Phenomenology of the pentaquark antidecuplet

The penta-quark(5Q) baryon is studied in anisotropic quenched lattice QCD with renormalized anisotropy as/at=4 for a high-precision mass measurement. The standard Wilson action at β = 5.75 and the O(a) improved Wilson quark action with κ=0.1210(0.0010)0.1240 are employed on a 12 3 ×96 lattice. Contribution of excited states is suppressed by using a smeared source. We investigate both the positive-and negative-parity 5Q baryons with I = 0 and spin J = 1/2 using a non-NK-type interpolating field. After chiral extrapolation, the lowest positive-parity state is found to have a mass, mΘ = 2.25 GeV, which is much heavier than the experimentally observed Θ + (1540). The lowest negative-parity 5Q appears at mΘ = 1.75 GeV, which is near the s-wave NK threshold. To distinguish spatially-localized 5Q resonances from NK scattering states, we propose a new general method imposing a "Hybrid Boundary Condition (HBC)", where the NK threshold is artificially raised without affecting compact five-quark states. The study using the HBC method shows that the negative-parity state observed on the lattice is not a compact 5Q but an s-wave NK-scattering state.

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“…Negative parity is supported by some other quark model calculations [3,4,23,24,25], and QCD sum rules [28].…”

Section: Introductionmentioning

confidence: 64%

“…Numerous theoretical studies of penta-quark baryons have appeared since its discovery [5,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36]. One of the important issues is the spin and parity of Θ + .…”

Section: Introductionmentioning

confidence: 99%

Pentaquark baryon in anisotropic lattice QCD

et al. 2005

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mentioning

confidence: 93%

“…Here an important issue is whether such nonstrange heavy pentaquark states are stable against strong decays [7,8,9,10,11]. Subsequent theoretical investigations on the Θ + include approaches based on the constituent quark model [12,13,14], Skyrme model [15,16,17,18,19], QCD sum rules [20,21], lattice QCD [22], chiral potential model [23], large N c QCD [24], and Group theory approach [25]. The production of the Θ + was also discussed in relativistic nuclear collisions [26], where the number of the anti-Θ + (1540) produced are expected to be similar to that of the Θ + (1540).…”

mentioning

confidence: 99%

“…As for the spin-parity of the Θ + , several works claim that J P = 1 2 − is more natural [13,21,22], which, however, is in contrast to the prediction of the soliton models, where the relative orbital angular momentum plays an important role [9, 11]. The J P = 1 2 + assignment is also consistent with the recent study of the quark model [27], which predicts the lowest mass pentaquark state to be in the P wave state.…”

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confidence: 99%

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Properties of the baryon antidecuplet

Kim

Lee

2004

Phys. Rev. D

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We study the group structure of baryon anti-decuplet containing the Θ + . We derive the SU(3) mass relations among the pentaquark baryons in the anti-decuplet, when there is either no mixing or ideal mixing with the pentaquark octet, as advocated by Jaffe and Wilczek. This constitutes the Gell-Mann-Okubo mass formula for the pentaquark baryons. We also derive SU(3) symmetric Lagrangian for the interactions of the baryons in the anti-decuplet with the meson octet and the baryon octet. Our analysis for the decay widths of the anti-decuplet states suggests that the N (1710) is ruled out as a pure anti-decuplet state, but it may have anti-decuplet component in its wavefunction if the multiplet is mixed with the pentaquark octet. The recent discovery of the Θ + baryon by LEPS Collaboration at SPring-8 [1], which has been confirmed by several groups [2], initiated a lot of theoretical works in the field of exotic hadrons. Experimentally, the Θ + is observed to have a mass of 1540 MeV and a decay width of < 25 MeV. Because of its positive strangeness, the Θ + baryon is exotic since its minimal quark content should be uudds. Other states that have positive strangeness but different charges are not observed, which suggests that the Θ + is an isosinglet. The existence of such an exotic state with narrow width was first predicted by Diakonov et al. [3] in the chiral soliton model, where the Θ + is a member of the baryon anti-decuplet. Although it should be confirmed by other experiments, the recently discovered Ξ −− 3/2 baryon [4] strongly supports the anti-decuplet nature of pentaquark baryons. The discussion on the existence of a baryon anti-decuplet has a longer history going back to the early 1970's [5], and in the Skyrme model [6]. Pentaquark states with a heavy antiquark (uuddc, uuddb) were also predicted in the Skyrme model. Here an important issue is whether such nonstrange heavy pentaquark states are stable against strong decays [7,8,9,10,11]. Subsequent theoretical investigations on the Θ + include approaches based on the constituent quark model [12,13,14], Skyrme model [15,16,17,18,19], QCD sum rules [20,21], lattice QCD [22], chiral potential model [23], large N c QCD [24], and Group theory approach [25]. The production of the Θ + was also discussed in relativistic nuclear collisions [26], where the number of the anti-Θ + (1540) produced are expected to be similar to that of the Θ + (1540).Several pressing issues that should be clarified are whether the Θ + has positive or negative parity, and whether the Roper N (1710) is included in the baryon anti-decuplet with the Θ + . As for the spin-parity of the Θ + , several works claim that J P = 1 2 − is more natural [13,21,22], which, however, is in contrast to the prediction of the soliton models, where the relative orbital angular momentum plays an important role 10

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Structure and reactions of pentaquark baryons

Hosaka

2006

Pramana - J Phys

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We review the current status of the exotic pentaquark baryons. After a brief look at experiments of both positive and negative results, we discuss theoretical methods to study the structure and reactions for the pentaquarks. First we introduce the quark model and the chiral soliton model, where we discuss the relation of mass spectrum and parity with some emphasis on the role of chiral symmetry. It is always useful to picture the structure of the pentaquarks in terms of quarks. As for other methods, we discuss a model independent method, and briefly mention the results from the lattice and QCD sum rule. Decay properties are then studied in some detail, which is one of the important properties of Θ + . We investigate the relation between the decay width and the quark structure having certain spin-parity quantum numbers. Through these analyses, we consider as plausible quantum numbers of Θ + , J P = 3/2 − . In the last part of this note, we discuss production reactions of Θ + which provide links between the theoretical models and experimental information. We discuss photoproductions and hadron-induced reactions which are useful to explore the nature of Θ + .

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Phenomenology of the pentaquark antidecuplet

Cited by 104 publications

References 21 publications

Pentaquark baryon in anisotropic lattice QCD

Pentaquark baryon in anisotropic lattice QCD

Properties of the baryon antidecuplet

Structure and reactions of pentaquark baryons

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