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K. Azizi

Publications and source records attributed to K. Azizi.

At least 145 records · Page 8Linked to original sources

Doubly charged vector tetraquark $Z_{\mathrm{V}}^{++}=[cu][\overline{s}\overline{d}]$

We explore properties of the doubly charged vector tetraquark $Z_{\mathrm{V} }^{++}=[cu][\overline{s}\overline{d}]$ built of four quarks of different flavors using the QCD sum rule methods. The mass and current coupling of $Z_{ \mathrm{V}}^{++}$ are computed in the framework of the QCD two-point sum rule approach by taking into account quark, gluon and mixed vacuum condensates up to dimension $10$. The full width of this tetraquark is saturated by $S$-wave $Z_{\mathrm{V}}^{++} \to π^{+}D_{s1}(2460)^{+},\ ρ^{+}D_{s0}^{\ast }(2317)^{+}$, and $P$-wave $Z_{\mathrm{V}}^{++} \to π^{+}D_{s}^{+},\ K^{+}D^{+}$ decays. Strong couplings required to find partial widths of aforementioned decays are calculated in the context of the QCD light-cone sum rule method and a soft-meson approximation. Our predictions for the mass $m=(3515 \pm 125)~\mathrm{MeV}$ and full width $ Γ_{\mathrm{full}}=156_{-30}^{+56}~\mathrm{MeV}$ of $Z_{\mathrm{V} }^{++} $ are useful to search for this exotic meson in various processes. Recently, the LHCb collaboration discovered neutral states $X_{0(1)}(2900)$ as resonance-like peaks in $D^{-}K^{+}$ invariant mass distribution in the decay $B^{+} \to D^{+}D^{-}K^{+}$. We argue that mass distribution of $ D^{+}K^{+}$ mesons in the same $B$ decay can be used to observe the doubly charged scalar $Z_{\mathrm{S}}^{++}$ and vector $Z_{\mathrm{V}}^{++}$ tetraquarks.

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New scalar resonance $X_0(2900)$ as a $\overline{D}^{*}K^{*}$ molecule: Mass and width

We explore features of the scalar structure $X_0(2900)$, which is one of the two resonances discovered recently by LHCb in the $D^{-}K^{+}$ invariant mass distribution in the decay $B^{+} \to D^{+}D^{-}K^{+}$. We treat $ X_0(2900)$ as a hadronic molecule composed of the conventional mesons $ \overline{D}^{* 0} $ and $K^{*0}$ and calculate its mass, coupling and width. The mass and coupling of $X_0(2900)$ are determined using the QCD two-point sum rule method by taking into account quark, gluon, and mixing vacuum condensates up to dimension $15$. The decay of this structure to final state $D^{-}K^{+}$ is investigated in the context of the light-cone sum rule approach supported by a soft-meson technique. To this end, we evaluate strong coupling $G$ corresponding to vertex $X_0D^{-}K^{+}$, which allows us to find width of the decay $X_0(2900) \to D^{-}K^{+}$. Obtained predictions for the mass of the hadronic molecule $\overline{D}^{*0 }K^{*0}$ $m=(2868 \pm 198)~\mathrm{MeV} $ and for its width $Γ=(49.6 \pm 9.3)~ \mathrm{MeV}$ can be considered as arguments in favor of molecule interpretation of $X_0(2900)$.

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Newly discovered $Ξ_c^{0}$ resonances and their parameters

The aim of the present article is investigation of the newly observed resonances $Ξ_c(2923)^{0}$, $Ξ_c(2939)^{0}$, and $Ξ_c(2965)^{0}$ which are real candidates to charm-strange baryons. To this end, we calculate the mass and pole residue of the ground-state and excited $1P$ and $2S$ spin-$% 1/2 $ flavor-sextet baryons $Ξ_{c}^{\prime 0}$, $Ξ_{c}^{\prime 0}(1/2^{-})$ and $Ξ_{c}^{\prime 0}(1/2^{+})$ with quark content $csd$, respectively. The masses and pole residues of the ground-state and excited spin-$3/2$ baryons $Ξ_{c}^{\star 0}$ are found as well. Spectroscopic parameters of these particles are computed in the context of the QCD two-point sum rule method. Widths of the excited baryons are evaluated through their decays to final states $Λ_{c}^{+}K^{-}$ and $% Ξ_{c}^{\prime 0}π$. These processes are explored by means of the full QCD light-cone sum rule method necessary to determine strong couplings at relevant vertices. Obtained predictions for the masses and widths of the four excited baryons, as well as previous results for $1P$ and $2S$ flavor-antitriplet spin-1/2 particles $Ξ_c^{0}$ are confronted with available experimental data on $Ξ_{c}^{0}$ resonances to fix their quantum numbers. Our comparison demonstrates that the resonances $Ξ_c(2923)^{0}$ and $Ξ_c(2939)^{0}$ can be considered as $1P$ excitations of the spin-$1/2$ flavor-sextet and spin-$3/2$ baryons, respectively. The resonance $Ξ_{c}(2965)^{0}$ may be interpreted as the excited $2S$ state of either spin-$% 1/2$ flavor-sextet or antitriplet baryon.

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Vector resonance $X_1(2900)$ and its structure

The new vector resonance $X_1(2900)$ observed recently by LHCb in the $ D^{-}K^{+}$ invariant mass distribution in the decay $B^{+} \to D^{+}D^{-}K^{+}$ is studied to uncover internal structure of this state, and calculate its physical parameters. In the present paper, the resonance $ X_1(2900)$ is modeled as an exotic vector state, $ J^P=1^- $, built of the light diquark $u^{T}Cγ_5d$ and heavy antidiquark $\overline{c} γ_μγ_5C\overline{s}^{T}$. The mass and current coupling of $ X_1(2900)$ are computed using the QCD two-point sum rule approach by taking into account various vacuum condensates up to dimension $10$. The width of the resonance $X_1(2900)$ is saturated by two decay channels $X_1 \to D^{-}K^{+}$ and $X_1 \to \overline{D}^{0}K^{0}$. The strong couplings $g_1$ and $g_2$ corresponding to the vertices $X_1D^{-}K^{+}$ and $X_1\overline{D} ^{0}K^{0}$ are evaluated in the context of the QCD light-cone sum rule method and technical tools of the soft-meson approximation. Results for the mass of the resonance $X_1(2900)$ $m=(2890~\pm 122)~\mathrm{MeV}$, and for its full width $Γ_{\mathrm{full}}=(93\pm 13)~\mathrm{MeV}$ are smaller than their experimental values reported by the LHCb collaboration. Nevertheless, by taking into account theoretical and experimental errors of investigations, interpretation of the state $X_1(2900)$ as the vector tetraquark does not contradict to the LHCb data. We also point out that analysis of the invariant mass distribution $D^{+}K^{+}$ in the same decay $ B^{+} \to D^{+}D^{-}K^{+}$ may reveal doubly charged four-quark structures $ [uc][\overline{s}\overline{d}]$.

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Investigation of $P_{cs}(4459)^0$ pentaquark via its strong decay to $ΛJ/Ψ$

Recently the observation of a new pentaquark state, the hidden-charmed strange $P_{cs}(4459)^0$, was reported by the LHCb Collaboration. The spin-parity quantum numbers of this state were not determined as a result of insufficient statistics. To shed light on its quantum numbers, we investigate its decay, $P_{cs}(4459)^0 \rightarrow J/ψΛ$, the mode that this state has been observed, within the QCD sum rule framework. We obtain the width of this decay assigning the spin-parity quantum numbers of $P_{cs}(4459)^0$ state as $J^P=\frac{1}{2}^-$ and its substructure as diquark-diquark-antiquark. To this end, we first calculate the strong coupling constants defining the considered decay and then use them in the width calculations. The obtained width is consistent with the experimental observation, confirming the quantum numbers $J^P=\frac{1}{2}^-$ and compact pentaquark nature for $P_{cs}(4459)^0$ state.

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Properties of $P_c(4312)$ pentaquark and its bottom partner

We present an analysis of the newly observed pentaquark $P_c(4312)^+$ to shed light on its quantum numbers. To do that, the QCD sum rule approach is used. The measured mass of this particle is close to $Σ_c^{++}\bar{D}^-$ threshold and has a small width, which supports the possibility of its being a molecular state. We consider an interpolating current in a molecular form and analyze both the positive and negative parity states with spin-$\frac{1}{2}$. We also consider the bottom counterpart of the state with similar molecular form. Our mass result for the charm pentaquark state supports that, the quantum numbers of the observed state are consistent with $J^P=\frac{1}{2}^{-}$.

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Semileptonic and nonleptonic decays of the axial-vector tetraquark $T_{bb;\overline{u} \overline{d}}^{-}$

The semileptonic and nonleptonic decays of the double-beauty axial-vector tetraquark $T_{bb;\overline{u} \overline{d}}^{-}$ to a state $\widetilde{T}_{bc; \overline{u}\overline{d}}^{0}$ (hereafter $T_{bb}^{-}$ and $\widetilde{T} _{bc}^{0}$, respectively) are investigated in the context of the QCD sum rule method. The final-state tetraquark $\widetilde{T}_{bc}^{0}$ is treated as an axial-vector particle built of a heavy axial-vector diquark $ b^{T}γ_{μ}Cc$ and light scalar antidiquark $\overline{u}Cγ_{5} \overline{d}^{T}$. Its spectroscopic parameters are calculated using the two-points sum rules by taking into account contributions of quark, gluon and mixed condensates up to dimension $10$. We study the dominant semileptonic $T_{bb}^{-} \to \widetilde{T}_{bc}^{0}l\overline{ν}_{l}$ and nonleptonic decays $T_{bb}^{-} \to \widetilde{T}_{bc}^{0}M$, where $M$ is one of the pseudoscalar mesons $π^{-}, K^{-}, D^{-}$ and $D_s^{-}$. The partial widths of these processes are computed in terms of weak form factors $G_{i}(q^2),\ i=1,2,3,4$, extracted by employing the QCD three-point sum rule approach. Predictions obtained for partial widths of considered decays are used to improve accuracy of theoretical predictions for full width and lifetime of the tetraquark $T_{bb}^{-}$, which are important for experimental exploration of this exotic meson.

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Determination of the possible quantum numbers for the newly observed $Ξ_b(6227)^0$ state

The LHCb Collaboration recently reported the observation of a new excited bottom baryon $Ξ_b(6227)^0$ and announced an improvement in the measurements related to the previously observed $Ξ_b(6227)^-$ state. We conduct an analysis for $Ξ_b(6227)^0$ state considering it as isospin partner of the $Ξ_b(6227)^-$ resonance and possibly $1P$ or $2S$ excited state with spin $J=\frac{3}{2}$. The corresponding masses for both possibilities have consistent results with the experimental data, indicating that only with the mass sum rules, one can not make exact decision on the nature and quantum numbers of this state. To go further, the decays of these possible excited states to $Ξ_b^- π^+$ final state are also considered and the relevant strong coupling constants are extracted from the light cone sum rules. The obtained decay width values support the possibility of $Ξ_b(6227)^0$ to be the $1P$ excited state of $Ξ_b(5945)^0$ baryon.

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The newly observed $ Z_{cs}(3985)^- $ state: in vacuum and a dense medium

We report on some properties of the newly observed charged hidden-charmed open strange $ Z_{cs}(3985)^- $ state by BESIII Collaboration. Assigning the quantum numbers $ J^{P} = 1^{+}$ and the quark composition $ c \bar c s\bar u $ and considering it as the strange partner of the famous $ Z_c(3900) $ state, we estimate the mass of the $ Z_{cs}(3985)^- $ resonance in vacuum and compare it with the experimental data. We also investigate its mass, current coupling and vector-self energy in a medium with finite density. Our result on the mass in vacuum agrees well with the experimental data. We estimate the mass and current coupling of the b-partner of this state, $ Z_{bs}$, in the vacuum as well. For its mass we get $ m_{Z_{bs}}= 10732^{+97}_{-46}~\mbox{MeV}$, which may be checked via other nonperturbative approaches as well as future experiments. We present the dependence of the spectroscopic parameters of $ Z_{cs}(3985)^- $ state on density and observe that these parameters are linearly changed with increasing in the density.

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Strong Coupling Constants of the Doubly Heavy Spin-1/2 Baryons with Light Pseudoscalar Mesons

The strong coupling constants of hadronic multiplets are fundamental parameters which carry information of the strong interactions among participating particles. These parameters can help us construct the hadron-hadron strong potential and gain information about the structure of the involved hadrons. Motivated by the recent observation of the doubly charmed $Ξ_{cc}$ state by LHCb, we determine the strong coupling constants among the doubly heavy spin-1/2 baryons, $ Ξ^{(\prime)}_{QQ^\prime }$, $ Ω^{(\prime)}_{QQ^\prime}$ and light pseudoscalar mesons, $ π$, $ K $, $η$ and $ η^\prime $ within the framework of the light cone QCD sum rules. The obtained results may help experimental groups in analysis of the related data at hadron colliders.

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Strong interaction of doubly heavy spin-3/2 baryons with light vector mesons

We calculate the strong coupling constants among the doubly heavy spin-$ \frac{3}{2} $ baryons $Ξ^*_{QQ}$ and $Ω^*_{QQ}$, with $ Q $ and $ Q' $ being $ c$ or $ b $ quark, with light vector meson by means of the light-cone QCD sum rules. The matrix elements defining these vertices are described by four coupling constants $ g_1$, $ g_2$, $ g_3$, and $ g_4 $. The unwanted pollution coming from the doubly heavy spin-$ \frac{1}{2} $ baryons are removed by a special ordering of Dirac matrices and selection of appropriate Lorentz structures. The strong coupling constants are basic parameters that carry information on the nature of the strong interaction among hadronic multiplets. Investigation of these parameters may help physicists in the construction of the strong potentials among the doubly heavy baryons and light vector mesons. The values obtained for the strong coupling constants may also help experimental groups in analyses of the data produced at various hadron colliders.

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Modifications on parameters of $Z(4430)$ in a dense medium

The charmonium-like resonance $ Z_c(3900) $ and its excited state $ Z(4430) $ are among the particles that are serious candidates for double heavy tetraquarks. Calculations of different parameters associated with these states both in the vacuum and the medium with finite density are of great importance. Such investigations help us clarify their nature, internal quark-gluon organization and quantum numbers. In this accordance, we extend our previous analyses on the ground state $ Z_c(3900) $ to investigate the medium modifications on different parameters of the excited $ Z(4430) $ state. In particular, we calculate the mass, vector self-energy and current coupling of $ Z(4430) $ in terms of density, up to a density comparable to the density of the cores of massive neutron stars. The obtained results may help experimental groups aiming to study the behavior of exotic states at higher densities.

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A family of double-beauty tetraquarks: Axial-vector state $T_{bb;\bar{u}\bar{s}}^{-}$

The spectroscopic parameters and decay channels of the axial-vector tetraquark $T_{bb;\overline{u}\overline{s}}^{-}$ (in what follows, $T_{b: \overline{s}}^{\mathrm{AV}}$) are explored using the quantum chromodynamics (QCD) sum rule method. The mass and coupling of this state are calculated using two-point sum rules by taking into account various vacuum condensates, up to 10 dimensions. Our prediction for the mass of this state $m=(10215\pm 250)~ \mathrm{MeV}$ confirms that it is stable with respect to strong and electromagnetic decays and can dissociate to conventional mesons only via weak transformations. We investigate the dominant semileptonic $T_{b:\overline{s} }^{\mathrm{AV}} \to \mathcal{Z}_{b:\overline{s}}^{0}l\overlineν_l$ and nonleptonic $T_{b:\overline{s}}^{\mathrm{AV}} \to \mathcal{Z}_{b:\overline{s} }^{0}M$ decays of $T_{b:\overline{s}}^{\mathrm{AV}}$. In these processes, $ \mathcal{Z}_{b:\overline{s}}^{0}$ is a scalar tetraquark $[bc][\overline{u} \overline{s}]$ built of a color-triplet diquark and an antidiquark, whereas $M$ is one of the vector mesons $ρ^{-}$, $K^{\ast}(892)$, $D^{\ast }(2010)^{-}$, and $D_{s}^{\ast -}$. To calculate the partial widths of these decays, we use the QCD three-point sum rule approach and evaluate the weak transition form factors $G_{i}$ $(i=0,1,2,3)$, which govern these processes. The full width $Γ_{\mathrm{full}} =(12.9\pm 2.1)\times 10^{-8}~\mathrm{MeV}$ and the mean lifetime $ τ=5.1_{-0.71}^{+0.99}~\mathrm{fs}$ of the tetraquark $T_{b:\overline{s}}^{ \mathrm{AV}}$ are computed using the aforementioned weak decays. The obtained information about the parameters of $T_{b:\overline{s}}^{\mathrm{AV}}$ and $ \mathcal{Z}_{b:\overline{s}}^{0}$ is useful for experimental investigations of these double-heavy exotic mesons.

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Effects of vector leptoquarks on $ Λ_b \rightarrow Λ_c~\ell ~ \overlineν_\ell$ decay

Experimental data on $ R(D^{(*)}) $, $ R(K^{(*)}) $ and $ R(J/ψ) $, provided by different collaborations, show sizable deviations from the SM predictions. To describe these anomalies many new physics scenarios have been proposed. One of them is leptoquark model with introducing the vector and scalar leptoquarks coupling simultaneously to the quarks and leptons. To look for similar possible anomalies in baryonic sector, we investigate the effects of a vector leptoquark $U_3 (3,3, \frac{2}{3})$ on various physical quantities related to the tree-level $ Λ_b \rightarrow Λ_c \ell ~ \overlineν_\ell$ decays ($ \ell=μ, ~τ$), which proceed via $ b \rightarrow c~\ell ~ \overlineν_\ell$ transitions at quark level. We calculate the differential branching ratio, forward-backward asymmetry and longitudinal polarizations of lepton and $Λ_{c}$ baryon at $ μ$ and $ τ$ lepton channels in leptoquark model and compare their behavior with respect to $ q^2 $ with the predictions of the standard model (SM). In the calculations we use the form factors calculated in full QCD as the main inputs and take into account all the errors coming from the form factors and model parameters. It is observed that ........

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Strong Coupling Constants of the Doubly Heavy $ Ξ_{QQ} $ Baryons with $ π$ Meson

The doubly charmed $Ξ_{cc}^{++} (ccu)$ state is the only listed baryon in PDG, which was discovered in the experiment. The LHCb collaboration gets closer to discovering the second doubly charmed baryon $Ξ_{cc}^{+} (ccd)$, hence the investigation of the doubly charmed/bottom baryons from many aspects is of great importance that may help us not only get valuable knowledge on the nature of the newly discovered states, but also in the search for other members of the doubly heavy baryons predicted by the quark model. In this context, we investigate the strong coupling constants among the $Ξ_{cc}^{+(+)}$ baryons and $π^{0(\pm)}$ mesons by means of light cone QCD sum rule. Using the general forms of the interpolating currents of the $Ξ_{cc}^{+(+)}$ baryons and the distribution amplitudes (DAs) of the $π$ meson, we extract the values of the coupling constants $g_{Ξ_{cc} Ξ_{cc} π}$. We extend our analyses to calculate the strong coupling constants among the b-partner baryons with $π$ mesons, as well, and extract the values of the strong couplings $g_{Ξ_{bb} Ξ_{bb} π}$. It is observed that the values of the couplings under study in bottom channels are about 4 times greater than those of the charmed channels. The results of this study may help experimental groups in the analyses of the data related to the strong coupling constants among the hadronic multiplets.

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New $Λ_b(6072)^0$ state as a $2S$ bottom baryon

As a result of continuous developments, the recent experimental searches lead to the observations of new particles at different hadronic channels. Among these hadrons are the excited states of the heavy baryons containing single bottom or charmed quark in their valance quark content. The recently observed $Λ_b(6072)^0$ state is one of these baryons and possibly $2S$ radial excitation of the $Λ_b$ state. Considering this information from the experiment, we conduct a QCD sum rule analysis on this state and calculate its mass and current coupling constant considering it as a $2S$ radially excited $Λ_b$ resonance. For completeness, in the analyses, we also compute the mass and current coupling constant for the ground state $Λ_b^0$ and its first orbital excitation. We also consider the $Λ_c^+$ counterpart of each state and attain their mass, as well. The obtained results are consistent with the experimental data as well as existing theoretical predictions.

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Nucleon resonances with spin $\frac{3}{2}$ and isospin $\frac{1}{2}$

Investigation of the nucleon's excited states has always become an important research topic because of the rich information they provide. Since their first observation, dating back about 70 years, the investigation of their various parameters contributed both to the development of the quark model and better understanding of the QCD as the theory of strong interaction. Their investigation still has importance. The researches conducted on the nucleon excited states are helpful to probe missing resonances predicted by the quark model but not observed yet. With this motivation, we study the low lying nucleon resonance with $I(J^P)=\frac{1}{2}(\frac{3}{2}^{-})$ and its corresponding orbital and radial excitations with $I(J^P)=\frac{1}{2}(\frac{3}{2}^+)$ and $I(J^P)=\frac{1}{2}(\frac{3}{2}^-)$, respectively. Using the QCD sum rule method, we calculate the masses and pole residues of these states. The obtained mass results are consistent with the mass ranges presented in PDG for the resonances $N^*(1520)(3/2^-)$, $N^*(1700)(3/2^-)$, and $N^*(1720)(3/2^+)$. The results of masses and residues of these states may be used as input parameters to calculate various quantities related to their electromagnetic, weak and strong interactions with other particles with the aim of getting more information on their nature and structure.

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Stable scalar tetraquark $T_{bb;\bar{u}\bar{d}}^{-}$

The mass and coupling of the scalar tetraquark $T_{bb;\overline{u}\overline{d }}^{-}$ (hereafter $T_{b:\overline{d}}^{-} $) are calculated in the context of the QCD two-point sum rule method. In computations we take into account effects of various quark, gluon and mixed condensates up to dimension ten. The result obtained for the mass of this state $m=(10135\pm 240)~\mathrm{MeV} $ demonstrates that it is stable against the strong and electromagnetic decays. We also explore the dominant semileptonic $T_{b:\overline{d}}^{-} \to \widetilde{Z}_{bc;\bar{u}\bar{d}}^{0}l\overline{ν}_{l}$ and nonleptonic decays $T_{b:\overline{d}}^{-} \to \widetilde{Z}_{bc;\bar{u}\bar{ d}}^{0}M$, where $\widetilde{Z}_{bc;\bar{u}\bar{d}}^{0}$ is the scalar tetraquark composed of color-sextet diquark and antidiquark, and $M$ is one of the final-state pseudoscalar mesons $π^{-}, K^{-}, D^{-}$ and $D_s^{-}$ , respectively. The partial widths of these processes are calculated in terms of the weak form factors $G_{1(2)}(q^2)$, which are determined from the QCD three-point sum rules. Predictions for the mass, full width $Γ_{\mathrm{full}} =(10.88\pm 1.88)\times 10^{-10}~\mathrm{MeV}$, and mean lifetime $τ=0.61_{-0.09}^{+0.13}~\mathrm{ps}$ of the $T_{b:\overline{d} }^{-}$ obtained in the present work can be used in theoretical and experimental studies of this exotic state.

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