ \ell^-$. Conversely, an observation of CP-violation in $c \to u\,…
在第四代夸克模型SM 4中研究了夸克能级跃迁$ b \to s$控制下的$Λ_b$重子的稀有衰变。最近的研究表明,作为标准模型的一个简单推广,SM4可以成功地解释$B$和$B_s$介子CP破坏参数中的几个异常现象。我们发现,在这个模型中,由于额外的贡献来自重$t'$夸克的环,分支比和其他观测值在罕见的$Λ_b$衰变偏离其SM值显着。其中一些模式是在LHCb实验的范围内,寻找这样的通道是有争议的。
Analysis of B_{C} --> D_{s}^{*}l^{+}l^{-} in the Standard Model Beyond Third Generation
The weak decays of B_{c} --> D_{s} ^{*}l^{+}l^{-} (l=mu,tau) are investigated in the Standard Model with fourth generation (SM4). Taking fourth generation quark mass m_{t'} of about 300 to 600 GeV with the CKM matrix elements V_{t'b} ^{*} V_{t's} in the range (0.03-1.2)*10^{-2} and using the new CP odd phase ( phi_{sb} ) to be 90^{o} the analysis of decay rates, forward-backward asymmetries, lepton polarization asymmetries and the helicity fractions of D_{s} ^{*} meson in B_{c} --> D_{s} ^{*}l^{+}l^{-} (l=mu,tau) is made. It is shown that the values of these physical observables are greatly in…
Motivated by the recent measurement of $D^0\toρ^0γ$ improved standard model (SM) predictions for branching ratios and CP asymmetries of radiative charm decay are given. Weak annihilation induced decays are probes of non-perturbative QCD approaches. Rare decays probe the SM and physics beyond the SM, e.g. leptoquark and supersymmetric models. Opportunities with $Λ_c\to pγ$ for future polarization measurements are presented.
Using the Bethe-Salpeter equation (BSE) we investigate the forward-backward asymmetries $( A_{FB}) $ in $Λ_b \rightarrow Λl^+ l^-(l=e,μ,τ)$ in the quark-diquark model. This approach provides precise form factors that are different from those of QCD sum rules. We calculate the rare decay form factors for $Λ_b \rightarrow Λl^+ l^-$ and investigate the (integrated) forward-backward asymmetries in these decay channels. We find that the integrated $A^l_{FB}$, $\bar{A}^l_{FB}(Λ_b \rightarrow Λe^+ e^-) \simeq -0.1371 $, $\bar{A}^l_{FB}(Λ_b \rightarrow Λμ^+ μ^- ) \simeq -0.1376 $, $\bar{A}^l_{FB}(Λ_b …