arXiv subjects

Y. Sarac

Publications and source records attributed to Y. Sarac.

At least 37 records · Page 2Linked to original sources

arXiv2020

$Λ_b(6146)^0$ state newly observed by LHCb

We study the bottom $Λ_b(6146)^0$ baryon, newly discovered by the LHCb Collaboration. By adopting an interpolating current of $(L_ρ, L_λ)=(0,2)$ type and $D$-wave nature with spin-parity quantum numbers $J^P=\frac{3}{2}^+$ for this heavy bottom baryon, we calculate its mass and residue. Using these spectroscopic parameters, we also investigate its dominant decays $Λ_b(6146)^0\rightarrowΣ_bπ$ and $Λ_b(6146)^0\rightarrowΣ^*_bπ$ and estimate the width of $Λ_b(6146)^0$ obtained via these channels. The obtained mass, $m_{Λ_b}=(6144\pm 68)$~MeV is in accord nicely with the experimental data. The width obtained via the dominant channels is also consistent with the experimental data of LHCb collaboration. We calculate the spectroscopic parameters and the same decay channels for the $c$-partner of $Λ_b(6146)^0$ state, namely $Λ_c(2860)^+$, as well. We compare the obtained results with the existing theoretical predictions as well as experimental data. The results indicate that the state $Λ_b(6146)^0$ and its charmed-partner $Λ_c(2860)^+$ can be considered as $1D$-wave baryons with $J^P=\frac{3}{2}^+$.

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arXiv2019

Lepton flavor universality violation in semileptonic tree level weak transitions

The recent deviations of the experimental data on some parameters of the tree-level semileptonic $B$ and $B_c$ mesons decays from the standard model (SM) predictions indicate considerable violations of the lepton flavor universality, and as a result possible new physics (NP) effects. To better understand the possible NP effects it is necessary to study deeply the physical quantities defining these decays from many aspects. The calculations of the physical quantities require the determinations of the hadronic form factors entering the matrix elements of the considered transitions as the main inputs. We calculate the form factors governing the tree-level $B_c\rightarrow J/ψl ν$ and $B_c \rightarrow η_c l ν$ transitions within the QCD sum rules method. The obtained form factors are used in the calculations of the branching ratios ($BR$s) of the $B_c \rightarrow J/ψl ν$ and $B_c \rightarrow η_cl ν$ transitions as well as $R(J/ψ)$ and $R(η_c)$. Our result on $R(J/ψ)$ supports the present tension between the SM theory prediction and the experimental data. Our result on $R(η_c)$ can be checked in future experiments.

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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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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

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

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

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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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

Analysis of $P_c^+(4380)$ and $P_c^+(4450)$ as pentaquark states in the molecular picture with QCD sum rules

To better understand the nature and internal structure of the exotic states discovered by many collaborations, more information on their electromagnetic properties and their strong and weak interactions with other hadrons is needed. The residue or current coupling constant of these states together with their mass are the main inputs in determinations of such properties. We perform QCD sum rules analyses on the hidden-charm pentaquark states with spin-parities $ J^{P}= \frac{3}{2}^{\pm}$ and $ J^{P}= \frac{5}{2}^{\pm}$ to calculate their residue and mass. In the calculations, we adopt a molecular picture for $ J^{P}= \frac{3}{2}^{\pm}$ states and a mixed current in a molecular form for $ J^{P}= \frac{5}{2}^{\pm}$. Our analyses show that the $P_c^+(4380)$ and $P_c^+(4450)$, observed by LHCb Collaboration, can be considered as hidden-charm pentaquark states with $ J^{P}= \frac{3}{2}^{-}$ and $ J^{P}= \frac{5}{2}^{+}$, respectively.

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arXiv2016

On the strong coupling $N^{()}N^{()}π$

We study the strong vertices $N^*Nπ$, $N^*N^*π$ and $NNπ$ in QCD, where $N^*$ denotes the negative parity $N (1535)$ state. We use the most general form of the interpolating currents to calculate the corresponding strong coupling constants. It is obtained that the coupling associated to $N^*Nπ$ vertex is strongly suppressed compared to those related to two other vertices. The strong coupling corresponding to $N^*N^*π$ is obtained to be roughly half of that of $NNπ$ vertex. We compare the obtained results on $N^*Nπ$ and $NNπ$ vertices with the existing predictions of other theoretical studies as well as those extracted from the experimental data.

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arXiv2015

Strong $Σ_bNB$ and $Σ_cND$ coupling constants in QCD

We study the strong interactions among the heavy bottom spin--1/2 $Σ_b$ baryon, nucleon and $B$ meson as well as the heavy charmed spin--1/2 $Σ_c$ baryon, nucleon and $D$ meson in the context of QCD sum rules. We calculate the corresponding strong coupling form factors defining these vertices by using a three point correlation function. We obtain the numerical values of the corresponding strong coupling constants via the most prominent structure entering the calculations.

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arXiv2015

Strong couplings of negative and positive parity nucleons to the heavy baryons and mesons

The strong coupling form factors related to the strong vertices of the positive and negative parity nucleons with the heavy $Λ_{b[c]}[Σ_{b[c]}]$ baryons and heavy $B^*[D^*]$ vector mesons are calculated using a three-point correlation function. Using the values of the form factors at $Q^2=-m^2_{meson}$ we compute the strong coupling constants among the participating particles.

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arXiv2014

The strong $Λ_bNB$ and $Λ_cND$ vertices

We investigate the strong vertices among $Λ_b$, nucleon and $B$ meson as well as $Λ_c$, nucleon and $D$ meson in QCD. In particular, we calculate the strong coupling constants $g_{Λ_bNB}$ and $g_{Λ_cND}$ for different Dirac structures entered the calculations. In the case of $Λ_cND$ vertex, the result is compared with the only existing prediction obtained at $Q^2=0$.

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arXiv2014

Analysis of the strong $D_{2}^{}(2460)^{0}\rightarrow D^+ π^- $ and $D_{s2}^{}(2573)^{+}\rightarrow D^{+} K^{0}$ transitions via QCD sum rules

The strong $D_{2}^{*}(2460)^{0}\rightarrow D^+ π^- $ and $D_{s2}^{*}(2573)^{+}\rightarrow D^{+} K^{0}$ transitions are analyzed via three point QCD sum rules. First, we calculate the corresponding strong coupling constants $g_{D_2^*Dπ}$ and $g_{D_{s2}^*DK}$. Then, we use them to calculate the corresponding decay widths and branching ratios. Making use of the existing experimental data on the ratio of the decay width in the pseudoscaler $D$ channel to that of the vector $D^*$ channel, finally, we estimate the decay width and branching ratio of the strong $D_2^*(2460)^0 \rightarrow D^*(2010)^+π^-$ transition.

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arXiv2013

Investigation of the $B_c\rightarrow χ_{c2} l \barν $ transition via QCD sum rules

We calculate the transition form factors of the semileptonic $B_c\rightarrow χ_{c2} l \barν $ in the framework of QCD sum rules taking into account the two-gluon condensate corrections. Using the obtained results of form factors we estimate the decay widths and branching ratios related to this transition at all lepton channels. A comparison of the obtained results with the predictions of other non-perturbative approaches are also made. The orders of branching ratios for different lepton channels indicate that the $B_c\rightarrow χ_{c2} l \barν $ transition can be studied at LHC using the collected or future data.

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arXiv2011

Semileptonic transition of $Σ_{b}$ to $Σ$ in Light Cone QCD Sum Rules

We use distribution amplitudes of the light $Σ$ baryon and the most general form of the interpolating current for heavy $Σ_b$ baryon to investigate the semileptonic $Σ_b\rightarrow Σl^+l^-$ transition in light cone QCD sum rules. We calculate all twelve form factors responsible for this transition and use them to evaluate the branching ratio of the considered channel. The order of branching fraction shows that this channel can be detected at LHC.

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arXiv2011

Light cone QCD sum rules study of the semileptonic heavy $Ξ_{Q}$ and $Ξ'_{Q}$ transitions to $Ξ$ and $Σ$ baryons

The semileptonic decays of heavy spin--1/2, $Ξ_{b(c)}$ and $Ξ'_{b(c)}$ baryons to the light spin-- 1/2, $Ξ$ and $Σ$ baryons are investigated in the framework of the light cone QCD sum rules. In particular, using the most general form of the interpolating currents for the heavy baryons as well as the distribution amplitudes of the $Ξ$ and $Σ$ baryons, we calculate all form factors entering the matrix elements of the corresponding effective Hamiltonians in full QCD. Having calculated the responsible form factors, we evaluate the decay rates and branching fractions of the related transitions.

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