Nonleptonic Decays Research Articles

Weak decays of stable open-bottom tetraquark by SU(3) symmetry analysis

The exotic state X(5568) which was observed by D0 Collaboration is very likely to be a tetraquark state with four different valence quark flavors, though the existence was not confirmed by other collaborations. The possibility of such state still generates lots of interests in theory. In the paper, we will study the properties of the state under the SU(3) flavor symmetry. The four quark states with a heavy bottom quark and three light quarks(anti-quark) can form {bar{3}}, 6 and {overline{15}} representations. The weak decays can be dominant and should be discussed carefully while these states are stable against the strong and electromagnetic interactions. Therefor we will study the multi-body semileptonic and nonleptonic weak decays systematically. With the help of SU(3) flavor symmetry, we can give the Hamiltonian in the hadronic level, then obtain the parameterized irreducible amplitudes and the relations of different channels. At the end of the article, we collect some Cabibbo allowed two-body and three-body weak decay channels which can be used to reconstruct X_{b6} states at the branching fraction up to be 10^{-5}.

Rare nonleptonic B¯s0 decays as probes of new physics behind b→sμμ¯ anomalies

The anomalous results of recent measurements on various $b\to s\mu^+\mu^-$ processes could be initial evidence of physics beyond the standard model (SM). Assuming this to be the case, we entertain the possibility that the underlying new physics also affects the rare nonleptonic decays of the $\bar B_s^0$ meson. We consider in particular new physics arising from the interactions of a heavy $Z'$ boson and investigate their influence on the decay modes $\bar B_s^0\to(\eta,\eta',\phi)\omega$, which receive sizable QCD- and electroweak-penguin contributions. These decays are not yet observed, and their rates are estimated to be relatively small in the SM. Taking into account the pertinent constraints, we find that the $Z'$ effects can greatly increase the rates of $\bar B_s^0\to(\eta,\phi)\omega$, by as much as two orders of magnitude, with respect to the SM expectations. We have previously shown that $\bar B_s^0\to(\eta,\phi)\pi^0$, with similarly suppressed SM rates, could also undergo substantial $Z'$-induced enhancement. These rare modes can therefore serve as complementary probes of the potential new physics which may be responsible for the $b\to s\mu^+\mu^-$ anomalies.

Ab initio three-loop calculation of the W -exchange contribution to nonleptonic decays of double charm baryons

We have made an ab initio three-loop quark model calculation of the $W$-exchange contribution to the nonleptonic two-body decays of the doubly charmed baryons $\Xi_{cc}^{++}$ and $\Omega_{cc}^{+}$. The $W$-exchange contributions appear in addition to the factorizable tree graph contributions and are not suppressed in general. We make use of the covariant confined quark model previously developed by us to calculate the tree graph as well as the $W$-exchange contribution. We calculate helicity amplitudes and quantitatively compare the tree graph and $W$-exchange contributions. Finally, we compare the calculated decay widths with those from other theoretical approaches when they are available.

Semileptonic and nonleptonic weak decays of Λb0

The recent experimental developments require a more precise theoretical study of weak decays of heavy baryon $\Lambda_b^0$. In this work, we provide an updated and systematic analysis of both the semi-leptonic and nonleptonic decays of $\Lambda^0_b$ into baryons $\Lambda^+_c$, $\Lambda$, $p$, and $n$. The diquark approximation is adopted so that the methods developed in the $B$ meson system can be extended into the baryon system. The baryon-to-baryon transition form factors are calculated in the framework of a covariant light-front quark model. The form factors $f_3, ~g_3$ can be extracted and are found to be non-negligible. The semi-leptonic processes of $\Lambda^0_b\to \Lambda^+_c(p)l^-\bar\nu_l$ are calculated and the results are consistent with the experiment. We study the non-leptonic processes within the QCD factorization approach. The decay amplitudes are calculated at the next-to-leading order in strong coupling constant $\alpha_s$. We calculate the non-leptonic decays of $\Lambda^0_b$ into a baryon and a s-wave meson (pseudoscalar or vector) including 44 processes in total. The branching ratios and direct CP asymmetries are predicted. The numerical results are compared to the experimental data and those in the other theoretical approaches. Our results show validity of the diquark approximation and application of QCD factorization approach into the heavy baryon system.

Resonant and non-resonant contributions of B → K∗(p1,𝜖1){Kπ,ππ,KK} decay modes

In this paper, the non-leptonic three-body decays [Formula: see text], [Formula: see text], [Formula: see text] are studied by introducing two-meson distribution amplitude for the [Formula: see text], [Formula: see text] and [Formula: see text] pairs in naive and QCD factorization (QCDF) approaches, such that the analysis is simplified into quasi-two body decays. By considering that the vector meson is being ejected in factorization, the resonant and non-resonant contributions are analyzed by using intermediate mesons in Breit–Wigner resonance formalism and the heavy meson chiral perturbation theory (HMChPT), respectively. The calculated values of the resonant and non-resonant branching ratio of [Formula: see text], [Formula: see text] and [Formula: see text] decay modes are compared with the experimental data. For [Formula: see text] and [Formula: see text], the non-resonant contributions are about 70–80% of experimental data, for which the total results by considering resonant contributions are in good agreement with the experiment.

Weak decays of doubly heavy baryons: W-exchange

Since the LHCb collaboration announced the observation of the doubly charmed baryon Xi _{cc}^{++}, a series of studies of doubly heavy baryons have been presented. In this work, I analyse the non-leptonic weak decays of doubly heavy baryons Xi _{bc} and Omega _{bc} under the flavor SU(3) symmetry. I mainly focus on the W-exchange diagrams, which will contribute to the decay channels with final states are light meson and light baryon. These channels would be helpful for searching for Xi _{bc} and Omega _{bc} at LHC. And these channels and relations of corresponding decay widths could be examined by the future experimental facilities such as LHC, Belle II and CEPC.

Weak decays of stable doubly heavy tetraquark states

In the light of the recent discovery of the $\Xi^{++}_{cc}$ by LHCb collaboration, we study the stable doubly heavy tetraquarks. These states are compact exotic hadrons which can be approximated as the diquark-anti-diquark correlations. In the flavor SU(3) symmetry, they form an SU(3) triplet or anti-sextet. The spectra of the stable doubly heavy tetraquark states are predicted by Sakharov-Zeldovich formula. We find that the $T^+_{cc\bar{u}\bar{d}}({\bf 3})$ is about 16MeV below the $DD^*$ threshold, while $T^{-}_{bb\bar{u}\bar{d}}({\bf 3})$ is about 73MeV below the $BB^*$ threshold. We then study the semileptonic and nonleptonic weak decays of the stable doubly heavy tetraquark states. The decay amplitudes are parametrized in terms of SU(3)-irreducible amplitudes. Ratios between decay widths of different channels are also derived. At the end, we collect the Cabibbo allowed two-body and three-body decay channels, which are most promising to search for the stable doubly heavy tetraquark states at LHCb and Belle II experiments.

Weak decays of doubly heavy baryons: the 1/2rightarrow 3/2 case

As a continuation of our previous work, we investigate the weak decays of doubly heavy baryons into a spin-3 / 2 singly or doubly heavy baryon. The light-front approach is adopted to handle the dynamics in the transitions, in which the two spectator quarks are approximated as a diquark. Results for the form factors are then used to calculate decay widths of semileptonic and nonleptonic processes. The flavor SU(3) symmetry and symmetry breaking effects in semileptonic decays modes are explored, and we point out that in the charm sector, there are sizable symmetry breaking effects. For nonleptonic decay modes, we study only the factorizable channels induced by external W-emission. We find that branching fractions for most 1/2 to 3/2 transitions are approximately one order of magnitude smaller than the corresponding ones for the 1/2 to 1/2 transitions. Parametric uncertainties are also investigated in detail. We suggest our experimental colleagues to search for the 1/2 to 1/2 process Xi _{cc}^{++}rightarrow Xi _{c}^{prime +}pi ^{+} and its 1/2 to 3/2 counterpart Xi _{cc}^{++}rightarrow Xi _{c}^{prime *+}pi ^{+}. Their branching ratios turn out to be around 5.00% and 1.02%. The former branching ratio is expected to be close to that of the recently discovered Xi _{cc}^{++}rightarrow Xi _{c}^{+}pi ^{+} process.

Weak decays of doubly heavy charm Omega _{cc}^{+} baryon

We investigate the two-body non-leptonic decays of doubly charm strange, Omega _{cc}^{+}, baryon. The branching ratios of the Omega _{cc}^{+} baryon decays involving a pseudoscalar meson for CKM-favored and -suppressed modes are determined by employing the pole model and the factorization hypothesis. We give the first estimates of the non-factorizable W-exchange contributions of Omega _{cc}^{+} decay in the pole model. We find that the branching ratios of some decays receive contributions, exclusively from the W-exchange diagrams, are as large as sim mathcal {O}(10^{-2}). The non-spectator contributions in doubly charmed decays are comparable to the factorizable contributions in most of the cases.

Heavy flavour physics: A portal to new physics

Heavy flavour physics, as one of the most important parts in the standard model (SM), plays important roles in testing the SM and probing the effects of new physics beyond SM. Thanks to the two B factories, Beijing spectrometer (BES) and large hadron collider beauty (LHCb) experiment, in the past decades, there is great development in heavy flavour physics, in both experimental and theoretical sides. In heavy flavour physics, the first work is to test SM by measuring three angles ($\alpha$, $\beta$ and $\gamma$) and sides of Cabbibo-Kobayashi-Maskawa (CKM) triangle. Though the current results are in agreement with SM, the fit becomes less constrained in the presence of new physics, and ${\cal~O}(20%$) contributions of new physics are still allowed. The charge conjugation and parity (CP) asymmetries measured by two B factories helped us to study the matter-antimatter asymmetry in the Universe, and the discovered CP asymmetry in $\rm~B\to~K_s~J/\psi$ had led to the nobel prize for Kobayashi and Maskawa. In addition, the mass differences between the neutral meson and their own anti-meson can present us the information of the scale of the new physics, because possible new particles might contribute to $\rm~D^0$, $\rm~B_d^0$, and $\rm~B_s^0$ meson mixing through box diagrams. The nonleptonic decays of B mesons afford us a new plate for studying the quantum chromodynamics (QCD) and factorization concept, as well as searching for the strong phases, which are important factors in CP asymmetries. Importantly, the rare decays induced by the flavour-changing neutral-current has attracted much interest, because the new physics can affect the observables remarkably through penguin diagrams. In addition, it is of interest to note that the recent anomalies, such as $R_{\rm~K^{(*)}}$, $R({\rm~D}^{(*)})$ and $P_5^\prime$, might be the hints of new physics beyond SM. In order to explain these anomalies, many models have been proposed, however, all of them should be further tested in the future on both experimental and theoretical sides. Moreover, heavy flavor physics also provides us an important plate for studying the new exotic states. Many new discovered exotic states in BES-III, B factories and LHCb, such as $\rm~X(3872)$, $\rm~Z_c(3900)$ and $\rm~P_c(4450,4380)$, motivate us to further study the quark model and QCD. In 2018, Belle-II will take data, where the total luminosity is predicted to be $50\rm~ab^{-1}$ and $10^{10}$ B meson pair could be produced. The proposed International Linear Collider, Circular Electron-Positron Collider and Hyper-Z Factory, can also produce large number of B mesons, as well as $\rm~B_s$, $\rm~B_c$ and $\Lambda_b$, when the collision energy is set to be ${\cal~O}(m_Z)$. These high precision or energy machines, together with the current LHCb experiment and its next generation, will lead heavy flavor physics to a new golden era.

Weak decays of heavy baryons in the light-front approach**Supported by National Natural Science Foundation of China (11575110, 11655002, 11735010) and Natural Science Foundation of Shanghai (15DZ2272100)

In this work, we analyse semi-leptonic and non-leptonic weak decays of the heavy baryons: Λb, Ξb, Ωb and Λc, Ξc, Ωc. For non-leptonic decay modes, we study only the factorizable channels induced by the external W-emission. The two spectator quarks in the baryonic transitions are treated as a diquark and form factors are calculated in the light-front approach. Using the results for form factors, we also calculate some corresponding semi-leptonic and non-leptonic decay widths. We find that our results are comparable with the available experimental data and other theoretical predictions. Decay branching fractions for many channels are found to reach the level 10−3 ∼ 10−2, which is promising for discovery in future measurements at BESIII, LHCb and Belle II. The SU(3) symmetry in semi-leptonic decays is examined and sources of symmetry breaking are discussed.

Confronting hadronic tau decays with non-leptonic kaon decays

In the chiral limit, the D = 6 contribution to the Operator Product Expansion (OPE) of the VV −AA correlator of quark currents only depends on two vacuum condensates, which can be related to hadronic matrix elements associated to CP violation in non-leptonic kaon decays. We use those relations to determine 〈(ππ)I=2|Q8|K〉, using the updated ALEPH spectral functions. Alternatively, we use those relations in the opposite direction. Taking the values of the matrix elements from the lattice to obtain the D = 6 vacuum elements provides a new short-distance constraint which allows for an inclusive determination of fπ and an updated value for the D = 8 condensate.

The decays [formula omitted] and Bc → J/ψ + π(K) in covariant confined quark model

In the wake of the recent measurements of the decays Bc→J/ψπ(K) and Bc→J/ψℓνℓ reported by the LHCb Collaboration we calculate the form factors for the Bc→J/ψ and Bc→ηc transitions in full kinematical region within covariant confined quark model. Then we use the calculated form factors to evaluate the partial decay widths of the above-mentioned semileptonic and nonleptonic decays of the Bc meson. We find that the theoretical predictions on the ratios of RK+/π+ and Rπ+/μ+ν are in good agreement with last LHCb-data. However, the prediction for the RJ/ψ is found to be underestimated.

Pseudoscalar or vector meson production in non-leptonic decays of heavy hadrons

We have addressed the study of non-leptonic weak decays of heavy hadrons (Lambda _b, Lambda _c, B and D), with external and internal emission to give two final hadrons, taking into account the spin-angular momentum structure of the mesons and baryons produced. A detailed angular momentum formulation is developed which leads to easy final formulas. By means of them we have made predictions for a large amount of reactions, up to a global factor, common to many of them, that we take from some particular data. Comparing the theoretical predictions with the experimental data, the agreement found is quite good in general and the discrepancies should give valuable information on intrinsic form factors, independent of the spin structure studied here. The formulas obtained are also useful in order to evaluate meson-meson or meson-baryon loops, for instance of B decays, in which one has PP, PV, VP or VV intermediate states, with P for pseudoscalar mesons and V for vector meson and lay the grounds for studies of decays into three final particles.

Weak decays of triply heavy baryons

After the experimental establishment of doubly heavy baryons, baryons with three quarks are the last missing pieces of the lowest-lying baryon multiplets in quark model. In this work we study semileptonic and nonleptonic weak decays of triply heavy baryons, $\Omega_{ccc}^{++}, \Omega_{ccb}^{+}, \Omega_{cbb}^{0}, \Omega_{bbb}^{-}$. Decay amplitudes for various channels are parametrized in terms of a few SU(3) irreducible amplitudes. We point out that branching fractions for Cabibbo allowed processes, $\Omega_{ccc}\to (\Xi_{cc}^{++} \overline K^0, \Xi_{cc}^{++}K^-\pi^+, \Omega_{cc}^{+}\pi^+, \Xi_{c}^+ D^+, \Xi_{c}^{\prime} D^+, \Lambda_c D^+\overline K^0, \Xi_{c}^+ D^0 \pi^+, \Xi_{c}^0 D^+\pi^+)$ may reach a few percents. We suggest our experimental colleagues to perform a search at hadron colliders and the electron and positron collisions in future, which will presumably lead to discoveries of triply heavy baryons and complete the baryon multiplets. Using the expanded amplitudes, we derive a number of relations for the partial widths which can be examined in future.

Connecting bto sell overline{ell} anomalies to enhanced rare nonleptonic {overline{B}}_s^0 decays in Z\u2032 model

The present data on a number of observables in b → sμ+μ− processes manifest some tensions with the standard model (SM). Assuming that these anomalies have a new physics origin, we consider the possibility that a Z′ boson is responsible for them. We further assume that its interactions with quarks also affect rare nonleptonic decays of the {overline{B}}_s^0 meson which are purely isospin-violating and tend to be dominated by electroweak-penguin contributions, namely {overline{B}}_s^0to left(eta, eta^{prime },phi right)left({pi}^0,{rho}^0right) . Most of these decays are not yet observed, and their rates are expected to be relatively small in the SM. Taking into account constraints from various measurements, including the evidence for {overline{B}}_s^0to phi {rho}^0 recently seen by LHCb, we find that the Z′ effects on {overline{B}}_s^0to left(eta, phi right){pi}^0 can make their rates bigger than the SM predictions by up to an order of magnitude. For {overline{B}}_s^0to {eta}^{prime }{pi}^0,left(eta, {eta}^{prime}right){rho}^0 , the enhancement factors are at most a few. Since the Z′ contributions to the different channels depend on different combinations of its couplings, observations of more of these decays in future experiments, along with improved b → sμ+μ− data, will probe this Z′ scenario more thoroughly.

Weak decays of doubly heavy baryons: multi-body decay channels

The newly-discovered Xi _{cc}^{++} decays into the Lambda _{c}^+ K^-pi ^+pi ^+, but the experimental data has indicated that this decay is not saturated by any two-body intermediate state. In this work, we analyze the multi-body weak decays of doubly heavy baryons Xi _{cc}, Omega _{cc}, Xi _{bc}, Omega _{bc}, Xi _{bb} and Omega _{bb}, in particular the three-body nonleptonic decays and four-body semileptonic decays. We classify various decay modes according to the quark-level transitions and present an estimate of the typical branching fractions for a few golden decay channels. Decay amplitudes are then parametrized in terms of a few SU(3) irreducible amplitudes. With these amplitudes, we find a number of relations for decay widths, which can be examined in future.

Quark diagram analysis of bottom meson decays emitting pseudoscalar and vector mesons

This paper presents the two body weak nonleptonic decays of B mesons emitting pseudoscalar (P) and vector (V) mesons within the framework of the diagrammatic approach at flavor SU(3) symmetry level. Using the decay amplitudes, we are able to relate the branching fractions of B PV decays induced by both b c and b u transitions, which are found to be well consistent with the measured data. We also make predictions for some decays, which can be tested in future experiments.

Estimates of W -exchange contributions to Ξcc decays

Encouraged by recent discovery of $\Xi_{cc}^{++}$ baryon, we investigate two body non-leptonic weak decays of doubly charmed, $\Xi_{cc}$, baryons. We calculate the branching ratios for CKM-favored and suppressed modes in factorization and pole model approach. We give the first estimates of nonfactorizable W-exchange contributions using pole model. We find that W-exchange contributions to $\Xi_{cc}$ decays being sizable can not be ignored.

Non-leptonic two-body weak decays of Λc(2286)

We study the non-leptonic two-body weak decays of Λc+(2286)→BnM with Bn (M) representing as the baryon (meson) states. Based on the SU(3) flavor symmetry, we can describe most of the data reexamined by the BESIII Collaboration with higher precisions. However, our result of B(Λc+→pπ0)=(5.6±1.5)×10−4 is larger than the current experimental limit of 3×10−4 (90% C.L.) by BESIII. In addition, we find that B(Λc+→Σ+K0)=(8.0±1.6)×10−4, B(Λc+→Σ+η′)=(1.0−0.8+1.6)×10−2, and B(Λc+→pη′)=(12.2−8.7+14.3)×10−4, which are accessible to the BESIII experiments.