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Register a new userRole of five-quark components in radiative and strong decays of the Lambda(1405) resonance
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Within an extended chiral constituent quark model, three- and five-quark structure of the $S_{01}$ resonance $Lambda(1405)$ is investigated. Helicity amplitudes for the electromagnetic decays ($Lambda(1405) to Lambda(1116)gamma$, $Sigma(1194)gamma$), and transition amplitudes for strong decays ($Lambda(1405)toSigma(1194)pi$, $ K^{-}p$) are drived, as well as the relevant decay widths. The experimental value for the strong decay width, $Gamma_{Lambda(1405)to (Sigma pi)^circ}=50pm 2$ MeV, is well reproduced with about 50% of five-quark admixture in the $Lambda(1405)$. Important effects due to the configuration mixings among $Lambda^{2}_{1}P_{A}$, $Lambda^{2}_{8}P_{M}$ and $Lambda^{4}_{8}P_{M}$ are found. In addition, transitions between the three- and five-quark components in the baryons turn out to be significant in both radiative and strong decays of the $Lambda(1405)$ resonance.
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Evidence has been accumulating for the existence of significant intrinsic non-perturbative five-quark components in various baryons. The inclusion of the five-quark components gives a natural explanation of the excess of $bar d$ over $bar u$, significant quark orbital angular momentum in the proton, the problematic mass and decay pattern of the lowest $1/2^-$ baryon nonet, etc.. A breathing mode of $qqqleftrightarrow qqqqbar q$ is suggested for the lowest $1/2^-$ baryon octet. Evidence of a predicted member of the new scheme, $Sigma^*(1/2^-)$ around 1380 MeV, is introduced.
We investigate the photoproduction of $K^*$ vector meson for the study of the $Lambda(1405)$ resonance. The invariant mass distribution of $piSigma$ shows a different shape from the nominal one, peaking at 1420 MeV. This is considered as a consequence of the double pole structure of $Lambda(1405)$, predicted in the chiral unitary model. Combined with other reactions, such as $pi^- p to K^0 piSigma$, experimental confirmation of this fact will reveal a novel structure of the $Lambda(1405)$ state.
Five-quark (5Q) picture of Lambda(1405) is studied using quenched lattice QCD with an exotic 5Q operator of Nbar{K} type. To discreminate mere Nbar{K} and Sigmapi scattering states, Hybrid Boundary Condition (HBC), a flavor-dependent boundary condition, is imposed on the quark fields along spatial direction. 5Q mass m_{5Q}simeq 1.89 GeV is obtained after the chiral extrapolation to the physical quark mass region, which is too heavy to be identified with Lambda(1405). Then, Lambda(1405) seems neither a pure 3Q state nor a pure 5Q state, and therefore we present an interesting possibility that Lambda(1405) is a mixed state of 3Q and 5Q states.
The photo-induced $K^*$ vector meson production is investigated for the study of the $Lambda(1405)$ resonance. This reaction is particularly suited to the isolation of the second pole in the $Lambda(1405)$ region which couples dominantly to the $bar K N$ channel. We obtain the mass distribution of the $Lambda(1405)$ which peaks at 1420 MeV, and differs from the nominal one. Combined with several other reactions, like the $pi^- p to K^0 pi Sigma$ which favours the first pole, this detailed study will reveal a novel structure of the $Lambda(1405)$ state.
The internal structure of the resonant Lambda(1405) state is investigated based on meson-baryon coupled-channels chiral dynamics. We evaluate Lambda(1405) form factors which are extracted from current-coupled scattering amplitudes in meson-baryon degrees of freedom. Using several probe currents and channel decomposition, we find that the resonant Lambda(1405) state is dominantly composed of widely spread Kbar around N, with escaping pi Sigma component.
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