Speaker
Description
The nature of the $\Lambda(1405)$ hyperon remains one of the longstanding open questions in hadron physics. Since the discovery of the $\Lambda(1405)$ resonance in 1961, its mass, lower than quark model predictions [1], has been the subject of extensive theoretical and experimental studies. The mass of $\Lambda(1405)$ lies below the N$\mathrm{\bar{K}}$ production threshold, which is not reproduced by static approaches. Furthermore, its line shape deviates from a Breit-Wigner distribution and depends on the production and decay channels. Interpretations of $\Lambda(1405)$ include a quasi-bound state of nucleon and anti-kaon [2, 3], and a dynamically generated meson-baryon molecule with two poles [4].
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 [5] 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 $\Lambda(1405)$ and $\Lambda(1520)$ resonances, as well as an enhancement near the masses of $\Lambda(1600)$, $\Lambda(1670)$, and $\Lambda(1690)$. Production of these states has been studied in function of the four-momentum transfer between the initial proton and the spectator proton.
The lineshape of $\Lambda(1405)$ has been analyzed with different approaches including an empirical fit to a two-pole model and a comparison with theoretical predictions.
The analysis strategy and preliminary results will be presented.
[1] N. Isgur and G. Karl, Phys. Rev. D 18, 4187 (1978)
[2] R. H. Dalitz and S. F. Tuan, Ann. Phys. 8, 100 (1959)
[3] R. H. Dalitz and S. F. Tuan, Phys. Rev. Lett. 2, 425 (1959)
[4] A. Ramos et al., Nucl. Phys. A 754, 202 (2005)
[5] HADES Collaboration, Eur. Phys. J. A 57, 138 (2021)