arXiv subjects

Mikhail A. Ivanov

Publications and source records attributed to Mikhail A. Ivanov.

At least 37 records · Page 2Linked to original sources

arXiv2021

Radiative transitions of charmonium states in the covariant confined quark model

We have studied the dominant radiative transitions of the charmonium $S$-and $P$-wave states within the covariant confined quark model. The gauge invariant leading-order transition amplitudes have been expressed by using either the conventional Lorentz structures, or the helicity amplitudes, where it was effective. The renormalization couplings of the charmonium states have been strictly fixed by the compositeness conditions that excludes the constituent degrees of freedom from the space of physical states. We use the basic model parameters for the constituent c-quark mass $m_c=1.80$ GeV and the global infrared cutoff $λ=0.181$ GeV. We additionally introduce only one adjustable parameter $\varrho>0$ common for the charmonium states $η_c({}^1\!S_0)$, $J/ψ({}^3\!S_1)$, $χ_{c0}({^{3}}\!P_{0})$, $χ_{c1}({^{3}}\!P_{1})$, $h_c({^{1}}\!P_{1})$, and $χ_{c2}({^{3}}\!P_{2})$ to describe the quark distribution inside the hadron. This parameter describes the ratio between the charmonium size and its physical mass. The optimal value $\varrho=0.485$ has been fixed by fitting the latest data for the partial widths of the one-photon radiative decays of the triplet $χ_{cJ}({^{3}}\!P_{J}), J=\{0,1,2\}$. Then, we calculate corresponding fractional widths for states $J/ψ({}^3\!S_1)$ and $h_c({^{1}}\!P_{1})$. Estimated results are in good agreement with the latest data. By using the fraction data from PDG2020 and our estimated partial decay width for $h_c({^{1}}\!P_{1})$ we recalculate the theoretical full width $Γ^{\rm theor}_{h_c} \simeq (0.57 \pm 0.12)$ MeV in comparison with latest data $Γ^{\rm exp}_{h_c} \simeq (0.7\pm 0.4)$ MeV. We also repeated our calculations by gradually decreasing the global cutoff parameter and revealed that the results do not change for any $λ<0.181$ GeV up to the deconfinement limit.

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arXiv2021

Analysis of the nonleptonic two-body decays of the $Λ$ hyperon

We systematically study two-body nonleptonic decays of light lambda hyperon $Λ\to p π^- (nπ^0)$ with account for both short- and long-distance effects. The short-distance effects are induced by five topologies of external and internal weak $W^\pm$ exchange, while long-distance effects are saturated by an inclusion of the so-called pole diagrams with intermediate $\frac{1}{2}^+$ and $\frac{1}{2}^-$ baryon resonances. The contributions from $\frac12^+$ resonances are calculated straightforwardly by account for nucleon and $Σ$ baryons whereas the contributions from $\frac{1}{2}^-$ resonances are calculated by using the well-known soft-pion theorem in the current-algebra approach. It allows one to express the parity-violating $S$-wave amplitude in terms of parity-conserving matrix elements. From our previous analysis of heavy baryons we know that short-distance effects induced by internal topologies are not suppressed in comparison with external $W$-exchange diagram and must be included for description of data. Here, in the case of $Λ$ decays we found that the contribution of external and internal $W$-exchange diagrams is sizably suppressed, e.g., by one order of magnitude in comparison with data, which are known with quite good accuracy. Pole diagrams play the major role to get consistency with experiment.

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arXiv2021

Form-factor-independent test of lepton universality in semileptonic heavy meson and baryon decays

In the semileptonic decays of heavy mesons and baryons the lepton-mass dependence factors out in the quadratic $\cos^2θ$ coefficient of the differential $\cosθ$ distribution. We call the corresponding normalized coefficient the convexity parameter. This observation opens the path to a test of lepton universality in semileptonic heavy meson and baryon decays that is independent of form-factor effects. By projecting out the quadratic rate coefficient, dividing out the lepton-mass-dependent factor and restricting the phase space integration to the $τ$ lepton phase space, one can define optimized partial rates which, in the Standard Model, are the same for all three $(e,μ,τ)$ modes in a given semileptonic decay process. We discuss how the identity is spoiled by New Physics effects. We discuss semileptonic heavy meson decays such as $\bar{B}^0 \to D^{(\ast)+} \ell^- \barν_\ell$ and $B_c^- \to J/ψ(η_c)\ell^- \barν_\ell$, and semileptonic heavy baryon decays such as $Λ_b \to Λ_c \ell^- \barν_\ell$ for each $\ell=e,μ,τ$.

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arXiv2020

$D^\ast$ Polarization as an Additional Constraint on New Physics in the $b\to cτ\barν_τ$ Transition

Measurements of the branching fractions of the semileptonic decays $B\to D^{(*)}τ\barν_τ$ and $B_c\to J/ψτ\barν_τ$ systematically exceed the Standard Model (SM) predictions, pointing to possible signals of new physics that can violate lepton flavor universality. The unknown origin of new physics realized in these channels can be probed using a general effective Hamiltonian constructed from four-fermion operators and the corresponding Wilson coefficients. Previously, constraints on these Wilson coefficients were obtained mainly from the experimental data for the branching fractions. Meanwhile, polarization observables were only theoretically studied. The situation has changed with more experimental data having become available, particularly those regarding the polarization of the tau and the $D^*$ meson. In this study, we discuss the implications of the new data on the overall picture. We then include them in an updated fit of the Wilson coefficients using all hadronic form factors from our covariant constituent quark model. The use of our form factors provides an analysis independent of those in the literature. Several new-physics scenarios are studied with the corresponding theoretical predictions provided, which are useful for future experimental studies.

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arXiv2020

Form factors for $B\to j_1j_2$ decays into two currents in QCD

We discuss the general properties of the $B$-meson decay form factors $F(q^2,q'^2)$, describing $B$-meson decays induced by two currents, e.g., $B$-decays into four leptons in the final state. We study the analytic properties of these complicated objects and identify those regions of $q^2$ and $q'^2$, where perturbative QCD can be applied for obtaining predictions for the physical form factors.

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arXiv2019

Analysis of the semileptonic and nonleptonic two-body decays of the double heavy charm baryon states $Ξ_{cc}^{++},\,Ξ_{cc}^{+}$ and $Ω_{cc}^+$

We calculate the semileptonic and a subclass of sixteen nonleptonic two-body decays of the double charm baryon ground states $Ξ_{cc}^{++},\,Ξ_{cc}^{+}$ and $Ω_{cc}^+$ where we concentrate on the nonleptonic decay modes. We identify those nonleptonic decay channels in which the decay proceeds solely via the factorizing contribution precluding a contamination from $W$-exchange. We use the covariant confined quark model previously developed by us to calculate the various helicity amplitudes which describe the dynamics of the $1/2^+ \to 1/2^+$ and $1/2^+ \to 3/2^+$ transitions induced by the Cabibbo favored effective $(c \to s)$ and $(d \to u)$ currents. We then proceed to calculate the rates of the decays as well as polarization effects and angular decay distributions of the prominent decay chains resulting from the nonleptonic decays of the double heavy charm baryon parent states.

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arXiv2019

Semileptonic decays of $ B_c$ mesons into charmonium states

In this work we study the semileptonic decays of $B_c$ meson. We evaluated $B_{c}\rightarrow D(D^{\ast})$, $B_{c}\rightarrow D_s(D_s^{\ast})$ and $B_{c}\rightarrow η_{c}(J/ψ)$ transitions form factors in the full kinematical region within the covariant quark model. The calculated form factors are used to evaluate the semileptonic decays of $B_c$ meson and it was defined ratios ($R_{η_{c}}$, $R_{J/ψ}$, $R_{ D}$ ,$R_{ D^{\ast}}$) of the branching ratios, which will be hopefully tested on LHC experiments.We compare the obtained results with the results from other theoretical approaches.

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arXiv2019

Novel ideas in nonleptonic decays of double heavy baryons

The recent discovery of double charm baryon states by the LHCb Collaborarion and their high precision mass determination calls for a comprehensive analysis of the nonleptonic decays of double and single heavy baryons. Nonleptonic baryon decays play an important role in particle phenomenology since they allow to study the interplay of long and short distance dynamics of the Standard Model (SM). Further, they allow one to search for New Physics effects beyond the SM. We review recent progress in experimental and theoretical studies of the nonleptonic decays of heavy baryons with a focus on double charm baryon states and their decays. In particular, we discuss new ideas proposed by the present authors to calculate the $W$-exchange matrix elements of the nonleptonic decays of double heavy baryons. An important ingredient in our approach is the compositeness condition of Salam and Weinberg, and an effective implementation of infrared confinement both of which allow one to describe the nonperturbative structure of baryons composed of light and heavy quarks. Further we discuss an ab initio calculational method for the treatment of the so-called $W$-exchange diagrams generated by $W^{\pm}$ boson exchange between quarks. We found that the $W^{\pm}$-exchange contributions are not suppressed in comparison with the tree-level (factrorizing) diagrams and must be taken into account in the evaluation of matrix elements. Moreover, there are decay processes such as the doubly Cabibbo-suppressed decay $Ξ_c^+ \to p ϕ$ recently observed by the LHCb Collaboration which is contributed to only by one single $W$-exchange diagram.

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arXiv2019

Exclusive semileptonic decays of $D$ and $D_s$ mesons in the covariant confining quark model

Recently, the BESIII collaboration has reported numerous measurements of various $D_{(s)}$ meson semileptonic decays with significantly improved precision. Together with similar studies carried out at BABAR, Belle, and CLEO, new windows to a better understanding of weak and strong interactions in the charm sector have been opened. In light of new experimental data, we review the theoretical description and predictions for the semileptonic decays of $D_{(s)}$ to a pseudoscalar or a vector meson. This review is essentially an extended discussion of our recently published results obtained in the framework of the covariant confining quark model.

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arXiv2019

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 $Ξ_{cc}^{++}$ and $Ω_{cc}^{+}$. 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.

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arXiv2019

Semileptonic $D_{(s)}$-meson decays in the light of recent data

Inspired by recent improved measurements of charm semileptonic decays at BESIII, we study a large set of $D(D_s)$-meson semileptonic decays where the hadron in the final state is one of $D^0$, $ρ$, $ω$, $η^{(\prime)}$ in the case of $D^+$ decays, and $D^0$, $ϕ$, $K^0$, $K^\ast(892)^0$, $η^{(\prime)}$ in the case of $D^+_s$ decays. The required hadronic form factors are computed in the full kinematical range of momentum transfer by employing the covariant confined quark model developed by us. A detailed comparison of the form factors with those from other approaches is provided. We calculate the decay branching fractions and their ratios, which show good agreement with available experimental data. We also give predictions for the forward-backward asymmetry and the longitudinal and transverse polarizations of the charged lepton in the final state.

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arXiv2019

Study of $B_s\to\ell^+\ell^-γ$ decays in covariant quark model

We study the rare radiative leptonic decays $B_s\to\ell^+\ell^-γ$ ($\ell=e,μ,τ$) within the Standard Model, considering both the structure-dependent amplitude and bremsstrahlung. In the framework of the covariant confined quark model developed by us, we calculate the form factors characterizing the $B_s\toγ$ transition in the full kinematical region of the dilepton momentum squared and discuss their behavior. We provide the analytic formula for the differential decay distribution and give predictions for the branching fractions in both cases: with and without long-distance contributions. Finally, we compare our results with those obtained in other approaches.

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arXiv2018

Nonleptonic two-body decays of single heavy baryons $Λ_Q$, $Ξ_Q$, and $Ω_Q$ $(Q=b,c)$ induced by $W$ emission in the covariant confined quark model

We have made a survey of heavy-to-heavy and heavy-to-light nonleptonic heavy baryon two-body decays and have identified those decays that proceed solely via $W$-boson emission, i.e. via the tree graph contribution. Some sample decays are $Ω_{b}^{-}\toΩ_{c}^{(*)0}ρ^{-}(π^{-}),\, Ω_{b}^{-}\toΩ^{-}J/ψ(η_{c}),\, Ξ_{b}^{0,-}\toΞ^{0,-}J/ψ(η_{c}),\, Λ_{b}\to ΛJ/ψ(η_{c}),\, Λ_{b}\to Λ_{c} D_{s}^{(\ast)},\, Ω_{c}^{0}\toΩ^{-}ρ^{+}(π^{+})$, and $Λ_c \to p ϕ$. We make use of the covariant confined quark model previously developed by us to calculate the tree graph contributions to these decays. We calculate rates, branching fractions and, for some of these decays, decay asymmetry parameters. We compare our results to experimental findings and the results of other theoretical approaches when they are available. Our main focus is on decays to final states with a lepton pair because of their clean experimental signature. For these decays we discuss two-fold polar angle decay distributions such as in the cascade decay $Ω_{b}^{-}\toΩ^{-}(\to Ξπ,ΛK^{-})+J/ψ(\to \ell^{+}\ell^{-})$. Lepton mass effects are always included in our analysis.

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arXiv2018

Dynamical picture for the exotic XYZ states

We present a dynamical approach for description of the multi-quark states that is based on an effective interaction Lagrangian describing the coupling of hadrons to their constituent quarks. First, we explore the consequences of treating the $X(3872)$ meson as a tetraquark bound state. We calculate the decay widths of the observed channels and conclude that for reasonable values of the size parameter of the $X(3872)$ one finds consistency with the available experimental data. Then we have critically checked the tetraquark picture for the $Z_c(3900)$ state by analyzing its strong decays. We found that $Z_c(3900)$ has a much more stronger coupling to $DD^\ast$ than to $J/ψπ$ that is in discord with experiment. As an alternative we have employed a molecular-type four-quark current to describe the decays of the $Z_c(3900)$ state as the charged particle in the isotriplet. We found that a molecular-type current gives the values of the above decays in accordance with the experimental observation. By using molecular-type four-quark currents for the recently observed resonances $Z_b(10610)$ and $Z_b(10650)$, we have calculated their two-body decay rates into a bottomonium state plus a light meson as well as into B-meson pairs.

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arXiv2018

Analyzing lepton flavor universality in the decays $Λ_b\toΛ_c^{(\ast)}(\frac12^\pm,\frac32^-) + \ell\,\barν_\ell$

Lepton flavor universality can be tested in the semileptonic decays $Λ_b\to Λ_c^{(\ast)}$ where $Λ_c^{(\ast)}$ denotes either the ground state $Λ_c(2286)$ (with $J^P=1/2^+$) or its orbital excitations $Λ_c(2595)$ (with $J^P=1/2^-$) and $Λ_c(2625)$ (with $J^P=3/2^-$). We calculate the differential decay rates as well as the branching fractions of these decays for both tauonic and muonic modes with form factors obtained from a covariant confined quark model previously developed by us. We present results for the rate ratios of the tauonic and muonic modes which provide important tests of lepton flavor universality in forthcoming experiments.

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arXiv2018

The decays $B_{c}\to J/ψ+\bar\ellν_\ell$ and $B_{c}\to J/ψ+ π(K)$ in covariant confined quark model

In the wake of the recent measurements of the decays $B_c\to J/ψ\,π(K)$ and $B_c\to J/ψ\,\ellν_\ell$ reported by the LHCb Collaboration we calculate the form factors for the $B_c\to J/ψ$ and $B_c\to η_{c}$ 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 $B_{c}$ meson. We find that the theoretical predictions on the ratios of $\mathcal{R}_{K^{+}/ π^{+}}$ and $\mathcal{R_{π^{+}/ μ^{+} ν}}$ are in good agreement with last LHCb-data. However, the prediction for the $\mathcal{R}_{J/ψ}$ is found to be underestimated.

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arXiv2018

b-s Anomaly Decays in Covariant Quark Model

The work is devoted to the study of b-s anomaly decays. We evaluated branching fractions of $B\to K^\ast μ^+μ^-$, $B^0_s\to ϕμ^+μ^-$ and $B_s\to μ^+μ^-$ decays and compared them with available experimental data and with results from other theoretical approaches.

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arXiv2018

Implications of new physics in the decays $B_c \to (J/ψ,η_c)τν$

We study the semileptonic decays of the $B_c$ meson into final charmonium states within the standard model and beyond. The relevant hadronic transition form factors are calculated in the framework of the covariant confined quark model developed by us. We focus on the tau mode of these decays, which may provide some hints of new physics effects. We extend the standard model by assuming a general effective Hamiltonian describing the $b\to cτν$ transition, which consists of the full set of the four-fermion operators. We then obtain experimental constraints on the Wilson coefficients corresponding to each operator and provide predictions for the branching fractions and other polarization observables in different new physics scenarios.

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