arXiv subjects
Publications and source records attributed to Nikolai Nikitin.
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.
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.
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.
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\%.
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.
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.
We obtain predictions for a number of radiative decays $B_{(s)}\to Vγ$, $V$ the vector meson, 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 latter subprocesses were not considered in the previous analyses but are found to have sizeable impact on the $B_{(s)}\to Vγ$ decay rate. 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\%.
We present a relativistic generalization of the Wigner inequality for the scalar and pseudoscalar particles decaying to two particles with spin (fermions and photons.) We consider Wigner's inequality with the full spin anticorrelation (with the non-relativistic analog) as well as the case with the full spin correlation. The latter case may be obtained by a special choice of the plane of measurement of the spin projections on the direction of propagation of fermions. The possibility for relativistic testing of Bohr's complementarity principle is shown.
We study the forward-backward and the CP-violating asymmetries (both time-independent and time-dependent) in rare semileptonic $B_d\toρ^0 l^+l^-$, $B_s\toϕl^+l^-$, and radiative leptonic $B_{d,s}\to γl^+l^-$ decays and investigate the sensitivity of these asymmetries to the extensions of the Standard model.
Long-distance QCD effects in $B_{d,s}\to\ell^+\ell^-γ$ decays are analyzed. We show that the contribution of the light vector-meson resonances related to the virtual photon emission from valence quarks of the $B$-meson, which was not considered in previous analyses, strongly influences the dilepton differential distrubution. Taking into account photon emission from the $b$-quark loop, weak annihilation, and Bremsstrahlung from leptons in the final state, we give predictions for dilepton spectrum in $B_{d, s}\to \ell^+\ell^-γ$ decays within the Standard model.
We analyse the corrections to factorization for the $B-\bar B$ mixing amplitude assuming that non-factorizable soft gluon exchanges can be described by the local gluon condensate. Within this approximation the $<α_s GG>$-correction to the mixing amplitude can be expressed through the $B$-meson transition form factors at zero momentum transfer. The correction is negative independent of the particular values of the form factors. As a next step, we study these form factors making use of the relativistic dispersion approach based on the constituent quark picture. We obtain spectral representations for the form factors in terms of the $B$-meson soft wave function and the propagator of the color-octet $b\bar q$ system. The $B$-meson wave function has been determined previously from weak exclusive B decays, so the main uncertainty in our estimates comes from the unknown details of the propagator in the nonperturbative region. We obtain $ΔB_{B_d}(m_b)=-0.06\pm 0.035 $ and $ΔB_{B_s}(m_b)=-0.05\pm 0.03 $.