Strong interaction studies with kaonic atoms

¹ Stefan-Meyer-Institut für subatomare Physik, Boltzmanngasse 3, 1090 Wien, Austria
² INFN, Laboratori Nazionali di Frascati, C.P. 13, Via E. Fermi 40, I-00044 Frascati (Roma), Italy
³ Dep. of Physics and Astronomy, University of Victoria, P.O.Box 3055 Victoria B.C. Canada V8W3P6
⁴ Politecnico di Milano, Dip. di Elettronica e Informazione, Piazza L. da Vinci 32, I-20133 Milano, Italy
⁵ Institutul National pentru Fizica si Inginerie Nucleara Horia Hulubei, Reactorului 30, Magurele, Romania
⁶ INFN Sez. di Roma I and Instituto Superiore di Sanita I-00161, Roma, Italy
⁷ University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, Japan
⁸ RIKEN, Institute of Physical and Chemical Research, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
⁹ Excellence Cluster Universe, Tech. Univ. München, Boltzmannstraße 2, D-85748 Garching, Germany
¹⁰ Universidade de Santiago de Compostela, Casas Reais 8, 15782 Santiago de Compostela, Spain
¹¹ Department of Physics, Faculty of Science, University of Zagreb, Croatia
¹² High Energy Accelerator Research Organization (KEK), Tsukuba, 305-0801, Japan

^a e-mail: johann.marton@oeaw.ac.at

Published online: 25 March 2016

Abstract

The strong interaction of antikaons (K⁻) with nucleons and nuclei in the low-energy regime represents an active research field connected intrinsically with few-body physics. There are important open questions like the question of antikaon nuclear bound states - the prototype system being K⁻pp. A unique and rather direct experimental access to the antikaon-nucleon scattering lengths is provided by precision X-ray spectroscopy of transitions in low-lying states of light kaonic atoms like kaonic hydrogen isotopes. In the SIDDHARTA experiment at the electron-positron collider DAΦNE of LNF-INFN we measured the most precise values of the strong interaction observables, i.e. the strong interaction on the 1s ground state of the electromagnetically bound K⁻p atom leading to a hadronic shift ϵ_1s and a hadronic broadening Γ_1s of the 1s state. The SIDDHARTA result triggered new theoretical work which achieved major progress in the understanding of the low-energy strong interaction with strangeness. Antikaon-nucleon scattering lengths have been calculated constrained by the SIDDHARTA data on kaonic hydrogen. For the extraction of the isospin-dependent scattering lengths a measurement of the hadronic shift and width of kaonic deuterium is necessary. Therefore, new X-ray studies with the focus on kaonic deuterium are in preparation (SIDDHARTA2). Many improvements in the experimental setup will allow to measure kaonic deuterium which is challenging due to the anticipated low X-ray yield. Especially important are the data on the X-ray yields of kaonic deuterium extracted from a exploratory experiment within SIDDHARTA.