06.12.2022 15:15

Model selection in kaon photoproduction

Dalibor Skoupil (Nuclear Institute Rež)

New models for photo- and electroproduction of kaons on the proton were constructed utilizing new experimental data from LEPS, GRAAL, and particularly CLAS collaborations. The higher spin nucleon (spin-3/2 and spin-5/2) and hyperon (spin-3/2) resonances were included using a consistent formalism and they were found to play an important role in the data description. In these analyses, we paid close attention to model predictions of the cross section at small kaon angles which are vital for accurate calculations of the hypernucleus-production cross section. In order to account for the unitarity corrections at the tree level, we have introduced energy-dependent widths of nucleon resonances, which affect the choice of hadron form factors and the values of their cutoff parameters extracted in the fitting procedure.

We have also implemented a new shape of electromagnetic form factors in order to be able to describe the electroproduction. Moreover, for a reliable description of K^+\Lambda electroproduction at small Q^2 within our models it is necessary to take into account also a longitudinal coupling of virtual photons to nucleon resonances.

After focusing on the K^+\Lambda channel, we utilize our isobar model to investigate the K^+ \Sigma^- photoproduction off a neutron target. Since a plain \chi^2 minimization cannot prevent us from overfitting the data, i.e. introducing more parameters (and thus resonances) than are needed for data description, we used a regularization method, the least absolute shrinkage selection operator, and information criteria for avoiding this issue and choosing the best fit. We were then able to arrive at a very economical model which includes only 17 parameters (in contrast to a model with 25 parameters when using the plain \chi^2 minimization).


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