We present the spectrum of the lightest pentaquark states of both parities and compare it with the present experimental evidence for these states. We have assumed that the main role for their mass splittings is played by the chromo-magnetic interaction. We have also kept into account the $SU(3)_F$ breaking for their contribution and for the spin orbit term. The resulting pattern is in good agreement with experiment.
We study the stability of the pentaquarks uuddQbar, uudsQbar and udssQbar (Q = c, b, or t) of positive parity in a constituent quark model based on Goldstone boson exchange interaction between quarks. The pentaquark parity is the antiquark parity times that of a quark excited to a p-shell. We show that the Goldstone boson exchange interaction favors these pentaquarks much more than the negative parity ones of the same flavour content but all quarks in the ground state. We find that the nonstrange pentaquarks are stable against strong decays.
The 1/N_c expansion for negative-parity heavy pentaquarks is developed using the formalism introduced for excited baryons in large N_c. Relations are found between the mass splittings of these pentaquarks and those of nonexotic baryons.
With the recent discovery of the $Θ(1540)$ pentaquark, the question of its parity is paramount since this will constrain the correct description of its internal structure. We show that the measurement of the spin singlet and triplet cross sections for the reaction $\vec{p}\vec{p} \to Σ^+ Θ^+$ will unambiguously determine the parity of the $Θ^+$.
The relativistic five-quark equations are found in the framework of the dispersion relation technique. The solutions of these equations using the method based on the extraction of the leading singularities of the amplitudes are obtained. The five-quark amplitudes for the low-lying pentaquarks including the u, d, s- quarks are calculated. The poles of these amplitudes determine the masses of the negative parity pentaquarks with I = 0, 1 and spin 3/2-, 5/2-. The mass of the lowest pentaquark with I = 0 and spin 3/2- is equal to 1514 MeV.
We consider the possibility that the lightest pentaquark is a parity even state, with one unit of orbital angular momentum. Working within the framework of a constituent quark model, we show that dominant spin-flavor interactions render certain parity-even states lighter than any pentaquark with all quarks in the spatial ground state. For such states, we focus on predicting the mass and decays of other members of the same SU(3) flavor multiplet. Specifically, we consider the strangeness -2 cascade pentaquarks, which are relatively immune to mixing. We take into account flavor SU(3) breaking ef…
We present two possibilities to determine the P-parity of the pentaquark $Θ^+$, in a model independent way, via the measurement of polarization observables in $p+p\to Θ^+ +Σ^+$, or $n+p\to Θ^+ +Λ^0$, in the near threshold region. Besides the measurement of the spin correlation coefficient, $A_{xx}=A_{yy}$, (in collisions of transversally polarized nucleons), the coefficient $D_{xx}$ of polarization transfer from the initial proton to the final $ Σ^+(Λ^0)$ hyperon is also unambiguously related to the $Θ^+$ parity.
We study determination of the parity of the pentaquark baryons in two different processes. First, we investigate the Theta^+ production via the vec{p} vec{p} -> Sigma^+ Theta^+ reaction process which was proposed to determine unambiguously the parity of Theta^+. We observe the clear differences in the total cross sections and the spin observable A_{xx}. As for the Xi_5 in the bar{K} N -> K Xi_5 reaction process, the total cross section for the positive parity presents about one hundred times lager than that of the negative one due to the huge destructive interference.
We derive, in model independent way, the spin structure of the matrix element for the reaction of associative $Θ^+$ pentaquark production, $π^{\pm}+D\to Θ^+ +Σ^{\pm}, $ in the threshold region and in collinear kinematics. The expressions for the polarization observables in this reaction are found assuming spin 1/2 and different parities for $Θ^+ .$ We have proved that such reaction can be used for a model independent determination of the P-parity of $Θ^+$ only by measuring the $Θ^+$ polarization. Other polarization observables, such as the dependence of the $Σ^{\pm}$ polarization on the vector…
We test a pentaquark model of the negative parity hyperon Lambda(1405). We use the model where valence four quarks and one antiquark move in a potential relativisticaly and interact with themselves and each other through gluon and NG boson. We calculate mass shift of the system and find that there are two Lambda(1405) with almost degenerate mass: one flavor singlet and one flavor octet. We calclate also sigma-term and scalar form factor of the hyperon and show their usefulness to deduce the number of valence quark in the hypeon.
We discuss model independent methods to measure the $P$-parity of the $Θ^+$-pentaquark, in the simplest processes of photoproduction, $γ+N\to \bar{K}+Θ^+$, using definite relations between T-even polarization observables, which depend on the $P$-parity of the $Θ^+$ baryon (with respect to the $NK$ system). One method, which holds for any photon energy and any $K$ meson production angle, is based on the relation between the $Σ_B$ asymmetry (induced by a linearly polarized photon beam, with unpolarized target) and the $D_{nn}$ component of the depolarization tensor (for unpolarized photon beam).…
We construct the complete set of positive parity pentaquarks, which correspond in the quark model to {\bar s} q^{Nc+1} states with one unit of orbital angular momentum L=1. In the large Nc limit they fall into the K=1/2 and K=3/2 irreps (towers) of the contracted SU(4)c symmetry. We derive predictions for the mass spectrum and the axial couplings of these states at leading order in 1/Nc. The strong decay width of the lowest-lying positive parity exotic state is of order O(1/Nc), such that this state is narrow in the large Nc limit. Replacing the antiquark with a heavy antiquark {\bar Q} q^{Nc+…
QCD sum rule is applied to the pentaquark spectroscopy. It is concluded that no positive parity state is seen in low energy region, while there may exist negative parity states at around 1.5 GeV. Choice of interpolating local operators and relation to the lattice calculations are discussed.
Assuming the two diquark structure for the pentaquark state as advocated in the Jaffe-Wilczek model, we study the strong decays of light and heavy parity-even pentaquark states using the light-front quark model in conjunction with the spectator approximation. The narrowness of the Theta width is ascribed to the p-wave configuration of the diquark pair. Taking the Theta width as a benchmark, we estimate the rates of the strong decays Xi_{3/2}-- to Xi- pi-, Sigma- K-, Sigma_{5c}0 to D_s- p, D_{s0}*- p and Xi_{5c}0 to D_s- Sigma+, D_{s0}^{*-} Sigma+ with Sigma_{5c} Xi_{5c} being antisextet charme…
Recently, the 1/Nc expansion has been applied to the study of exotic baryons containing both quarks and antiquarks. We extend this approach to exotic states with mixed symmetric spin-flavor symmetry, which correspond in the quark model to negative parity pentaquarks, and discuss the large Nc predictions for their mass spectrum. The heavy exotics Qbar q^4 transform as 3, 6bar,15 and 15' under flavor SU(3), while the light states include the exotic multiplets 10bar, 27, 35. We give mass relations among these multiplets following from the 1/Nc expansion. In the quark model, the mass splittings be…
We perform a QCD sum rule calculation to determine the mass and the parity of the lowest lying pentaquark state. We include operators up to dimension $d=13$ in the OPE and the direct instanton contributions. We find evidence for a positive parity state. The contribution from operators of dimension $d>5$ is instrumental in determining the parity of the state and achieving the convergence of the sum rule.
In this article, we construct the scalar-diquark-scalar-diquark-antiquark type current to study the ground state triply charmed pentaquark states with the QCD sum rules. We separate the contributions of the negative-parity and positive parity triply charmed pentaquark states explicitly, and take the energy scale formula $μ=\sqrt{M^2_{P}-(3{\mathbb{M}}_c)^2}$ to determine the optimal energy scales of the QCD spectral densities. The predicted pentaquark masses can be confronted to the experimental data in the future.
In a diquark-diquark-antiquark picture of the pentaquark we study the decay $Θ\to K^{+} n$ within the framework of QCD sum rules. After evaluation of the relevant three-point function, we extract the coupling $g_{ΘnK}$ which is directly related to the pentaquark width. Restricting the decay diagrams to those with color exchange between the meson-like and baryon-like clusters reduces the coupling constant by a factor of four. Whereas a small decay width might be possible for a positive parity pentaquark, it seems difficult to explain the measured width for a pentaquark with negative parity.
In a diquark-diquark-antiquark picture of the pentaquark we study the decay $Θ\rightarrow K^{+} n$ within the framework of QCD sum rules. After evaluation of the relevant three-point function, we extract the coupling $g_{ΘnK}$ which is directly related to the pentaquark width. Restricting the decay diagrams to those with color exchange between the meson-like and baryon-like clusters reduces the coupling constant by a factor of four. Whereas a small decay width might be possible for a positive parity pentaquark, it seems difficult to explain the measured width for a pentaquark with negative par…
We have investigated uudd\sbar pentaquarks by employing quark models with the meson exchange and the effective gluon exchange as qq and q\qbar interactions. The system for five quarks is dynamically solved; two quarks are allowed to have a diquark-like qq correlation. It is found that the lowest mass of the pentaquark is about 1947 -- 2144 MeV. There are parameter sets where the mass of the lowest positive-parity state become lower than that of the negative-parity states. Which parity corresponds to the observed peak is still an open question. Relative distance of two quarks with the attractiv…
The stability of strange pentaquarks $uudd\bar s$ is studied in a constituent quark model based on a flavor-spin hyperfine interaction between quarks. With this interaction model, which schematically represents the Goldstone boson exchange interaction between constituent quarks, the lowest lying strange pentaquark is a $p-$shell state with positive parity. The flavor-spin interaction lowers the energy of the lowest $p-$shell state below that of the lowest $s-$shell state, which has negative parity because of the negative parity of the strange antiquark. It is found that the strange pentaquark …
We discuss a possible interpretation for the pentaquark baryon $Θ^+$ which has an exotic quantum number of strangeness $S = +1$. The role of the pion which modifies the structure of single-particle levels of quarks is examined. When the pion field is sufficiently strong, the ground state of five quarks for $Θ^+$ acquires positive parity. If this is the case, an excited state may appear slightly above the ground state with negative parity.
We consider exotic baryons with hidden charm as antiquark-diquark-diquark composite systems. Spin and isospin structure of such exotic states is given and masses are estimated. The data for production of pentaquarks in the reaction $Λ_b\to K^-p J/ψ$ are discussed. We suggest that the narrow peak in $pJ/ψ$ spectra at 4450 MeV is antiquark-diquark-diquark state with negative parity, $5/2^{-}(4450)$, while the broad bump $3/2^{+}(4380)$ is the result of rescatterings in the ($pJ/ψ$)-channel. Positions of other pentaquarks with negative parity are estimated.
A critical look is taken at both positive and null evidence for the $Θ^+$ pentaquark. Potential problems with experiments will be discussed and the question of what conclusion can be drawn from both the positive and the null results is examined. First the question of existence of the $Θ^+$ pentaquark is considered, followed by a discussion of new experiments that are either planned or in progress to answer questions about its mass, width and isospin. Finally, indirect evidence for the parity of the $Θ^+$ is examined, and suggestions for experiments to measure its parity directly are given.
We study a few of the lowest states of the pentaquark $uudc\overline{c}$, of positive and negative parity, in a constituent quark model with an SU(4) flavor-spin hyperfine interaction. For positive parity we introduce space wave functions of appropriate permutation symmetry with one unit of orbital angular momentum in the internal motion of the four-quark subsystem or an orbital excitation between the antiquark and the four quark subsystem which remains in the ground state. We show that the lowest positive parity states $1/2^+, 3/2^+$ are provided by the first alternative and are located below…
In this article, we study the doubly heavy baryon states and pentaquark states with the QCD sum rules by carrying out the operator product expansion up to the vacuum condensates of dimension $7$ and $13$ respectively in a consistent way. In calculations, we separate the contributions of the negative parity and positive parity hadron states unambiguously, and study the masses and pole residues of the doubly heavy baryon states and pentaquark states in details. The present predictions can be confronted to the experimental data in the future.
Recent LHCb experiments have shown us that there are two resonances in the $J/ψp$ channel in the $Λ_b$ decay, whose spin and parity are most probably (3/2$^-$ 5/2$^+$). In this work, we investigate the $I(J^P)=1/2(1/2^-)$, $1/2(3/2^-)$, and $1/2(5/2^-)$ $uudc{\bar c}$ pentaquark states by employing the quark cluster model. It is found that the color-octet isospin-1/2 spin-3/2 $uud$ configuration gives an attraction to such five-quark systems. This configuration together with the color-octet $c{\bar c}$ pair gives structures around the $Σ_c^{(*)}{\bar D}{}^{(*)}$ thresholds: one bound state, tw…
Recent experimental evidence for the Theta^+(1540) has given rise to much theoretical interest in exotic baryons. The Theta^+ is a baryon that has strangeness S=+1, meaning that it contains an anti-strange quark. Thus it cannot be constructed from three quarks, unlike all other known baryons; it needs at least an extra quark-antiquark pair. It is usually modeled as a pentaquark state in the 10 bar representation of flavor SU(3), with flavor content \bar{s}uudd. This thesis considers possible heavy pentaquarks, in which the antiquark is charmed or bottom rather than strange. In the context of t…
In this article, we study the axialvector-diquark-scalar-diquark-antiquark type charmed pentaquark states with $J^P={\frac{3}{2}}^\pm$ with the QCD sum rules by carrying out the operator product expansion up to the vacuum condensates of dimension $13$ in a consistent way. In calculations, we separate the contributions of the negative parity and positive parity pentaquark states unambiguously, and choose three sets input parameters to study the masses and pole residues of the charmed pentaquark states $uuuc\bar{u}$ and $sssc\bar{s}$ in details. Then we estimate the masses of the charmed pentaqu…
We study the spectrum of the isoscalar pentaquark $udsc\overline{c}$, of either positive or negative parity, in a constituent quark model with linear confinement and a flavor-spin hyperfine interaction previously extended to SU(4) and used to describe the spectrum of the $uudc\overline{c}$ pentaquarks observed at LHCb in 2019. For positive parity we make a distinction between the case where one unit of angular momentum is located in the subsystem of four quarks and the case where the angular momentum is located in the relative motion between a ground state four-quark subsystem and the antiquar…
Radiative decays of the spin 1/2 baryonic resonances R with the decay mode R -> KN in case of small energy release are considered. Pentaquark is an example of such resonance. It is shown that in case of positive resonance parity corrections to the soft photon radiation formula are large even at low photon energies > 20 MeV and structure terms contributions may be essential, if R size > 1 fm. This effect is absent in case of negative parity. Particularly, measurements of the gamma spectrum in pentaquark radiative decays may allow us to determine its parity.
We discuss the possibility of determining the parity of the $Θ^+$ baryon from photoproduction $γN\to KΘ^+$ process near threshold. We utilize the conservation laws of parity and angular momentum for the analysis of angular distributions and spin observables near threshold. Since the discussion is in essence a partial wave analysis of the production mechanism the result should be less dependent on the model parameters. Our analysis shows that the angular distribution and photon polarization asymmetry for the process of neutron target are sensitive to the parity of the $Θ^+$, but not for the cas…
We study $IJ^P=0{3/2}^\pm$ and $1{3/2}^\pm$ pentaquark states with $S=+1$ in the QCD sum rule approach. The QCD sum rule for positive parity states and that for negative parity are independently derived. The sum rule suggests that there exist the $0{3/2}^-$ and the $1{3/2}^-$ states. These states may be observed as extremely narrow peaks since they can be much below the $S$-wave threshold and since the only allowed decay channels are $NK$ in $D$-wave, whose centrifugal barriers are so large that the widths are strongly suppressed. The $0{3/2}^-$ state may be assigned to the observed $Θ^+(1540)…
We test a pentaquark model of the negative parity hyperon Lambda(1405). We use a model where valence four quarks and one antiquark move in a potential relativistically and interact with each other and themselves through gluon and NG boson. Fall-apart decay rate of the system is studied and strong model dependence is pointed out.
We make an exhaustive investigation on the pentaquark states $qqqc\bar{c}$ ($q=u, d$ and $s$) and discuss the effect of color structures in a multiquark color flux-tube model. We exhibit a novel picture of the structure and properties of the states $P_c$ and $P_{cs}$ observed by the LHCb Collaboration. We can describe the states as the compact pentaquark states in the model. The spin-parity of the group of $P_c(4312)^+$ and $P_c(4337)^+$ is $\frac{1}{2}^-$ while that of the group of $P_c(4380)^+$, $P_c(4440)^+$ and $P_c(4457)^+$ is $\frac{3}{2}^-$. Their structures are pentagon, diquark, penta…
We investigate the production of the pentaquark $Θ^+$ baryon via the $γn\to K^-Θ^+$ and $γp\to \bar{K}^0 Θ^+$ processes, focusing on the parity of the $Θ^+$. Using the effective Lagrangians, we calculate the total and differential cross sections with the spin of the $Θ^+$ presumed to be 1/2. We employ the coupling constant of the $KNΘ$ vertex determined by assuming its mass and the decay width to be $1540 {\rm MeV}$ and $15 {\rm MeV}$. That of the $K^*NΘ$ is taken to be about a half of the $KNΘ$ coupling constant. We estimate the cutoff parameter by reproducing the total cross section of the $…
It is shown that the decay amplitude for the Jaffe-Wilczek type pentaquarks is not suppressed by chiral symmetry. On the other hand, pentaquarks of positive or negative parity built up of an antiquark and two chirally different diquarks in an $S$-state are stable in the limit of a strictly unbroken chiral symmetry. These states can decay only via the spontaneous breaking of chiral symmetry. However, this breaking is strong because of the sizeable magnitude of the quark condensate. Thus, chiral symmetry cannot be the cause of a tiny decay amplitude, even for pentaquarks which are stable in the …
We investigate the effect of chiral phase transition on the pentaquark $Θ^+$ mass and width at one-loop level of $NΘ^+K$ coupling at finite temperature and density. The behavior of the mass, especially the width in hadronic medium is dominated by the characteristics of chiral symmetry restoration at high temperature and high density. The mass and width shifts of positive-parity $Θ^+$ are much larger than that of negative-parity one, which may be helpful to determine the parity of $Θ^+$ in high energy nuclear collisions.
Spin observables of a binary reaction $1+2\to 3+4$ are discussed at the threshold in general form using P-parity and angular momentum conservation. General formulae for polarization transfer, spin-spin correlation parameters in the initial and final states and induced tensor polarization are derived for arbitrary spins of participating particles. This formalism is worked out in detail for the $NN\to YΘ^+$ reaction. Assuming that the spin of the pentaquark $Θ^+$ takes the values 1/2, 3/2 and 5/2, whereas the spin of the hyperon $Y$ equals 1/2, explicite formulae are obtained for the observables…
The splittings between positive parity pentaquarks containing a single heavy (c,b) antiquark and four light (u,d) quarks are investigated in models having spin-dependent interactions generated by either effective Goldstone boson exchange or effective color magnetic exchange. Model-independent features of these splittings are emphasized. Overlaps to the ``fall-apart'' decay configurations ND, ND* or NB, NB*, relevant to decay couplings for the various 2-body pentaquark decays, are also computed.
We study a pentaquark model of the negative parity hyperon Lambda(1405). We choose a specific quark configuration for trial, and use the perturbative chiral quark model extended to four quarks and one anti-quark system. We calculate a sigma-term and a scalar form factor of the hyperon and demonstrate their usefulness to study the nature of the hyperon.
The newly discovered exotic $Θ$ baryon of mass 1540 MeV (and very small width) truly has a very low mass, if it is a pentaquark system of even parity. A schematic model in which the coherent interaction of $u\bar s$ and $d\bar s$ pairs leads to a very large residual (non-confining) attractive interaction is introduced. This collective vibrational model accounts for the mass and small decay width to the $KN$ channel, but yields a significant coupling to the virtual $K^*N$ channel. The schematic model predicts an attractive $Θ$-nucleon interaction strong enough to bind a $Θ$ particle to a nucleu…
We present a QCD sum rule analysis for the anti-charmed pentaquark state with and without strangeness. While the sum rules for most of the currents are either non-convergent or dominated by the $DN$ continuum, the one for the non-strange pentaquark current composed of two diquarks and an antiquark, is convergent and has a structure consistent with a positive parity pentaquark state after subtracting out the $DN$ continuum contribution. Arguments are presented on the similarity between the result of the present analysis and that based on the constituent quark models, which predict a more stable…
We study the pentaquark $uudd\bar s$ with $J=3/2$ and I=1 ($Θ^{++}$) in the QCD sum rule approach. We derive the QCD sum rules for positive and negative parity states of the pentaquark. The QCD sum rule predicts that there exists $Θ^{++}$ with negative parity and its mass is $1.5\sim1.6$ GeV. The negative parity $Θ^{++}$ can be extremely narrow, since it lies much below the $ΔK$ threshold and the decay into $KN$ state is strongly suppressed due to the $D$-wave centrifugal barrier. Also, the possibility of the existence of the $Θ^{++}$ with positive parity is not excluded. Although it nearly de…
We investigate the production of the newly found pentaquark exotic baryon Xi_5 in the bar{K} N -> K Xi_5 and the bar{K} N -> K* Xi_5 reactions at the tree level. We consider both positive- and negative parities of the Xi_5. The reactions are dominated by the s- and u-channel processes, and the resulting cross sections depend very much on the parity of Xi_5 and on the type of form factor. We have seen that the cross sections for the positive-parity Xi_5 are generally about a hundred times larger than those of the negative-parity one. This large difference in the cross sections will be useful fo…
Using the picture of the flux tube model, we propose that the $Θ_5$ pentaquark as the first candidate of the three-dimensional non-planar hadron with the extremely stable diamond structure. The up and down quarks lie at the corners of the diamond while the anti-strange quark sits in the center. Various un-excited color flux tubes between the five quarks bind them into a stable and narrow color-singlet. Such a configuration allows the lowest state having the negative parity naturally. The decay of the $Θ_5$ pentaquark into the nucleon and kaon requires the breakup of the non-planar diamond conf…
Spin structure of the reaction ${\vec p}{\vec n}\to {\vec Λ^0} {\vec Θ}$ is analysed at the threshold in a model independent way under assumption that the $Θ^+$ is an isosinglet. We found that the sign of the spin-spin correlation parameter $C_{x,x}$ being measured in a double-spin experiment, determines the P-parity of the $Θ^+$ unambiguously. Furthermore we show that the polarization coefficients $K_x^x,K_y^y$ and $K_z^z$ which describe the polarization transfer from polarized beam or target to the final $Λ^0$ and $Θ^+$ are nonzero for a positive parity of the $Θ^+$ and equal zero for a nega…
We demonstrate that a five quark state of positive parity with an internal P-wave structure - usually pictured as a composite of an antiquark and two diquarks in a P-wave state - can couple to nucleons and Goldstone particles in a chirally invariant way. The corresponding decay width is generally not suppressed. A pentaquark of positive or negative parity with an internal S-wave structure, which may be viewed as a composite of an antiquark and two chirally different diquarks in an S-state, does not couple to nucleons and light mesons in the limit of an unbroken chiral symmetry. It is stable in…
We apply the dynamical diquark model to predict the spectrum of hidden-charm pentaquark states in both unflavored and open-strange sectors. Using only Hamiltonian parameters introduced in the tetraquark $S$- and $P$-wave multiplets, the model naturally produces the level spacing supported by the most recent LHCb results for $P_c$ structures. Furthermore, using model inputs obtained from data of hidden-charm, open-strange tetraquarks ($Z_{cs}$), we predict the spectrum of $P_{cs}$ states, including the recently observed $P_{cs}(4459)$. We find all pentaquark candidates observed to date to belon…
I present results of a heavy hadron chiral perturbation theory analysis of the decays and masses of the recently discovered excited charm mesons. The present data on the electromagnetic branching ratios are consistent with heavy quark symmetry predictions and disfavor a molecular interpretation of these states. I also discuss model independent predictions for the strong decays of pentaquarks in the 10-bar representation of SU(3) which can be used to constrain the angular momentum and parity quantum numbers of these states.
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 i…
We study spin 1/2 isoscalar and isovector candidates in both parity channels for the recently discovered Θ^+(1540) pentaquark particle in quenched lattice QCD. Our analysis takes into account all possible uncertainties, such as statistical, finite size and quenching errors when performing the chiral and continuum extrapolations and we have indications that our signal is separated from scattering states. The lowest mass that we find in the I^P=0^- channel is in complete agreement with the experimental value of the Θ^+ mass. On the other hand, the lowest mass state in the opposite parity I^P=0^+…
The recent experimental results of LHCb collaboration suggested the existence of pentaquark states with charmonium. To understand the structure of the states, a dynamical calculation of 5-quark systems with quantum numbers $IJ^P=\frac{1}{2}(\frac{1}{2})^\pm$, $\frac{1}{2}(\frac{3}{2})^\pm$ and $\frac{1}{2}(\frac{5}{2})^\pm$ is performed in the framework of chiral quark model with the help of gaussian expansion method. The results show that the negative parity states can be bound states while all of the positive parity states are the scattering states. The $P_c(4380)$ state is suggested to be t…
A candidate triple strange pentaquark state, $P_{csss}$, is investigated through its strong decay channel $P_{csss} \rightarrow Ω^-J/ψ$. To calculate the relevant strong coupling constants, two possible interpolating currents with spin-parity $J^P=\frac{1}{2}^{-}$ are used. Though the chosen currents for the state under consideration have spin-parity quantum numbers $J^P=\frac{1}{2}^{-}$, they couple to both the positive and negative parity states simultaneously and the corresponding decay widths are obtained for both parities. These widths are obtained as $Γ(P_{csss} \rightarrow J/ψΩ^-)=201.4…
We study $np\to ΛΘ^{+}$ and $np\to Σ^{0}Θ^{+}$ processes for both of the positive and negative parities of the $Θ^{+}$. Employing the effective chiral Lagrangians for the $KNY$ and $K^*NY$ interactions, we calculate differential cross sections as well as total cross sections for the $np\to Σ^0 Θ^+$ and $np\to ΛΘ^+$ reactions. The total cross sections for the positive-parity $Θ^+$ turn out to be approximately ten times larger than those for the negative parity $Θ^+$ in the range of the CM energy $\sqrt{s}_{\rm th}\le \sqrt{s}\le 3.5 {\rm GeV}$. The results are rather sensitive to the mechanism …
The assumption of strong diquark correlations in the QCD spectrum suggests flavor multiplets of hadrons that are degenerate in the chiral limit. Generally it would be unnatural for there to be degeneracy in the hadron spectrum that is not protected by a QCD symmetry. Here we show --for pentaquarks constructed from diquarks-- that these degeneracies can be naturally protected by the full chiral symmetry of QCD. The resulting chiral multiplet structure recovers the ideally-mixed pentaquark mass spectrum of the diquark model, and interestingly, requires that the axial couplings of the pentaquarks…
