arXiv subjects

Aidos Issadykov

Publications and source records attributed to Aidos Issadykov.

18 recordsLinked to original sources

arXiv2025

Angular observables and branching ratio for $B_s\to \phi \ell^+ \ell^-$ decay

In this paper, an analysis of the $B_s\to \phi \ell^+ \ell^-$ rare decay is presented within the framework of the covariant confined quark model. The $B_s\to \phi$ transition form factors are calculated and then used to compute the branching fractions and angular observables in various $q^2$ bins, including the forward-backward asymmetry $A_{FB}$, the longitudinal polarization $F_L$, and the optimized observables $A_i$ and $S_i$. The results show agreement with the latest experimental data given by LHCb collaboration and compared with available theoretical predictions.

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arXiv2025

Revisiting radiative transitions of charmonium states in covariant confined quark model

We calculate the amplitudes and branching fractions of $\chi_{cJ}$, $h_c$, $J/\psi$, and $\psi(2S)$ radiative decays in the framework of the covariant confined quark model. First, we explicitly show that all calculated amplitudes are gauge invariant. Next, we use experimental data for three decay channels $J/\psi\to \eta_c\gamma$, $\chi_{c0}\to J/\psi\gamma$, and $\psi(2S)\to \chi_{c0}\gamma$ to fit the model parameters including the charm quark mass and the meson size parameter. Finally, we use the obtained parameters to predict the branching fractions of the decays $h_c\to\eta_c\gamma$, $\chi_{c1(c2)}\to J/\psi\gamma$, and $\psi(2S)\to\chi_{c1(c2)}\gamma$. Our predictions agree well with experimental data.

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arXiv2025

A realistic photon spectra in polarized {\gamma}{\gamma} processes in SANCphot

This work presents an approach to improve the precision of polarized photon-photon collisions simulation implemented in the SANCphot package. The basic linear Compton approximation of the incoming photon spectrum is extended to a general energy distribution and a realistic description of circular or linear polarizations as expected to be seen at photon-photon colliders.

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arXiv2024

Two-loop QED/QCD corrections for polarized $\gamma\gamma\rightarrow\gamma\gamma$ process in SANCphot

The new version of the SANCphot integrator has been prepared for fast and stable numerical calculations up to two loops for polarized light-by-light scattering. One-loop modules based on the helicity formalism with massive particles and two-loop modules with massless particles inside the loops are used. The presented study is driven by the potential of polarized photon beams to probe the high energy region. This study is a contribution to the research program of the CEPC project being under development in China.

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arXiv2023

Anomalies in Weak Decays of Hadrons Containing a b Quark

A brief review of the current state of observed deviations of theoretical predictions from experimental data in semileptonic decays of $B$ and $B_c$ mesons is given. A theoretical analysis of these decays is carried out, taking into account the effects of new physics, which appear due to the introduction of new four-fermion operators, which are absent in the basis of the Standard Model (SM) operators. The necessary form factors are calculated within the framework of the covariant quark model developed in our papers.

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arXiv2023

$B^{*}_c$ meson parameters and radiative decay width within the covariant confined quark model

In this work we tried to predict the parameters of $B^{*}_c$ meson. Simple assumptions gave us following parametres $m_{B_{c}^{*}}=6329\pm 10$ MeV and $f_{B_{c}^{*}}= 535.5\pm57.8$ MeV (for $\Lambda_{B_{c}^{*}}=2.26\pm 0.14$ GeV in covariant confined quark model). We calculated widths of radiative decays of $B^*_{q}$ mesons, where $q=u/d,s,c$ and compared them with other theoretical works. It was shown that the width of the $B_{c}^{*}$ meson very sensitive to the mass $m_{B_{c}^{*}}$ as expected and less to the size parameter $\Lambda_{B_{c}^{*}}$.

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arXiv2022

$B \to K^{(\ast)} \nu \bar{\nu}$ in covariant confined quark model

We study the $B \to K^{(\ast)} \nu \bar{\nu}$ decays within the Standard Model (SM) by using the relevant transition form factors obtained from the covariant confined quark model (CCQM) developed by us. The $B \to K$ and $B\to K^\ast$ transition form factors are calculated in the full kinematic $q^2$ range. The branching fractions are then calculated. It is shown that our results are in an agreement with those obtained in other theoretical approaches. Currently, the Babar and Belle collaborations provide us by the upper limits at 90\% confidence limit. The obtained bounds are roughly an order of magnitude larger than the SM predictions. This should stimulate experimental collaborations to set up experiments that allow one to obtain more accurate branching values, which is quite achievable on the updated LHCb and Belle machines. If the discrepancies between theory and experiment are confirmed, this will open up opportunities for constructing models with new particles and interactions leading to an extension of the SM.

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arXiv2021

Form factors and branching fraction calculations for $B_s \to D_s^{(*)} \ell^+ \nu_\ell$ in view of LHCb observation

In light of the LHCb observations about the $B_s \to D_s^{(*)}\ell \nu_\ell$ semileptonic decays, we study these channels within the Standard Model framework of covariant confined quark model. The necessary transition form factors are computed in the entire dynamical range of momentum transfer squared with built-in infrared confinement. Our computed ratios of the decay widths from tau mode to muon mode for $D_s$ and $D_s^*$ mesons are found to be $R(D_s) = 0.271 \pm 0.069$ and $R(D_s^*) = 0.240 \pm 0.038$. We further determine the ratio of the decay width from $D_s$ and $D_s^*$ channel for muon mode $\Gamma(B_s \to D_s \mu^+ \nu_\mu)/\Gamma(B_s \to D_s^* \mu^+ \nu_\mu) = 0.451 \pm 0.093$. Our results are in excellent agreement with the data from the latest LHCb experiments as well as lattice quantum chromodynamics simulations. We also compare the shape of differential decay distribution for $B_s \to D_s^* \mu^+ \nu_\mu$ with the LHCb data and our results are in very good agreement throughout all the individual bins. Some other physical observables such as forward-backward asymmetry and longitudinal polarizations of leptons in the final state are also computed.

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arXiv2020

Rare $b \to d$ decays in covariant confined quark model

In this article, we study the rare decays corresponding to $b \to d$ transition in the framework of the covariant confined quark model. The transition form factors for the channels $B^{+(0)} \to (\pi^{+(0)}, \rho^{+(0)},\omega)$ and $B_s^0 \to K^{(*)0}$ are computed in the entire dynamical range of momentum transfer squared. Using the form factors, we compute the branching fractions of the rare decays and our results are found to be matching well with the experimental data. We also compute the ratios of the branching fractions of the $b \to s$ to $b \to d$ rare decays using the inputs from previous papers on $b \to s \ell^+\ell^-$ using this model. Further, using the form factors, model dependent and independent parameters, we also compute different other physical observables such as forward backward asymmetry, longitudinal polarization and angular observables in the entire $q^2$ range as well as in $q^2$ bins [0.1 -- 0.98] GeV$^2$ and [1.1 -- 6] GeV$^2$. We also compare our findings with different theoretical predictions.

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arXiv2020

$Y(4260)$ as four-quark state

We treat the $Y(4260)$ resonance as a four-quark state in the framework of the covariant confining quark model. We study two choices of the interpolating current, either the molecular-type current which effectively corresponds to the product of $D$ and $\bar D_1$ quark currents or tetraquark one. In both cases we calculate the widths of decays $Y(4260)\to Z_c(3900)+\pi$ and $Y(4260)\to D^{(\ast)}+\bar D^{(\ast)}$. It is found that in both approches the mode $Y\to Z^+_c + \pi^-$ is enhanced compared with the open charm modes. However the absolute value of the $Y\to Z^+_c + \pi^-$ decay width obtained in molecular picture is arguably too large. On the other hand the value obtained in tetraquark picture is reasonable.

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arXiv2020

$B \to \rho$ Decay Form Factors from Covariant Confined Quark Model

We evaluate $B \rightarrow \rho$ transition form factors in the full kinematical region within the covariant confined quark model. We compare the obtained results with the results from light-cone sum rules. The calculated form factors can be used to calculate the $B^+ \rightarrow \rho^+ {\mu}^+ {\mu}^-$ rare decay branching ratio.

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arXiv2019

Semileptonic decays of $ B_c$ mesons into charmonium states

In this work we study the semileptonic decays of $B_c$ meson. We evaluated $B_{c}\rightarrow D(D^{\ast})$, $B_{c}\rightarrow D_s(D_s^{\ast})$ and $B_{c}\rightarrow \eta_{c}(J/\psi)$ transitions form factors in the full kinematical region within the covariant quark model. The calculated form factors are used to evaluate the semileptonic decays of $B_c$ meson and it was defined ratios ($R_{\eta_{c}}$, $R_{J/\psi}$, $R_{ D}$ ,$R_{ D^{\ast}}$) of the branching ratios, which will be hopefully tested on LHC experiments.We compare the obtained results with the results from other theoretical approaches.

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arXiv2019

$B_{s}\rightarrow K^{\ast 0}$ decay form factors from covariant confined quark model

We evaluate $B_{s}\rightarrow K^{\ast 0}$ transition form factors in the full kinematical region within the covariant confined quark model. The calculated form factors can be used to calculate the $B_{s}\rightarrow K^{\ast 0}\mu^+ \mu^-$ rare decay branching ratio, which was recently measured by LHCb collaboration.

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arXiv2018

b-s Anomaly Decays in Covariant Quark Model

The work is devoted to the study of b-s anomaly decays. We evaluated branching fractions of $B\to K^\ast \mu^+\mu^-$, $B^0_s\to \phi\mu^+\mu^-$ and $B_s\to \mu^+\mu^-$ decays and compared them with available experimental data and with results from other theoretical approaches.

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arXiv2018

The decays $B_{c}\to J/\psi+\bar\ell\nu_\ell$ and $B_{c}\to J/\psi + \pi(K)$ in covariant confined quark model

In the wake of the recent measurements of the decays $B_c\to J/\psi\,\pi(K)$ and $B_c\to J/\psi\,\ell\nu_\ell$ reported by the LHCb Collaboration we calculate the form factors for the $B_c\to J/\psi$ and $B_c\to \eta_{c}$ transitions in full kinematical region within covariant confined quark model. Then we use the calculated form factors to evaluate the partial decay widths of the above-mentioned semileptonic and nonleptonic decays of the $B_{c}$ meson. We find that the theoretical predictions on the ratios of $\mathcal{R}_{K^{+}/ \pi^{+}}$ and $\mathcal{R_{\pi^{+}/ \mu^{+} \nu}}$ are in good agreement with last LHCb-data. However, the prediction for the $\mathcal{R}_{J/\psi}$ is found to be underestimated.

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arXiv2017

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

In the wake of recent measurements of the decays $B_c^+\to J/\psi D^+_s$ and $B_c^+\to J/\psi D^{\ast\,+}_s$ 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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arXiv2016

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

Our article is devoted to the study of the rare $B_s\to \phi \ell^+\ell^-$ decay where $\ell=\mu,\tau$. 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 $B\to \phi(\to K^+K^-)\ell^+\ell^-$. We compare the obtained results with available experimental data and the results from other theoretical approaches.

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arXiv2015

Form factors of the B-S-transitions in the covariant quark model

In the wake of exploring uncertainty in the full angular distribution of the $B\to K\pi+\mu^+\mu^-$ caused by the presence of the intermediate scalar $K^\ast_0$ meson, we perform the straightforward calculation of the $B(B_s)\to S$ (S is a scalar meson) transition form factors in the full kinematical region within the covariant quark model. We restrict ourselves by the scalar mesons below 1 GeV: $a_0(980), f_0(500), f_0(980), K^\ast_0(800)$. As an application of the obtained results we calculate the widths of the semileptonic and rare decays $B(B_s)\to S\ell\bar\nu$, $B(B_s)\to S\ell\bar\ell$ and $B(B_s)\to S\nu\bar\nu$. We compare our results with those obtained in other approaches.

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