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Makiko Nagashima

Publications and source records attributed to Makiko Nagashima.

At least 19 recordsLinked to original sources
arXiv2010

New-physics contributions to the forward-backward asymmetry in B -> K* mu+ mu-

We study the forward-backward asymmetry (AFB) and the differential branching ratio (DBR) in B -> K* mu+ mu- in the presence of new physics (NP) with different Lorentz structures. We consider NP contributions from vector-axial vector (VA), scalar-pseudoscalar (SP), and tensor (T) operators, as well as their combinations. We calculate the effects of these new Lorentz structures in the low-q^2 and high-q^2 regions, and explain their features through analytic approximations. We find two mechanisms that can give a significant deviation from the standard-model predictions, in the direction indicated by the recent measurement of AFB by the Belle experiment. They involve the addition of the following NP operators: (i) VA, or (ii) a combination of SP and T (slightly better than T alone). These two mechanisms can be distinguished through measurements of DBR in B -> K* mu+ mu- and AFB in B -> K mu+ mu-.

hep-ph↗
arXiv2010

New Physics in Bs -> J/psi phi: a General Analysis

Recently, the CDF and D0 collaborations measured indirect CP violation in Bs -> J/psi phi and found a hint of a signal. If taken at face value, this can be interpreted as a nonzero phase of Bs-Bsbar mixing (beta_s), in disagreement with the standard model, which predicts that beta_s ~= 0. In this paper, we argue that this analysis may be incomplete. In particular, there can be new physics (NP) in the bbar -> sbar c cbar decay. If so, the value of beta_s is different than for the case in which NP is assumed to be present only in the mixing. We have examined several models of NP and found that, indeed, there can be significant contributions to the decay. These effects are consistent with measurements in B -> J/psi K* and Bd -> J/psi Ks. Due to the NP in the decay, polarization-dependent indirect CP asymmetries and triple-product asymmetries are predicted in Bs -> J/psi phi.

hep-ph↗
arXiv2009

CP Violation in Three-Body Chargino Decays

CP violation in supersymmetry can give rise to rate asymmetries in the decays of supersymmetric particles. In this work we compute the rate asymmetries for the three-body chargino decays \tildeχ^\pm_2 \to \tildeχ^\pm_1 HH, \tildeχ^\pm_2 \to \tildeχ^\pm_1 ZZ, \tildeχ^\pm_2 \to \tildeχ^\pm_1 W^+ W^- and \tildeχ^\pm_2 \to tildeχ^\pm_1 ZH. Each of the decays contains contributions mediated by neutral Higgs bosons that can possibly go on shell. Such contributions receive a resonant enhancement; furthermore, the strong phases required for the CP asymmetries come from the widths of the exchanged Higgs bosons. Our results indicate that the rate asymmetries can be relatively large in some cases, while still respecting a number of important low-energy bounds such as those coming from B meson observables and electric dipole moments. For the parameters that we consider, rate asymmetries of order 10% are possible in some cases.

hep-ph↗
arXiv2008

Final-state Polarization in Bs Decays

Certain Bs --> V_1V_2 decays (V_i is a vector meson) can be related by flavor SU(3) symmetry to corresponding Bd --> V_3V_4 decays. In this paper, we show that the final-state polarization can be predicted in the Bs decay, assuming polarization measurements of the Bd decay. This can be done within the scenario of penguin annihilation (PA), which has been suggested as an explanation of the unexpectedly large transverse polarization in B-->phi K^*. PA is used to estimate the breaking of flavor SU(3) symmetry in pairs of decays. Two of these for which PA makes a reasonably precise prediction of the size of SU(3) breaking are (Bs --> phiphi, Bd --> phi K^{0*}) and (Bs --> phi {\bar K}^{0*}, Bd --> {\bar K}^{0*} K^{0*}). The polarization measurement in the Bd decay can be used to predict the transverse polarization in the Bs decay, and will allow a testing of PA.

hep-ph↗
arXiv2008

CP violation in tau -> K pi pi nu_tau

We consider CP-violating effects in tau->K pi pi nu_tau, assuming that a charged Higgs boson provides a new amplitude that can interfere with the usual Standard Model amplitude. We consider four CP-odd observables -- the regular rate asymmetry, two modified rate asymmetries and a triple-product asymmetry. The regular rate asymmetry is expected to be small because it requires the interference of the new physics amplitude with the standard model amplitude containing the hadronic scalar form factor. The other CP asymmetries may be more promising in terms of their new physics reach. Numerical estimates indicate that the maximum obtainable values for the modified and triple-product asymmetries are on the order of a percent.

hep-ph↗
arXiv2008

U-spin Implication for B_s Physics and New Physics

With U-spin symmetry, b->s and b->d penguin decays could be a subtle probe of CP violating new physics contributions. We show that, for B->PP (P stands for a pseudoscalar meson), the U-spin relation is expected to be violated for only one decay pair by assuming that new physics affects only b->s transition processes. We also very shortly discuss the polarizations of two types of U-spin pairs for B->VV (V stands for a vector meson).

hep-ph↗
arXiv2008

Study of Polarization in B -> VT Decays

In this paper, we examine B -> VT decays (V is a vector and T is a tensor meson), whose final-state particles can have transverse or longitudinal polarization. Measurements have been made of B -> ϕK_2^*, and it is found that fT/fL is small, where fT (fL) is the fraction of transverse (longitudinal) decays. We find that the standard model (SM) naively predicts that fT/fL << 1. The two extensions of the naive SM which have been proposed to explain the large fT/fL in B -> ϕK^* -- penguin annihilation and rescattering -- make no firm predictions for the polarization in B -> ϕK_2^*. The two new-physics scenarios, which explain the data in B -> πK and the ϕ(ρ) K^* polarization measurements, can reproduce the fT/fL data in B -> ϕK_2^* only if the B -> T form factors obey a certain hierarchy. Finally, we present the general angular analysis which can be used to get helicity information using two- and three-body decays.

hep-ph↗
arXiv2008

U-Spin Tests of the Standard Model and New Physics

Within the standard model, a relation involving branching ratios and direct CP asymmetries holds for the B-decay pairs that are related by U-spin. The violation of this relation indicates new physics (NP). In this paper, we assume that the NP affects only the Delta S = 1 decays, and show that the NP operators are generally the same as those appearing in B -> pi K decays. The fit to the latest B -> pi K data shows that only one NP operator is sizeable. As a consequence, the relation is expected to be violated for only one decay pair: Bd -> K0 pi0 and Bs -> Kbar0 pi0.

hep-ph↗
arXiv2007

Testing Explanations of the $B\toϕK^*$ Polarization Puzzle

$B\toϕK^*$ ($\btos$) is three separate decays, one for each polarization of the final-state vector mesons (one longitudinal, two transverse). It is observed that the fraction of transverse decays, $\fT$, and the fraction of longitudinal decays, $\fL$, are roughly equal: $\fTfL \simeq 1$, in opposition to the naive expectation that $\fT \ll \fL$. If one requires a single explanation of all polarization puzzles, two possibilities remain within the standard model: penguin annihilation and rescattering. In this paper we examine the predictions of these two explanations for $\fTfL$ in $\btod$ decays. In $B \to ρρ$ decays, only $\bd \to ρ^0ρ^0$ can possibly exhibit a large $\fTfL$. In B decays related by U-spin, we find two promising possibilities: (i) $B^+ \to K^{*0} ρ^+$ ($\btos$) and $B^+ \to \Kbar^{*0} K^{*+}$ ($\btod$) and (ii) $\bs \to K^{*0} \Kbar^{*0}$ ($\btos$) and $\bd \to \Kbar^{*0} K^{*0}$ ($\btod$). The measurement of $\fTfL$ in these pairs of decays will allow us to test penguin annihilation and rescattering. Finally, it is possible to distinguish penguin annihilation from rescattering by performing a time-dependent angular analysis of $\bd \to \Kbar^{*0} K^{*0}$.

hep-ph↗
arXiv2007

Large Time-dependent CP Violation in B_s^0 System and Finite D^0-D^0bar Mass Difference in Four Generation Standard Mode

Combining the measured B_s mixing with b \to s\ell^+\ell^- rate data, we find a sizable 4 generation t' quark effect is allowed, for example with m_{t'} \sim 300 GeV and V_{t's}^*V_{t'b} \sim 0.025 e^{\pm i 70^\circ}, which could underly the new physics indications in CP violation studies of b \to s qbar q transitions. With positive phase, large and negative mixing-dependent CP violation in B_s system is predicted, \sin 2Φ_{B_s} \sim -0.5 to -0.7. This can also be probed via width difference methods. As a corollary, the short distance generated D^0-D^0bar mass difference is found to be consistent with, if not slightly higher than, recent B factory measurements, while CP violation is subdued with \sin 2Φ_D \sim -0.2.

hep-ph↗
arXiv2007

Fourth Generation CP Violation Effect on B -> K pi, phi K and rho K in NLO PQCD

We study the effect from a sequential fourth generation quark on penguin-dominated two-body nonleptonic B meson decays in the next-to-leading order perturbative QCD formalism. With an enhancement of the color-suppressed tree amplitude and possibility of a new CP phase in the electroweak penguin, we can account better for A_{CP}(B^0 -> K^+ pi^-)-A_{CP}(B^+ -> K^+ pi^0). Taking |V_{t's}V_{t'b}| \sim 0.02 with phase just below 90^\circ, which are consistent with the b -> s l^+ l^- rate and the B_s mixing parameter Δm_{B_s}, we find a downward shift in the mixing-induced CP asymmetries of B^0 -> K_S pi^0 and phi K_S. The predicted behavior for B^0 -> rho^0 K_S is opposite.

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arXiv2006

Direct CP Violation in B+ to J/psi K+ Decay as Probe for New Physics

Currently there are New Physics hints in mixing-induced CP violation S(phi K0), S(pi0 K0) < S(J/psi K0), unequal direct CP violation A(K+ pi-) differs A(K+ pi0), and maybe even in measured S(J/psi K0) vs prediction from global fit to other data. However, these hints either suffer from experimental uncertainties, or uncertain hadronic corrections, and are not yet unequivocal. Motivated by these hints, however, we point out that a unique probe may be direct CP violation in B to JψK mode. An asymmetry observed at 1% or higher would indicate New Physics.

hep-ph↗
arXiv2006

Four Generation CP Violation in B -> phi K^0, pi^0 K^0, eta' K^0 and Hadronic Uncertainties

The fourth generation can give the correct trend of S_{phi K^0}, S_{pi^0 K^0} < sin2phi_1/beta, as indicated by data, and the effect, being largely leading order, is robust against hadronic uncertainties. The effect on S_{eta' K^0}, however, is diluted away by hadronic effects, and S_{eta' K^0} \simeq sin2phi_1/beta is expected. The near maximal arg[V^*_{t's}V_{t'b}] \lesssim 90^\circ that is needed could resolve the unequal direct CP violation seen in B -> K^+ pi^- and K^+ pi^0 modes, and is consistent with b ->s l^+l^- and B_s mixing constraints.

hep-ph↗
arXiv2006

Impact of Right-handed Strange-beauty Squark on b <-> s Transitions

As the hint for CP violating new physics in B-> phi Ks has weakened, we reconsider the possibility of near maximal mixing between \tilde s_R-\tilde b_R squarks. Such a right-handed strange-beauty squark \widetilde{sb}_{1} can be realized by combining supersymmetry with an approximate Abelian flavor symmetry, and comes with a unique new CP violating phase from right-handed quark mixing. Naturally heavy strange-beauty squark and gluino, of order 0.5 to 1 TeV, are easily accommodated by recent time-dependent CP violation measurements in Bd -> phi K^0 and pi^0 K^0. Because of near maximal mixing, even with such heavy masses, the \widetilde{sb}_{1} and \tilde g can still strongly impact on Bs mass difference and generate CP violation in the mixing, which can still be probed at Tevatron Run II. But if the scenario is realized, the LHC will provide definitive information on the new CP phase, and possibly discover the \widetilde{sb}_{1} squark. Time-dependent CP violation in Bd -> K^{*0} gamma can be probed at the future B factory upgrades. Other b -> s decays influenced by large right-handed dynamics are also discussed.

hep-ph↗
arXiv2005

Baryon Number Violation Involving Higher Generations

Proton stability seems to constrain rather strongly any baryon number violating process. We investigate the possibility of baryon number violating processes involving right-handed dynamics or higher generation quarks. Our results strongly suggest that there will be no possibility to observe baryon number violation in tau or higher generation quark decays, at any future machine.

hep-ph↗
arXiv2005

Enhanced KL to pi0 nu nubar from Direct CP Violation in B to K pi with Four Generations

Recent CP violation results in B decays suggest that Z penguins may have large weak phase. This can be realized by the four generation (standard) model. Concurrently, B to Xs l+ l- and Bs mixing allow for sizable Vt's* Vt'b only if it is nearly imaginary. Such large effects in b to s transitions would affect s to d transitions, as kaon constraints would demand Vt'd different from zero. Using Gamma(Z to b bbar) to bound |Vt'b|, we infer sizable |Vt's| < |Vt'b| < |Vus|$. Imposing epsilon_K, K+ to pi+ nu nubar and epsilon'/epsilon constraints, we find Vt'd* Vt's = few x 10^(-4) with large phase, enhancing KL to pi0 nu nubar to 5x10^(-10) or even higher. Interestingly, Delta_mBd and sin(2PhiBd) are not much affected, as |Vt'd* Vt'b| << |Vtd* Vtb| = 0.01.

hep-ph↗
arXiv2005

Difference in B^+ and B^0 Direct CP Asymmetry as Effect of a Fourth Generation

Direct CP violation in B^0-> K^+π^- decay has emerged at -10% level, but the asymmetry in B^+ -> K^+π^0 mode is consistent with zero. This difference points towards possible New Physics in the electroweak penguin operator. We point out that a sequential fourth generation, with sizable V^*_{t's}V_{t'b} and near maximal phase, could be a natural cause. We use the perturbative QCD factorization approach for B-> Kπamplitudes. While the B^0-> K^+π^- mode is insensitive to t', we critically compare t' effects on direct CP violation in B^+ -> K^+π^0 with b-> s\ell^+\ell^- and B_s mixing. If the K^+π^0-K^+π^- asymmetry difference persists, we predict \sin2Φ_{B_s} to be negative.

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