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R. N. Faustov

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

At least 37 records · Page 2Linked to original sources
arXiv2017

Rare $Λ_b\toΛl^+l^-$ and $Λ_b\toΛγ$ decays in the relativistic quark model

Rare $Λ_b\toΛl^+l^-$ and $Λ_b\toΛγ$ decays are investigated in the relativistic quark model based on the quark-diquark picture of baryons. The decay form factors are calculated with the account of all relativistic effects including relativistic transformations of baryon wave functions from rest to moving reference frame and the contribution of the intermediate negative energy states. The momentum transfer squared dependence of the form factors is explicitly determined in the whole accessible kinematical range. The calculated decay branching fractions, various forward-backward asymmetries for the rare decay $Λ_b\toΛμ^+μ^-$ are found to be consistent with recent detailed measurements by the LHCb Collaboration. Predictions for the $Λ_b\toΛτ^+τ^-$ decay observables are given.

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arXiv2017

Radiative nonrecoil nuclear finite size corrections of order $α(Z α)^5$ to the Lamb shift in light muonic atoms

On the basis of quasipotential method in quantum electrodynamics we calculate nuclear finite size radiative corrections of order $α(Z α)^5$ to the Lamb shift in muonic hydrogen and helium. To construct the interaction potential of particles, which gives the necessary contributions to the energy spectrum, we use the method of projection operators to states with a definite spin. Separate analytic expressions for the contributions of the muon self-energy, the muon vertex operator and the amplitude with spanning photon are obtained. We present also numerical results for these contributions using modern experimental data on the electromagnetic form factors of light nuclei.

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arXiv2017

Rare $Λ_b\to n l^+l^-$ decays in the relativistic quark-diquark picture

The form factors of the rare $Λ_b\to n l^+l^-$ decays are calculated in the framework of the relativistic quark-diquark picture of baryons with the consistent account of the relativistic effects. Their momentum transfer squared dependence is determined explicitly in the whole accessible kinematical range. The decay branching fractions, forward-backward asymmetries and the fractions of longitudinally polarized dileptons are determined. The branching fraction of the rare $Λ_b\to nμ^+μ^-$ decay are found to be ${\rm Br}(Λ_b\to nμ^+μ^-)=(3.75\pm0.38)\times10^{-8}$ and thus could be measured at the LHC. Prediction for the branching fraction of the rare radiative $Λ_b\to n γ$ decay is also given.

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arXiv2017

The contribution of pseudoscalar mesons to hyperfine structure of muonic hydrogen

In the framework of the quasipotential method in quantum electrodynamics we calculate the contribution of pseudoscalar mesons to the interaction operator of a muon and a proton in muonic hydrogen atom. The parametrization of the transition form factor of two photons into $π$, $η$ 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.

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arXiv2016

Semileptonic decays of $Λ_c$ baryons in the relativistic quark model

Motivated by recent experimental progress in studying weak decays of the $Λ_c$ baryon we investigate its semileptonic decays in the framework of the relativistic quark model based on the quasipotential approach with the QCD-motivated potential. The form factors of the $Λ_c\to Λlν_l$ and $Λ_c\to nlν_l$ decays are calculated in the whole accessible kinematical region without extrapolations and additional model assumptions. Relativistic effects are systematically taken into account including transformations of baryon wave functions from the rest to moving reference frame and contributions of the intermediate negative-energy states. Baryon wave functions found in the previous mass spectrum calculations are used for the numerical evaluation. Comprehensive predictions for decay rates, asymmetries and polarization parameters are given. They agree well with available experimental data.

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arXiv2016

Semileptonic decays of $Λ_b$ baryons in the relativistic quark model

Semileptonic $Λ_b$ decays are investigated in the framework of the relativistic quark model based on the quasipotential approach and the quark-diquark picture of baryons. The decay form factors are expressed through the overlap integrals of the initial and final baryon wave functions. All calculations are done without employing nonrelativistic and heavy quark expansions. The momentum transfer dependence of the decay form factors is explicitly determined in the whole accessible kinematical range without any extrapolations or model assumptions. Both the heavy-to-heavy $Λ_b\toΛ_c\ellν_\ell$ and heavy-to-light $Λ_b\to p\ellν_\ell$ decay branching fractions are calculated. The results agree within error bars with the experimental value of the branching fraction of the $Λ_b\toΛ_c^+l^-\barν_l$ decay. From the recent LHCb data on the ratio of the branching fractions of the heavy-to-light and heavy-to-heavy semileptonic $Λ_b$ decays the ratio of the Cabbibo-Kobayashi-Maskawa matrix elements $|V_{ub}|/|V_{cb}|$ is obtained. It is consistent with the corresponding ratio determined from the inclusive $B$ meson decays.

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arXiv2015

Hyperfine structure of P-states in muonic deuterium

On the basis of quasipotential approach to the bound state problem in quantum electrodynamics we calculate hyperfine structure intervals Delta E^{hfs}(2P_{1/2}) and Delta E^{hfs}(2P_{3/2}) for P-states in muonic deuterium. The tensor method of projection operators for the calculation of the hyperfine structure of P-states with definite quantum numbers of total atomic momentum F and total muon momentum j in muonic deuterium is formulated. We take into account vacuum polarization, relativistic, quadrupole and structure corrections of orders alpha^4, alpha^5 and alpha^6. The obtained numerical values of hyperfine splittings are useful for the analysis of new experimental data of the CREMA collaboration regarding to muonic deuterium.

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arXiv2015

Strange baryon spectroscopy in the relativistic quark model

Mass spectra of strange baryons are calculated in the framework of the relativistic quark model based on the quasipotential approach. Baryons are treated as the relativistic quark-diquark bound systems. It is assumed that two quarks with equal constituent masses form a diquark. The diquark excitations and its internal structure are consistently taken into account. Calculations are performed up to rather high orbital and radial excitations of strange baryons. On this basis the Regge trajectories are constructed. The obtained results are compared with available experimental data and previous predictions. It is found that all masses of the 4- and 3-star, as well as most of the 2- and 1-star states of strange baryons with established quantum numbers are well reproduced. The developed relativistic quark-diquark model predicts less excited states than three-quark models of strange baryons.

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arXiv2015

Strong decays of vector mesons to pseudoscalar mesons in the relativistic quark model

Strong decays of vector ($^3S_1$) mesons to the pair of pseudoscalar ($^1S_0$) mesons are considered in the framework of the microscopic decay mechanism and the relativistic quark model based on the quasipotential approach. The quark-antiquark potential, which was previously used for the successful description of meson spectroscopy and electroweak decays, is employed as the source of the $q\bar q$ pair creation. The relativistic structure of the decay matrix element, relativistic contributions and boosts of the meson wave functions are comprehensively taken into account. The calculated rates of strong decays of light, heavy-light mesons and heavy quarkonia agree well with available experimental data.

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arXiv2014

Relativistic description of weak decays of $B_s$ mesons

The branching fractions of the semileptonic and rare $B_s$ decays are calculated in the framework of the QCD-motivated relativistic quark model. The form factors of the weak $B_s$ transitions are expressed through the overlap integrals of the initial and final meson wave functions in the whole accessible kinematical range. The momentum transfer dependence of the form factors is explicitly determined without additional model assumptions and extrapolations. The obtained results agree well with available experimental data.

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arXiv2014

Rare $B\to πl\bar l$ and $B\toρl \bar l$ decays in the relativistic quark model

The branching fractions of the rare weak $B\to πl^+l^-(ν\barν)$ and $B\toρl^+l^-(ν\barν)$ decays are calculated in the framework of the relativistic quark model based on the quasipotential approach. The form factors parametrizing weak decay matrix elements are explicitly determined in the whole kinematical $q^2$ range without additional assumptions and extrapolations. Relativistic effects are systematically taken into account including recoil effects in meson wave functions and contributions of the intermediate negative-energy states. New experimental data on the differential distributions in the semileptonic heavy-to-light $B\toπlν_l$ and $B\toρlν_l$ decays are analyzed in detail. Good agreement of the predictions and data is found. The obtained results for the branching fractions of the rare semileptonic decays are found to be in agreement with other theoretical estimates and recent experimental data available for the $B^+\toπ^+ μ^+μ^-$ decay.

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arXiv2014

Hyperfine structure of S-states in muonic deuterium

On the basis of quasipotential method in quantum electrodynamics we calculate corrections of order $α^5$ and $α^6$ to hyperfine structure of S-wave energy levels of muonic deuterium. Relativistic corrections, effects of vacuum polarization in first, second and third orders of perturbation theory, nuclear structure and recoil corrections are taken into account. The obtained numerical values of hyperfine splitting $ΔE^{hfs}(1S)=50.2814$ meV (1S state) and $ΔE^{hfs}(2S)=6.2804$ meV (2S state) represent reliable estimate for a comparison with forthcoming experimental data of CREMA collaboration. The hyperfine structure interval $Δ_{12}=8ΔE^{hfs}(2S)-ΔE^{hfs}(1S)=-0.0379$ meV can be used for precision check of quantum electrodynamics predictions for muonic deterium.

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arXiv2014

Radiative nonrecoil nuclear finite size corrections of order $α(Zα)^5$ to the hyperfine splitting of S-states in muonic hydrogen

On the basis of quasipotential method in quantum electrodynamics we calculate nuclear finite size radiative corrections of order $α(Zα)^5$ to the hyperfine structure of S-wave energy levels in muonic hydrogen and muonic deuterium. For the construction of the particle interaction operator we employ the projection operators on the particle bound states with definite spins. The calculation is performed in the infrared safe Fried-Yennie gauge. Modern experimental data on the electromagnetic form factors of the proton and deuteron are used.

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arXiv2013

Rare $B_s$ decays in the relativistic quark model

The branchings fractions of the rare $B_s$ decays are calculated in the framework of the QCD-motivated relativistic quark model. The form factors of the weak $B_s$ transitions to light mesons are expressed through the overlap integral of the initial and final meson wave functions in the whole accessible kinematical range. Explicit determination of the momentum transfer dependence of the form factors without additional model assumptions and extrapolations significantly improve the reliability of the obtained results. The approximate analytical form of the form factors is given in order to simplify the comparison with other predictions and experiment. The calculated form factors are applied for the investigations of the rare semileptonic, radiative and nonleptonic $B_s$ decays. The factorization approximation is used for the description of the nonleptonic decays. All results agree well with available experimental data.

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arXiv2013

Charmless weak $B_s$ decays in the relativistic quark model

The form factors of the weak $B_s$ transitions to the ground state and orbitally excited strange mesons are calculated in the framework of the QCD-motivated relativistic quark model based on the quasipotential approach. These form factors are expressed through the overlap integrals of meson wave functions found in their mass spectrum evaluations. The momentum dependence of the form factors is determined in the whole accessible kinematical range without any additional assumptions and extrapolations. Relativistic effects, including the wave function transformation from the rest to a moving reference frame as well as contributions of the intermediate negative-energy states, are consistently taken into account. The calculated form factors are used for the evaluation of the charmless semileptonic decay rates and two-body nonleptonic $B_s$ decays in the factorization approximation. The obtained results are confronted with previous predictions and available experimental data.

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arXiv2013

Weak decays of $B_s$ mesons to $D_s$ mesons in the relativistic quark model

The form factors of weak decays of $B_s$ mesons to ground state $D_s^{(*)}$ mesons as well as to their radial $D_s^{(*)}(2S)$ and orbital $D_{sJ}^{(*)}$ excitations are calculated in the framework of the relativistic quark model based on the quasipotential approach. All relativistic effects, including contributions of intermediate negative-energy states and boosts of the meson wave functions, are consistently taken into account. As a result the form factors are determined in the whole kinematical range without additional phenomenological parametrizations and extrapolations. On this basis semileptonic decay branching fractions are calculated. Two-body nonleptonic $B_s$ decays are considered within the factorization approximation. The obtained results agree well with available experimental data.

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arXiv2012

Exclusive weak B decays involving $τ$ lepton in the relativistic quark model

Semileptonic and leptonic B decays are analyzed in the framework of the relativistic quark model. Special attention is payed to the decays involving $τ$ lepton. It is found that the calculated particular decay branching fractions are consistent with available experimental data within error bars. However, the predicted and recently measured ratios $R(D^{(*)})$ of the $B\to D^{(*)}τν_τ$ and $B\to D^{(*)}lν_l$ branching fractions differ by 1.75$σ$ for $R(D)$ and by 2.4$σ$ for $R(D^*)$.

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