arXiv subjects
Publications and source records attributed to R. Mohanta.
In the presence of penguin contributions, the indirect CP asymmetry in B^0(t) --> pi^+ pi^- measures sin 2alpha_{eff}, where alpha_{eff} deviates from the true value of the CKM phase alpha by an amount theta, i.e. alpha_{eff} = alpha + theta. Using the measured value of direct CP asymmetry in B^0(t) --> pi^+ pi^-, we derive new bound on |2 theta|.
The rare decay $B^+ \to D_s^+ ϕ$ can occur only via annihilation type diagram in the standard model. The small branching ratio predicted in the standard model makes this channel sensitive to new physics contributions. We analyze this decay mode, both in the standard model and in several extensions of it. The models considered are minimal supersymmetric model with R-parity violation and two Higgs doublet model. The experimental verification of our findings of large branching ratio and/or nonzero CP asymmetry may signal the presence of new physics.
We explore the possibility of extracting the weak phase $γ$ from pure tree decays $Λ_b \to Λ(D^0, \bar{D^0}, D^0_{CP})$ in a model independent way. The CP violating weak phase $γ$ can be determined cleanly, without any hadronic uncertainties, as these decay modes are free from the penguin pollutions. Furthermore, neither tagging nor time dependent studies are required to extract the angle $γ$ with these modes.
We note that it is possible to determine the weak phase γfrom the time dependent measurements of the decays $B_s^0(t) (\bar B_s^0 (t)) \to \bar D^0 ϕwithout any hadronic uncertainties. These decays are described by the color suppressed tree diagrams and hence are free from the penguin pollutions. We further demonstrate that γcan also be extracted with no hadronic uncertainties from an angular analysis of corresponding vector vector modes, $B_s^0(t) (\bar B_s^0 (t)) \to \bar D^{* 0} ϕ$. Although the branching ratios for these decay modes are quite small $ {\cal O} (10^{-5}-10^{-6})$, the strategies presented here appear to be particularly interesting for the "second generation" experiments at hadronic B factories.
We note that the two body nonleptonic pure tree decays $B_c^\pm \to D_s^\pm D^0(\bar D^0)$ and the corresponding vector-vector modes $B_c^\pm \to D_s^{* \pm} D^{*0}(\bar D^{* 0}) $ are well suited to extract the weak phase $γ$ of the unitarity triangle. The CP violating phase $γ$ can be determined cleanly as these decay modes are free from the penguin pollutions.
We investigate the possibility of observing the direct CP violation in the decay modes $B^- \to D^0 D_s^-$ and $D^0 D^-$ within the Standard Model. Including the contributions arising from the tree, annihilation, QCD as well as electroweak penguins with both time- and space-like components, we find that the direct CP asymmetry in $B^- \to D^0 D_s^-$ is very small $\sim 0.2$ % but in $B^- \to D^0 D^- $ decay it can be as large as 4%. Approximately $10^7$ charged $B$ mesons are required to experimentally observe the CP asymmetry parameter for the later case. Since this is easily accessible with the currently running B factories, the decay mode $B^- \to D^0 D^-$ may be pursued to look for CP violation.
Using a theoretical framework based on the next-to-leading order QCD improved effective Hamiltonian, we have estimated the branching ratios and asymmetry parameters for the two body charmless nonleptonic decay modes of $Λ_b$ baryon i.e. $Λ_b \to p (π/ρ),~p(K/K^*)$ and $Λ(π/ρ)$, within the framework of generalized factorization. The nonfactorizable contributions are parametrized in terms of the effective number of colors, $N_c^{eff}$. So in addition to the naive factorization approach ($N_c^{eff}=3 $), here we have taken two more values for $N_c^{eff}$ i.e., $N_c^{eff}=2 $ and $\infty $. The baryonic form factors at maximum momentum transfer ($ q_m^2 $) are evaluated using the nonrelativistic quark model and the extrapolation of the form factors from $q_m^2$ to the required $q^2$ value is done by assuming the pole dominance. The obtained branching ratios for $Λ_b \to pπ, ~pK$ processes lie within the present experimental upper limit .
We have studied new CP violating effects in $Λ_b \to p π$ decay mode, that can arise in Minimal Supersymmetric Standard Model with R-parity violation. We have estimated how much R-parity violation modifies the Standard Model predictions for CP asymmetries within the present bounds. We found that in the R-parity violating model, the rate asymmetry ($a_{cp}$) is suppressed (about 10 times) and the asymmetry parameter $A(α)$ is enhanced (approximately $10^2$ times) with respect to the SM predictions.
The two body non-leptonic $Λ_b$ decays are analyzed in the HQET with factorization approximation and large $N_c$ limit. In this limit, $Λ_b$ and $Λ_c$ baryons can be treated as the bound states of chiral soliton and heavy meson, and consequently the Isgur-Wise function comes out in a straight forward manner. The results obtained remain well below their previously predicted upper limit.