arXiv subjects
Publications and source records attributed to L. T. Handoko.
Longitudinal lepton polarization asymmetry in B_q -> l l (q = d, s$ and l = e, mu, tau) decays is investigated. The analysis is done in a general manner by using the effective operators approach. It is shown that the longitudinal lepton polarization asymmetry would provide a direct search for the scalar and pseudoscalar type interactions, which are induced in all variants of Higgs-doublet models.
The top quark decay process $\tcups$ is studied in the Standard Model and the Minimal Supersymmetric Standard Model with conserved and violated $R-$parity. In dealing with the heavy quarkonium, $\ups$, production, we take both color-singlet and -octet mechanisms into consideration. With numerical analysis it is found that within the Standard Model the decay rate of the concerned process is beyond the border of reachable level of the next round of experiment, though it is much larger than that of the rare top decays, while extra new contributions from beyond the Standard Model could enhance the decay rate by several orders. It is also noticed that a precise measurement of the charged Higgs mass without $\tanβ$ dependence is possible via this process.
We discuss the isospin symmetry breaking quantity Δ^{\pm 0} = Γ(B^\pm -> ρ^\pm γ)/[2 Γ(B^0 -> ρ^0 γ)] - 1, and the direct CP violation in B^\pm -> ρ^\pm γwithin and beyond the standard model. After showing that the leading-order calculation would be a good approximation in such models, we argue that measurements of these quantities would be able to disentagle physics beyond the standard model.
We argue that one can search for physics beyond the standard model through measurements of the isospin-violating quantity $Δ^{-0} \equiv Γ(B^- \to ρ^- γ)/2Γ(B^0 \to ρ^0 γ)-1$, its charge conjugate $Δ^{+0}$, and direct CP violation in the partial decay rates of $B^\pm \to ρ^\pm γ$. We illustrate this by working out theoretical profiles of the charge-conjugate averaged ratio $Δ\equiv {1 \over 2}(Δ^{+0} +Δ^{-0})$ and the CP asymmetry $A_{CP}(B^\pm \to ρ^\pm γ)$ in the standard model and in some variants of the minimal supersymmetric standard model. We find that chargino contributions in the large $\tan β$ region may modify the magnitudes and flip the signs of $Δ$ and $A_{CP}(B^\pm \to ρ^\pm γ)$ compared to their standard-model values, providing an unmistakeable signature of supersymmetry.
Using improved theoretical calculations of the decay form factors in the Light Cone-QCD sum rule approach, we investigate the decay rates, dilepton invariant mass spectra and the forward-backward (FB) asymmetry in the decays $B \to (K,K^*) \ell^+ \ell^-$ ($\ell^\pm =e^\pm,μ^\pm,τ^\pm$) in the standard model (SM) and a number of popular variants of the supersymmetric (SUSY) models. Theoretical precision on the differential decay rates and FB-asymmetry is estimated in these theories taking into account various parametric uncertainties. We show that existing data on $B \to X_s γ$ and the experimental upper limit on the branching ratio ${\cal B}(B \to K^* μ^+ μ^-)$ provide interesting bounds on the coefficients of the underlying effective theory. We argue that the FB-asymmetry in $B \to K^* \ell^+ \ell^-$ constitutes a precision test of the SM and its measurement in forthcoming experiments may reveal new physics. In particular, the presently allowed large-$\tan β$ solutions in SUGRA models, as well as more general flavor-violating SUSY models, yield FB-asymmetries which are characteristically different from the corresponding ones in the SM.
Semi-inclusive top decays, $t \to q_i \v$, are examined in the framework of the standard model, with $q_i = u {\rm or} c$, $\v$ : vector meson formed by $q_j \qb_j$ ($q_j = d, s, b$). By using a simple model of hadronization, that is $ 0 ł| \qb_j γ^μq_j \r| \v = \mv \fv \evj^μ$, the total branching ratio is expected to be $\br(\tivj) < ({ł| \vij^\ast \vtj \r|}/{ł| \vtb \r|})^2 \times O({10}^{-3})$ depends on the size of the coupling constant $\fv$. On the other hand, the CP asymmetry should be induced only by the long-distance effects of intermediate state $q_k \qb_k$ ($q_k = d, s, b$) that subsequent scatters into the vector meson. The analytical results including the continuum contributions are given with keeping all masses. However, it yields the CP asymmetry to be small, i.e. $\acp (\tivj) < {\im [(\vij^\ast \vtj)^\ast (\vik^\ast \vtk)]}/{ł| \vij^\ast \vtj \r|^2} \times O({10}^{-2})$ for an identified $q_k \qb_k$ intermediate state, and suppressed more again by a factor of $\sim {({m_b}^2 - {m_s}^2)}/{\mv^2}$ for summing up all of them. Particularly, $\acp (t \to u Υ) \simeq \pm 1%$, induced by the intermediate state $d\bar{d}$ or $s\bar{s}$.
Semi-inclusive decays, $\hlx$, are studied in the framework of the minimal supersymmetric standard model without $R-$parity, where $\qh$ ($\ql$) are the second or third (first or second) generation quarks with the same charge and $ξ$ is a vector meson formed by $q_j \qb_j$. The study is focused on the contributions of sfermions with $m_{\sf} < m_{\rm top}$. In this mass region, CP asymmetries in top decays can be induced by taking into account the decay-widths of the exchanged-bosons, while in light-quark decays it can be generated due to the long-distance effects. The contributions of sfermions also alter the branching-ratios destructively or constructively depend on the phases of complex couplings of the $R-$parity violation interactions.
I point out that $B \to X_q ł^+ ł^-$ decays $(q = s, d)$ are sensitive probes of possible violation of CKM unitarity. I compute the decay rates and asymmetries in a minimal extension of the Standard Model containing an additional isosinglet charge (-1/3) quark, which leads to a deviation from CKM unitarity. It is shown that even for small mixing ratios $|{z_{qb}}/{(V_{tq}^\ast V_{tb})}| \sim O({10}^{-2})$, the contribution of the tree-level $Z-$FCNC appearing in the model should change the rates and asymmetries significantly. Especially the CP asymmetry, $A_{CP} (B \to X_s ł^+ ł^-)$, can be enhanced to be few percents, while in the standard model the size is less than $O({10}^{-3})$. On the other hand, $A_{CP} (B \to X_d ł^+ ł^-)$ is not altered so much. Constraints for the mixing ratios are extracted from the experiments of $B \to X_s γ$ for $q = s$ and $B_d^0 - \bar{B}_d^0$ mixing for $q = d$ under a natural assumption that the couplings of the tree-level $Zf\bar{f}$ are almost unity, i.e. $z_{αα} \sim 1$.
The possibility to test the unitarity triangle of CKM matrix is examined by using the semileptonic rare $B$ decays, $B \rightarrow X_q \, ł^+ \, ł^-$ with $q = d, s$ and $ł$'s are leptons. The discussion is emphasized on the CP asymmetry in the framework of standard and beyond the standard models. For the beyond standard model, a minimal extension of the standard model containing an additional isosinglet charge (-1/3) charge quark, which leads to a deviation from CKM unitarity, is considered. As the results, in the standard model the CP asymmetry is visible only for $B \rightarrow X_d \, ł^+ \, ł^-$, while in the latter model it is sizeable even for $B \rightarrow X_s \, ł^+ \, ł^-$.
We study the effects of a vector-like SU(2) quark doublet as a fourth generation. In this model we examine the chiral structure and the FCNC in the quark sector by using radiative B meson decays in the allowed region for parameters from $R_b = {Γ_{qq}}/{Γ_{had.}}$. We compute the ratio $R = {Br (b \to d γ)}/{Br (b \to s γ)}$ in the model which realizes a different chiral structure as well as FCNC. The constraints has been extracted from the experimental results of B meson decays, the $T_{new}$ parameter of oblique corrections and $R_b$. Under the natural assumption that the violation of the $V-A$ structure in the light-quark sector is small, we can determine the allowed region for most of the mixings parameters and the vector-like quark masses. We show that there will be significant deviations in $R$ from the SM prediction due to the FCNC's and the violation of the $V-A$ structure.
I examine a possibility to extract the angle $γ$ of the Cabibbo-Kobayashi-Maskawa unitarity triangle by the inclusive $B \to X_d ł^+ ł^- $ decay. An independent information for the angle is expected from the non-trivial contribution induced in $u \bar{u}$ and $c \bar{c}$ loops. The contributions induce CP asymmetry which has high sensitivity to the angle $γ$ in the whole dilepton invariant mass region. Particularly, in the low dilepton invariant mass region, the sensitivity is also recognized in the branching-ratio with any dilepton final states and the lepton polarization asymmetry with dimuon final state. In the high dilepton invariant mass region, the sensitivity is tiny in all measurements with the exception of the CP asymmetry, that make them to be good probes to confirm the measurement of ${V_{td}}^\ast V_{tb}$ in addition to the present data from $B_d^0-\bar{B}_d^0$ mixing. The decay rate and asymmetries are examined in the Standard Model with taking into account the long-distance contributions due to vector-mesons as well as its momentum dependences that would reduce the long-distance backgrounds in the channel.
We investigate the leading power corrections to the decay rates and distributions in the decay $B \rightarrow X_s \ell^+ \ell^- $ in the standard model (SM) using heavy quark expansion (HQE) in $(1/m_b)$ and a phenomenological model implementing the Fermi motion effects of the b quark bound in the B hadron. In the HQE method, we find that including the leading power corrections the decay width decreases by about 4% and the branching ratio by about 1.5% from their (respective) parton model values. The dilepton invariant mass spectrum is found to be stable against power corrections over a good part of this spectrum. However, near the high-mass end-point this distribution becomes negative with the current value of the non-perturbative parameter $λ_2$ (the $λ_1$-dependent corrections are found to be inoccouos), implying the breakdown of the HQE method in this region. Our results are at variance with the existing ones in the literature in both the decay rate and the invariant dilepton mass distribution calculated in the HQE approach. As an alternative, we implement the non-perturbative effects in the decay $B \rightarrow X_s \ell^+ \ell^- $ using a phenomenologically motivated Gaussian Fermi motion model. We find small corrections to the branching ratio, but the non-perturbative effects are perceptible in both the dilepton mass distribution and the Forward-Backward asymmetry in the high dilepton mass region. Using this model for estimating the non-perturbative effects, we present the decay rates and distributions for the inclusive process $B \rightarrow X_s \ell^+ \ell^- $ in the SM.
The contributions of $s-$channel Higgs in $l^+ l^- \rightarrow q \bar{q}$ processes in the general lepton collider ($l^+ l^-$ collider) within Standard Model is studied. A new idea to extract the contribution by using the data from both electron and future heavy-lepton colliders at same center-of-mass energy is proposed. Deviations due to the $s-$channel Higgs contributions are analysed and discussed for the heavy-quark final states by using the total cross-section, forward-backward asymmetry and its ratio. It is shown that significant deviations are expected for the top quark final state.
We study the effect of the FCNC on rare $B$ decays in the beyond standard model with vector like singlet quarks. It has been shown that $b \rightarrow s γ$ does not receive sizable contribution compared with that of the standard model while $b \rightarrow d γ$, $b \rightarrow s(d) l^+ l^-$, can be changed from the predictions of the standard model.
We study the implications of a vector-like quark, especially a down-type vector-like quark in $b \rightarrow s(d) γ$ including the neutral Higgs in the calculation. After analyzing some possible constraints for the mixing, the contribution may be significant for the $b \rightarrow d γ$, but not for the $b \rightarrow s γ$. We also find that the FCNC among ordinary quarks vanishes for a special form of down-type quark mass matrix.