Reanalyzing Pentaquark Θ+(1540) in Framework of QCD Sum Rules Approach with Direct Instantons

In this article, we study the pentaquark state Θ⁺(1540) with a (scalar) diquark-(pseudoscalar) diquark-antiquark type interpolating current in the framework of the QCD sum rules approach by including the contributions from the direct instantons. The numerical results indicate that the contributions from the direct instantons are very small and can be safely neglected.     

Calculation of the pentaquark width using QCD sum rules

The pentaquark width Γ_? has been calculated using the QCD sum rules. The estimate shows that the width does not exceed 1 MeV. The main conclusion is that the sum rules indeed predict a narrow width of the pentaquark ?⁺, and the decay width is suppressed both parametrically and numerically.     

Pentaquarks: Facts and puzzles

On the occasion of the celebration of the 70th birthday of Prof. Yu.A. Simonov, we contribute a brief review of the status of exotic baryons, which are most likely pentaquark states. We summarize the experimental status of exotic baryons, discuss the baryon antidecuplet to which exotic baryons possibly belong, and review theoretical expectations for the masses and widths of recently discovered Θ and Ξ_3/2 baryons which have come from studies of QCD sum rules, lattice QCD, and quark models. We also pay special attention to the dynamical calculation of pentaquark masses in a framework of the QCD string approach originally elaborated by Simonov for baryons and using the Jaffe-Wilczek \([ud]^2 \bar q\) approximation for the pentaquark states.     

Analysis of the excited Ωc states as the $\tfrac{1}{2}$± pentaquark states with QCD sum rules

We construct both the scalar-diquark-scalar-diquark-antiquark type and axialvector-diquark-axialvector-diquark-antiquark type interpolating currents to study the charmed pentaquark states ${susc}\bar{u}$ with ${J}^{P}={\tfrac{1}{2}}^{\pm }$. We employ the QCD sum rules to investigate the masses and pole residues of the charmed pentaquark states by taking into account the vacuum condensates up to dimension 13 in the operator product expansion. Our calculation results indicate that the scalar-diquark-scalar-diquark-antiquark type and axialvector-diquark-axialvector-diquark-antiquark type charmed pentaquark states ${susc}\bar{u}$ with ${J}^{P}={\tfrac{1}{2}}^{-}$ can be possible candidates of the excited Ω_c states observed in the LHCb collaboration.     

$1/2^ + uudd\bar s$ pentaquark and instanton-induced forces

The mass of the 1/2 ⁺ pentaquark is calculated within the framework of a semirelativistic effective Hamiltonian approach to QCD with instanton-induced forces, using a diquark picture. This approximation allows a correct treatment of the confinement, assumed here to be a Y-junction. With the [ud] diquark mass fitted on the -baryon, the ground-state pentaquark is found around 2.2 GeV.Received: 28 April 2004, Revised: 11 May 2004, Published online: 19 October 2004PACS: 12.39.Pn Potential models - 12.39.Ki Relativistic quark model - 14.20.-c Baryons (including antiparticles)C. Semay: FNRS Research Associate;     

Pentaquarks uudds with one color sextet diquark

The masses of pentaquarks uudds are calculated within the framework of a semirelativistic effective QCD Hamiltonian using a diquark picture. This approximation allows a correct treatment of the confinement, assumed here to be similar to a Y junction. With only color antitriplet diquarks, the mass of the pentaquark candidate Theta with positive parity is found around 2.2 GeV. It is shown that, if a color sextet diquark is present, the lowest uudds pentaquark is characterized by a much smaller mass with a negative parity. A mass below 1.7 GeV is computed if the masses of the color antitriplet and color sextet diquarks are taken similar.     

Revisiting hidden-charm pentaquarks from QCD sum rules

We revisit hidden-charm pentaquark states P_c(4380) and P_c(4450) using the method of QCD sum rules by requiring the pole contribution to be greater than or equal to 30% in order to better that the one-pole parametrization is valid. We find two mixing currents, and our results suggest that P_c(4380) and P_c(4450) can be identified as hiddencharm pentaquark states having J~P= 3/2~-and 5/2~+, respectively. However, there still exist other possible spin-parity assignments, such as J~P = 3/2~+ and J~P = 5/2~-, which must be clarified in further theoretical and experimental studies.     

Wandering in color-space why is the life of pentaquark so long?

The problem of the long life time of the pentaquark Θ⁺ is investigated on the basis of the color molecular dynamics simulation. We find that it takes a long time (typically of 50–100 fm/c) for the initial pentaquark state to rearrange its color and spatial positions to decay into the nucleon+kaon final state. Structure of the potential surface in the color and position spaces also supports this picture. Pentaquark wanders on the potential surface to find a narrow channel to decay.     

Pentaquarks in the Jaffe-Wilczek approximation

The masses of \(uudd\bar s,{\text{ }}uudd\bar d\), and \(uuss\bar d\) pentaquarks are evaluated in a framework of both the effective Hamiltonian approach to QCD and the spinless Salpeter equation using the Jaffe-Wilczek diquark approximation and the string interaction for the diquark-diquark-antiquark system. The pentaquark masses are found to be in the region above 2 GeV. That indicates that the Goldstone boson exchange effects may play an important role in the light pentaquarks. The same calculations yield the mass of \([ud]^2 \bar c\) pentaquark ～3250 MeV and \([ud]^2 \bar b\) pentaquark ～6509 MeV.     

Quarks,diquarks, tetraquarks,and pentaquarks

A particle about 50% more massive than a proton, with positive charge, positive strangeness and positive baryon number, has been claimed in several experiments. Such a particle cannot be made from three quarks; its minimal configuration requires four quarks and an antiquark and it became known as a ‘pentaquark’. This article summarizes the evidence and concentrates on the theoretical interest that it has excited into the nature of correlations among quarks and antiquarks in the strong interaction limit of QCD.     

Fragmentation Production of Θ0c(uuddc-) and Θ+b(uuddb-) Pentaquarks in the Diquark Model

Heavy hadrons have been the focus of attention because of their worthwhile properties. So far the fragmentation function (FF) and total fragmentation probability (F.P) for heavy baryons and mesons have been calculated in quark model and diquark model in leading order of perturbative QCD. After the discovery of pentaquarks, their fragmentation probabilities were estimated based on the known measurementsof c or b quarks into mesons and baryons. In this note we calculate the direct fragmentation function of \( \overline{c}\to {\varTheta}_c^0\left( uudd\overline{c}\right) \) and \( \overline{b}\to {\varTheta}_b^{+}\left( uudd\overline{b}\right) \) processes in leading order of perturbative QCD, employing the diquark model with considerable precision. Consistent with such a process we set up the kinematics of the fragmentation of a heavy antiquark into a pentaquark such that the effect of the Fermi motion of the constituents is ignored. We show that using the diquark model for studying pentaquark can provide reasonably good theoretical results. The findings of this study accord with those in the previous studies.

     

五夸克态Θ的手征夸克模型研究(英文)

在手征夸克模型的框架下, 研究了五夸克态 uudd的结构. 分别考虑了 Jπ=(1/2)-和Jπ=(1/2)+的各四个组态. 结果表明对于不同的模型, 不论 Jπ=(1/2)-和 Jπ=(1/2)+, T=0的态的能量总是最低的. 但是最低态的能量的理论计算值仍比Θ质量的实验值高250—300 MeV.     

Anticharmed pentaquark from B decays

We explore the possibility of observing the anticharmed pentaquark state from the theta(c)npi(+) decay of B mesons produced in B-factory experiments. We first show that the observed branching ratio of the B(+) to lambda(-)(c)p pi(+), as well as its open histograms, can be remarkably well explained by assuming that the decay proceeds first through the pi(+) D(0) (or D(*0)) decay, and then through the subsequent decay of the virtual D(0) or D(*0) mesons to lambda(-)(c)p. We then note that the theta(c)can be similarly produced when the virtual D(0) or D(*0) decay into an antinucleon and a theta(c). Combining the present theoretical estimates for the ratio g(DNlambda(c))/g(DNtheta(c)) approximately 13 and g(D*Ntheta(c)) approximately 1/3g(DNtheta(c)), we find that the anticharmed pentaquark theta(c), which was predicted to be bound by several model calculations, can be produced via B(+)--> theta(c)npi(+), and be observed from the B-factory experiments through the weak decay of theta(c)--> pK(+) pi(-) pi(-).     

Analysis of Y(4660) and Related Bound States with QCD Sum Rules

In this article, we take the vector charmonium-like state Y(4660) as a ψ'f₀(980) bound state (irrespective of the hadro-charmonium and the molecular state) tentatively, and study its mass using the QCD sum rules. The numerical value M_Y=4.71 ± 0.26 GeV is consistent with the experimental data. Considering the SU(3) symmetry of the light flavor quarks and the heavy quark symmetry, we also study the bound states ψ' σ (400-1200), Υ''f₀(980), and Υ'' σ(400-1200) with the QCD sum rules, and make reasonable predictions for their masses.     

B0-B(-)0 mixing beyond factorization in QCD sum rules

We present a calculation of the B0-B(-)0 mixing matrix element in the framework of QCD sum rules for three-point functions. We compute alpha(s) corrections to a three-point function at the three-loop level in QCD perturbation theory, which allows one to extract the matrix element with next-to-leading order (NLO) accuracy. This calculation is imperative for a consistent evaluation of experimentally measured mixing parameters since the coefficient functions of the effective Hamiltonian for B0-B(-)0 mixing are known at NLO. We find that radiative corrections violate factorization at NLO; this violation is under full control and amounts to 10%. The resulting value of the B parameter is found to be B(B)(m(b))=1+0.1(PT)-0.05(non-PT).     

Magnetic moment of the pentaquark Θ+(1540) as diquark-diquark-antiquark state with QCD sum rules

In this article, we study the magnetic moment of the pentaquark state Θ⁺(1540) as a diquark-diquark-antiquark ( ) state with the QCD sum rules in an external weak electromagnetic field (EFSR) and the light-cone QCD sum rules (LCSR) respectively. The numerical results indicate that the magnetic moment is about for the EFSR and - for the LCSR. As the values obtained from the EFSR are more stable than the corresponding ones from the LCSR, is more reliable. Received: 29 March 2005, Revised: 28 June 2005, Published online: 21 October 2005 PACS: 12.38.Aw, 12.38.Lg, 12.39.Ba, 12.39.-x     

Pentaquarks — An experimental overview

Since the recent observation of a pentaquark $(\Theta ^ + = qqqq\bar q)$ state (see Nakano et al. (LEPS Collaboration), Phys. Rev. Lett. 91 (2003) 012002-1) several positive and negative experimental results have emerged. These results are overviewed, with a trial to find common features among them.     

具有双Y-型结构的Θ+的研究

采用由单胶子交换产生的库仑势加上流管模型给出的双Y-型禁闭势之和的相互作用势,分别计算了正、负宇称态的Θ⁺的质量, 给出负宇称态Θ⁺的质量为1.935GeV, 正宇称态Θ⁺的质量为2.082GeV. 其中较低的负宇称态仍比实验给出的Θ⁺(1540)的共振峰高出近400MeV.     

Exotic baryon states in topological soliton models

The novel observation of an exotic strangeness S=+1 baryon state at 1.54 GeV is to trigger an intensified search for this and other baryons with exotic quantum numbers. This state was predicted long ago in topological soliton models. We use this approach together with the new datum in order to investigate its implications for the baryon spectrum. In particular, we estimate the positions of other pentaquark and septuquark states with exotic and with nonexotic quantum numbers.