Penguin Diagrams Research Articles

Penguin diagram dominance in radiative weak decays of bottom baryons

Radiative weak decays of antitriplet bottom baryons are studied under the assumption of penguin diagram dominance and flavor-SU(3) (or SU(2)) symmetry. Relations among decay rates of various decay modes are derived.

CP violation in [formula omitted] decays

Establishing CP violation in B 0 ( B ¯ 0 ) → l + l − decays requires a measurement of polarization of the final lepton pair, or a precise determination of the B 0 → l + l − and B ¯ 0 → l + l − rates. We first argue that if the amplitudes of these decays are dominated by the scalar and pseudoscalar Higgs penguin diagrams, as happens, e.g., in supersymmetry with large tan β , the CP asymmetries depend practically on only one CP violating phase. This phase can be large, of the order of the CKM phase, leading to large CP asymmetries in the τ + τ − decay channel of B d 0 ( B ¯ d 0 ) mesons, potentially measurable in Belle or BaBar experiments. Secondly, we show that the existing TAUOLA τ-lepton decay library supplemented by its universal interface can efficiently be used to search for B 0 ( B ¯ 0 ) → τ + τ − decays, and to investigate how the CP asymmetry is reflected in realistic experimental observables.

Penguin diagrams for improved staggered fermions

We calculate, at the one-loop level, penguin diagrams for improved staggered fermion operators constructed using various fat links. The main result is that diagonal mixing coefficients with penguin operators are identical between the unimproved operators and the improved operators using such fat links as Fat7, $\mathrm{F}\mathrm{a}\mathrm{t}7+\mathrm{L}\mathrm{e}\mathrm{p}\mathrm{a}\mathrm{g}\mathrm{e}$, $\overline{\mathrm{F}\mathrm{a}\mathrm{t}7}$, HYP (I) and HYP (II). In addition, it turns out that the off-diagonal mixing vanishes for those constructed using fat links of Fat7, $\overline{\mathrm{F}\mathrm{a}\mathrm{t}7}$ and HYP (II). This is a consequence of the fact that the improvement by various fat links changes only the mixing with higher dimension operators and off-diagonal operators. The results of this paper, combined with those for current-current diagrams, provide complete matching at the one-loop level with all corrections of $\mathcal{O}({g}^{2})$ included.

Effects of enhancedZpenguin diagrams on lepton polarizations inB→Xsℓ+ℓ−

The sensitivity of the $B\ensuremath{\rightarrow}\ensuremath{\pi}K$ mode to electroweak penguin diagrams and the recent experimental data for the $B\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\pi},\ensuremath{\pi}K$ modes has given rise to what is known as the ``$B\ensuremath{\rightarrow}\ensuremath{\pi}K$ puzzle.'' Recently it has been observed that this puzzle can be resolved by considering the new physics which can enter via ${Z}^{0}$ penguin diagrams. In this note we analyze the effect of these enhanced ${Z}^{0}$ penguin diagrams on the lepton polarization asymmetries of $b\ensuremath{\rightarrow}s{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$.

Indication of new physics in B <FONT FACE=Symbol>® F</FONT>Ks decays at the BELLE experiment

The BELLE experiment at the asymmetric e + e − (3.5 GeV and 8 GeV) accelerator KEK-B at Tsukuba, Japan, has recorded 152 Million BB meson pairs in 4 years of data taking. In the standard model, the size of CP violation in the B meson system is characterized by a quantity called sin(2ϕ1), in which ϕ1 denotes one of the angles in the unitarity triangle. This quantity was determined precisely to be sin(2ϕ1)=0.733±0.059±0.028, based upon N =1997 events with the decay B→J/ΨKs and N =914 other B→charmonium+Kaon decays [1] [2] [3]. The measurement is consistent with the measurement of the BABAR detector at SLAC [4]. In the standard model, the decay B→ΦKs is expected to show identical CP violation. However, a measurement of N =68 events revealed −0.96±0.50+0.09−0.11 (opposite sign from expectation), which is a 3.5σ deviation from the expected standard model value [1] [5]. The probability of obtaining the observed result for B→ΦKs as a statistical fluctuation of the B→J/ΨKs result is less than 0.1%. In the standard model, B→ΦKs is dominated by a penguin diagram with a W boson and a top quark in a loop. The top quark itself radiates a gluon which creates an ss pair. Two additional decay channels, namely B→η � Ks and B→K + K − Ks are dominated by the same diagram. However, their CP violation seems to be consistent (within still large statistical errors) with the sin(2ϕ1) value from B→J/ΨKs [6] [7]. The difference between the three different decay channels is given by the spin of the Φ meson J P =1 − (vector meson), while all Kaons and the η � are J=0 − (pseudoscalar mesons). In an additional analysis, angular distributions have been investigated. In the case of B→ VV 1 a helicity analysis can be performed. For this purpose, the B→J/ΨK ∗ [8] (pseudoscalar meson Ks replaced by vector meson K ∗ )a ndB→ΦKs [9] were compared. As pointed out recently by Grossman [10], differences between the two decay channels seem visible, and are difficult to be explained within the standard model. BELLE will resume data taking in 10/2003, with an improved Silicon Vertex Detector (4 layers, larger angular coverage). An update of the analysis results is envisaged for summer 2004.

DIRECT CP VIOLATION AND NEW PHYSICS EFFECTS IN THE DECAY MODE B+→ϕK+

We study the direct CP violation effect in the decay mode B+→ϕK+. This decay mode is dominated by the loop induced [Formula: see text] penguin diagram with a tiny contribution from the annihilation diagram. Therefore, the standard model expectation of direct CP violation is negligibly small. Using QCD factorization approach we find the CP asymmetry in the standard model to be at percent level. We consider then two scenarios beyond the standard model, the model with an extra vector-like down quark (VLDQ) and the R-parity violating supersymmetric model (RPV) and show that the direct CP violating asymmetry in B+→ϕK+ could be as large as ~ 85% (70%) in VLDQ (RPV) model.

Branching ratio andCPasymmetry ofBs→π+π−decays in the perturbative QCD approach

In this paper, we calculate the decay rate and CP asymmetry of the $B_s \to \pi^+\pi^-$ decay in perturbative QCD approach with Sudakov resummation. Since none of the quarks in final states is the same as those of the initial $B_s$ meson, this decay can occur only via annihilation diagrams in the standard model. Besides the current-current operators, the contributions from the QCD and electroweak penguin operators are also taken into account. We find that (a) the branching ratio is about $4 \times 10^{-7}$; (b) the penguin diagrams dominate the total contribution; and (c) the direct CP asymmetry is small in size: no more than $3% $; but the mixing-induced CP asymmetry can be as large as ten percent testable in the near future LHC-b experiments.

A two-loop contribution to Bs→μ+μ− at large tanβ in the MSSM

We consider a two-loop contribution of Higgs-mediated penguin diagram to B(Bs→μ+μ−) at large tanβ in the MSSM, motivated by a recently proposed two-loop magnetic penguin diagrams by Chen and Geng [hep-ph/0403188]. Typically the two-loop diagram is a αs correction to the one-loop contributions. However the new contribution can dominate one-loop contributions in a region of parameter space where μ, At and Ab are very large and scalar top, scalar bottom and charged Higgs are light. Both constructive and destructive interferences are possible. The total branching ratio can be drastically changed from the one-loop result.

Penguin diagrams for the HYP staggered fermions

We present results of the one-loop corrections originating from the penguin diagrams for the improved staggered fermion operators constructed using various fat links such as Fat7, Fat7+Lepage, $\bar{\rm Fat7}$, HYP (I) and HYP (II). The main results include the diagonal/off-diagonal mixing coefficients and the matching formula between the continuum and lattice operators.

Time-dependent CP violation in B0→ K0 s φ, $K^0_s\eta'$ and K0 s K+ K– in the Belle and BaBar experiments

Both the Belle and BaBar collaborations have recently measured time-dependent CP violation in B0 decays to $ss\overline{s}$ states and compared the results to those for $sc\overline{c}$ states for which quite precise results were previously available. Within the framework of the standard model the same results should be expected for both cases. The decays to $ss\overline{s}$ states are dominated by penguin diagrams and may be sensitive to physics beyond the standard model. For these states, compared to the results for $sc\overline{c}$ states, a discrepancy in the mixing-induced CP violation of 2.7 standard deviations was found, and may be interpreted as an indication for physics beyond the standard model. PACS: 11.30.Er Charge conjugation, parity, time reversal, andother discrete symmetries – 12.15.Hh Determination of Kobayashi-Maskawa matrix elements – 13.25.Hw Decays of bottom mesons

Recent progress in calculating weak matrix elements using staggered fermions

We present a chronological review of the progress in calculating weak matrix elements using staggered fermions. We review the perturbative calculation of one-loop matching formula including both current-current diagrams and penguin diagrams using improved staggered fermions. We also present preliminary results of weak matrix elements relevant to CP violation calculated using the improved (HYP (II)) staggered fermions. Since the complete set of matching coefficients at the one-loop level became available recently, we have constructed lattice operators with all the $g^2$ corrections included. The main results include both $\Delta I = 3/2$ and $\Delta I = 1/2$ contributions.

FLAVOR VIOLATION FROM Z PENGUINS IN THE LEFT–RIGHT SUPERSYMMETRIC MODEL

We analyze the effects of flavor-changing ZL penguin diagrams on rare kaon decays in a left–right supersymmetric model (LRSUSY). Using the mass-insertion approximation and including up to second-order effects, we show that the constraints obtained on up-sector flavor violating parameters can be stronger than previous bounds. These effects present a sensitive test of an extended gauge sector in supersymmetry and can be used to distinguish LRSUSY from other supersymmetric models.

B→φKs versus electric dipole moment of 199Hg atom in supersymmetric models with right-handed squark mixing

The correlation between the CP asymmetry in B→φKs (SφKs) and the chromoelectric dipole moment (CEDM) of strange quark (dsC), which is constrained by the electric dipole moment (EDM) of 199Hg, is studied in the supersymmetric (SUSY) models with the right-handed squark mixing. It is known that, if the right-handed bottom and strange squarks have a CP-violating mixing, such as in the SUSY SU(5) GUT with right-handed neutrinos, the induced gluon penguin diagram may give a sizable contribution to SφKs. However, when the left-handed bottom and strange squarks also have a mixing, the conspiracy of the left and right-handed squarks may lead to a sizable dsC, which is enhanced by mb/ms. While the estimate for the EDM of 199Hg, induced by dCs, might have large uncertainties due to the hadron and nuclear dynamics, the current bound implies the gluon penguin contribution by the right-handed squarks to SφKs should be suppressed and the deviation of SφKs from the Standard Model may not be so large. Also, we discuss the constraint from the EDM of 199Hg in the SUSY SU(5) GUT with the right-handed neutrinos.

The impact of universal extra dimensions on B→ Xsγ, B→ Xs gluon, B→ Xsμ+μ−, KL→ π0e+e− and ε′/ ε

We calculate the contributions of the Kaluza–Klein (KK) modes to the γ-penguins, gluon-penguins, γ-magnetic penguins and chromomagnetic penguins in the Appelquist, Cheng and Dobrescu (ACD) model with one universal extra dimension. Together with our previous calculation of Z 0 penguin diagrams [Nucl. Phys. B 660 (2003) 225] this allows to study the impact of the KK modes on the decays B→ X s γ, B→ X s gluon, B→ X s μ + μ − and K L → π 0 e + e − and on the CP-violating ratio ε′/ ε. For the compactification scale 1/ R=300 GeV the perturbative part of the branching ratio for B→ X s μ + μ − is enhanced by 12% while the zero in the A FB asymmetry is shifted from s ̂ 0=0.162 to s ̂ 0=0.142 . The sizable suppressions of Br( B→ X s γ) (20%) and Br( B→ X s gluon) (40%) could have interesting phenomenological implications on the lower bound on 1/ R provided the experimental and theoretical uncertainties will be decreased. Similar comments apply to ε′/ ε that is suppressed relative to the Standard Model expectations with the size of the suppression depending sensitively on the hadronic matrix elements. The impact on K L → π 0 e + e − is below 10%. We point out a correlation between the zero s ̂ 0 in the A FB asymmetry and Br( B→ X s γ) that should be valid in most models with minimal flavour violation.

Lepton flavor violation ine±e−→l±e−(l=μ,τ)induced byR-conserving supersymmetry

The lepton-flavor-violating signals ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\mathcal{l}}^{+}{e}^{\ensuremath{-}}$ and ${e}^{\ensuremath{-}}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\mathcal{l}}^{\ensuremath{-}}{e}^{\ensuremath{-}}(\mathcal{l}=\ensuremath{\mu},\ensuremath{\tau})$ are studied in the context of low-energy R-parity-conserving supersymmetry at center-of-mass energies of interest for the next generation of linear colliders. Loop level amplitudes receive contributions from electroweak penguin and box diagrams involving sleptons and gauginos. Lepton flavor violation is due to off-diagonal elements in a ${\mathrm{SU}(2)}_{L}$ doublet slepton mass matrix. These masses are treated as model-independent free phenomenological parameters in order to discover regions in parameter space where the signal cross section may be observable. The results are compared with (a) the experimental bounds from the nonobservation of rare radiative lepton decays $\ensuremath{\mu},\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\tau}}e\ensuremath{\gamma}$ and (b) the general MSUGRA theoretical scenario with the seesaw mechanism where off-diagonal slepton matrix entries are generated by renormalization group evolution of neutrino Yukawa couplings induced by the presence of new energy scales set by the heavy ${\mathrm{SU}(2)}_{L}$ singlet neutrino masses. It is found that in ${e}^{\ensuremath{-}}{e}^{\ensuremath{-}}$ collisions the $(e\ensuremath{\tau})$ signal can be observable with a total integrated luminosity of $100{\mathrm{fb}}^{\ensuremath{-}1}$ and the background can be easily suppressed. In ${e}^{+}{e}^{\ensuremath{-}}$ collisions the cross section is smaller and higher luminosities are needed. The experimental bound on the decay $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\mu}}e\ensuremath{\gamma}$ prevents the $(e\ensuremath{\mu})$ signal from being observable.

Possibility of a large electroweak penguin contribution inB→Kπmodes

We discuss the possibility of a large electroweak penguin contribution in $\stackrel{\ensuremath{\rightarrow}}{B}K\ensuremath{\pi}$ from recent experimental data. The several relations among the branching ratios which realize when the contributions from tree type and electroweak penguin contributions are small compared with the gluon penguin can be treated as the expansion parameters do not satisfy the data. The difference comes from the ${r}^{2}$ term which is the square of the ratio with the gluon penguin diagram and the main contribution comes from the electroweak penguin diagram. We find that the electroweak penguin contribution may be too large to explain the experimental data. If the magnitude estimated from experiment is quite large compared with the theoretical estimation, then it may be including some new physics effects.

Calculation of nonleptonic kaon decay amplitudes fromK→πmatrix elements in quenched domain-wall QCD

We explore application of the domain wall fermion formalism of lattice QCD to calculate the $K\to\pi\pi$ decay amplitudes in terms of the $K\to\pi$ and $K\to 0$ hadronic matrix elements through relations derived in chiral perturbation theory. Numerical simulations are carried out in quenched QCD using domain-wall fermion action for quarks and an RG-improved gauge action for gluons on a $16^3\times 32\times 16$ and $24^3\times 32\times 16$ lattice at $\beta=2.6$ corresponding to the lattice spacing $1/a\approx 2$GeV. Quark loop contractions which appear in Penguin diagrams are calculated by the random noise method, and the $\Delta I=1/2$ matrix elements which require subtractions with the quark loop contractions are obtained with a statistical accuracy of about 10%. We confirm the chiral properties required of the $K\to\pi$ matrix elements. Matching the lattice matrix elements to those in the continuum at $\mu=1/a$ using the perturbative renormalization factor to one loop order, and running to the scale $\mu=m_c=1.3$ GeV with the renormalization group for $N_f=3$ flavors, we calculate all the matrix elements needed for the decay amplitudes. With these matrix elements, the $\Delta I=3/2$ decay amplitude shows a good agreement with experiment in the chiral limit. The $\Delta I=1/2$ amplitude, on the other hand, is about 50--60% of the experimental one even after chiral extrapolation. In view ofthe insufficient enhancement of the $\Delta I=1/2$ contribution, we employ the experimental values for the real parts of the decay amplitudes in our calculation of $\epsilon'/\epsilon$. We find that the $\Delta I=3/2$ contribution is larger than the $\Delta I=1/2$ contribution so that $\epsilon'/\epsilon$ is negative and has a magnitude of order $10^{-4}$. Possible reasons for these unsatisfactory results are discussed.

Testing QCD factorization and charming penguin diagrams in charmlessB→PV

We try a global fit of the experimental branching ratios and CP-asymmetries of the charmless $B\to PV$ decays according to QCD factorisation. We find it impossible to reach a satisfactory agreement, the confidence level (CL) of the best fit is smaller than .1 %. The main reason for this failure is the difficulty to accomodate several large experimental branching ratios of the strange channels. Furthermore, experiment was not able to exclude a large direct CP asymmetry in $\bar {B^0}\to\rho^+ \pi^-$, which is predicted very small by QCD factorisation. Trying a fit with QCD factorisation complemented by a charming-penguin inspired model we reach a best fit which is not excluded by experiment (CL of about 8 %) but is not fully convincing. These negative results must be tempered by the remark that some of the experimental data used are recent and might still evolve significantly.

The impact of universal extra dimensions on the unitarity triangle and rare K and B decays

We calculate the contributions of the Kaluza–Klein (KK) modes to the K L – K S mass difference Δ M K , the parameter ε K , the B 0 d, s – B 0 d,s mixing mass differences Δ M d, s and rare decays K +→π +ν ν ̄ , K L→π 0ν ν ̄ , K L → μ + μ −, B→X s,dν ν ̄ and B s,d→μ μ ̄ in the Appelquist, Cheng and Dobrescu (ACD) model with one universal extra dimension. For the compactification scale 1/ R=200 GeV the KK effects in these processes are governed by a 17% enhancement of the Δ F=2 box diagram function S( x t ,1/ R) and by a 37% enhancement of the Z 0 penguin diagram function C( x t /1/ R) relative to their Standard Model (SM) values. This implies the suppressions of | V td | by 8%, of η ̄ by 11% and of the angle γ in the unitarity triangle by 10°. Δ M s is increased by 17%. Δ M K is essentially uneffected. All branching ratios considered in this paper are increased with a hierarchical structure of enhancements: K +→π +ν ν ̄ (16%) , K L→π 0ν ν ̄ (17%) , B→X dν ν ̄ (22%) , (K L→μ μ ̄ ) SD (38%) , B→X sν ν ̄ (44%) , B d→μ μ ̄ (46%) and B s→μ μ ̄ (72%) . For 1/ R=250 (300) GeV all these effects are decreased roughly by a factor of 1.5 (2.0). We emphasize that the GIM mechanism assures the convergence of the sum over the KK modes in the case of Z 0 penguin diagrams and we give the relevant Feynman rules for the five-dimensional ACD model. We also emphasize that a consistent calculation of branching ratios has to take into account the modifications in the values of the CKM parameters. As a byproduct we confirm the dominant O(g 2G F m t 4R 2) correction from the KK modes to the Z 0b b ̄ vertex calculated recently in the large m t limit.

Bs→ μ+μ− and B→ Xsμ+μ− in MSSM

Pure leptonic and semileptonic rare B decays, B s → μ + μ − and B→ X s μ + μ − in the minimal supersymmetric Standard Model (MSSM), in particular, gluino and neutralino contributions to the decays, are discussed under Br( B→ X s γ) and other experimental constraints. The general scalar quark mass matrices as the new sources of flavor violation are considered. We present Wilson coefficients of bs transitions from γ, Z, and neutral Higgs boson penguin diagrams by using vertex mixing method to deal with scalar down-type quark flavor changing and also give their expressions in MIA to show different sources of enhancements. We find that under the experimental constraints, with large mixing of left- and right-handed sbottom, C (′) 10 can be enhanced by 10% compared with SM, in two cases, heavy gluino and fine-tuning between δ dLL 23( δ dRR 23) and δ dLR 23( δ dRL 23) terms in C (′) 7. Particularly, C 10 and C 10′ can reach a 20% enhancement in some regions of parameters under experimental constraints. When CP-odd Higgs A 0 is not too heavy (∼250 GeV), and tan β is large (∼40), neutral Higgs boson penguins with gluino and down-type squark in the loop can significantly contribute to the bs transition and the contributions can compete with those due to the chargino and up-type squark loop.