Speaker
Steffen Maurus
(TUM)
Description
The precision measurement of two solar mass neutron stars (NS) and recent observation of the neutron star merger give stringent constraints to the equation of states (EOS) of models describing such dense objects.
While the allowed phase space is reduced by all these experimental observations, the hyperon puzzle, that question the presence of hyperons within NS, is still unresolved.
For all these EOS, the interaction of the hyperons with (normal) nuclear matter is a crucial ingredient.
The $\Lambda$ hyperon having the lowest rest mass among all hyperons is expected to appear first.
So far, the $\Lambda$N interaction is constraint by scattering experiments and the existence of hypernuclei demonstrates its attractive nature, but no differential study of lambda propagation within nuclear matter has been performed yet.
In 2014 the HADES collaboration performed a dedicated campaign with secondary pion beams $\pi^- + A$ ( A = C, W) with a $\pi^-$ momentum of $p_{\pi^-} = 1.7 $ GeV/c.
Since the reaction cross-section of the $\pi^-$ is sizable, the production of hyperons is likely to occur close to the upstream surface of the nucleus.
Thus $\pi A$ reactions provide an ideal environment to study the in-medium properties of the produced hyperons, since the average path length inside the nucleus is quite large.
In our experimental approach we select the semi-exclusive channel of $\pi^-+p \rightarrow \Lambda + K^0 + X$ reconstructed in terms of its associated dominant charged decay channel in a light (C) and heavy (W) nuclear environment.
Our data sample contains also the $\Sigma^0$ production channels ($\pi^-+p \rightarrow \Sigma^0 + K^0 + X$, $\Sigma^0 \rightarrow \Lambda + \gamma, BR \approx 100\%$ ) as from experimental point of view without electromagnetic calorimeter we cannot distinguish
between both hyperons.
To test different scenarios of the hyperon interaction with nuclear matter the GiBUU model has been employed.
As the hyperons are produced together with a $K^0$ the $K N$ interaction is addressed as well.
For the first time we test the repulsive potential of $\Sigma^0$, predicted by the $\chi$-effective theory.
We will report on the results of the analysis and present our sensitivity to the different scenarios of hyperon interaction with nuclear matter.
Primary author
Steffen Maurus
(TUM)
