arXiv subjects

K. Azizi

Publications and source records attributed to K. Azizi.

At least 181 records · Page 10Linked to original sources

arXiv2019

Properties of $Σ_Q^{}$, $Ξ_Q^{}$ and $Ω_Q^{*}$ heavy baryons in cold nuclear matter

The in-medium properties of the heavy spin-3/2 $Σ_Q^{*}$, $Ξ_Q^{*}$ and $Ω_Q^{*}$ baryons with $Q$ being $b$ or $c$ quark are investigated. The shifts in some spectroscopic parameters of these particles due to the saturated cold nuclear matter are calculated. The variations of those parameters with respect to the changes in the density of the cold nuclear medium are studied, as well. It is observed that the parameters of $Σ_Q^{*}$ baryons are considerably affected by the nuclear matter compared to the $Ξ_Q^{*}$ and $Ω_Q^{*}$ particles that roughly do not see the medium. The results obtained may be used in analyses of the data to be provided by the in-medium experiments like PANDA.

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arXiv2019

Determination of the quantum numbers of $Σ_b(6097)^{\pm}$ via their strong decays

The progresses in the experimental sector have been the harbinger of the observations of many new hadrons. Very recently, LHCb Collaboration announced the observation of two new $Σ_b(6097)^{\pm}$ states in the $Λ^0_bπ^{\pm}$ invariant mass distribution, which are considered as the excited states of the ground state $Σ^{(*)}_b$ baryon. Though, almost all of the ground state baryons have been observed, having a limited number of excited states observed so far makes them intriguing. Understanding the properties of the excited baryons improve our knowledge on the strong interaction as well as the nature and internal structures of these baryons. To specify the quantum numbers of the $Σ_b(6097)^{\pm}$ an analysis on their strong decays to $Λ_b^0$ and $π^{\pm}$ is performed within the light cone QCD sum rule formalism. To this end, they are considered as possible $1P$ or $2S$ excitation of either the ground state $Σ_b$ baryon with $J=\frac{1}{2}$ or $Σ_b^{*}$ baryon with $J=\frac{3}{2}$. The corresponding masses are also calculated considering the same scenarios for their quantum numbers. The results of the analyses indicate that the $Σ_b(6097)^{\pm}$ baryons are excited $1P$ baryons having quantum numbers $J^P=\frac{3}{2}^-$.

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arXiv2019

Fate of the doubly heavy spin$-3/2$ baryons in a dense medium

We investigate the behavior of the doubly heavy spin$-3/2$ baryons in cold nuclear matter. In particular, we study the variations of the spectroscopic parameters of the ground state $Ξ^*_{QQ'}$ and $Ω^*_{QQ'}$ particles, with $ Q $ and $ Q' $ being $b $ or $ c $ quark, with respect to the changes in the density of the nuclear medium. We find the shifts on the parameters under question at saturation medium density compared to their vacuum values. It is observed that the parameters of the $Ξ^*_{QQ'}$ states containing two heavy quarks and one up or down quark are affected by the medium, considerably. The parameters of the $Ω^*_{QQ'}$ states containing two heavy quarks and one strange quark, however, do not show any sensitivity to the density of the cold nuclear medium. We also discuss the variations of the vector self-energy at each channel with respect to the changes in the density. The negative shifts in the mass of $Ξ^*_{QQ'}$ states due to nucleons in the medium can be used to study the doubly heavy baryons' interactions with the nucleons. The results obtained can also be used in analyses of the results of the future in-medium experiments.

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arXiv2019

New charged resonance $Z_{c}^{-}(4100)$: the spectroscopic parameters and width

The mass, coupling and width of the newly observed charged resonance $ Z_{c}^{-}(4100)$ are calculated by treating it as a scalar four-quark system with a diquark-antidiquark structure. The mass and coupling of the state $ Z_{c}^{-}(4100)$ are calculated using the QCD two-point sum rules. In these calculations we take into account contributions of the quark, gluon and mixed condensates up to dimension ten. The spectroscopic parameters of $ Z_{c}^{-}(4100)$ obtained by this way are employed to study its $S$-wave decays to $η_c(1S)π^{-}$, $η_c(2S)π^{-}$, $D^{0}D^{-}$, and $ J/ψρ^{-}$ final states. To this end, we evaluate the strong coupling constants corresponding to the vertices $Z_{c}η_c(1S)π^{-}$, $ Z_{c}η_c(2S)π^{-}$, $Z_{c}D^{0}D^{-}$, and $Z_{c}J/ψρ^{-}$ respectively. The couplings $g_{Z_cη_{c1} π}$, $g_{Z_{c}η_{c2} π}$ , and $g_{Z_{c}DD}$ are computed by means of the QCD three-point sum rule method, whereas $g_{Z_{c}J/ψρ}$ is obtained from the QCD light-cone sum rule approach and soft-meson approximation. Our results for the mass $ m=(4080 \pm 150)~\mathrm{MeV}$ and total width $Γ=(147 \pm 19)~\mathrm{ MeV}$ of the resonance $Z_{c}^{-}(4100)$ are in excellent agreement with the existing LHCb data.

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arXiv2019

Semileptonic $Λ_{b}\rightarrow Λ_{c}{\ell}\barν_{\ell}$ Transition in Full QCD

The tree-level $b\rightarrow c{\ell}\barν_{\ell}$ based hadronic transitions have been on the focus of much attention since recording significant deviations of the experimental data, on the ratios of the branching fractions in $ τ$ and $ e-μ$ channels of the semileptonic $ B \rightarrow D $ transition, from the SM predictions by BaBar Collaboration in 2012. It can be of great importance to look whether similar discrepancies take place in the semileptonic baryonic $Λ_{b}\rightarrow Λ_{c}{\ell}\barν_{\ell}$ decay channel or not. In this accordance we estimate the decay width as well as the ratios of the branching fractions in $ τ$ and $ e-μ$ channels of this baryonic transition by calculating the form factors, entering the amplitude of this transition as the main inputs, in the framework of QCD sum rules in full theory. We compare the obtained results with the predictions of other theoretical studies. Our results may be compared with the corresponding future experimental data to look for possible deviations of data from the SM predictions.

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arXiv2019

Weak decays of the axial-vector tetraquark $T_{bb;\bar{u} \bar{d}}^{-}$

The weak decays of the axial-vector tetraquark $T_{bb;\bar{u} \bar{d}}^{-}$ to the scalar state $Z_{bc;\bar{u} \bar{d}}^{0}$ are investigated using the QCD three-point sum rule approach. In order to explore the process $T_{bb; \bar{u} \bar{d}}^{-} \to Z_{bc;\bar{u} \bar{d}}^{0}l \bar{ν_l}$, we recalculate the spectroscopic parameters of the tetraquark $T_{bb;\bar{u} \bar{d}}^{-}$ and find the mass and coupling of the scalar four-quark system $Z_{bc;\bar{u} \bar{d}}^{0}$, which are important ingredients of calculations. The spectroscopic parameters of these tetraquarks are computed in the framework of the QCD two-point sum rule method by taking into account various condensates up to dimension ten. The mass of the $T_{bb;\bar{u} \bar{ d}}^{-}$ state is found to be $m=(10035~\pm 260)~\mathrm{MeV}$, which demonstrates that it is stable against the strong and electromagnetic decays. The full width $Γ$ and mean lifetime $τ$ of $T_{bb;\bar{u} \bar{d} }^{-}$ are evaluated using its semileptonic decay channels $T_{bb; \bar{u} \bar{d}}^{-} \to Z_{bc;\bar{u} \bar{d}}^{0}l \bar{ν_l}$, $l=e,μ$ and $τ$. The obtained results, $Γ=(7.17\pm 1.23)\times 10^{-8\ \ } \mathrm{MeV}$ and $τ=9.18_{-1.34}^{+1.90}~\mathrm{fs}$, can be useful for experimental investigations of the doubly-heavy tetraquarks.

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arXiv2019

On the mass and decay constant of the P-wave ground and radially excited $h_{c}$ and $h_{b}$ axial-vector mesons

The mass and decay constant of the heavy quarkonia $h_{Q}(1P)$ and $h_{Q}(2P)$ (Q = b, c) with quantum numbers $J^{PC} =1^{+-}$ are calculated in the framework of the two-point QCD sum rule method by taking into account the vacuum condensates up to eight dimensions. We compare our results for parameters of the $h_{b}(1P)$ and $h_{c}(1P)$ quarkonia, and their first radially excited states $h_{b}(2P)$ and $h_{c}(2P)$ with available experimental data as well as predictions of other theoretical studies existing in the literature. The results of present work may shed light on experimental searches for the $h_{c}(2P)$ state.

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arXiv2019

The nonet of the light scalar tetraquarks: the mesons $a_0(980)$ and $K_{0}^{\ast }(800)$

The spectroscopic parameters and partial decay widths of the light mesons $ a_0(980) $ and $K_{0}^{\ast}(800)$ are calculated by treating them as scalar diquark-antidiquark states. The masses and couplings of the mesons are found in the framework of QCD two-point sum rule approach. The widths of the decay channels $a_0(980) \to ηπ$ and $a_0(980) \to K \bar{K}$, and $ K_{0}^{\ast}(800) \to K^{+} π^{-}$ and $K_{0}^{\ast}(800) \to K^{0} π^{0} $ are evaluated using QCD sum rules on the light-cone and technical tools of the soft meson approximation. Our results for the mass of the mesons $m_{a_0}=991^{+29}_{-27} \ \mathrm{MeV}$ and $m_{K^{ \ast}}=767^{+38}_{-29} \ \mathrm{MeV}$, as well as their total width $Γ_{\mathrm{a_0}}=62.01\pm 14.37\ \mathrm{MeV}$ and $Γ_{\mathrm{ K_0^{\ast}}}=401.1\pm 87.1\ \mathrm{MeV}$ are compared with last experimental data.

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arXiv2018

The doubly charmed pseudoscalar tetraquarks $T_{cc;\bar{s} \bar{s}}^{++}$ and $T_{cc;\bar{d} \bar{s}}^{++}$

The mass and coupling of the doubly charmed $J^P=0^{-}$ diquark-antidiquark states $T_{cc;\bar{s} \bar{s}}^{++}$ and $T_{cc;\bar{d} \bar{s}}^{++}$ that bear two units of the electric charge are calculated by means of QCD two-point sum rule method. Computations are carried out by taking into account vacuum condensates up to and including terms of tenth dimension. The dominant $S$-wave decays of these tetraquarks to a pair of conventional $ D_{s}^{+}D_{s0}^{\ast +}(2317)$ and $D^{+}D_{s0}^{\ast +}(2317)$ mesons are explored using QCD three-point sum rule approach, and their widths are found. The obtained results $m_{T}=(4390~\pm 150)~\mathrm{MeV}$ and $Γ=(302 \pm 113~\mathrm{MeV}$) for the mass and width of the state $T_{cc;\bar{ s} \bar{s}}^{++}$, as well as spectroscopic parameters $\widetilde{m} _{T}=(4265\pm 140)~\mathrm{MeV}$ and $\widetilde{Γ}=(171~\pm 52)~ \mathrm{MeV}$ of the tetraquark $T_{cc;\bar{d} \bar{s}}^{++}$ may be useful in experimental studies of exotic resonances.

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arXiv2018

Structure of the $Ξ_b(6227)^-$ Resonance

We explore the recently observed $Ξ_b(6227)^{-}$ resonance to fix its quantum numbers. To this end, we consider various possible scenarios: It can be considered as either 1P/2S excitations of the $Ξ_b^-$ and $Ξ_b'(5935)^{-}$ ground state baryons with spin-$\frac{1}{2}$ or 1P/2S excitations of the ground state $Ξ_b(5955)^{-}$ with spin-$\frac{3}{2}$. We calculate the masses of the possible angular-orbital $1P$ and $2S$ excited states corresponding to each channel employing the QCD sum rule technique. It is seen that all the obtained masses are in agreement with the experimentally observed value, implying that the mass calculations are not enough to distinguish the quantum numbers of the state under question. Therefore, we extend the analysis to investigate the possible decays of the same excited states into $Λ_b^0 K^-$ and $Ξ_b^-π$. Using the light cone QCD sum rule method, we calculate the corresponding strong coupling constants, which are used to extract the decay widths of the modes under consideration. Our results on decay widths indicate that the $Ξ_b(6227)^{-}$ is $1P$ angular-orbital excited state of the $Ξ_b(5955)^{-}$ baryon with quantum numbers $J^P=\frac{3}{2}^{-}$.

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arXiv2018

Nature of the $Ω$(2012) through its strong decays

We extend our previous analysis on the mass of the recently discovered $Ω(2012)$ state by investigation of its strong decays and calculation of its width employing the method of light cone QCD sum rule. Considering two possibilities for the quantum numbers of $Ω(2012)$ state, namely $1P$ orbital excitation with $J^P=\frac{3}{2}^-$ and $2S$ radial excitation with $J^P=\frac{3}{2}^+$, we obtain the strong coupling constants defining the $Ω(1P/2S)\rightarrowΞK$ decays. The results of the coupling constants are then used to calculate the decay width corresponding to each possibility. Comparison of the obtained results on the total widths in this work with the experimental value and taking into account the results of our previous mass prediction on the $Ω(2012)$ state, we conclude that this state is $1P$ orbital excitation of the ground state $Ω$ baryon, whose quantum numbers are $J^P=\frac{3}{2}^-$.

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arXiv2018

Resonance $Y(4660)$ as a vector tetraquark and its strong decay channels

The spectroscopic parameters and partial widths of the strong decay channels of the vector meson $Y(4660)$ are calculated by treating it as a bound state of a diquark and antidiquark. The mass and coupling of the $J^{PC}=1^{--}$ tetraquark $Y(4660) $ are evaluated in the context of the two-point sum rule method by taking into account the quark, gluon and mixed condensates up to dimension 10. The widths of the $Y(4660)$ resonance's strong $S$-wave decays to $J/ψf_{0}(980)$ and $ψ(2S) f_{0}(980)$ as well as to $ J/ψf_{0}(500)$ and $ψ(2S) f_{0}(500)$ final states are computed. To this end, strong couplings in the relevant vertices are extracted from the QCD sum rule on the light cone supplemented by the technical methods of the soft approximation. The obtained result for the mass of the resonance $ m_Y=4677^{+71}_{-63}\ \mathrm{MeV}$ and the prediction for its total width $ Γ_{Y}= (64.8 \pm 10.8)\ \mathrm{MeV}$ is in nice agreement with the experimental information.

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arXiv2018

Possible Molecular Pentaquark States with Different Spin and Quark Configurations

We investigate three possible pentaquark candidates, one of which contains a single charm quark and the other two contain triple charm quarks in their substructure. To this end we apply QCD sum rule method and take into account both the positive and negative parity states corresponding to each possible pentaquark channel having spin $3/2$ or $1/2$. Insisting on the importance of identification of the members of pentaquark family we obtain their spectroscopic parameters such as masses and residues. These parameters are the main inputs in the searches for their electromagnetic, strong and weak interactions.

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arXiv2018

The electromagnetic multipole moments of the possible charm-strange pentaquarks in light-cone QCD

We investigate the electromagnetic properties of possible charm-strange pentaquarks in the framework of the light-cone QCD sum rule using the photon distribution amplitudes. In particular, by calculating the corresponding electromagnetic form factors defining the radiative transitions under consideration we estimate the magnetic dipole and electric quadrupole moments of the pentaquark systems of a charm, an anti-strange and three light quarks. We observe that the values of magnetic dipole moments are considerably large, however, the quadrupole moments are very small. Any future measurements of the electromagnetic parameters under consideration and comparison of the obtained data with the theoretical predictions can shed light on the quark-gluon organization as well as the nature of the pentaquarks.

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arXiv2018

On the nature of $Ξ_c(2930)$

The single charmed excited $Ξ_c(2930)$ state was discovered many years ago by BABAR collaboration and recently confirmed by Belle experiment. However, both of these experiments, unfortunately, could not fix the quantum numbers of this particle and its nature is under debates. In the present study, we calculate its mass and width of its dominant decay to $ Λ_c K $. To this end we consider $Ξ_c(2930)$ state once as angularly excited and then radially excited single charmed baryon in $ Ξ_c$ channel. Comparison of the obtained results with the experimental data suggests assignment of $Ξ_c(2930)$ state as the angular excitation of the ground state $Ξ_c$ baryon with quantum numbers $J^P=\frac{1}{2}^{-}$.

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arXiv2018

Interpretation of the newly discovered $Ω$(2012)

Very recently Belle Collaboration reported observation of a narrow state called $Ω(2012)$ with mass $2012.4 \pm 0.7$~(stat)~$\pm 0.6$(syst)~MeV and width $6.4^{+2.5}_{-2.0}$~(stat)~$\pm 1.6$~(syst)~MeV. We calculate the mass and residue of $Ω(2012)$ state by employing the QCD sum rule method. Comparison of the obtained results with the experimental data allows us to interpret this state as $1P$ orbital excitation of the ground state $Ω$ baryon, i.e. with quantum numbers $J^P=\frac{3}{2}^-$.

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arXiv2018

Probing an axial-vector tetraquark $Z_s$ via its semileptonic decay $Z_s \to X(4274)\overline{l} ν_l$

The semileptonic decays of the open charm-bottom axial-vector tetraquark $ Z_{s}=[cs][\overline{b}\overline{s}]$ to $X(4274)\overline{l} ν_l$, $l=e, μ, τ$ are explored by means of the QCD three-point sum rule method. Both $Z_{s}$ and $X(4274)=[cs][\overline{c}\overline{s}]$ are treated as color sextet diquark-antidiquark states. The full width of the decays $Z_s \to X(4274)\overline{l} ν_l$ is found. Obtained predictions for $ Γ(Z_s \to X(4274)\overline{l} ν_l)$ demonstrate that, as in the case of the conventional hadrons, the semileptonic transitions form a very small part of its full width.

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arXiv2018

Beautiful mathematics for beauty-full and other multi-heavy hadronic systems

In most non-perturbative methods in hadron physics the calculations are started with a correlation function in terms of some interpolating and transition currents in $ x $-space. For simplicity, the calculations are then transformed to the momentum space by a Fourier transformation. To suppress the contributions of the higher states and continuum; and enhance the ground state contribution, Borel transformation as well as continuum subtraction are applied by the help of quark-hadron duality assumption. In the present study we work out the mathematics required for these processes in the case of light and multi-heavy hadrons. We address a well-known problem in subtraction of the effects of the higher states and continuum and discuss how we find finite results without any divergence by using an appropriate representation of the modified Bessel functions, appearing in the heavy quark propagator, and successive applications of the Borel transformations, which lead to more suppression of the higher states and continuum contributions. The results obtained can be used in determination of the spectroscopic and decay properties of the multi-heavy standard and non-conventional (exotic) systems in many non-perturbative methods, specially the QCD sum rules.

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