arXiv subjects

Zhomart Tyulemissov

Publications and source records attributed to Zhomart Tyulemissov.

8 recordsLinked to original sources

arXiv2025

Revisiting radiative transitions of charmonium states in covariant confined quark model

We calculate the amplitudes and branching fractions of $χ_{cJ}$, $h_c$, $J/ψ$, and $ψ(2S)$ radiative decays in the framework of the covariant confined quark model. First, we explicitly show that all calculated amplitudes are gauge invariant. Next, we use experimental data for three decay channels $J/ψ\to η_cγ$, $χ_{c0}\to J/ψγ$, and $ψ(2S)\to χ_{c0}γ$ to fit the model parameters including the charm quark mass and the meson size parameter. Finally, we use the obtained parameters to predict the branching fractions of the decays $h_c\toη_cγ$, $χ_{c1(c2)}\to J/ψγ$, and $ψ(2S)\toχ_{c1(c2)}γ$. Our predictions agree well with experimental data.

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arXiv2024

Analyzing leptonic decays of heavy quarkonia in covariant confined quark model

The leptonic decay widths of heavy quarkonia are complementary observables to the semileptonic decays of heavy mesons and provide additional insight into the possible lepton flavor universality breaking. We analyze the former in the framework of the covariant confined quark model, introducing a novel approach for the description of the radially excited quarkonia states, which is based on constituent quark mass running and the orthogonality of the states. We are able to describe the experimental observations by our approach within the Standard model, which does not support new physics explanations.

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arXiv2023

Study of the nonleptonic decay $Ξ^0_c \to Λ^+_c π^-$ in the covariant confined quark model

The nonleptonic decay $Ξ^0_c \to Λ^+_c π^-$ with $ΔC=0$ is systematically studied in the framework of the covariant confined quark model with accounting for both short and long distance effects. The short distance effects are induced by four 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 an intermediate $\frac12^+$ and $\frac12^-$ baryon resonances. The contributions from $\frac12^+$~resonances are calculated straightforwardly by accounting for single charmed $Σ^0_c$ and $Ξ^{'\,+}_c$~baryons whereas the contributions from $\frac12^-$~resonances are calculated by using the well-known soft-pion theorem in the current-algebra approach. It allows to express the parity-violating S-wave amplitude in terms of parity-conserving matrix elements. It is found that the contribution of external and internal $W$-exchange diagrams is significantly suppressed by more than one order of magnitude in comparison with data. The pole diagrams play the major role to get consistency with experiment.

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arXiv2023

Form factors and branching fraction calculations for $B_s \to D_s^{(*)} \ell^+ ν_\ell$ in view of LHCb observation

In light of the LHCb observations about the $B_s \to D_s^{(*)}\ell ν_\ell$ semileptonic decays, we study these channels within the Standard Model framework of covariant confined quark model. The necessary transition form factors are computed in the entire dynamical range of momentum transfer squared with built-in infrared confinement. Our computed ratios of the decay widths from tau mode to muon mode for $D_s$ and $D_s^*$ mesons are found to be $R(D_s) = 0.271 \pm 0.069$ and $R(D_s^*) = 0.240 \pm 0.038$. We further determine the ratio of the decay width from $D_s$ and $D_s^*$ channel for muon mode $Γ(B_s \to D_s μ^+ ν_μ)/Γ(B_s \to D_s^* μ^+ ν_μ) = 0.451 \pm 0.093$. Our results are in excellent agreement with the data from the latest LHCb experiments as well as lattice quantum chromodynamics simulations. We also compare the shape of differential decay distribution for $B_s \to D_s^* μ^+ ν_μ$ with the LHCb data and our results are in very good agreement throughout all the individual bins. Some other physical observables such as forward-backward asymmetry and longitudinal polarizations of leptons in the final state are also computed.

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arXiv2023

Weak nonleptonic decays of vector B-mesons

We study the radiative and weak nonleptonic decays of vector B-mesons within the covariant confined quark model (CCQM) developed in our previous papers. First, we calculate the matrix elements and decays widths of the radiative decays $B^\ast\to Bγ$. The obtained results are compared with those obtained in other approaches. Then we consider the nonleptonic decays $B^\ast\to D^\ast V$ which proceed via tree-level quark diagrams. It is shown that the analytical expressions for the amplitudes correspond to the factorization approach. In the framework of our model we calculate the leptonic decay constants and the form factors of the $B^\ast\to D^\ast(V)$ transitions in the entire physical region of the momentum transfer squared. Finally, we calculate the two-body decay widths and compare our results with other models.

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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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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

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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