Charming Penguins Research Articles

Bs→μ+μ−γ decay rate at large q2 from lattice QCD

We determine, by means of lattice QCD calculations, the local form factors describing the Bs→μ+μ−γ decay, in the so-called electroquenched approximation. For this analysis we make use of the gauge configurations produced by the ETM Collaboration with Nf=2+1+1 flavor of Wilson-Clover twisted-mass fermions at maximal twist. To obtain the Bs meson form factors, we perform simulations for several heavy-strange meson masses mHs in the range mHs∈[mDs,2mDs], and extrapolate to the physical Bs meson point mBs≃5.367 GeV making use of the HQET scaling laws. We cover the region of large dimuon invariant masses q2>4.16 GeV, and use our results to determine the branching fraction for Bs→μ+μ−γ, which has been recently measured by LHCb in the region q2>4.9 GeV. The largest contribution to the uncertainty in the partial branching fractions at values of q2<4.8 GeV is now due to resonance and other long-distance effects, including those from “charming penguins,” which we estimate by summing over the contributions from the JP=1− charmonium resonances. Published by the American Physical Society 2024

Constraints on lepton universality violation from rare B decays

The LHCb Collaboration has recently released a new study of ${B}^{+}\ensuremath{\rightarrow}{K}^{+}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ and $B\ensuremath{\rightarrow}{K}^{*0}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ ($\ensuremath{\ell}=e$, $\ensuremath{\mu}$) decays, testing lepton universality with unprecedented accuracy using the whole Run 1 and 2 dataset. In addition, the CMS Collaboration has reported an improved analysis of the branching ratios ${B}_{(d,s)}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$. While these measurements offer, per se, a powerful probe of new physics, global analyses of $b\ensuremath{\rightarrow}s{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ transitions also rely on the assumptions about nonperturbative contributions to the decay matrix elements. In this work, we perform a global Bayesian analysis of new physics in (semi)leptonic rare $B$ decays, paying attention to the role of charming penguins which are difficult to evaluate from first principles. We find data to be consistent with the Standard Model once rescattering from intermediate hadronic states is included. Consequently, we derive stringent bounds on lepton universality violation in $|\mathrm{\ensuremath{\Delta}}B|=|\mathrm{\ensuremath{\Delta}}S|=1$ (semi)leptonic processes.

Charming penguins and lepton universality violation in varvec{b rightarrow s ell ^+ ell ^-} decays

The LHCb experiment has recently presented new results on Lepton Universality Violation (LUV) in B rightarrow K^{(*)} ell ^+ ell ^- decays involving K_S in the final state, which strengthen the recent evidence of LUV obtained in B^+ rightarrow K^{+} ell ^+ ell ^- decays and the previous measurements of B rightarrow K^{*0} ell ^+ ell ^-. While LUV observables in the Standard Model are theoretically clean, their predictions in New Physics scenarios are sensitive to the details of the hadronic dynamics, and in particular of the charming penguin contribution. In this work, we show how a conservative treatment of hadronic uncertainties is crucial not only to assess the significance of deviations from the Standard Model but also to obtain a conservative picture of the New Physics responsible for LUV. Adopting a very general parameterization of charming penguins, we find that: (i) current data hint at a sizable q^2 and helicity dependence of charm loop amplitudes; (ii) conservative NP solutions to B anomalies favour a left-handed or an axial lepton coupling rather than a vector one.

Global analysis of charmless B decays into two vector mesons in soft-collinear effective theory

Under the framework of soft-collinear effective theory, we analyze the charmless $B\to VV$ decays in a global way at leading power in $1/m_b$ and leading order in $\alpha_s$ with $V$ denoting a light vector meson. In the flavor SU(3) symmetry, decay amplitudes for the 28 decay modes are expressed in terms of 8 nonperturbative parameters. With 35 experimental results, we fit these 8 nonperturbative parameters. Annihilation contributions are neglected due to power suppression in the $m_b\to \infty$ limit, so we include in the fit the nonperturbative charm penguins, which will play an important role in understanding the direct CP asymmetries. Charming penguins are also responsible for the large transverse polarizations of penguin-dominated and color-suppressed decays. With the best fitted parameters, we calculate all possible physical observables of 28 decay modes, including branching fractions, direct CP asymmetries, and the complete set of polarization observables. Most of our results are compatible with the present experimental data when available, while the others can be examined on the ongoing LHCb experiment and the forthcoming Belle-II experiment. Moreover, the agreements and differences with results in QCD factorization and perturbative QCD approach are also discussed. A few observables are suggested to discriminate these different approaches.

B d → π − K (*)+ and B s → π +(ρ +)K − decays with QCD factorization and flavor symmetry

The QCD factorization (QCDF) method usually contains infrared divergences which introduce large model dependence to its predictions on charmless B decays. The amplitudes of charmless B decays can be decomposed into “tree” and “penguin” parts which are conventionally defined, not from the topology of the dominant diagrams, but through their associated CKM factors V ub * V uq and V tb * V tq , respectively, with q = d, s. We find that for B d,s → π ∓ K ± decays, the “tree” amplitude can be well estimated in QCDF with small errors, as the endpoint singularities have been canceled to a large extent. With this as the only input from QCDF and combined with flavor symmetry, the branching ratio of B s → π + K − is estimated to be significantly larger than the CDF measurement. This contradiction could be solved if the form factor \( {F^{{B_s}K}} \) is smaller than the light cone sum rules estimation or the “tree” amplitude has been over estimated in QCDF. The latter possibility could happen if charming penguins are nonperturbative and not small, as argued in soft collinear effective theory. To differentiate between these two possibilities, we examine the similar B s → ρ + K − decay with the same technique. It is found that a large part of the uncertainties are canceled in the ratio \( {{\mathcal{B}\left( {{B_s} \to {\rho^{+} }{K^\user1{ - }}} \right)} \mathord{\left/{\vphantom {{\mathcal{B}\left( {{B_s} \to {\rho^{+} }{K^\user1{ - }}} \right)} {\mathcal{B}\left( {{B_s} \to {\pi^{+} }{K^\user1{ - }}} \right)}}} \right.} {\mathcal{B}\left( {{B_s} \to {\pi^{+} }{K^\user1{ - }}} \right)}} \). In QCDF, it is predicted to be 2.5 ± 0.2 which is independent on the form factor. However if charming penguins are important, this ratio could be very different from the QCDF prediction. Therefore the ratio of these two branching ratios could be an interesting indicator of the role of charming penguins in charmless B decays.

Charmless Two-body [formula omitted] decays In Soft-Collinear-Effective-Theory

We analyze the charmless two-body B → P P , V P decays in the soft-collinear-effective-theory (SCET), where V ( P ) denotes a light vector (pseudoscalar) meson. Using the current experimental data, we find two solutions in χ 2 fit for the 16 non-perturbative inputs responsible for the 87 B → P P and B → V P decay channels in SU(3) symmetry. Chirally enhanced penguins can only change several charming penguins sizably, since they share the same topology. The ( S − P ) ( S + P ) annihilation penguins in the perturbative QCD approach have the same topology with charming penguins in SCET, which play an important role in direct CP asymmetries. We also give the predictions for the mixing induced CP asymmetry measurements sin 2 β e f f of various B → V P modes in SCET.

What can we learn fromB→a1(1260)(b1(1235))π(K)decays?

We investigate the $B\ensuremath{\rightarrow}{a}_{1}(1260)({b}_{1}(1235))\ensuremath{\pi}(K)$ decays under the factorization scheme and find many discrepancies between theoretical predictions and the experimental data. In the tree-dominated processes, large contributions from color-suppressed tree diagrams are required in order to accommodate the large decay rates of ${B}^{\ensuremath{-}}\ensuremath{\rightarrow}{a}_{1}^{0}{\ensuremath{\pi}}^{\ensuremath{-}}$ and ${B}^{\ensuremath{-}}\ensuremath{\rightarrow}{a}_{1}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$. For ${\overline{B}}^{0}\ensuremath{\rightarrow}({a}_{1}^{+},{b}_{1}^{+}){K}^{\ensuremath{-}}$ decays which are induced by $b\ensuremath{\rightarrow}s$ transition, theoretical predictions on their decay rates are larger than the data by a factor of 2.8 and 5.5, respectively. Large electroweak penguins or some new mechanism are expected to explain the branching ratios of ${B}^{\ensuremath{-}}\ensuremath{\rightarrow}{b}_{1}^{0}{K}^{\ensuremath{-}}$ and ${B}^{\ensuremath{-}}\ensuremath{\rightarrow}{a}_{1}^{\ensuremath{-}}{\overline{K}}^{0}$. The soft-collinear effective theory has the potential to explain large decay rates of ${B}^{\ensuremath{-}}\ensuremath{\rightarrow}{a}_{1}^{0}{\ensuremath{\pi}}^{\ensuremath{-}}$ and ${B}^{\ensuremath{-}}\ensuremath{\rightarrow}{a}_{1}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ via a large hard-scattering form factor ${\ensuremath{\zeta}}_{J}^{B\ensuremath{\rightarrow}{a}_{1}}$. We will also show that, with proper charming penguins, predictions on the branching ratios of ${\overline{B}}^{0}\ensuremath{\rightarrow}({a}_{1}^{+},{b}_{1}^{+}){K}^{\ensuremath{-}}$ can also be consistent with the data.

Nonperturbative charming penguin contributions to isospin asymmetries in radiativeBdecays

Recent experimental data on the radiative decays B{yields}V{gamma}, where V is a light vector meson, find small isospin violation in B{yields}K*{gamma} while isospin asymmetries in B{yields}{rho}{gamma} are of order 20%, with large uncertainties. Using soft-collinear effective theory, we calculate isospin asymmetries in these radiative B decays up to O(1/m{sub b}), also including O(v{alpha}{sub s}) contributions from nonperturbative charming penguins (NPCP). In the absence of NPCP contributions, the theoretical predictions for the asymmetries are a few percent or less. Including the NPCP can significantly increase the isospin asymmetries for both B{yields}V{gamma} modes. We also consider the effect of the NPCP on the branching ratio and CP asymmetries in B{sup {+-}}{yields}V{sup {+-}}{gamma}.

Charmless two-bodyB(s)→VPdecays in soft collinear effective theory

We provide the analysis of charmless two-body $B\ensuremath{\rightarrow}VP$ decays under the framework of the soft collinear effective theory (SCET), where $V(P)$ denotes a light vector (pseudoscalar) meson. Besides the leading power contributions, some power corrections (chiraly enhanced penguins) are also taken into account. Using the current available $B\ensuremath{\rightarrow}PP$ and $B\ensuremath{\rightarrow}VP$ experimental data on branching fractions and $CP$ asymmetry variables, we find two kinds of solutions in ${\ensuremath{\chi}}^{2}$ fit for the 16 nonperturbative inputs which are essential in the 87 $B\ensuremath{\rightarrow}PP$ and $B\ensuremath{\rightarrow}VP$ decay channels. Chiraly enhanced penguins can change several charming penguins sizably, since they share the same topology. However, most of the other nonperturbative inputs and predictions on branching ratios and $CP$ asymmetries are not changed too much. With the two sets of inputs, we predict the branching fractions and $CP$ asymmetries of other modes especially ${B}_{s}\ensuremath{\rightarrow}VP$ decays. The agreements and differences with results in QCD factorization and perturbative QCD approach are analyzed. We also study the time-dependent $CP$ asymmetries in channels with $CP$ eigenstates in the final states and some other channels such as ${\overline{B}}^{0}/{B}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\rho}}^{\ensuremath{\mp}}$ and ${\overline{B}}_{s}^{0}/{B}_{s}^{0}\ensuremath{\rightarrow}{K}^{\ifmmode\pm\else\textpm\fi{}}{K}^{*\ensuremath{\mp}}$. In the perturbative QCD approach, the $(S\ensuremath{-}P)(S+P)$ penguins in annihilation diagrams play an important role. Although they have the same topology with charming penguins in SCET, there are many differences between the two objects in weak phases, magnitudes, strong phases, and factorization properties.

Okubo-Zweig-Iizuka-rule violation andB→η(′)Kbranching ratios

We show that the few-percent Okubo-Zweig-Iizuka-rule violating effects in the quark-flavor basis for the $\ensuremath{\eta}\ensuremath{-}{\ensuremath{\eta}}^{\ensuremath{'}}$ mixing can enhance the chiral scale associated with the ${\ensuremath{\eta}}_{q}$ meson a few times. This enhancement is sufficient for accommodating the dramatically different data of the $B\ensuremath{\rightarrow}{\ensuremath{\eta}}^{\ensuremath{'}}K$ and $B\ensuremath{\rightarrow}\ensuremath{\eta}K$ branching ratios. We comment on other proposals for resolving this problem, including flavor-singlet contributions, axial $U(1)$ anomaly, and nonperturbative charming penguins. Discrimination of the above proposals by means of the $B\ensuremath{\rightarrow}{\ensuremath{\eta}}^{(\ensuremath{'})}\ensuremath{\ell}\ensuremath{\nu}$ and ${B}_{s}\ensuremath{\rightarrow}{\ensuremath{\eta}}^{(\ensuremath{'})}\ensuremath{\ell}\ensuremath{\ell}$ data is suggested.

Probing electroweak physics for allB→XMdecays in the endpoint region

Using soft-collinear effective theory we describe at leading order in $1/{m}_{b}$ all the semi-inclusive hadronic $B\ensuremath{\rightarrow}XM$ decays near the endpoint, where an energetic light meson $M$ recoils against an inclusive jet $X$. Here we extend to the decays in which spectator quarks go into the jet $X$, and also include the decays involving $\ensuremath{\eta}$, ${\ensuremath{\eta}}^{\ensuremath{'}}$ mesons that receive additional contributions from gluonic operators. The predicted branching ratios and $CP$ asymmetries depend on fewer hadronic parameters than the corresponding two-body $B$ decays. This makes semi-inclusive hadronic $B\ensuremath{\rightarrow}XM$ decays a powerful probe of the potential nonperturbative nature of charming penguins as well as a useful probe of new physics effects in electroweak flavor changing transitions. A comparison with $B\ensuremath{\rightarrow}KX$ data from BABAR points to an enhanced charming penguin, albeit with large experimental errors.

Semi-inclusive hadronicBdecays in the endpoint region

We consider in the soft-collinear effective theory semi-inclusive hadronic $B$ decays, $B\ensuremath{\rightarrow}XM$, in which an energetic light meson $M$ near the endpoint recoils against an inclusive jet $X$. We focus on a subset of decays where the spectator quark from the $B$ meson ends up in the jet. The branching ratios and direct $CP$ asymmetries are computed to next-to-leading order accuracy in ${\ensuremath{\alpha}}_{s}$ and to leading order in $1/{m}_{b}$. The contribution of charming penguins is extensively discussed, and a method to extract it in semi-inclusive decays is suggested. Subleading $1/{m}_{b}$ corrections and $SU(3)$ breaking effects are discussed.

Long-distance effects and final state interactions in [formula omitted] and [formula omitted] decays

B decays into ππK and KK¯K, where the ππ and K¯K pairs interact in isospin zero S-wave, are studied in the ππ effective mass range from threshold to 1.2 GeV. The interplay of strong and weak decay amplitudes is analyzed using an unitary ππ and KK¯ coupled channel model. Final state interactions are described in terms of four scalar form factors constrained by unitarity and chiral perturbation theory. Branching ratios for the B→f0(980)K decay, calculated in the factorization approximation with some QCD corrections, are too low as compared to recent data. In order to improve agreement with experiment, we introduce long-distance contributions called charming penguins. Effective mass distributions, branching ratios and asymmetries are compared with the existing data from BaBar and Belle Collaborations. A particularly large negative asymmetry in charged B decays is predicted for one set of the charming penguin amplitudes.

Charming penguins in B→PP decays and the extraction of γ

It is shown that inclusion of charming penguins of the size suggested by short-distance dynamics may shift down by 10°–15° the value of γ extracted via the overall fit to the B→PP branching ratios. A substantial dependence of the fit on their precise values is found, underscoring the need to improve the reliability of data.

Factorization fits and the unitarity triangle in charmless two-bodyBdecays

We present fits to charmless hadronic B decay data from the BaBar, Belle and Cleo experiments using two theoretical models: (i) the QCD factorization model of Beneke et al. and (ii) QCD factorization complemented with the so-called charming penguins of Ciuchini et al. When we include the data from pseudoscalar-vector decays the results favor the incorporation of the charming penguin terms. We also fit results for the unitarity triangle parameters and the CP-violating asymmetries.

Charming penguin contributions inB→K*π,K(ρ,ω,φ)decays

We evaluate the decays B => K* pi, K (rho,omega,phi) adding the long distance charming penguin contributions to the short distance: Tree+Penguin amplitudes. We estimate the imaginary part of the charming penguin by an effective field theory inspired by the Heavy Quark Effective Theory and parameterize its real part. The final results for branching ratios depend on only two real parameters and show a significant role of the charming penguins. The overall agreement with the available experimental data is satisfactory.

QCD light-cone sum rule estimate of charming penguin contributions in B→ππ

Employing the QCD light-cone sum rule approach we calculate the B→ππ hadronic matrix element of the current–current operator with c quarks in the penguin topology (“charming penguin”). The dominant contribution to the sum rule is due to the c-quark loop at short distances and is of O(αs) with respect to the factorizable B→ππ amplitude. The effects of soft gluons are suppressed at least by O(αsmb−2). Our result indicates that sizable nonperturbative effects generated by charming penguins at finite mb are absent. The same is valid for the penguin contractions of the current–current operators with light quarks.

QCD light-cone sum rule estimate of charming penguin contributions in B→ππ

Employing the QCD light-cone sum rule approach we calculate the B→ππ hadronic matrix element of the current–current operator with c quarks in the penguin topology (“charming penguin”). The dominant contribution to the sum rule is due to the c-quark loop at short distances and is of O(αs) with respect to the factorizable B→ππ amplitude. The effects of soft gluons are suppressed at least by O(αsmb−2). Our result indicates that sizable nonperturbative effects generated by charming penguins at finite mb are absent. The same is valid for the penguin contractions of the current–current operators with light quarks.

Probing the standard model and its extensions in rare exclusive b → sℓ + ℓ − decays

Long-distance effects on the forward-backward and longitudinal lepton polarization asymmetries in rare B → (K, K*)l+l- decays are investigated. The lepton asymmetries are found to be largely unaffected by the theoretical uncertainties in the long-distance contributions, induced both by the long-range charming penguins in the l+ l− channel and by the transition form factors in the meson channels, while they are mainly determined by the short-distance Wilson coefficients, providing in this way a test of the possible presence of New Physics. We also show that within left-right models one can expect a strong enhancement of the right-handed K* production in B → K*l+ l− decays compared to models including only left-handed quark currents. Hence an experimental study of the transverse asymmetry of the produced K* mesons provides a clean possibility to discriminate between the MSSM and LR extensions of the SM.

Lepton asymmetries in exclusive b→ sℓ +ℓ − decays as a test of the standard model

We argue that the longitudinal lepton polarization and the forward-backward asymmetries in exclusive B→(K,K ∗)ℓ +ℓ − decays are largely unaffected by the theoretical uncertainties in the long-distance contributions both induced by the long-range charming penguins in the ℓ +ℓ − channel and those in the meson channels encoded in the meson transition form factors, and are mainly determined by the short-distance Wilson coefficients at the low-energy scale μ≃ m b . Thus, the abovementioned asymmetries provide a powerful probe of the Standard Model and its extensions.