arXiv subjects

K. Azizi

Publications and source records attributed to K. Azizi.

At least 199 records · Page 11Linked to original sources

arXiv2018

The strong decays of the light scalar mesons $f_0(500)$ and $f_0(980)$

The partial width of the decay channels $f_0(500) \to ππ$, $f_0(980) \to ππ$ and $f_0(980) \to K \bar K$ are calculated using QCD light-cone sum rules method and a technique of the soft meson approximation. The scalar particles are treated as mixtures of the heavy $|H\rangle =([su][\bar s \bar u]+[sd][\bar s \bar d])/\sqrt 2$ and light $|L\rangle =[ud][\bar u \bar d]$ scalar diquark-antidiquark components. Obtained results for the full width of the $f_0(500)$ meson $Γ_{\mathrm{th}.}=434.7\pm 72.3~\mathrm{MeV}$ and for the $f_0(980)$ meson $Γ_{\mathrm{th.}}=42.12\pm 6.70~\mathrm{MeV }$ are compared with the world averages for these parameters, and a reasonable agreement between them is found.

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arXiv2018

Strong Decay of $P_c(4380)$ Pentaquark in a Molecular Picture

There are different assumptions on the substructure of the pentaquarks $P_c(4380)$ and $P_c(4450)$, newly founded in $J/ψN $ invariant mass by the LHCb collaboration, giving consistent mass results with the experimental observations. The experimental data and recent theoretical studies on their mass suggest interpretation of these states as spin-3/2 negative-parity and spin-5/2 positive-parity pentaquarks, respectively. There may exist opposite-parity states corresponding to these particles, as well. Despite a lot of studies, however, the nature and internal organization of these pentaquarks in terms of quarks and gluons are not clear. To this end we need more theoretical investigations on other physical properties of these states. In this accordance, we study a strong and dominant decay of the $P_c(4380)$ to $J/ψ$ and $N$ in the framework of three point QCD sum rule method. An interpolating current in a molecular form is applied to calculate six strong coupling form factors defining the transitions of the positive and negative parity spin-3/2 pentaquark states. The values of the coupling constants are used in the calculation of the decay widths of these transitions. The obtained results are compared with the existing experimental data.

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arXiv2018

Electromagnetic multipole moments of the $P_c^+(4380)$ pentaquark in light-cone QCD

We calculate the electromagnetic multipole moments of the $P_c^+(4380)$ pentaquark by modeling it as the diquark-diquark-antiquark and $\bar D^*Σ_c$ molecular state with quantum numbers $J^P = \frac{3}{2}^-$. In particular, the magnetic dipole, electric quadrupole and magnetic octupole moments of this particle are extracted in the framework of light-cone QCD sum rule. The values of the electromagnetic multipole moments obtained via two pictures differ substantially from each other, which can be used to pin down the underlying structure of $P_c^+(4380)$. The comparison of any future experimental data on the electromagnetic multipole moments of the $P_c^+(4380)$ pentaquark with the results of the present work can shed light on the nature and inner quark organization of this state.

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arXiv2018

Analysis of the structure of $Ξ(1690)$ through its decays

The mass and pole residue of the first orbitally and radially excited $ Ξ$ state as well as the ground state residue are calculated by means of the two-point QCD sum rules. Using the obtained results for the spectroscopic parameters, the strong coupling constants relevant to the decays $Ξ(1690)\rightarrow ΣK$ and $Ξ(1690) \rightarrow ΛK$ are calculated within the light-cone QCD sum rules and width of these decay channels are estimated. The obtained results for the mass of $ \widetildeΞ $ and ratio of the $Br\Big(\widetildeΞ\rightarrow ΣK\Big)/Br\Big(\widetildeΞ\rightarrow ΛK\Big)$, with $ \widetildeΞ $ representing the orbitally excited state in $ Ξ$ channel, are in nice agreement with the experimental data of the Belle Collaboration. This allows us to conclude that the $Ξ(1690)$ state, most probably, has negative parity.

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arXiv2018

The structure, mixing angle, mass and couplings of the light scalar $f_0(500)$ and $f_0(980)$ mesons

The mixing angle, mass and couplings of the light scalar mesons $f_0(500)$ and $f_0(980)$ are calculated in the framework of QCD two-point sum rule approach by assuming that they are tetraquarks with diquark-antidiquark structures. The mesons are treated as mixtures of the heavy $|H\rangle =([su][\bar s \bar u]+[sd][\bar s \bar d])/\sqrt 2$ and light $|L\rangle =[ud][\bar u \bar d]$ scalar diquark-antidiquark components. We extract from corresponding sum rules the mixing angles $φ_H$ and $φ_L$ of these states and evaluate the masses and couplings of the particles $ f_0(500) $ and $f_0(980)$.

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arXiv2018

Mass and residue of $ Λ(1405)$ as hybrid and excited ordinary baryon

The nature of the $ Λ(1405) $ has been a puzzle for decades, whether it is a standard three-quark baryon, a hybrid baryon or a baryon-meson molecule. More information on the decay channels of this particle and its strong, weak and electromagnetic interactions with other hadrons is needed to clarify its internal organization. The residue of this particle is one of the main inputs in investigation of its decay properties in many approaches. We calculate the mass and residue of $Λ(1405)$ state in the context of QCD sum rules considering it as a hybrid baryon with three-quark---one gluon content as well as an excited ordinary baryon with quantum numbers $I(J^{P})=0(1/2^{-})$. The comparison of the obtained results on the mass with the average experimental value presented in PDG allows us to interpret this state as a hybrid baryon.

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arXiv2018

The new $a_1(1420)$ state: structure, mass and width

The structure, spectroscopic parameters and width of the resonance with quantum numbers $J^{PC}=1^{++}$ discovered by the COMPASS Collaboration and classified as the $a_1(1420)$ meson are examined in the context of QCD sum rule method. In the calculations the axial-vector meson $a_1(1420)$ is treated as a four-quark state with the diquark-antidiquark structure. The mass and current coupling of $a_1(1420)$ are evaluated using QCD two-point sum rule approach. Its observed decay mode $a_1(1420) \to f_0(980)π$, and kinematically allowed ones, namely $a_1 \to K^{\ast \pm}K^{\mp}$, $a_1 \to K^{\ast 0} \bar{K}^{0}$ and $a_1 \to \bar {K}^{\ast 0} K^{0}$ channels are studied employing QCD sum rules on the light-cone. Our prediction for the mass of the $a_1(1420)$ state $m_{a_{1}}=1416_{-79}^{+81}\ \mathrm{MeV}$ is in excellent agreement with the experimental result. Width of this state $ Γ=145.52 \pm 20.79 \mathrm{MeV}$ within theoretical and experimental errors is also in accord with the COMPASS data.

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arXiv2018

The electromagnetic multipole moments of the charged open-flavor $Z_{\bar cq}$ states

The electromagnetic multipole moments of the open-flavor $Z_{\bar cq}$ states are investigated by assuming a diquark-antidiquark picture for their internal structure and quantum numbers $J^{PC} = 1^{+-}$ for their spin-parity. In particular, their magnetic and quadrupole moments are extracted in the framework of light-cone QCD sum rule by the help of the photon distribution amplitudes. The electromagnetic multipole moments of the open-flavor $Z_{\bar cq}$ states are important dynamical observables, which encode valuable information on their underlying structure. The results obtained for the magnetic moments of different structures are considerably large and can be measured in future experiments. We obtain very small values for the quadrupole moments of $Z_{\bar cq}$ states indicating a nonspherical charge distribution.

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arXiv2018

Testing the doubly charged charm-strange tetraquarks

The spectroscopic parameters and decay channels of the doubly charged scalar, pseudoscalar and axial-vector charm-strange tetraquarks $Z_{ \overline{c}s}=[sd][\overline u \overline c]$ are explored within framework of the QCD sum rule. The masses and current couplings of these diquark-antidiquark states are calculated by means of two-point correlation functions and taking into account the vacuum condensates up to eight dimensions. To compute the strong couplings of $Z_{\overline{c}s}$ states with $D,\ D_{s},\ D^{\ast},\ D_{s}^{\ast},\ D_{s1}(2460),\ D_{s0}^{\ast}(2317),\ π$ and $K$ mesons we use QCD light-cone sum rules and evaluate width of their $S$- and $P$-wave decays to a pair of negatively charged conventional mesons: For the scalar state $Z_{\overline{c}s}\to D_s π,\ DK, \ D_{s1}(2460)π$, for the pseudoscalar state $Z_{\overline{c}s} \to D_{s}^{\ast}π,\ D^{\ast}K, \ D_{s0}^{\ast}(2317)π,$ and for the axial-vector state $Z_{\overline{c}s} \to D_{s}^{\ast}π,\ D^{\ast}K,\ D_{s1}(2460)π$ decays are investigated. Obtained predictions for the spectroscopic parameters and decay widths of the $Z_{\overline{c}s}$ tetraquarks may be useful for experimental investigations of the doubly charged exotic hadrons.

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arXiv2018

Magnetic dipole moment of $Z_b(10610)$ in light-cone QCD

The magnetic dipole moment of the exotic $Z_b(10610)$ state is calculated within the light cone QCD sum rule method using the diquark-antidiquark and molecule interpolating currents. The magnetic dipole moment is obtained as $μ_{Z_b}=1.73\pm 0.63~μ_N$ in diquark-antidiquark picture and $μ_{Z_b}=1.59\pm 0.58~μ_N$ in the molecular case. The obtained results in both pictures together with the results of other theoretical studies on the spectroscopic parameters of the $Z_b(10610)$ state may be useful in determination of the nature and quark organization of this state.

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arXiv2017

Spectroscopic parameters and decays of the resonance $Z_b(10610)$

The resonance $Z_b(10610)$ is investigated as the diquark-antidiquark $ Z_b=[bu][\overline b \overline d]$ state with spin-parities $J^{PC}=1^{+-}$. The mass and current coupling of the resonance $Z_b(10610)$ are evaluated using QCD two-point sum rule and taking into account the vacuum condensates up to ten dimensions. We study the vertices $ Z_bΥ(nS)π (n=1,2,3)$ by applying the QCD light-cone sum rule to compute the corresponding strong couplings $g_{Z_bΥ(nS)π}$ and widths of the decays $Z_b \to Υ(nS)π$. We explore also the vertices $Z_b h_{b}(mP)π (m=1,2)$ and calculate the couplings $g_{Z_b h_{b}(mP)π}$ and width of the decay channels $Z_b \to h_{b}(mP)π$. To this end, we calculate the mass and decay constants of the $h_b(1P)$ and $h_b(2P) $ mesons. The results obtained are compared with experimental data of the Belle Collaboration.

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arXiv2017

Hidden Bottom Pentaquark States with Spin 3/2 and 5/2

Theoretical investigations of the pentaquark states which were recently discovered provide important information on their nature and structure. It is necessary to study the spectroscopic parameters like masses and residues of particles belong to the class of pentaquarks and ones having similar structures. The mass and pole residue are quantities which emerge as the main input parameters in exploration of the electromagnetic, strong and weak interactions of the pentaquarks with other hadrons in many frameworks. This work deals with a QCD sum rule analysis of the spin-$3/2$ and spin-$5/2$ bottom pentaquarks with both positive and negative parities aiming to evaluate their masses and residues. In calculations, the pentaquark states are modeled by molecular-type interpolating currents: for particles with $J=5/2$ a mixing current is used. We compare the results obtained in this work with the existing predictions of other theoretical studies. The predictions on the masses may shed light on experimental searches of the bottom pentaquarks.

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arXiv2017

Magnetic and quadrupole moments of the $Z_c(3900)$

The electromagnetic properties of the tetraquark state $Z_c(3900)$ are investigated in the diquark-antidiquark picture and its magnetic and quadrupole moments are extracted. To this end, the light-cone QCD sum rule in electromagnetic background field is used. The magnetic and quadrupole moments encode the spatial distributions of the charge and magnetization in the particle. The result obtained for the magnetic moment is quite large and can be measured in future experiments. We obtain a nonzero but small value for the quadrupole moment of $Zc(3900)$ indicating a nonspherical charge distribution.

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arXiv2017

Decay widths of the excited $Ω_b$ baryons

The LHCb Collaboration recently observed five narrow $Ω_c^{0}$ resonances, and measured their masses and widths through the decays $ Ω_c^{0} \to Ξ_c^{+}K^{-}$. Motivated by this discovery, and also by the fact that the ground-state bottom baryon $Ω_b^{-}$ with spin-1/2 was already found experimentally, we perform theoretical investigation of the spin-1/2 and spin-3/2, $Ω_b$, baryons by calculating decay width of their first orbitally and radially excited states to $Ξ_b^{0} K^{-}$. For this purpose, we employ QCD sum rule method on the light-cone by including into analysis the $K$ meson distribution amplitudes up to twist-4. Obtained analytical expressions are utilized to extract parameters of these decay processes which may be useful for forthcoming experimental studies of bottom baryons.

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arXiv2017

Impact of scalar leptoquarks on heavy baryonic decays

We present a study on the impact of scalar leptoquarks on the semileptonic decays of $ Λ_b$, $Σ_b $ and $Ξ_b $. To this end, we calculate the differential branching ratio and lepton forward-backward asymmetry defining the processes $ Λ_b \rightarrow Λ\ell^+ \ell^-$, $Σ_b \rightarrow Σ\ell^+ \ell^-$ and $Ξ_b \rightarrow Ξ\ell^+ \ell^-$, with $\ell$ being $μ$ or $τ$, using the form factors calculated via light cone QCD in full theory. In calculations, the errors of form factors are taken into account. We compare the results obtained in leptoquark model with those of the standard model as well as the existing lattice QCD predictions and experimental data.

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arXiv2017

Treating $Z_c(3900)$ and $Z(4430)$ as the ground-state and first radially excited tetraquarks

Exploration of the resonances $Z_c(3900)$ and $Z(4430)$ are performed by assuming that they are ground-state and first radial excitation of the same tetraquark with $J^{P}=1^{+}$. The mass and current coupling of the $ Z_c(3900)$ and $Z(4430)$ states are calculated using QCD two-point sum rule method by taking into account vacuum condensates up to eight dimensions. We investigate the vertices $Z_cM_hM_l$ and $ZM_hM_l$, with $M_h$ and $M_l $ being the heavy and light mesons, and evaluate the strong couplings $ g_{Z_cM_hM_l}$ and $g_{ZM_hM_l}$ using QCD sum rule on the light cone. The extracted couplings allow us to find the partial width of the decays $ Z_c(3900) \to J/ψπ; \,ψ^{\prime} π;\, η_c ρ$ and $Z(4430) \to ψ^{\prime} π;\, J/ψπ;\, η_c^{\prime}ρ;\, η_cρ$, which may help in comprehensive investigation of these resonances. We compare width of the decays of $Z_c(3900)$ and $Z(4430)$ resonances with available experimental data as well as existing theoretical predictions.

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arXiv2017

Exploring the resonances $X(4140)$ and $X(4274)$ through their decay channels

Investigation of the resonances $X(4140)$ and $X(4274)$, which were recently confirmed by the LHCb Collaboration [1], is carried out by treating them as the color triplet and sextet $[cs][\bar{c}\bar {s}]$ diquark-antidiquark states with the spin-parity $J^{P}=1^{+}$, respectively. We calculate the masses and meson-current couplings of these tetraquarks in the context of QCD two-point sum rule method by taking into account the quark, gluon and mixed vacuum condensates up to eight dimensions. We also study the vertices $X(4140)J/ψϕ$ and $X(4274)J/ψϕ$, and evaluate corresponding strong couplings $g_{X(4140)J/ψϕ}$ and $ g_{X(4274)J/ψϕ}$ by means of QCD light-cone sum rule method, and a technique of the soft-meson approximation. In turn, these couplings contain a required information to determine the width of the $X(4140)\to J/ψϕ$ and $X(4274) \to J/ψϕ$ decay channels. We compare our results for the masses and decay widths of the $X(4140)$ and $X(4274)$ resonances with the LHCb data, and alternative theoretical predictions.

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arXiv2017

Open charm-bottom axial-vector tetraquarks and their properties

The charged axial-vector $J^{P}=1^{+}$ tetraquarks $Z_{q}=[cq][\bar {b} \bar q ]$ and $Z_{s}=[cs][\bar {b} \bar s]$ with the open charm-bottom contents are studied in the diquark-antidiquark model. The masses and meson-current couplings of these states are calculated by employing QCD two-point sum rule approach, where the quark, gluon and mixed condensates up to eight dimensions are taken into account. These parameters of the tetraquark states $ Z_{q}$ and $Z_{s}$ are used to analyze the vertices $Z_q B_c ρ$ and $Z_s B_c ϕ$ to determine the strong $g_{Z_qB_c ρ}$ and $g_{Z_sB_c ϕ}$ couplings. For these purposes, QCD light-cone sum rule method and its soft-meson approximation are utilized. The couplings $g_{Z_qB_c ρ}$ and $ g_{Z_sB_c ϕ}$, extracted from this analysis, are applied for evaluating of the strong $Z_q \to B_c ρ$ and $Z_s \to B_c ϕ$ decays' widths, which are essential results of the present investigation. Our predictions for the masses of the $Z_{q}$ and $Z_{s}$ states are confronted with similar results available in the literature.

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