arXiv subjects

R. N. Faustov

Publications and source records attributed to R. N. Faustov.

At least 19 recordsLinked to original sources

arXiv2022

Fully-heavy tetraquark spectroscopy in the relativistic quark model

Masses of the ground and excited (1P, 2S, 1D, 2P, 3S) states of the fully-heavy tetraquarks, composed of charm ($c$) and bottom ($b$) quarks and antiquarks, are calculated in the diquark-antidiquark picture within the relativistic quark model based on the quasipotential approach and quantum chromodynamics. The quasipotentials of the quark-quark and diquark-antidiquark interactions are constructed similarly to the previous consideration of mesons and baryons. Relativistic effects are consistently taken into account. A tetraquark is considered as a bound state of a diquark and an antidiquark. The finite size of the diquark is taken into account, using the form factors of the diquark-gluon interaction. It is shown that most of the investigated states of tetraquarks lie above the decay thresholds into a meson pair, as a result they can be observed only as broad resonances. The narrow state X(6900) recently discovered in the di-$J/ψ$ production spectrum by the LHCb, CMS and ATLAS Collaborations corresponds to an excited state of the fully-charmed tetraquark. Other recently discovered exotic heavy resonances X(6200), X(6400), X(6600), X(7200), X(7300) can also be interpreted as the different excitations of the fully-charmed tetraquark.

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arXiv2022

Relativistic corrections to paired production of charmonium and bottomonium in decays of the Higgs boson

Rare decay process of the Higgs boson into a pair of $J/Ψ$ and $Υ$ particles is studied within perturbative Standard Model and relativistic quark model. The relativistic corrections connected with the relative motion of quarks are calculated in the production amplitude and the wave functions of the bound states. Numerical values of the decay widths of the Higgs boson are obtained, which can be used for comparison with experimental data.

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arXiv2022

Rare radiative $Ξ^{-}_{b}\to Ξ^-γ$ decay in the relativistic quark model

Recently the LHCb collaboration put the upper limit on the $Ξ^{-}_{b} \rightarrow Ξ^{-}γ$ decay branching ratio $Br(Ξ^{-}_{b} \rightarrow Ξ^{-}γ)< 1.3\times 10^{-4}$. The measured value is below the light-cone sum rule prediction. In this paper the rare radiative decay of the $Ξ^{-}_{b}$ baryon is studied in the framework of the relativistic quark model based on the quasipotential approach and QCD. The decay form factors are calculated with the comprehensive account of the relativistic effects. The obtained result for the branching ratio is found to be below the upper limit set by LHCb and is consistent with theoretical predictions based on the SU(3) flavor-symmetry, light-front quark model and light-cone QCD sum rules in full theory within theoretical uncertainties.

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arXiv2022

Relativistic description of the semileptonic decays of bottom mesons

The form factors of the semileptonic $B$, $B_s$ and $B_c$ meson decays are calculated in the framework of the relativistic quark model based on the quasipotential approach in QCD. They are expressed through the overlap integrals of the meson wave function. All relativistic effects are consistently taken into account. The momentum transfer $q^2$ behavior of form factors is determined in the whole accessible kinematical range. We do not use any extrapolations, heavy quark $1/m_Q$ expansion or model assumptions about the shape of form factors. Convenient analytic expressions of the form factors are given, which very accurately reproduce the numerical results of our calculation. On the basis of these form factors and helicity formalism, the differential and total branching fractions of various semileptonic decays of bottom meson are calculated. The mean values of the forward-backward asymmetry $\langle A_{FB}\rangle$, lepton-side convexity parameter $\langle C^\ell_{F}\rangle$, longitudinal $\langle P^\ell_{L}\rangle$ and transverse $\langle P^\ell_{T}\rangle$ polarization of the charged lepton, and the longitudinal polarization fraction $\langle F_{L}\rangle$ for final-state vector meson are also evaluated. We present a detailed comparison of the obtained predictions with the calculations based on the covariant light-front quark model and confront them to available lattice QCD and experimental data. It is found that although both models predict close values of the total branching fractions, the differential distributions and forward-backward asymmetry and polarization parameters differ significantly, especially for the heavy-to-light semileptonic decays. We identify observables which measurement can help to discriminate between models.

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arXiv2022

Ground state hyperfine structure of light muon-electron ions

The ground state hyperfine splitting of light muon-electron ions of lithium, beryllium, boron and helium is calculated on the basis of analytical perturbation theory in terms of small parameters of the fine structure constant and electron-muon mass ratio. The corrections of vacuum polarization, nuclear structure and recoil effects and electron vertex corrections are taken into account. The dependence of the corrections on the nucleus charge Z is studied. The obtained total values of hyperfine splitting intervals can be used for comparison with future experimental data.

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arXiv2021

Hadronic Vacuum Polarization and Test of Quantum Electrodynamics at Low Energies

A hadronic vacuum polarization correction to the photon propagator is found by using the Dubnicka-Meshcheryakov parameterization of the pion electromagnetic form factor and new experimental data on the $e^+e^-$ hadrons annihilation cross section. Then, the contribution from the hadronic vacuum polarization to the muon anomalous magnetic moment and the Lamb shift in muonic atoms are calculated.

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arXiv2021

Triply heavy baryon spectroscopy in the relativistic quark model

Triply heavy baryons are investigated in the framework of the relativistic quark model based on the quark-diquark picture in the quasipotential approach in QCD. Masses of the ground and excited states of the $Ω_{ccc}$, $Ω_{bbb}$, $Ω_{ccb}$ and $Ω_{cbb}$ baryons are calculated. Orbital and radial excitations between the diquark and quark as well as between quarks inside the diquark are considered. The diquark internal structure is consistently taken into account by the form factor of the diquark-gluon interaction expressed through the overlap integral of the diquark wave functions. The detailed comparison with previous calculations is given.

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arXiv2021

Higgs boson decay to the pair of S- and P-wave $B_c$ mesons

We investigate the rare production of the pair of $S-$ and $P-$ wave $B_c$-meson in the Higgs boson decay in the perturbative Standard Model and relativistic quark model. Relativistic amplitudes and decay widths are constructed with the account of the relative motion of heavy quarks forming $B_c$ mesons. When constructing the Higgs boson decay amplitudes, the method of projection operators on the $S-$ and $P-$wave states of quarks is used. Relativistic corrections are expressed in terms of special relativistic parameters and are calculated numerically in the quark model. The dependence of the decay widths of the Higgs boson on various sources of relativistic corrections is investigated.

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arXiv2021

Heavy tetraquarks in the relativistic quark model

We give a review of the calculations of the masses of tetraquarks with two and four heavy quarks in the framework of the relativistic quark model based on the quasipotential approach and QCD. The diquark-antidiquark picture of heavy tetraquarks is used. The quasipotentials of the quark-quark and diquark-antidiquark interactions are constructed similarly to the previous consideration of mesons and baryons. Diquarks are considered in the colour triplet state. It is assumed that the diquark and antidiquark interact in the tetraquark as a whole and the internal structure of the diquarks is taken into account by the calculated form factor of the diquark-gluon interaction. All parameters of the model are kept fixed from our previous calculations of meson and baryon properties. A detailed comparison of the obtained predictions for heavy tetraquark masses with available experimental data is given. Many candidates for tetraquarks are found. It is argued that the structures in the di-$J/ψ$ mass spectrum observed recently by the LHCb Collaboration can be interpreted as $cc\bar c\bar c$ tetraquarks.

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arXiv2021

Masses of the $QQ\bar Q\bar Q$ tetraquarks in the relativistic diquark--antidiquark picture

Masses of the ground-state teraquarks composed from heavy $c$ and $b$ quarks and antiquarks are calculated in the diquark-antidiquark picture in the framework of the relativistic quark model based on the quasipotential approach. The quasipotentials of the quark-quark and diquark-antidiquark interactions are constructed similarly to the previous consideration of mesons and baryons. It is assumed that the diquark and antidiquark interact in the tetraquark as a whole and the internal structure of the diquarks is taken into account. All such tetraquarks are found above the thresholds of decays to two heavy quarkonia. This is a result of the consideration of the diquark not to be a point-like object. Therefore such tetraquarks can be observed as broad structures decaying dominantly to quarkonia. The broad structure next to the di-$J/ψ$ mass threshold, recently observed by the LHCb Collaboration, can correspond to the ground $2^{++}$-state tetraquark consisting of four charm quarks.

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arXiv2020

Energy interval 3S-1S in muonic hydrogen

The energy interval $ (3S-1S) $ in muonic hydrogen is calculated on the basis of quasipotential approach in quantum electrodynamics. We take into account different corrections of orders $α^3÷α^6 $, which are determined by relativistic effects, the effects of vacuum polarization, nuclear structure and recoil, as well as combined corrections including the above. Nuclear structure effects are expressed in terms of the charge radius of the proton in the case of one-photon interaction and the proton electromagnetic form factors in the case of two-photon exchange interaction. The value of the energy interval (3S-1S) can be used for a comparison with future experimental data and determining the proton charge radius with greater accuracy.

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arXiv2020

Photonic production of the pair of $B_c$ mesons

We study the pair production of $B_c$ mesons in the photon-photon interaction in the framework of perturbative quantum chromodynamics and the relativistic quark model. The production amplitudes of a pair of pseudoscalar and vector $B_c$ mesons are constructed in the nonrelativistic approximation and taking into account relativistic effects. Relativistic corrections related to the relative motion of heavy quarks in the production amplitude, as well as in the wave function of the bound state of heavy quarks, are taken into account. Analytical expressions are constructed for the relativistic differential and total cross sections for the pair $B_c$ meson production. Based on them, numerical values of the production cross sections are obtained for various energies and scattering angles.

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arXiv2019

Semileptonic decays of $D$ and $D_s$ mesons in the relativistic quark model

The form factors parameterizing the weak $D$ and $D_s$ transitions to light pseudoscalar and vector mesons are calculated in the framework of the relativistic quark model based on the quasipotential approach. The special attention is paid to the systematic account of the relativistic effects including transformation of the meson wave function from the rest to moving reference frame and contributions of the intermediate negative-energy states. The form factors are expressed through the overlap integrals of the meson wave functions, which are taken from previous studies of meson spectroscopy. They are calculated in the whole range of the transferred momentum $q^2$. Convenient parameterization of the form factors which accurately reproduces numerical results is given. The obtained values of the form factors and their ratios at $q^2=0$ agree well with the ones extracted form the experimental data. On the basis of these form factors and helicity formalism, differential and total semileptonic decay rates of $D$ and $D_s$ mesons as well as different asymmetries and polarization parameters are calculated. The detailed comparison of the obtained results with other theoretical calculations and experimental data is given.

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arXiv2019

Semileptonic $Ξ_c$ baryon decays in the relativistic quark model

The form factors of the weak $Ξ_c\to Ξ(Λ)$ transitions are calculated in the framework of the relativistic quark model based on the quasipotential approach. All relativistic effects including transformations of the baryon wave functions from the rest to moving reference frame and contributions of the intermediate negative energy states are systematically taken into account. The explicit analytic expressions which reliably approximate the momentum transfer $q^2$ dependence of the form factors in the whole accessible kinematical range are given. The calculated form factors are applied for the evaluation of the semileptonic $Ξ_c\to Ξ\ellν_\ell$ and $Ξ_c\to Λ\ellν_\ell$ ($\ell=e,μ$) decay rates, different asymmetry and polarization parameters within helicity formalism. The obtained results are compared with available experimental data and previous calculations.

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arXiv2018

Heavy baryon spectroscopy

Masses of heavy baryons are calculated in the relativistic quark-diquark picture. Obtained results are in good agreement with available experimental data including recent measurements by the LHCb Collaboration. Possible quantum numbers of excited heavy baryon states are discussed.

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arXiv2018

Relativistic description of the $Ξ_b$ baryon semileptonic decays

Semileptonic decays of the $Ξ_b$ baryon are studied in the framework of the relativistic quark-diquark model based on the quasipotential approach. The weak decay form factors are calculated with the comprehensive account of all relativistic effects without employing nonrelativistic and heavy quark expansions. On this basis differential and total decay rates as well as different asymmetry parameters are calculated for the heavy-to-heavy $Ξ_b\to Ξ_c\ellν_\ell$ and heavy-to-light $Ξ_b\to Λ\ellν_\ell$ semileptonic decays. Predictions for the ratios of such decays involving $τ$ lepton and muon are presented.

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arXiv2018

Rare $Λ_c\to p \ell^+\ell^-$ decay in the relativistic quark model

The relativistic quark model based on the quasipotential approach with the QCD-motivate potential is employed for the calculation of the form factors of the $Λ_c\to p$ rare weak transitions. Their momentum dependence is explicitly determined without additional assumptions and extrapolations in the whole kinematical range of the momentum transfer squared $q^2$. The differential $Λ_c\to p l^+l^-$ decay branching fractions and angular distributions are calculated on the basis of these form factors. Both the perturbative and effective Wilson coefficients, which include contributions of vector meson resonances, are used. The calculated branching fraction of the $Λ_c\to p μ^+μ^-$ rare decay is well consistent with the experimental upper limit very recently set by the LHCb Collaboration.

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arXiv2018

The contribution of pseudoscalar and axial-vector mesons to hyperfine structure of muonic hydrogen

In the framework of the quasipotential method in quantum electrodynamics we calculate the contribution of light pseudoscalar (PS) and axial-vector (AV) mesons to the interaction operator of a muon and a proton in muonic hydrogen atom. The coupling of mesons with the muon is via two-photon intermediate state. The parametrization of the transition form factor of two photons into PS and AV mesons, based on the experimental data on the transition form factors and QCD asymptotics, is used. Numerical estimates of the contributions to the hyperfine structure of the spectrum of the S and P levels are presented. It is shown that such contribution to the hyperfine splitting in muonic hydrogen is rather important for a comparison with precise experimental data.

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