Abstract
The interaction of antikaons with nucleons and nuclei in the low-energy regime represents an active research field in hadron physics with still many important open questions. The investigation of light kaonic atoms is, in this context, a unique tool to obtain precise information on this interaction. The energy shift and broadening of the lowest-lying states of such atoms, induced by the kaon-nucleus strong interaction, can be determined with high precision from atomic X-ray spectroscopy. This experimental method provides unique information to understand the low energy kaon-nucleus interaction at threshold. The lightest atomic systems, kaonic hydrogen and kaonic deuterium, deliver the isospin-dependent kaon-nucleon scattering lengths. The most precise kaonic hydrogen measurement to date, together with an exploratory measurement of kaonic deuterium, were carried out by the SIDDHARTA collaboration at the DAΦNE electron-positron collider of LNF-INFN, by combining the excellent quality kaon beam delivered by the collider with new experimental techniques, as fast and precise X-ray detectors: Silicon Drift Detectors. The measurement of kaonic deuterium will be realized in the near future by SIDDHARTA-2, a major upgrade of SIDDHARTA. In this paper an overview of the main results obtained by SIDDHARTA together with the future plans, are given.
Highlights
The strong interaction, described in the framework of the Standard Model by the QCD, is still not well understood, especially in the low-energy limit, the so called non-perturbative regime
Experimental setup The SIDDHARTA setup consisted of two main components, the light-weight cryogenic target cell and a specially developed large area, high resolution X-ray detector system composed of Silicon Drift Detectors (SDDs)
The kaons leaving the interaction point through the SIDDHARTA beam pipe were degraded in energy and entered the cryogenic gaseous hydrogen target placed above the beam pipe, forming a kaonic atom and emitting X-rays
Summary
The strong interaction, described in the framework of the Standard Model by the QCD, is still not well understood, especially in the low-energy limit, the so called non-perturbative regime. Effective field theories contain appropriate degrees of freedom to describe physical phenomena occurring at the nucleon-meson scale, and chiral perturbation theory was extremely successful in describing systems like pionic atoms It is not directly applicable for kaonic systems, where non-perturbative coupled-channel techniques should be used ([3]).These theories are still needing experimental information and confirmation. The other method consists in precision X-ray measurements of the shift and the broadening of the energy levels of light kaonic atoms caused by the kaon-nucleus strong interaction. This latter method, exploited by the SIDDHARTA and SIDDHARTA-2 collaborations ([7, 8, 9, 10, 11, 12, 13]), is of significant importance, since it is the only method able to provide direct experimental information on the kaon-nucleus interaction at threshold
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