Spin-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mn>3</mml:mn><mml:mo>/</mml:mo><mml:mn>2</mml:mn></mml:math>pentaquark in the QCD sum rule approach

We propose a new approach in QCD sum rules applied for exotic hadrons with a number of quarks, exemplifying the pentaquark Θ + (I = 0, J = 1/2) in the Borel sum rule. Our approach enables reliable extraction of the pentaquark properties from the sum rule with good stability in a remarkably wide Borel window. The appearance of its valid window originates from a favorable setup of the correlation functions with the aid of chirality of the interpolating fields on the analogy of the Weinberg sum rule for the vector currents. Our setup leads to large suppression of the continuum contributions which have spoiled the Borel stability in the previous analyses, and consequently enhances importance of the higher-dimensional contributions of the OPE, which are indispensable for investigating the pentaquark properties. Implementing the OPE analysis up to dimension 15, we find that the sum rules for the chiral-even and odd parts independently give the Θ + mass of 1.68 ± 0.22 GeV with uncertainties of the condensate values. Our sum rule indeed gives rather flat Borel curves almost independent of the continuum thresholds both for the mass and pole residue. Finally, we also discuss possible isolation of the observed states from the KN scattering state on view of chiral symmetry.

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Θ+formation in inclusiveγD→pK−X

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Kämpfer

Daté

et al. 2006

Phys. Rev. C

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We analyze the possibility to produce an intermediate Θ + via a KN → Θ + formation process in γD → pK − X (X = nK + , pK 0 ) reactions at some specific kinematical conditions, in which a pK − pair is knocked out in the forward direction and its invariant mass is close to the mass of Λ * (Λ * ≡ Λ( 1520)). The Θ + signal may appear in the [γD, pK − ] missing mass distribution. The ratio of the signal (cross section at the Θ + peak position) to the smooth background processes varies from 0.7 to 2.5 depending on the spin and parity of Θ + , and it decreases correspondingly if the pK − invariant mass is outside of the Λ * -resonance region. We analyze the recent CLAS search for the Θ + in the γD → pK − nK + reaction and show that the conditions of this experiment greatly reduce the Θ + formation process making it difficult to extract a Θ + peak from the data.

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Spin-3/2pentaquark in the QCD sum rule approach

Cited by 12 publications

References 31 publications

Spin 3/2 pentaquarks

Spin 3/2 pentaquarks

Pentaquark state in pole-dominated QCD sum rules

Θ+formation in inclusiveγD→pK−X

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