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Register a new userElectromagnetic mean squared radii of Lambda(1405) in chiral dynamics
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Authors
T. Sekihara
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The electromagnetic mean squared radii, <r^2>_E and <r^2>_M, of Lambda(1405) are calculated in the chiral unitary model. We describe the excited baryons as dynamically generated resonances in the octet meson and octet baryon scattering. We evaluate values of <r^2>_E and <r^2>_M for the Lambda(1405) on the resonance pole and obtain their complex values. We also consider Lambda(1405) obtained by neglecting decay channels. For the latter case, we obtain negative and larger absolute electric mean squared radius than that of typical ground state baryons. This implies that Lambda(1405) has structure that K^- is widely spread around p.
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The electric mean squared radii <r^2>_E of Lambda(1405) are calculated in the chiral unitary model. We describe the Lambda(1405) as a dynamically generated resonance fully in the octet meson and octet baryon scattering. We also consider ``Lambda(1405) as a bound state of KbarN. For the later ``Lambda(1405), we obtain negative and larger absolute value of electric mean squared radius than that of ordinary baryons, which implies that Lambda(1405) have structure of widely spread K^- around p.
The K^- induced production of Lambda(1405) is investigated in K^- d to pi Sigma n reactions based on coupled-channels chiral dynamics, in order to discuss the resonance position of the Lambda(1405) in the KbarN channel. We find that the K^-d to Lambda(1405)n process favors the production of Lambda(1405) initiated by the KbarN channel. The present approach indicates that the Lambda(1405) resonance position is 1420 MeV rather than 1405 MeV in the pi Sigma invariant mass spectra of K- d to pi Sigma n reactions. This is consistent with an observed spectrum of the K^- d to pi^+ Sigma^- n with 686-844 MeV/c incident K^- by bubble chamber experiments done in the 70s. Our model also reproduces the measured Lambda(1405) production cross section.
We discuss several aspects of the Lambda(1405) resonance in relation to the recent theoretical developments in chiral dynamics. We derive an effective single-channel KbarK N interaction based on chiral SU(3) coupled-channel approach, emphasizing the important role of the pi Sigma channel and the structure of the Lambda(1405) in Kbar N phenomenology. In order to clarify the structure of the resonance, we study the behavior with the number of colors (Nc) of the poles associated with the Lambda(1405), and argue the physical meaning of the renormalization procedure.
Recent CLAS data for the pi Sigma invariant mass distributions (line-shapes) in the gamma p -> K^+ pi Sigma reaction are theoretically investigated. The line-shapes have peaks associated with the Lambda(1405) excitation. Our model consists of gauge invariant photo-production mechanisms, and the chiral unitary model that gives the rescattering amplitudes where Lambda(1405) is contained. It is found that, while the pi Sigma line-shape data in the Lambda(1405) region are successfully reproduced by our model for all the charge states, the production mechanism is not so simple that we need to introduce parameters associated with short-range dynamics to fit the data. Our detailed analysis suggests that the nonresonant background contribution is not negligible, and its sizable effect shifts the Lambda(1405) peak position by several MeV. We also analyze the data using a Breit-Wigner amplitudes instead of those from the chiral unitary model. We find that the fitted Breit-Wigner parameters are closer to the higher pole position for Lambda(1405) of the chiral unitary model. This work sets a starting point for a fuller analysis in which line-shape as well as K^+ angular distribution data are simultaneously analyzed for extracting Lambda(1405) pole(s).
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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