The kaonic atoms research program at DAΦNE: from SIDDHARTA to SIDDHARTA-2

¹ INFN, Laboratori Nazionali di Frascati, Frascati (Roma), Italy
² Politecnico di Milano, Dipartimento di Elettronica, Informazione e Bioingegneria and INFN Sezione di Milano, Milano, Italy
³ Stefan-Meyer-Institut für Subatomare Physik, Vienna, Austria
⁴ Physics Department, University of Zagreb, Zagreb, Croatia
⁵ Horia Hulubei National Institute of Physics and Nuclear Engineering (IFIN-HH), Magurele, Romania
⁶ Excellence Cluster Universe, Technische Universität München, Garching, Germany
⁷ University of Tokyo, Tokyo, Japan
⁸ The M. Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland
⁹ Museo Storico della Fisica e Centro Studi e Ricerche “Enrico Fermi”, Roma, Italy
¹⁰ Lund Univeristy, Lund, Sweden

^* e-mail: alessandro.scordo@lnf.infn.it

Published online: 25 June 2018

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, in which one electron is replaced by a negatively charged kaon, is a unique tool to provide precise information on this interaction; the energy shift and the broadening of the low-lying states of such atoms, induced by the kaon-nucleus hadronic interaction, can be determined with high precision from the atomic X-ray spectroscopy, and this experimental method provides unique information to understand the low energy kaon-nucleus interaction at the production threshold. The lightest atomic systems, like the kaonic hydrogen and the kaonic deuterium deliver, in a model-independent way, 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 in 2009 by the SIDDHARTA collaboration at the DAΦNE electron-positron collider of LNF-INFN, combining the excellent quality kaon beam delivered by the collider with new experimental techniques, as fast and very precise X-ray detectors, like the Silicon Drift Detectors. The SIDDHARTA results triggered new theoretical work, which achieved major progress in the understanding of the low-energy strong interaction with strangeness reflected by the antikaon-nucleon scattering lengths calculated with the antikaon-proton amplitudes constrained by the SIDDHARTA data. The most important open question is the experimental determination of the hadronic energy shift and width of kaonic deuterium; presently, a major upgrade of the setup, SIDDHARTA-2, is being realized to reach this goal. In this paper, the results obtained in 2009 and the proposed SIDDHARTA-2 upgrades are presented.