TY - JOUR

T1 - A comprehensive search for the +pentaquark on the lattice

AU - Katz, S. D.

AU - Csikor, F.

AU - Fodor, Z.

AU - Kovács, T. G.

AU - Tóth, B. C.

N1 - Funding Information:
The ratio of E1 to the threshold is 1.151, 1.166, 1.177, 1.202 for κ = 0.1550, 0.1555, 0.1558 and 0.1563, respectively for our larger volumes. For the smaller volume (Ls = 20) at κ = 0.1550 this ratio is 1.211. We can see that in all cases the measured mass ratios are consistent with the scattering states. The expected and measured volume dependences of the first excited state for negative parity and the ground state for positive parity is shown in Fig. 2. For the highest quark mass, where we had the largest statistics we also performed the whole analysis for the isovector channel. The extracted masses and their volume dependence turned out to be qualitatively similar to those in the isoscalar channel. The individual results in the odd and even parity channels can be summarized as follows (based on the statistically most significant, highest quark mass and assuming that mΘ+/(mN+mK) does not change significantly with the quark mass). 1. Odd parity. We extracted the two lowest lying states. The lower one is identified as the lowest scattering state with appropriate volume dependence (in this case the p=0 scattering means no volume dependence). This state is 6σ below the Θ+ state. The volume dependence of the second lowest state is consistent with that of a scattering state with non-zero relative momentum. For our larger/smaller volumes this state is 1.8/2.1σ above the Θ+ state. None of these two states could be interpreted as the Θ+ pentaquark. 2. Even parity. The two lowest lying states are identified. The volumes are chosen such that even the lowest scattering state is above the expected Θ+ pentaquark state. The volume dependence of the lowest state suggests that it is a scattering state. For both volumes this state is 6σ above the Θ+ state. Since the energy of the second lowest state is even larger, none of them could be interpreted as the Θ+ pentaquark. To summarize in both parity channels we identified all the nearby states both below and above the expected Θ+ state. Having done that no additional resonance state was found. This is an indication that in our wave function basis no Θ+ pentaquark exists (though it might appear in an even larger, more exotic basis, with smaller dynamical quark masses or approaching the continuum limit). The comparison of our results with those of others is not an easy task. Nevertheless, it is fair to say that existing lattice studies ([3, 4, 5, 6, 8, 9]) are not precise enough so that – contrary to first impression – really strong contradictions can not be claimed to exist. Acknowledgements: This work was partially supported by Hungarian Scientific Grants, OTKA-T34980, T37615, M37071, T32501, T046925, AT049652. This research is part of the EU Integrated Infrastructure Initiative Hadronphysics project under contract No. RII3-CT-20040506078. Support by the Hungarian Research and Technological Innovation Fund, and the Croatian Ministry of Science, Education and Sports is gratefully acknowledged.
Publisher Copyright:
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PY - 2005

Y1 - 2005

N2 - We study spin 1/2 isoscalar and isovector, even and odd parity candidates for the +(1540) pentaquark particle using large scale lattice QCD simulations. Previous lattice works led to inconclusive results because so far it has not been possible to unambiguously identify the known scattering spectrum and tell whether additionally a genuine pentaquark state also exists. Here we carry out this analysis using several possible wave functions (operators), including spatially non-trivial ones with unit orbital angular momentum. The cross correlator matrix we compute is 14×14 with 60 non-vanishing elements. We can clearly distinguish the lowest scattering state(s) in both parity channels up to above the expected location of the pentaquark, but we find no trace of the latter. We conclude that there are most probably no pentaquark bound states at our quark masses, corresponding to mπ=400-630 MeV. However, we cannot rule out the existence of a pentaquark state at the physical quark masses or pentaquarks with a more exotic wave function.

AB - We study spin 1/2 isoscalar and isovector, even and odd parity candidates for the +(1540) pentaquark particle using large scale lattice QCD simulations. Previous lattice works led to inconclusive results because so far it has not been possible to unambiguously identify the known scattering spectrum and tell whether additionally a genuine pentaquark state also exists. Here we carry out this analysis using several possible wave functions (operators), including spatially non-trivial ones with unit orbital angular momentum. The cross correlator matrix we compute is 14×14 with 60 non-vanishing elements. We can clearly distinguish the lowest scattering state(s) in both parity channels up to above the expected location of the pentaquark, but we find no trace of the latter. We conclude that there are most probably no pentaquark bound states at our quark masses, corresponding to mπ=400-630 MeV. However, we cannot rule out the existence of a pentaquark state at the physical quark masses or pentaquarks with a more exotic wave function.

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M3 - Conference article

AN - SCOPUS:85055839488

VL - 22

JO - Proceedings of Science

JF - Proceedings of Science

SN - 1824-8039

M1 - 008

T2 - 29th Johns Hopkins Workshop on Current Problems in Particle Theory: Strong Matter in the Heavens, JHW 2005

Y2 - 1 August 2005 through 3 August 2005

ER -