Abstract
Kaonic atoms measure the antikaon-nucleus interaction at almost zero relative energy, allowing one to determine basic low-energy quantum chromodynamics (QCD) quantities, namely, the antikaon-nucleon ( K ¯ N) scattering lengths. The latter are important for extracting the sigma terms which are built on the symmetry breaking part of the Hamiltonian, thereby providing a measure of chiral and SU(3) symmetries breaking. After discussing the sigma terms and their relations to the kaonic atoms, we describe the most precise measurement in the literature of kaonic hydrogen, performed at LNF-INFN by the SIDDHARTA experiment. Kaonic deuterium is still to be measured, and two experiments are planned. The first, SIDDHARTA-2 at LNF-INFN was installed on DA Φ NE in spring 2019 and will collect data in 2020. The second, E57 at J-PARC, will become operative in 2021.
Highlights
Kaonic atoms experiments contribute to a deeper understanding of the quantum chromodynamics (QCD), the strong interaction theory, in the non-perturbative regime, and can be used to investigate primary problems concerning global symmetries: the origin of symmetry breaking, its nature, the breaking mechanisms, and to what extent symmetries are broken
This enables the unique opportunity of investigating the antikaon-nucleon/nucleus interaction almost “at threshold”, which grants access to the antikaon-nucleon scattering lengths’, basic low-energy QCD parameters
A very useful instrument to study the chiral and SU(3) symmetries breaking mechanisms is the measurement of X-ray transitions in kaonic hydrogen and kaonic deuterium
Summary
Kaonic atoms experiments contribute to a deeper understanding of the quantum chromodynamics (QCD), the strong interaction theory, in the non-perturbative regime, and can be used to investigate primary problems concerning global symmetries: the origin of symmetry breaking, its nature, the breaking mechanisms, and to what extent symmetries are broken. Kaonic atoms allow to measure the antikaon-nucleus interaction “at threshold”, from which fundamental low-energy QCD parameters, such as the antikaon-nucleon (KN) scattering lengths are extracted. The latter are related to the sigma terms, which are built on the symmetry breaking part of the Hamiltonian, thereby providing a measure of chiral and SU(3) symmetries breaking. We introduce the most precise measurement in the literature of the kaonic hydrogen, done at LNF-INFN by the SIDDHARTA experiment. The second, E57 at J-PARC, will become operative in 2021 Both of these experiments, as described in the paper, have in common stringent experimental requirements which need to be satisfied in order to be ready for the difficult kaonic deuterium measurement
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