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Register a new userStudy of $Lambda(1405)$ in photoproduction of $K^*$
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T. Hyodo
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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.
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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.
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).
Since the discovery of the $Lambda(1405)$, it remains poorly described by conventional constituent quark models, and it is a candidate for having an exotic meson-baryon or penta-quark structure, similar to states recently reported in the hidden charm sector. The $Lambda(1405)$ can be produced in the reaction $gamma p rightarrow K^+Lambda(1405)$. The pure I=0 decay mode into $Sigma^0pi^0$ is prohibited for the mass-overlapping $Sigma(1385)$. Combining a large aperture forward magnetic spectrometer and a central BGO crystal calorimeter, the BGO-OD experiment is ideally suited to measure this decay with the $K^+$ in the forward direction. Preliminary results are presented. *Supported by DFG (PN 388979758, 405882627).
We investigate the photoproduction of Lambda(1405,1/2^-) = Lambda* off the proton target using the effective Lagrangian in the Born approximation. We observed that, depending on the choice of the K* N Lambda* coupling strength, the total cross section becomes 0.1 <~ sigma_Lambda* <~ 0.2 mu b near the threshold and starts to decrease beyond E_gamma ~ 1.6 GeV, and the angular dependence shows a mild enhancement in the forward direction. It turns out that the energy dependence of the total cross section is similar to that shown in the recent LEPS experiment. This suggests that the production mechanism of the Lambda* is dominated by the s-channel contribution.
The $K^{-}$ induced production of $Lambda(1405)$ in the $K^{-} d to pi Sigma n$ reaction is investigated having in mind the conditions of the DAFNE facility at Frascati. We find that the fastest kaons from the decay of the $phi$ at DAFNE are well suited to see this resonance if one selects forward going neutrons in the center of mass, which reduce the contribution of single scattering and stress the contribution of the double scattering where the signal of the resonance appears clearer. We take advantage to report briefly on a recent work in which in addition to the $bar{K}NN$ system with total spin S=0, we find a less bound state (although with equally large width) with S=1, like in the $K^{-} d$ reported in the first part.
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