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A. I. Sanda

Publications and source records attributed to A. I. Sanda.

At least 19 recordsLinked to original sources
arXiv2010

Decays of $B$ meson to two charmed mesons

The factorization theorem in Decays of $B_{(s)}$ mesons to two charmed mesons (both pseudoscalar and vector) can still be proved in the leading order in $m_D/m_B$ and $Λ_{\rm{QCD}}/m_D$ expansion. Working in the perturbative QCD approach, we find that the factorizable emission diagrams are dominant. Most of branching ratios we compute agree with the experimental data well, which means that the factorization theorem seems to be reliable in predicting branching ratios for these decays. In the decays of a $B$ meson to two vector charmed mesons, the transverse polarization states contribute $40%-50%$ both in the processes with an external W emission and in the pure annihilation decays. This is in agreement with the present experimental data. We also calculate the CP asymmetry parameters. The results show that the direct CP asymmetries are very small. Thus observation of any large direct CP asymmetry will be a signal for new physics. The mixing induced CP asymmetry in the neutral modes is large. This is also in agreement with the current experimental measurements. They can give a cross check of the $\sin 2β$ measurement from other channels.

hep-ph↗
arXiv2010

Physics at Super B Factory

This report presents the results of studies that investigate the physics reach at a Super $B$ factory, an asymmetric-energy $e^+e^-$ collider with a design luminosity of $8 \times 10^{35}$ cm$^{-2}$s$^{-1}$, which is around 50 times as large as the peak luminosity achieved by the KEKB collider. The studies focus on flavor physics and CP violation measurements that could be carried out in the LHC era. The physics motivation, key observables, measurement methods and expected precisions are presented.

hep-ex↗
arXiv2007

Analysis of Lepton Flavor Violating τ^\pm \to μ^\pm μ^\pm μ^\mp Decays

Supposing only Lorentz and the gauge invariances of the Lagrangian, we derive energy and angular distributions for $τ^\pm \to μ^\pm μ^\pm μ^\mp$ lepton flavor violating decay process. Using these results, we discuss methods to determine the parameters associated with the lepton flavor violating interactions.

hep-ph↗
arXiv2007

A Solution for Little Hierarchy Problem and b --> s gamma

We show that all the parameters which destabilize the weak scale can be taken around the weak scale in the MSSM without conflicting with the SM Higgs mass bound set by LEP experiment. The essential point is that if the lightest CP-even Higgs h in the MSSM has only a small coupling to Z boson, g_{ZZh}, LEP cannot generate the Higgs sufficiently. In the scenario, the SM Higgs mass bound constrains the mass of the heaviest CP-even Higgs H which has the SM like g_{ZZH} coupling. However, it is easier to make the heaviest Higgs heavy by the effect of off-diagonal elements of the mass matrix of the CP-even Higgs because the larger eigenvalue of 2 times 2 matrix becomes larger by introducing off-diagonal elements. Thus, the smaller stop masses can be consistent with the LEP constraints. Moreover, the two excesses observed at LEP Higgs search can naturally be explained as the signals of the MSSM Higgs h and H in this scenario. One of the most interesting results in the scenario is that all the Higgs in the MSSM have the weak scale masses. For example, the charged Higgs mass should be around 130 GeV. This looks inconsistent with the lower bound obtained by the b --> s gamma process as m_{H^\pm}>350GeV. However, we show that the amplitude induced by the charged Higgs can naturally be compensated by that of the chargino if we take the mass parameters by which the little hierarchy problem can be solved. The point is that the both amplitudes have the same order of magnitudes when all the fields in the both loops have the same order of masses.

hep-ph↗
arXiv2006

Mixing-induced CP asymmetry in B-> K* gamma decays with perturbative QCD approach

The mixing-induced CP asymmetries in B-> K* gamma -> K_S pi^0 gamma and B-> K* gamma -> K_L pi^0 gamma are expected to be small within the standard model. So they are among the most promising decay modes to test the standard model. In this paper, we compute the mixing-induced CP asymmetries in these decay modes, within the framework of the standard model, using perturbative QCD, and our conclusion is S_{K_S pi^0 gamma}=-S_{K_L pi^0 gamma}=-(3.5\pm 1.7)\times 10^{-2}.

hep-ph↗
arXiv2005

Resolution to the B -> pi K puzzle

We calculate the important next-to-leading-order contributions to the B -> pi K, pi pi decays from the vertex corrections, the quark loops, and the magnetic penguins in the perturbative QCD approach. It is found that the latter two reduce the leading-order penguin amplitudes by about 10%, and modify only the B -> pi K branching ratios. The main effect of the vertex corrections is to increase the small color-suppressed tree amplitude by a factor of 3, which then resolves the large difference between the direct CP asymmetries of the B^0 -> pi^\mp K^\pm and B^\pm -> pi^0 K^\pm modes. The puzzle from the large B^0 -> pi^0 pi^0 branching ratio still remains.

hep-ph↗
arXiv2005

A "Known" CP Asymmetry in $τ$ Decays

We point out that dynamics known from the observed CP violation in $K_L\to π^{\mp}l^{\pm}ν$ generate a CP asymmetry of $3.3\cdot 10^{-3}$ in $τ^{\pm} \to νK_Lπ^{\pm}$. CPT invariance requires the same asymmetry in the more approachable transitions $τ^{\pm} \to νK_Sπ^{\pm}$. While little new can be learnt from this fact, it has to be accounted for, since CP asymmetries in $τ\to νKπ$ channels are prime candidates for revealing the intervention of New Physics. This `known' CP asymmetry provides a very useful calibration point in such searches. It also provides a test of CPT symmetry (as well as the $ΔQ = ΔS$ selection rule).

hep-ph↗
arXiv2005

CP asymmetry, branching ratios and isospin breaking effects of B -> K* gamma with the perturbative QCD approach

The radiative B -> K* gamma mode is caused by a penguin operator which is a quantum correction. Thus this mode may be useful in the search for physics beyond the standard model. In this paper, we compute the branching ratio, direct CP asymmetry, and isospin breaking effects within the Standard Model in the framework perturbative QCD, and discuss how new physics might show up in this decay.

hep-ph↗
arXiv2005

Nonfactorizable contributions to $B \to D^{(*)} M$ decays

While the factorization assumption works well for many two-body nonleptonic $B$ meson decay modes, the recent measurement of $\bar B\to D^{(*)0}M^0$ with $M=π$, $ρ$ and $ω$ shows large deviation from this assumption. We analyze the $B\to D^{(*)}M$ decays in the perturbative QCD approach based on $k_T$ factorization theorem, in which both factorizable and nonfactorizable contributions can be calculated in the same framework. Our predictions for the Bauer-Stech-Wirbel parameters, $|a_2/a_1|= 0.43\pm 0.04$ and $Arg(a_2/a_1)\sim -42^\circ$ and $|a_2/a_1|= 0.47\pm 0.05$ and $Arg(a_2/a_1)\sim -41^\circ$, are consistent with the observed $B\to Dπ$ and $B\to D^*π$ branching ratios, respectively. It is found that the large magnitude $|a_2|$ and the large relative phase between $a_2$ and $a_1$ come from color-suppressed nonfactorizable amplitudes. Our predictions for the ${\bar B}^0\to D^{(*)0}ρ^0$, $D^{(*)0}ω$ branching ratios can be confronted with future experimental data.

hep-ph↗
arXiv2005

Search for New Physics in B Decays

We review recent important progresses at the B factories and discuss the future prospects. We also comment on how we might proceed to search for new physics.

hep-ph↗
arXiv2004

On the Sign of $ΔM_B$, $M_{12}$, sin$2ϕ_1$ and all that

We are withdrawing our paper hep-ph/0411135 since its main conclusion is wrong as we have learnt with the assistance of Bob Cahn and Jerome Charles. The sign of $ΔM_B$ does not matter in interpreting the CP asymmetry in $B_d \to ψK_S$, as we could have seen from our very own Eq.(13). We know now how to derive the correct result of Grossman, Kayser and Nir also using our phase convention. Nostra culpa! As Bob Cahn told us we should have had more confidence in our own book.

hep-ph↗
arXiv2004

Physics at Super B Factory

This report presents the results of studies that investigate the physics reach at a Super B factory, an asymmetric-energy e^+e^- collider with a design luminosity of 5 x 10^35 cm^-2s^-1, which is around 40 times as large as the peak luminosity achieved by the KEKB collider. The studies focus on flavor physics and CP violation measurements that could be carried out in the LHC era. The physics motivation, key observables, measurement methods and expected precisions are presented. The sensitivity studies are a part of the activities associated with the preparation of a Letter of Intent for SuperKEKB, which has been submitted recently.

hep-ex↗
arXiv2004

Analysis of Supersymmetric Effects on B -> phi K Decays in the PQCD Approach

We study the effects of the MSSM contribution on B -> phi K decays using the perturbative QCD approach. In this approach, strong phases can be calculated, so that we can predict the values of CP asymmetries with the MSSM contribution. We predict a large relative strong phase between the penguin amplitude and the chromomagnetic penguin amplitude. If there is a new CP violating phase in the chromomagnetic penguin amplitude, then the CP asymmetries may change significantly from the SM prediction. We parametrize the new physics contributions that appear in the Wilson coefficients. We maximize the new physics parameters up to the point where it is limited by experimental constraints. In the case of the LR insertion, we find that the direct CP asymmetries can reach about 85% and the indirect CP asymmetry can reach about -30%.

hep-ph↗
arXiv2004

Is Super-$B$ Sufficiently Superb? -- On the Motivation for a Super-$B$ Factory

Despite the great success of the $Υ(4S)$ $B$ factories at KEK and SLAC and the guaranteed addition of high sensitivity measurements on beauty decays to be performed at the Tevatron and LHC, a strong case can be made for an $e^+e^-$ Super-$B$ factory yielding data samples of order $10^{10}$ $B \bar B$ pairs as a necessity rather than luxury. It has to be justified through its ability to not only establish deviations from the Standard Model, but also diagnose and interpret those in terms of specific features of the New Dynamics. The role to be played by a Super-$B$ factory is thus analogous {\em and even in parallel} to that of a linear collider. The latter's goal is to provide more detailed information on previously discovered New Physics involved in the electroweak phase transition. Likewise a Super-$B$ factory would provide precision probes for analyzing whether such New Dynamics has an impact on heavy flavour dynamics -- a need particularly manifest if the New Physics is housed under the `big tent' of SUSY. The huge statistics of a Super-$B$ factory and the comprehensive body of accurate measurements uniquely possible there would be harnessed in several classes of studies, among them more precise extractions of $V(ub)/V(cb)$ and $V(td)/V(ts)$, more detailed analyses of $B\to γX_{s,d}, l^+l^-X$ and novel data on $B\to τν, τνD, ν\bar νX$ and maybe even on $Υ(5S) \to B_s \bar B_s$ -- all in addition to a host of CP asymmetries.

hep-ph↗
arXiv2003

Calculation of Magnetic Penguin Amplitudes in B -> phi K Decays using PQCD Approach

New physics contributions to B decays often arise through chromo-magnetic penguin operators. To look for new physics effects in B decays, it is useful to be able to estimate the hadronic matrix elements for the chromo-magnetic operator. We compute this contribution to B ->phi K decays using PQCD methods. It is shown that, if the Wilson coefficient of the new physics is same order of magnitude as that of the Standard Model, this operator gives a non-negligible contribution compared to that of the Standard Model (about 30%). We also investigate the value of q^2, which is the momentum transferred by the gluon in the chromo-magnetic penguin operator. We find that the expectation value is approximately M^2_B/4, in agreement with a naive guess. This result, however, is very sensitive to the scale dependence of the Wilson coefficient. We also show that the matrix element for the chromo-magnetic penguin operator is independent of the choice of energy scale to a very good approximation.

hep-ph↗
arXiv2003

CP Violation and Nonleptonic B-meson Decays

We discuss the perturbative QCD approach for exclusive non-leptonic two body B-meson decays. We briefly review its ingredients and some important theoretical issues related to the factorization approach. PQCD results are compatible with present experimental data for the charmless B-meson decays. We predict the possibility of large direct CP violation effects in $B^0 \to π^{+}π^{-}$ $(23\pm7 %)$ and $B^0\to K^{+}π^{-}$ $(-17\pm5%)$. For charmed decay $B \to D^{(*)}π$, we get large non-factorizable contributions for Color-suppressed decays and obtain $|a_2/a_1|\sim 0.4-0.5$ and $Arg(a_2/a_1)\sim -42^{o}$. In the last section we investigate the method to extract the weak phases $ϕ_2$ from $B \to ππ$ decay and $ϕ_3$ from $Kπ$ modes. From BaBar measurement of CP asymmetry for the $π^{+}π^{-}$ decay, the prefered CKM weak phases are: $ϕ_1=(24\pm2)^{o}$, $ϕ_2=(78\pm 22)^{o}$ and $ϕ_3=(78\pm 22)^{o}$.

hep-ph↗
arXiv2002

$B \to D^{(*)}$ form factors in perturbative QCD

We calculate the $B\to D^{(*)}$ form factors in the heavy-quark and large-recoil limits in the perturbative QCD framework based on $k_T$ factorization theorem, assuming the hierachy $M_B\gg M_{D^{(*)}}\gg \barΛ$, with the $B$ meson mass $M_B$, the $D^{(*)}$ meson mass $M_{D^{(*)}}$, and the heavy meson and heavy quark mass difference $\barΛ$. The qualitative behavior of the light-cone $D^{(*)}$ meson wave function and the associated Sudakov resummation are derived. The leading-power contributions to the $B\to D^{(*)}$ form factors, characterized by the scale $\barΛ\sqrt{M_B/M_{D^{(*)}}}$, respect the heavy-quark symmetry. The next-to-leading-power corrections in $1/M_B$ and $1/M_{D^{(*)}}$, characterized by a scale larger than $\sqrt{\barΛM_B}$, are estimated to be less than 20%. The $D^{(*)}$ meson wave function is determined from the fit to the observed $B\to D^{(*)} lν$ decay spectrum, which can be employed to make predictions for nonleptonic decays, such as $B\to D^{(*)}π(ρ)$.

hep-ph↗