arXiv subjects

Anastasiia Kozachuk

Publications and source records attributed to Anastasiia Kozachuk.

9 recordsLinked to original sources

arXiv2020

Constraints on the anomalous $Wtb$ couplings from $B$-physics experiments

We analyze constraints on the anomalous $Wtb$ couplings from $B$-physics experiments, performing a correlated analysis and allowing all anomalous couplings to differ simultaneously from their Standard-Model (SM) values. The $B$-physics observables allow one to probe three linear combinations out of the four anomalous couplings, which parameterize the $Wtb$ vertex under the assumption that the SM symmetries remain the symmetries of the effective theory. The constraints in this work are obtained by taking into account the following $B$-physics observables: the $\bar B^0-B^0$ oscillations, the leptonic $B\to μ^+μ^-$ decays, the inclusive radiative $B\to X_sγ$ decays, and the differential branching fractions in the semileptonic inclusive $B\to X_s μ^+ μ^-$ and exclusive $B\to (K,K^*)μ^+μ^-$ decays at small $q^2$, $q$ the momentum of the $μ^+μ^-$ pair. We find that the SM values of the anomalous couplings belong to the 95\% CL allowed region obtained this way but lie beyond the 68\% allowed region. We also report that the distributions of the anomalous couplings obtained within our scenario differ from the results of the 1D scenario, when only one of the couplings is allowed to deviate from its SM value.

hep-ph↗

arXiv2018

Revisiting nonfactorizable charm-loop effects in exclusive FCNC $B$-decays

We revisit the calculation of nonfactorizable corrections induced by charm-quark loops in exclusive FCNC $B$-decays. For the sake of clarity, we make use of a field theory with scalar particles: this allows us to focus on the conceptual issues and to avoid technical complications related to particle spins in QCD. We perform a straightforward calculation of the appropriate correlation function and show that it requires the knowledge of the full generic three-particle distribution amplitude with non-aligned arguments, $\langle 0|\bar s(y)G_{μν}(x)b(0)|B(p)\rangle$. Moreover, the dependence of this quantity on the variable $(x-y)^2$ is essential for a proper account of the $\left(Λ_{\rm QCD}m_b/m_c^2\right)^n$ terms in the amplitudes of FCNC $B$-decays.

hep-ph↗

arXiv2018

Long-distance QCD effects in FCNC $B\to γl^+l^-$ decays

This presentation reviews the main results of our recent work [A.K., D.M., N.N., Phys. Rev. D97, 053007 (2018)] on rare radiative leptonic decays $B_{d,s}\toγμ^+μ^-$ and $B_{d,s}\toγe^+e ^-$ induced by flavour-changing neutral currents (FCNC) in the Standard Model.

hep-ph↗

arXiv2018

Rare FCNC radiative leptonic $B_{s,d}\to γl^+l^-$ decays in the Standard Model

We revisit rare radiative leptonic decays $B_{s,d}\to γe^+e^-$ and $B_{s,d}\to γμ^+μ^-$ in the Standard Model and provide the updated estimates for various differential distributions (the branching ratios, the forward-backward asymmetry, and $R_{μ/e}$, the ratio of the differential distribution for muons over electrons in the final state). The new ingredients of this work compared to the existing theoretical analyses are the following: (i) we calculate all $B_d\toγ$ and $B_s\toγ$ form factors induced by the vector, axial-vector, tensor and pseudotensor quark currents within the relativistic dispersion approach based on the constituent quark picture; (ii) we perform a detailed analysis of the charm-loop contributions to radiative leptonic decays: we obtain constraints imposed by the electromagnetic gauge invariance and discuss the existing ambiguities in the charmonia contributions.

hep-ph↗

arXiv2017

Rare FCNC radiative leptonic decays $B\toγ\ell^+\ell^-$

We present our recent results for long-distance QCD effects in the FCNC radiative leptonic decays $B\toγ\ell^+\ell^-$, $\ell=\{e,μ\}$. One encounters here two distinct types of long-distance effects: those encoded in the $B\toγ$ transition form factors induced by the $b\to q$ quark currents, and those related to the charm-loop effects. We calculate the $B\toγ$ form factors in a broad range of the momentum transfers making use of the relativisitc dispersion approach based on the constituent quark picture which has proven to provide reliable predictions for many weak-transition form factors. Concerning the description of the charm-loop contributions, we point out two observations: First, the precise description of the charmonium resonances, in particular, the relative phases between $ψ$ and $ψ'$, has impact on the differential distributions and on the forward-backward asymmetry, $A_{\rm FB}$, in a broad range of $q^2\ge 5$ GeV$^2$. Second, the shape of $A_{\rm FB}$ in $B\toγ\ell^+\ell^-$ and in $B\to V\ell^+\ell^-$ ($V$ the vector meson) {\it in the $q^2$-region between $ψ$ and $ψ'$} provides an unambiguous probe of the relative phases between $ψ$ and $ψ'$. Fixing the latter will lead to a strong reduction of the theoretical uncertainties in $A_{\rm FB}$ at $q^2=5-9$ GeV$^2$ where it has the sensitivity to physics beyond the SM.

hep-ph↗

arXiv2016

Weak annihilation rare radiative B-decays

We give predictions for the branching ratios of several rare radiative B-decays which proceed only through weak annihilation mechanism. In addition to previous analysis we estimate the branching ratios of $\bar{B}^0_s\to D^{*0}γ$ and $B_c^-\toρ^-γ$ decays and obtain $2.87\cdot 10^{-9}$ and $2.59\cdot 10^{-7}$ for them correspondingly. The accuracy of the predictions is at the level of 20\%.

hep-ph↗

arXiv2016

Form factors and differential distributions in rare radiative leptonic B-decays

We study rare radiative leptonic decays $B_{(s)}\to e^+e^-γ$ and $B_{(s)}\to μ^+μ^-γ$ within relativistic quark model. In addition to previous analysis we give the estimations of the branching ratios for four values of the minimal photon energy, which correspond to photon selection criteria of the Belle and LHCb detectors. We find out that the branching ratios only slightly change. The highest values corresponding to $E^γ_{min}=80 \textrm{MeV}$ are ${\cal B}(\bar B^0_s\to e^+e^-γ)=18.5\times10^{-9}$ and ${\cal B}(B^0_s\to μ^+μ^-γ)=11.9\times10^{-9}$. We present the distribution of the forward-backward asymmetry.

hep-ph↗

arXiv2016

Rare radiative leptonic B-decays

We obtain predictions for $B_{(s)}\to e^+e^-γ$ and $B_{(s)}\to μ^+μ^-γ$ decays. All the contributions containing long-distance QCD effects are calculated in the framework of relativistic quark model. The contributions of the light vector-meson resonances related to the virtual photon emission from valence quarks of the $B$-meson are included. The highest branching ratios for the radiative leptonic B-decays are ${\cal B}(\bar B^0_s\to e^+e^-γ)=18.8\times10^{-9}$ and ${\cal B}(B^0_s\to μ^+μ^-γ)=12.2\times10^{-9}$. We also give the distribution of the foward-backward asymmetry.

hep-ph↗

arXiv2015

Weak-annihilation rare radiative decays of B-mesons

In this talk, we present the predictions for a number of radiative decays $B_{(s)}\to Vγ$, with the vector meson in the final state, which proceed through the weak-annihilation mechanism. Within the factorization approximation, we take into account the photon emission from the $B$-meson loop and from the vector-meson loop. The highest branching ratios for the weak-annihilation reactions reported here are ${\cal B}(\bar B^0_s\to J/ψγ)=1.5\cdot 10^{-7}$ and ${\cal B}(B^-\to \bar D_s^{*-}γ)=1.7\cdot 10^{-7}$, the estimated accuracy of these predictions being at the level of 20%.

hep-ph↗