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Register a new userLattice Calculation of Baryon Masses using the Clover Fermion Action
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We present a calculation of the lowest-lying baryon masses in the quenched approximation to QCD. The calculations are performed using a non-perturbatively improved clover fermion action, and a splitting is found between the masses of the nucleon and its parity partner. An analysis of the mass of the first radial excitation of the nucleon finds a value considerably larger than that of the parity partner of the nucleon, and thus little evidence for the Roper resonance as a simple three-quark state
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We present a calculation of the mass of the lowest-lying negative-parity J=1/2- state in quenched QCD. Results are obtained using a non-perturbatively O(a)-improved clover fermion action, and a splitting is found between the mass of the nucleon and its parity partner. The calculation is performed on two lattice volumes and at three lattice spacings, enabling a study of both finite-volume and finite lattice-spacing uncertainties. A comparison is made with results obtained using the unimproved Wilson fermion action.
We study the strangeness electromagnetic form factors of the nucleon from the N_f=2+1 clover fermion lattice QCD calculation. The disconnected insertions are evaluated using the Z(4) stochastic method, along with unbiased subtractions from the hopping parameter expansion. In addition to increasing the number of Z(4) noises, we find that increasing the number of nucleon sources for each configuration improves the signal significantly. We obtain G_M^s(0) = -0.017(25)(07), where the first error is statistical, and the second is the uncertainties in Q^2 and chiral extrapolations. This is consistent with experimental values, and has an order of magnitude smaller error. We also study the strangeness second moment of the partion distribution function of the nucleon, <x^2>_{s-bar{s}}.
The calculation of the light-hadron spectrum in the quenched approximation to QCD using an anisotropic clover fermion action is presented. The tuning of the parameters of the action is discussed, using the pion and rho dispersion relation. The adoption of an anisotropic lattice provides clear advantages in the determination of the baryonic resonances, and in particular that of the so-called Roper resonance, the lightest radial excitation of the nucleon.
Quark-model hyperon-nucleon and hyperon-hyperon interactions by the Kyoto-Niigata group are applied to the two-Lambda plus alpha system in a new three-cluster Faddeev formalism using two-cluster resonating-group method kernels. The model fss2 gives a reasonable two-Lambda separation energy Delta B_{Lambda Lambda}=1.41 MeV, which is consistent with the recent empirical value, Delta B^{exp}_{Lambda Lambda}=1.01 +/- 0.20 MeV, deduced from the Nagara event. Some important effects that are not taken into account in the present calculation are discussed.
The description of baryon resonance decays represents a major challenge of strong interaction physics. We will report on a relativistic approach to mesonic decays of light and strange baryon resonances within constituent quark models. The calculations are performed in the point-form of relativistic quantum mechanics, specifically focussing on the strange sector. It is found that the relativistic predictions generally underestimate the experimental data. The nonrelativistic approximation of the approach leads to the decay operator of the elementary emission model. It is seen that the nonrelativistic reduction has considerable effects on the decay widths.
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