arXiv subjects

Mikhail A. Ivanov

Publications and source records attributed to Mikhail A. Ivanov.

At least 55 records · Page 3Linked to original sources

arXiv2017

Test of the multiquark structure of $a_1(1420)$ in strong two-body decays

We present an analysis of strong two-body decays of the $a_1(1420)$ with $J^{PC} = 1^{++}$ recently reported by the COMPASS Collaboration at CERN. Following the interpretation of the COMPASS Collaboration that the $a_1$ is an unusual state with a four-quark $q\bar q s \bar s$ structure we consider two possible configurations for this state --- hadronic molecular and color diquark-antidiquark structures. We find that the dominant decay mode of the $a_1$ is the decay into $K$ and $K^*$. In particular, we calculate that the four decay modes $a_1 \to VP$ with $VP = K^{*\pm}K^\mp$, $K^{*0}\bar K^0$, $\bar K^{*0}K^0$ together give a dominant contribution to the measured total width of about 150 MeV. The observational mode $a_1 \to f_0(980) + π^0$ is significantly suppressed by one order of magnitude.

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arXiv2017

The invariant and helicity amplitudes in the transitions $Λ_b\toΛ^\ast(\frac12^\pm,\frac32^\pm)+J/ψ$

We present results for the invariant and helicity amplitudes in the transitions $Λ_b\toΛ^{(\ast)}(J^P)+J/ψ$ where the $Λ^{(\ast)}(J^P)$ are $Λ(sud)$-type ground and excited states with $J^P$ quantum numbers $J^P=\frac12^{\pm},\frac32^{\pm}$. The calculations are performed in the framework of a covariant confined quark model. This analysis is important for the identification of the hidden charm pentaquark states $P_c^+(4380)$ and $P_c^+(4450)$ which were discovered by the LHCb Coll. We also discuss the possible New Physics effects in the exclusive decays $\bar{B}^0 \to D^{(\ast)} τ^- \barν_τ$. We extend the Standard Model by taking into account right-handed vector (axial), left- and right-handed (pseudo)scalar, and tensor current contributions. The $\bar{B}^0 \to D^{(\ast)}$ transition form factors are calculated in the full kinematic $q^2$ range by employing a covariant quark model.

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arXiv2017

Study of $B_c$ decays into charmonia and $D$ mesons

In the wake of recent measurements of the decays $B_c^+\to J/ψD^+_s$ and $B_c^+\to J/ψD^{\ast\,+}_s$ performed by the LHCb and ATLAS Collaborations, we recalculate their branching fractions in the framework of the covariant confined quark model. We compare the obtained results with available experimental data, our previous findings and numbers from other approaches.

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arXiv2017

Decay chain information on the newly discovered double charm baryon state $Ξ_{cc}^{++}$

We interprete the new double charm baryon state found by the LHCb Collaboration in the invariant mass distribution of the set of final state particles $(Λ_c^+\,K^-\,π^+\,π^+)$ as being at the origin of the decay chain $Ξ_{cc}^{++} \to Σ_c^{++} (\to Λ_c^+ π^+) +\bar K^{*0} (\to K^- π^+)$. The nonleptonic decay $Ξ_{cc}^{++} \to Σ_c^{++} + \bar K^{*0}$ belongs to a class of decays where the quark flavor composition is such that the decay proceeds solely via the factorizing contribution precluding a contamination from internal $W$-exchange. We use the covariant confined quark model previously developed by us to calculate the four helicity amplitudes that describe the dynamics of the transition $Ξ_{cc}^{++} \to Σ_c^{++}$ induced by the effective $(c \to u)$ current. We then proceed to calculate the rate of the decay as well as the polarization of the $Σ_c^{++}$ and $Λ_c^+$ baryons and the longitudinal/transverse composition of the $\bar K^{*0}$. We estimate the decay $Ξ_{cc}^{++} \to Σ_c^{++} \bar K^{*0}$ to have a branching rate of $B(Ξ_{cc}^{++} \to Σ_c^{++} \bar K^{*0}) \sim 10.5 \%$. As a byproduct of our investigation we have also analyzed the decay $Ξ_{cc}^{++} \to Σ_c^{++} \bar K^{0}$ for which we find a branching ratio of $B(Ξ_{cc}^{++} \to Σ_c^{++} \bar K^0) \sim 2.5 \%$.

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arXiv2017

Theoretical description of the decays $Λ_b \to Λ^{(\ast)}(\frac12^\pm,\frac32^\pm) + J/ψ$

We calculate the invariant and helicity amplitudes for the transitions $Λ_b~\to~Λ^{(\ast)}(J^P)~+~J/ψ$ where the $Λ^{(\ast)}(J^P)$ are $Λ(sud)$-type ground and excited states with $J^P$ quantum numbers $J^P=\frac12^{\pm},\frac32^{\pm}$. The calculations are performed in the framework of a covariant confined quark model previously developed by us. We find that the values of the helicity amplitudes for the $Λ^\ast(1520,\,\frac32^-)$ and the $Λ^\ast(1890,\,\frac32^+)$ are suppressed compared with those for the ground state $Λ(1116,\,\frac12^+)$ and the excited state $Λ^\ast(1405,\,\frac12^-)$. This analysis is important for the identification of the hidden charm pentaquark states $P_c^+(4380)$ and $P_c^+(4450)$ which were discovered in the decay chain $Λ_b^0~\to~P_c^+(~\to~p~J/ψ)~+~K^- $ because the cascade decay chain $Λ_b~\to~Λ^\ast(\frac32^\pm)(~\to~pK^-)~+~J/ψ$ involves the same final state.

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arXiv2017

$Z_b(10610)$ and $Z_b'(10650)$ decays in a covariant quark model

We present a calculation of the strong decays of the exotic states $Z_b(10610)$ and $Z_b'(10650)$ using a covariant quark model. We use a molecular-type four-quark current for the coupling of the $Z_b(10610)$ and $Z_b'(10650)$ to the constituent heavy and light quarks.

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arXiv2017

Analyzing New Physics in $\bar{B}^0 \to D^{(\ast)}τ^-\barν_τ$

We discuss possible new physics (NP) effects beyond the standard model (SM) in the exclusive decays $\bar{B}^0 \to D^{(\ast)} τ^- \barν_τ$. Starting with a model-independent effective Hamiltonian including non-SM four-Fermi operators, we show how to obtain experimental constraints on different NP scenarios and investigate their effects on a large set of physical observables. The $\bar{B}^0 \to D^{(\ast)}$ transition form factors are calculated in the full kinematic $q^2$ range by employing the covariant confined quark model developed by our group.

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arXiv2017

Probing new physics in $\bar{B}^0 \to D^{(\ast)} τ^- \barν_τ$ using the longitudinal, transverse, and normal polarization components of the tau lepton

We study the longitudinal, transverse, and normal polarization components of the tau lepton in the decays $\bar{B}^0 \to D^{(\ast)} τ^- \barν_τ$ and discuss their role in searching for new physics (NP) beyond the standard model (SM). Starting with a model-independent effective Hamiltonian including non-SM four-Fermi operators, we obtain experimental constraints on different NP scenarios and investigate their effects on the polarization observables. In the SM the longitudinal and transverse polarizations of the tau lepton differ substantially from the corresponding zero lepton mass values of $P_L=-1$ and $P_T=0$. In addition, $P_L$ and $P_T$ are very sensitive to NP effects. For the transverse polarization this holds true, in particular, for the effective tensor operator in the case of $\bar{B}^0 \to D^\ast$ and for the scalar operator in the case of $\bar{B}^0 \to D$. The $T$-odd normal polarization $P_N$, which is predicted to be negligibly small in the SM, can be very sizable assuming NP complex Wilson coefficients. We also discuss in some detail how the three polarization components of the tau lepton can be measured with the help of its subsequent leptonic and semihadronic decays.

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arXiv2017

Exclusive decays $J/ψ\to D_{(s)}^{(*)-} {\ell}^+ ν_{\ell}$ in a covariant constituent quark model with infrared confinement

We investigate the exclusive semileptonic decays $J/ψ\to D_{(s)}^{(*)-} {\ell}^+ ν_{\ell}$, where $\ell=e,μ$, within the Standard Model. The relevant transition form factors are calculated in the framework of a relativistic constituent quark model with built-in infrared confinement. Our calculations predict the branching fractions $\mathcal{B}(J/ψ\to D_{(s)}^{(*)-} {\ell}^+ ν_{\ell})$ to be of the order of $10^{-10}$ for $D_s^{(*)-}$ and $10^{-11}$ for $D^{(*)-}$. Most of our numerical results are consistent with other theoretical studies. However, some branching fractions are larger than those calculated in QCD sum rules approaches but smaller than those obtained in the covariant light-front quark model by a factor of about $2-3$.

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arXiv2016

Nucleon tensor form factors in a relativistic confined quark model

We present results for the isotriplet and isosinglet tensor form factors of the nucleon in the relativistic confined quark model. The model allows us to calculate not only their normalizations at $Q^2=0$ and the related tensor charges, but also the full $Q^2$-dependence. Our results are compared to existing data and predictions of other theoretical approaches. We stress the importance of these form factors for the phenomenology of physics beyond the Standard Model.

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arXiv2016

Isospin-violating strong decays of scalar single-heavy tetraquarks

We present a study of the isospin-violating one-pion strong decays of single heavy tetraquarks $X_Q = X(s q \bar q \bar Q)$, $Q=c, b$, and $q=u, d$ with spin-parity $J^P = 0^+$. We assume that the tetraquarks have the configuration of a color diquark and a antidiquark. Three mechanisms of isospin violation can contribute to the decay rate: (1) mixing of the $X(s u \bar u \bar Q)$ and $X(s d \bar d \bar Q)$ tetraquark currents, (2) an explicit $m_d-m_u$ quark mass difference in the quark diagrams describing the corresponding decay transitions and (3) $π^0-η$ mixing in the final state. Our main results are: (1) It is quite likely that the investigated tetraquark states are isosinglet states with a small admixture of an isotriplet component; (2) The first isospin-breaking mechanism affects the decay rater more significantly than the others; (3) Our calculations contain a size parameter $Λ_{X_Q}$, characterizing the distribution of the quarks in the tetraquark state $X_Q$. Absolute decay rates depend very much on the choice of $Λ_{X_Q}$, varied from 1 to 2 GeV, reflecting the compactness of the multiquark system.

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arXiv2016

Four-quark structure of Zc(3900), Z(4430) and Xb(5568) states

We examine the four-quark structure of the recently discovered charged $Z_c(3900)$, $Z(4430)$, and $X_b(5568)$ states. We calculate the widths of the strong decays $Z_c^+ \to J/ψπ^+$ ($η_cρ^+$, $\bar D^0D^{\ast\,+}$, $\bar D^{\ast\,0}D^+$), $Z(4430)^+ \to J/ψπ^+$ ($ψ(2s) π^+$), and $X^+_b\to B_sπ^+$ within a covariant quark model previously developed by us. We find that the tetraquark-type current widely used in the literature for the $Z_c(3900)$ leads to a significant suppression of the $\bar D D^\ast$ and $\bar D^\ast D$ modes. Contrary to this a molecular-type current provides an enhancement by a factor of 6-7 for the $\bar D D^\ast$ modes compared with the $Z_c^+\to J/ψπ^+$, $η_cρ^+$ modes in agreement with recent experimental data from the BESIII Collaboration. In case of the $Z(4430)$ state we test a sensitivity of the ratio $R_Z$ of the $Z(4430)^+ \to ψ(2s) π^+$ and $Z(4430)^+ \to J/ψπ^+$ decay rates to a choice of the size parameter $Λ_{Z(4430)}$ of the $Z(4430)$. Using upper constraint for the sum of these two modes deduced from the LHCb Collaboration data we find that $R_Z$ varies from 4.64 to 4.08 when $Λ_{Z(4430)}$ changes from 2.2 to 3.2 GeV. Also we make the prediction for the $Z(4430)^+ \to D^{\ast\,+} \bar D^{\ast\,0}$ decay rate.

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arXiv2016

Analyzing new physics in the decays $\bar{B}^0 \to D^{(\ast)}τ^-\barν_τ$ with form factors obtained from the covariant quark model

We study possible New Physics (NP) effects in the exclusive decays $\bar{B}^0 \to D^{(\ast)} τ^- \barν_τ$. We extend the Standard Model (SM) by taking into account right-handed vector (axial), left- and right-handed (pseudo)scalar, and tensor current contributions. The $\bar{B}^0 \to D^{(\ast)}$ transition form factors are calculated in the full kinematic $q^2$ range by employing a covariant quark model developed by us. We provide constraints on NP operators based on measurements of the ratios of branching fractions $R(D^{(\ast)}) \equiv \mathcal{B}(\bar{B}^0 \to D^{(\ast)} τ^- \barν_τ)/ \mathcal{B}(\bar{B}^0 \to D^{(\ast)} μ^- \barν_μ)$ and consider the effects of these operators on physical observables in different NP scenarios. We also derive the four-fold angular distribution for the cascade decay $\bar {B}^0\to D^{\ast\,+}(\to D^0π^+)τ^-\barν_τ$ which allows one to analyze the polarization of the $D^{\ast}$ meson in the presence of NP effects. We discuss several strategies to distinguish between various NP contributions.

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arXiv2016

Decay $B_s\to ϕ\ell^+ \ell^-$ in covariant quark model

Our article is devoted to the study of the rare $B_s\to ϕ\ell^+\ell^-$ decay where $\ell=μ,τ$. We compute the relevant form factors in the framework of the covariant quark model with infrared confinement in the full kinematical momentum transfer region. The calculated form factors are used to evaluate branching fractions and polarization observables in the cascade decay $B\to ϕ(\to K^+K^-)\ell^+\ell^-$. We compare the obtained results with available experimental data and the results from other theoretical approaches.

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arXiv2015

Semileptonic decays $Λ_c^+ \to Λ\ell^+ ν_\ell\,\,(\ell=e,μ)$ in the covariant quark model and comparison with the new absolute branching fraction measurements of Belle and BESIII

We present precise theoretical predictions for the absolute branching fractions of $Λ_c^+ \to Λ\ell^+ ν_\ell\,(\ell=e,μ)$ decays in the covariant confined quark model. This study is motivated by two recent and accurate measurements of the absolute branching fractions of $Λ_c^+ \to p K^- π^+$ and $Λ_c^+ \to Λe^+ ν_e$ by the Belle Collaboration at the KEKB and by the BESIII Collaboration at the BEPCII. Our predictions for the branching fractions are consistent with both experimental results. We also provide detailed numerical results for differential decay distributions and polarization observables.

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arXiv2015

Decay $B\to K^\ast(\to Kπ) \ell^+ \ell^-$ in covariant quark model

Our article is devoted to the study of the rare $B\to K^\ast \ell^+\ell^-$~decay where $\ell=e,μ,τ$. We compute the relevant form factors in the framework of the covariant quark model with infrared confinement in the full kinematical momentum transfer region. The calculated form factors are used to evaluate branching fractions and polarization observables in the cascade decay $B\to K^\ast(\to Kπ)\ell^+\ell^-$. We compare the obtained results with available experimental data and the results from other theoretical approaches.

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arXiv2015

Exclusive decays $B \to \ell^-\barν$ and $B \to D^{(\ast)}\ell^-\barν$ in the covariant quark model

We study the exclusive leptonic and semileptonic $B$ decays $B \to \ell^- \barν$ and $B \to D^{(\ast)} \ell^-\barν$ in the framework of the covariant quark model with built-in infrared confinement. We compute the relevant form factors in the full kinematical momentum transfer region. The calculated form factors are used to evaluate branching fractions and polarization observables of the above transitions. We compare our results with experimental data and results from other theoretical studies.

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arXiv2015

Towards an assessment of the ATLAS data on the branching ratio Gamma(Lambda_b(0) -> psi(2S) Lambda(0))/Gamma(Lambda_b(0) -> J/psi Lambda(0))

Recently the ATLAS Collaboration at CERN reported on the measurement of the branching ratio R(Lambda_b) = Gamma(Lambda_b(0) -> psi(2S) Lambda(0))/Gamma(Lambda_b(0) -> J/psi Lambda(0)). The measured branching ratio R(Lambda_b) = 0.501 pm 0.033$ (stat) pm 0.019 (syst) was found to be lower than the covariant quark model prediction of R(Lambda_b) = 0.8 pm 0.1 calculated by us recently. We present a detailed analysis of the branching ratio R(Lambda_b) using a model-independent framework for the heavy-to-light form factors based on results from our previos papers.

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