Effects Of Fourth Generation Research Articles

The effects of fourth generation on the total branching ratio and the lepton polarization in Λb→ Λell+ell−decay

This study investigates the influence of the fourth generation quarks on the total branching ratio and the single lepton polarizations in \Lambda_b --> \Lambda \ell^+ \ell^- decay. Taking $|V_{t's}V_{t'b}| {0.01-0.03} with phase just below $90^\circ$, which is consistent with the b\to s\ell^+\ell^- rate and the B_s mixing parameter \Delta m_{B_s}, we obtain that the total branching ratio and the single lepton(\mu, \tau) polarizations are quite sensitive to the existence of fourth generation. It can serve as a good tool to search for new physics effects, precisely, to search for the fourth generation quarks(t', b').

Fourth generation effects in processes induced by the $b \rightarrow s$ transition

We study the effects of sequential fourth quark generation in rare "B -> K(K*) l^+ l^-" decays induced by "b -> s" transition and in "B_s^0 - bar{B}_s^0" mixing. Using the experimental values on branching ratios of the "B -> X_s gamma" and "B -> K(K*) l^+ l^-" decays, the allowed regions for $\vel V_{tb} V_{ts}^\ast\ver$ and "|V_{t'b} V_{t's}*| are determined as a function of the (t') quark mass.

Fourth-generation effects on the rare B → K*νν̄ decay

The rare B→K*νν̄ decay is analysed witha new up-like quark in a sequential fourth-generation model. Two possible solutions for the fourth-generation CKM (Cabibbo-Kabayashi-Maskawa)factor obtained as a function of the new -quark mass are used. The branching ratio (BR) and missing-energy spectrum of this decay in the two cases are estimated. Inone case, it is shown that for GeVa significant enhancement to the BR and the missing-energy spectrum of this decay over the SM (standard model) is recorded, whilethe results are almost same in the other case. If a fourthgeneration should exist in nature and nature chooses this case,this B-meson decay mode could be a good probe for the existenceof the fourth generation, or perhaps a signal for a new physics.

Constraints on the Fourth Generation Effect on CP Violation in Penguin-Dominated b → s Decays

The direct CP-violating asymmetries for the penguin-dominated b → sg, b → sγ, and b → sl+l- decays are reexamined using the generalized 4×4 Kobayashi-Maskawa matrix proposed by Bjorken. We find that the fourth generation effect on these asymmetries are significantly constrained by the sign of sin ϕ3/sinϕ1, the imaginary part of the loop integral function for c-quark Im(Ic), and the mass of t'-quark. Most of the previous predictions for this effect are too optimistic.

Fourth-generation effects in Z0 to bb-bar decay

Possible fourth-generation effects in partial widths in Z0 into bb-bar decay are discussed with the consideration of all quark mixing within the minimal standard model. The authors show that it is possible to disentangle the effects from the fourth generation especially when mt is much heavier than top and mod Vtb mod is small enough.

Fourth-generation effect on CP violation in Bd hadronic decays.

Du, Dunietz, and Wu examined $\mathrm{CP}$ violation in partial-decay-rate asymmetries of neutral $b$-flavored mesons in the standard Kobayashi-Maskawa (KM) model. We calculate in the four-generation model the same $\mathrm{CP}$ asymmetry in ${B}_{d}$ hadronic decays in light of the large ${B}_{d}\ensuremath{-}{\overline{B}}_{d}$ mixing obtained by the ARGUS and CLEO Collaborations. The general 4\ifmmode\times\else\texttimes\fi{}4 KM matrix proposed by Botella and Chau is used. The effect of the fourth generation on asymmetry is found to be sizable for various mixings of the fourth with the preceding three generations, changing signs of the asymmetry in the modes $\overline{b}\ensuremath{\rightarrow}\overline{u}\mathrm{ud}$ and $\overline{b}\ensuremath{\rightarrow}\overline{c}c\overline{d}$, and enhancing magnitudes in the modes $\overline{b}\ensuremath{\rightarrow}\overline{u}c\overline{d}$ and $\overline{b}\ensuremath{\rightarrow}\overline{c}u\overline{d}$ from their standard-model predictions.

Fourth generation effects in B physics

Effects of a fourth generation in B s 0− B s 0 mixing ( x s) and CP violation in the B system are discu ssed. Although four-generation models can accomodate practically any value of x s, most of the four-generation parameter space predicts x s to be in the standard model range. At most ∼1% of the parameter space predicts small B s 0−B s 0 mixing ( x s<2). The effects are much more striking in CP violating hadronic decay asymmetries. The CP asymmetry in B d→ ΨK s is found to be negative in about half of the four- generation parameter space, and ∼40% of the space predicts an asymmetry ∥ A(B s→ Ψφ)∥>0.2.

Fourth-generation effect on CP violation in B-->K phi decays.

CP-violating asymmetries in the B\ensuremath{\rightarrow}K\ensuremath{\varphi} decays are studied in the four-generation model. The absorptive part in the penguin amplitude leads to the CP-violating asymmetry in the ${B}_{U}^{\ifmmode\pm\else\textpm\fi{}}$\ensuremath{\rightarrow}${K}^{\ifmmode\pm\else\textpm\fi{}}$\ensuremath{\varphi} decays, which could be as large as \ifmmode\pm\else\textpm\fi{}15% in the four-generation model, although it is at most a few percent in the three-generation model. The asymmetry between the ${B}_{d}^{0}$\ensuremath{\rightarrow}${K}_{S}^{0}$\ensuremath{\varphi} and B${\ifmmode\bar\else\textasciimacron\fi{}}_{d}^{0}$\ensuremath{\rightarrow}${K}_{S}^{0}$\ensuremath{\varphi} decays is also expected to be \ifmmode\pm\else\textpm\fi{}10% on \ensuremath{\Upsilon}(4S) through the penguin absorptive part with the contribution of the fourth-generation quark.

Fourth-generation effect on anticharm-charm asymmetry in B0 inclusive decays.

Dunietz and Sachs calculated the CP asymmetry A(c,c\ifmmode\bar\else\textasciimacron\fi{}) between inclusive charmed and anticharmed modes in ${B}^{0}$,B\ifmmode\bar\else\textasciimacron\fi{} $^{0}$ decay in the standard Kobayashi-Masakawa model. We calculate the same asymmetry in the four-generation model by using a naive extension of the Dunietz-Sachs scheme. It is shown that \ensuremath{\Vert}A(c,c\ifmmode\bar\else\textasciimacron\fi{})\ensuremath{\Vert}0.015 for the ${B}_{d}$ meson and \ensuremath{\Vert}A(c,c\ifmmode\bar\else\textasciimacron\fi{})\ensuremath{\Vert}0.017 for the ${B}_{s}$ meson, which are almost the same as in the three-generation model. The reason for this small effect of the fourth generation is investigated. Some comments are also given for the case of the two-Higgs-doublet and left-right-symmetric models.