Speaker
Description
The nature of the $\mathrm{\Lambda(1405)}$ hyperon remains one of the longstanding open questions in hadron physics. Since its prediction and discovery in the 1960s, its structure is still widely debated. With a mass located below the $\mathrm{\bar{K}N}$ threshold, it cannot be explained within the constituent quark model. Furthermore, its line shape deviates from a Breit–Wigner distribution and depends on the production and decay channels. Interpretations of $\mathrm{\Lambda(1405)}$ include a quasi-bound state $\mathrm{\bar{K}N}$ and a dynamically generated meson–baryon molecule with a two-pole structure.
The exclusive channel $\mathrm{pK^{+}\Lambda(1405)\rightarrow(\Sigma^{0}(\rightarrow\Lambda(\rightarrow p\pi^{-})\gamma)\pi^{0}(\rightarrow\gamma\gamma))}$ has been investigated using the HADES detector in proton–proton collisions at a beam energy of 4.5 GeV. The reconstructed invariant mass spectrum of $\mathrm{\Sigma^{0}\pi^{0}}$ shows clear contributions from the $\mathrm{\Lambda(1405)}$ and $\mathrm{\Lambda(1520)}$ resonances, as well as an enhancement near the masses of $\mathrm{\Lambda(1600)}$, $\Lambda(1670)$, and $\Lambda(1690)$. Production of these states has been studied in function of the four-momentum transfer between the initial proton and the outgoing $\mathrm{K^{+}}$. The obtained $\mathrm{\Lambda(1405)\rightarrow\Sigma^{0}\pi^{0}}$ mass distribution can be analyzed together with the $\mathrm{pK^{-}}$ invariant mass distribution, which shows an enhancement near the $\mathrm{\bar{K}N}$ threshold. Potential for this study using a ${K}$-matrix formalism within a coupled-channel model will also be presented.
| Collaboration | HADES |
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