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The SIDDHARTA-2 collaboration developed an innovative large area Silicon Drift Detectors technology to perform high precision spectroscopy for the investigation of the K¯ N strong interaction in the low-energy regime, in the strangeness sector. The SIDDHARTA-2 devices take advantage of special geometry to maximize the experimental geometrical acceptance together with a dedicated Front End electronics able to provide energy resolution of 163 1 eV at 170 K for the Fe Kα line and a linear response better than 10-3, both preserved along the whole DAQ analog-digital chain in a colliding beams challenging environment. In this work the SIDDHARTA-2 Silicon Drift Detectors spectroscopic characterization and the preliminary results obtained at the DAΦNE collider of Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali di Frascati are presented.

X-ray spectroscopy of kaonic atoms provides a versatile tool to study the strong interaction at low energies via a direct observation of its influence on the ground state of kaonic hydrogen atoms. The SIDDHARTA experiment provided precise results on the energy shift and width of the kaonic hydrogen 1s state induced by the strong interaction. To enable the extraction of the antikaon-nucleon scattering lengths a0 and a1, SIDDHARTA-2 aims to determine the energy shift and width in kaonic deuterium with precisions of 30 eV and 75 eV, respectively. This measurement is aggravated by the low kaonic deuterium X-ray yield and a high background environment and will only be possible by implementing a severe upgrade on the SIDDHARTA apparatus.

The excellent quality kaon beam provided by the DA\PhiΦNE collider of LNF-INFN (Italy) together with SIDDHARTA/SIDDHARTA-2 new experimental techniques, as very precise and fast-response X-ray detectors, allow to perform unprecedented measurements on light kaonic atoms crucial for a deeper understanding of the low-energy quantum chromodynamics (QCD) in the strangeness sector. In this paper an overview of the main results obtained by the SIDDHARTA collaboration, as well as the future plans related to the SIDDHARTA-2 experiment, are discussed.

The VIP collaboration is performing high precision tests of the Pauli Exclusion Principle for electrons in the extremely low cosmic background environment of the Underground Gran Sasso Laboratories of INFN (Italy). The experimental technique consists in introducing a DC current in a copper conductor, searching for the X-rays emission due to a PEP-forbidden atomic transition from the L shell to the K shell of copper when the K shell is already occupied by two electrons. VIP set un upper limit on the PEP violation probability 1 2 β 2 < 4.7 × 10 − 29 , the aim of the upgraded VIP-2 experiment is to improve this result by two orders of magnitude at least. The experimental setup and the results of preliminary data analyses will be presented.

The main steps for the analysis of the Λp correlated production in low-energy K− captures on Carbon nuclei, performed by the AMADEUS collaboration, are presented. The goal is to perform the first comprehensive study of the K− absorption on two, three and four nucleons, exploiting the lowmomentum K−s (pK ~ 127 MeV/c) produced at the DAΦNE collider, and to measure the low-energy cross sections and branching ratios of the K− multinucleon absorption processes in both the Λp and Σ0p channels. An integrated luminosity of 1.74 fb−1 collected during the KLOE 2004/2005 data campaign is analysed by reconstructing the Λp final state.

The precision of the charged kaon mass is an order of magnitude worse than the precision of the charged pion mass mainly due to two inconsistent measurements. We plan to improve this precision by determining the charged kaon mass with the requested accuracy in the measurements of X-ray transitions in kaonic atoms of selected solid targets with the HPGe detector at DAΦNE in Laboratori Nazionali di Frascati, Italy. The measurements will be performed in parallel with SIDDHARTA-2 measurements of X-ray transitions in gaseous targets. The status of the preparation of the measurements will be presented.

The goal of the AMADEUS experiment is to shed light on unsolved fundamental issues in the non-perturbative strangeness QCD sector through the study of lowenergy K- hadronic interactions with light nuclear targets. The main open questions are the controversial nature of the Δ(1405) state, which is investigated in hyperon-pion correlation studies, and the possible existence of exotic antikaon multi-nucleon clusters, whose search in K- induced reactions is intimately related to the studies of the K- multi-nucleon absorption processes in hyperon-nucleon/nucleus channels. The DAΦNE collider at the INFN-LNF provides unique monochromatic low-momentum kaons from the φ meson decay almost at-rest, suitable for the AMADEUS studies. The KLOE detector is exploited as an active target, in order to obtain excellent acceptance and resolution data for K- nuclear capture on H, 4He, 9Be and 12C, both at-rest and in-flight.

In the exotic atoms in which one electron is replaced by a negatively charged kaon, the kaon-nucleus hadronic interaction introduces an energy shift and broadening of the low-lying states of the kaonic atoms. The shift and width 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.

SIDDHARTA collaboration performed the highest precision measurement of the shift and width of the kaonic hydrogen 1s state induced by the strong interaction at the DAΦNE collider of Laboratori Nazionali di Frascati. The result provides vital constraints on the theoretical description of the low-energy \({\bar{K} N}\) interactions.

The low-energy strong interaction of antikaons (K-) with nuclei has many facets and rep- resents a lively and challenging research field. It is interconnected to the peculiar role of strangeness, since the strange quark is rather light, but still much heavier than the up and down quarks. Thus, when strangeness is involved one has to deal with spontaneous and explicit symmetry breaking in QCD. It is well known that the antikaon interaction with nucleons is attractive, but how strong ? Is the interaction strong enough to bind nucleons to form kaonic nuclei and, if so, what are the properties (binding energy, decay width)? There are controversial indications for such bound states and new results are expected to come soon. The existence of antikaon mediated bound states might have important consequences since it would open the possibility for the formation of cold baryonic matter of high density which might have a severe impact in astrophysics for the understanding of the composi- tion of compact (neutron) stars. New experimental opportunities could be provided by the AMADEUS experiment at the DA?NE electron-positron collider at LNF-INFN (Frascati, Italy). Pre-AMADEUS studies on the antikaon interaction with nuclei are carried out by analysis of data collected by KLOE in till 2005 and in special data runs using a carbon target insert. Studies for the dedicated AMADEUS detector setup taking advantage of the low-energy antikaons from Phi-meson decay delivered by DAFNE are in progress. Some re- sults obtained so far and the perspectives of the AMADEUS experiment are presented and discussed., 6 pages, 3 figures, Proceedings LEAP2016

The antikaon interaction on nucleons and nuclei in the low-energy regime is neither simple nor well understood. Rather direct access to this field is provided by x-ray spectroscopy of light kaonic atoms like kaonic hydrogen, deuterium and helium isotopes. A series of precision measurements on kaonic atoms was performed very successfully by the SIDDHARTA Collaboration at the DAΦNE electron-positron collider at LNF-INFN (Frascati, Italy). Consequently, new precision data on the strong interaction observables (i.e. energy shift and broadening of low-lying atomic states) were delivered having an important impact on the theory of low-energy QCD with strangeness. Presently, the follow-up experiment, SIDDHARTA-2, is in preparation, aiming at a determination of the strong interaction observables in kaonic deuterium as the highest priority; other type of measurements (light and heavier kaonic atoms) are as well foreseen. With the kaonic deuterium data the antikaon-nucleon isospin-resolved scattering lengths can be extracted for the first time. An overview of the progress and present status of experimental studies and an outlook to future perspectives in this fascinating research field is given.

The Multi-Pixel Photon Counter (MPPC) detectors consist of hundreds of micro silicon Avalanche PhotoDiodes (APD) working in Geiger mode. The high gain and the small dimensions typical of these devices, together with their good performances in magnetic field, make them ideal readout devices for scintillating fibers as trigger detectors in particle and nuclear physics experiments like AMADEUS, where such a system is planned to be used to trigger on charged kaons. A prototype setup for this trigger system, consisting of 5 scintillating fibers readout by 10 MPPCs, was built and tested in laboratory and mounted inside the DA Φ NE collider at LNF-Frascati to measure the back-to-back K + K − pairs emitted in the Φ - decay processes. The ad hoc readout electronics was designed and realized at Laboratori Nazionali di Frascati (INFN). A 64 channels setup, with a new dedicated electronics, was then built and characterized in the laboratory. The results of the tests are presented and discussed.

Large-area silicon drift detectors (SDDs) were used for the first time in the background condition of a collider for precision spectroscopy of the kaonic atom X-rays in the SIDDHARTA experiment for the study of the strong interaction in a low-energy regime. The measurements were performed at the DA Φ NE electron–positron collider (LNF, Italy), using gas targets of hydrogen, deuterium, helium-3, and helium-4. A test measurement using the kaonic 4 He X-rays showed an excellent performance of the SDD devices under the beam conditions, and a good background suppression capability using the time correlation between the kaonic atom X-rays and the back-to-back correlated K + K − pairs produced by φ decays.

The SIDDHARTA experiment (SIlicon Drift Detector for Hadronic Atom Research by Timing Application) had the aim to perform a precise measurement of K-series kaonic hydrogen x-rays and the first-ever measurement of the kaonic deuterium x-rays to determine the strong-interaction energy-level shifts and widths of the lowest lying atomic states. These measurements offer a unique possibility to precisely determine the isospin-dependent kaon-nucleon(KN) scattering lengths which are directly connected with the physics of the KN interaction. The experiment combined the excellent low-energy kaon beam generated at DAΦNE, allowing to use gaseous targets, with excellent fast X-rays detectors: Silicon Drift Detectors. SIDDHARTA was installed on DAΦNE in autumn 2008 and took data till late 2009. Apart of the kaonic hydrogen and kaonic deuterium measurements, we have performed the kaonic helium transitions to the 2 p level (L-lines) measurements: for the first time in a gaseous target for kaonic helium 4 and for the first time ever for kaonic helium 3. In this paper, an overview of this experiment and preliminary results are presented, together with future plans.

The K ¯ N system at rest makes a sensitive testing ground for chiral SU(3) symmetry in QCD, especially for the explicit symmetry breaking induced by the relatively large mass of the strange quark. At the DAΦNE electron-positron collider of Laboratori Nazionali di Frascati we study kaonic atoms, taking advantage of the low-energy kaons from Φ-mesons decaying nearly at rest. The low-energy antikaon-nucleon interaction in kaonic hydrogen and kaonic deuterium can be investigated under favorable conditions. The DEAR (DAΦNE Exotic Atom Research) experiment at LNF delivered the most precise data on kaonic hydrogen up to now. DEAR and its follow-up experiment SIDDHARTA (Silicon Drift Detector for Hadronic Atom Research by Timing Application) are using X-ray spectroscopy of kaonic atoms to measure the strong interaction induced shift and width of the ground state. SIDDHARTA is the first experiment on kaonic deuterium ever, and kaonic hydrogen is remeasured with improved precision. From the shift and width in K-p and K-d the isospin-dependent antikaon-nucleon scattering lengths can be determined, quantities essential as constraints for low-energy QCD.

The planned series of measurements with AMADEUS will provide a high precision data set to study antikaon nucleus/nucleon dynamics at low energy. To achieve these goals AMADEUS will make use of the KLOE detector system at LNF, which is ideally suited for our measurements due to their large drift chamber with excellent charge particle tracking and identification probability. An almost 4 π calorimeter is available for the detection of neutral particles. R&D work has already started to construct a dedicated target and trigger system for further improvements on kaon stopping efficiency and background suppression.

Recently, the shift of the kaonic helium-4 2p state was precisely determined by the E570 and SIDDHARTA experiments. Prior to the experiment by E570, the average of three earlier experimental results showed - 43±8 eV, while most of the theoretical calculations give ∼ 0 eV. This five-sigma discrepancy between theory and experiment was known as the "kaonic helium puzzle". A recent theoretical model showed a possible resonance-like shift of maximum 10 eV for a certain value of a deep antikaon-nucleon interaction potential, which is different in helium 3 and helium 4. The E570 experiment determined the shift of the kaonic helium-4 2p state as +2±2 (stat)±2 (sys) eV in 2007. The SIDDHARTA experiment determined the shift as 0±6 (stat)±2 (sys) eV in 2009. The results of these experiments resolved the long-standing puzzle. A new experiment of the kaonic helium-3 X-ray measurement is being prepared by the J-PARC E17 collaborators, and the kaonic helium-3 X-ray data taken very recently by the SIDDHARTA experiment are on the way to be analyzed. The results of the E570, E17 and SIDDHARTA experiments examine the strong interaction for light nuclei with different isospin, and test furthermore recent theoretical predictions. © 2010 American Institute of Physics.

The kaonic helium-4 3 d → 2 p X-ray transition was measured in a gaseous target, where Compton scattering in helium is negligible. The X-rays were detected with large-area Silicon Drift Detectors (SDDs) using the timing information of the K + K − pairs produced by ϕ decays at the DAΦNE e + e − collider. A new value of the strong interaction shift of the kaonic 4He 2p state was determined to be 0 ± 6 (stat) ± 2 (syst) eV , which confirms the recently obtained result by the KEK-PS E570 group.

The DAΦNE electron-positron collider at the Frascati National Laboratories has made available a unique “beam” of negative kaons. The SIDDHARTA (SIlicon Drift Detector for Hadronic Atom Research by Timing Application) experiment, successor of DEAR (DAΦNE Exotic Atom Research), aims at a precision measurement of the strong interaction shift and width of the fundamental 1s level, via the measurement of the x-ray transitions to this level, for kaonic hydrogen and kaonic deuterium. The final goal is to extract the isospin dependent antikaon-nucleon scattering lengths which contribute to the understanding of aspects of non-perturbative QCD in the strangeness sector. Other possible hadronic atoms measurements at DAΦNE are under study.

Hadronic atoms being Coulomb-bound systems in which the electron is substituted by a hadron like a negatively charged K meson are perfect probes for the study of strong interaction at lowest energies using x-ray spectroscopy. New large area x-ray detectors (silicon drift detectors, SDDs) were developed to provide excellent energy resolution as well as timing capability. For the first time large area SDDs were employed to measure the L-lines of kaonic helium at high precision thus succeeding in clarifying a puzzle persisting for 30 years since the 70's. An array of about 200 even more sophisticated SDDs (1 cm2 SDDs with monolithically integrated FET) will be used to perform precision measurements (i.e., at the eV level) of kaonic hydrogen and kaonic deuterium at the DAFNE Phi factory of LNF/Italy. The new x-ray detectors and their performance for precision experiments in the accelerator environment are presented.

The interaction of antikaons (K−) with nucleons and nuclei in the low-energy regime represents an active research field in hadron physics. There are important open questions like the existence of antikaon nuclear bound states like the prototype system being K− pp. 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 in light kaonic atoms like kaonic hydrogen and helium 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 energy shift and broadening 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 reflected by the antikaon-nucleon scattering lengths calculated with the K−-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 which is planned by the SIDDHARTA-2 Collaboration.

With precise X-ray spectroscopy on kaonic hydrogen at the DAΦNE electron-positron collider at Laboratori Natzionali di Frascati the chiral symmetry breaking scenario in the strangeness sector will be investigated by studying the K − p and K − d s-wave interaction at threshold. The strong interaction induced shift and width of the kaonic hydrogen 1s atomic state was measured with DEAR (DAΦNE Exotic Atom Research) and in future with SIDDHARTA (Silicon Drift Detector for Hadronic Atom Research with Timing Application) the kaonic hydrogen system will be measured with utmost precision. In addition, data for the K − d system will become available for the first time. Kaonic hydrogen together with precision measurements of kaonic helium will allow the study of the sub-threshold Λ(1405) resonance, which might act as a doorway for the formation of antikaon-mediated deeply bound nuclear states in light nuclei. Therefore, these precision measurements are a powerful tool to test chiral symmetry breaking in systems with strangeness.

The AMADEUS collaboration is performing experimental investigations in the sector of the low energy strangeness hadron physics by taking advantage of the DAΦNE collider, which provides a unique source of monochromatic low-momentum kaons and exploiting the KLOE detector as an active target. The K− single and multi-nuclear absorption on H, 4He, 9Be and 12C, both at-rest and in-flight, are studied with the aim to determine the nature of the controversial Λ(1405), the non-resonant hyperon pion formation amplitude below the K̅N threshold, the yield and cross sections of K− multi-nucleon absorptions intimately connected to the antikaon multi-nucleon clusters properties and the K− scattering cross sections on light nuclear targets. These studies have a strong impact on the non-perturbative strangeness QCD with implications ranging from nuclear physics to the equation of state of neutron stars.

The AMADEUS experiment aims to provide unique quality data for K − interaction with nucleons and light nuclei, both at-rest and in-flight (for K − momenta of about 100 MeV). The goal is to solve longstanding open issues in the non-perturbative QCD in the strangeness sector, like the nature of the Λ(1405) state, the resonant versus non-resonant yield in nuclear K − capture and the properties of kaonic nuclear clusters which are strongly related to the multi-nucleon absorption processes. We can take advantage of the DA ΦNE collider representing a unique source of monochromatic low-momentum kaons, whose nuclear interaction with the materials of the KLOE detector (used as an active target) furnish us excellent acceptance and resolution data for K − capture on H, 4He, 9Be and 12C, both at-rest and in-flight. AMADEUS step 0 consisted in the analysis of the 2004-2005 KLOE data. A second step consisted in the implementation in the central region of the KLOE detector of a pure graphite target, providing a high statistic sample of K − 12 C nuclear captures at rest. For the future, new setups for various dedicated targets are under preparation.

The strong-interaction shifts and widths of kaonic hydrogen, deuterium, 3 He, and 4 He were measured in the SIDDHARTA experiment. The most precise values of the shift and width of the kaonic hydrogen 1s state were determined to be ϵ1s = −283 ± 36(stat) ±6(syst) eV and Γ1s = 541 ±89(stat) ±22(syst) eV. The upper limit of the kaonic deuterium Kα yield was found to be ≤ 0.39%. In addition, the shifts and widths of the kaonic 3 He and 4 He 2p states were determined to be ϵ2p( 3 He) = −2 ± 2(stat) ± 4(syst) eV and Γ2p( 3 He) = 6 ± 6(stat) ± 7(syst) eV; ϵ2p( 4 He) = +5 ± 3(stat) ± 4(syst) eV and Γ2p( 4 He) = 14 ±8(stat) ±5(syst) eV. These values are important for the constraints of the low-energy ¯ KN interaction in theoretical approaches.

We measured K -series kaonic hydrogen X-rays in the SIDDHARTA experiment performed at the DAΦNE electron-positron collider of Laboratori Nazionali di Frascati. With a gaseous hydrogen target of density 15 ρ STP , preliminary values of the absolute yields, defined as the number of atomic X-rays emitted per kaon stopped inside the target, were determined to be 0.012 −0.004 +0.003 for K α transition and 0.045 −0.012 +0.009 for K tot , the summation of all the emitted K -series transitions.

The AMADEUS experiment aims to provide unique quality data of $K^-$ hadronic interactions in light nuclear targets, in order to solve fundamental open questions in the non-perturbative strangeness QCD sector, like the controversial nature of the $\Lambda(1405)$ state, the yield of hyperon formation below threshold, the yield and shape of multi-nucleon $K^-$ absorption, processes which are intimately connected to the possible existence of exotic antikaon multi-nucleon clusters. AMADEUS takes advantage of the DA$\Phi$NE collider, which provides a unique source of monochromatic low-momentum kaons and exploits the KLOE detector as an active target, in order to obtain excellent acceptance and resolution data for $K^-$ nuclear capture on H, ${}^4$He, ${}^{9}$Be and ${}^{12}$C, both at-rest and in-flight. During the second half of 2012 a successful data taking was performed with a dedicated pure carbon target implemented in the central region of KLOE, providing a high statistic sample of pure at-rest $K^-$ nuclear interactions. For the future dedicated setups involving cryogenic gaseous targets are under preparation., Comment: 14 pages, 6 figures

The study of the KbarN system at very low energies plays a key role for the understanding of the strong interaction between hadrons in the strangeness sector. At the DAFNE electron-positron collider of Laboratori Nazionali di Frascati we studied kaonic atoms with Z=1 and Z=2, taking advantage of the low-energy charged kaons from Phi-mesons decaying nearly at rest. The SIDDHARTA experiment used X-ray spectroscopy of the kaonic atoms to determine the transition yields and the strong interaction induced shift and width of the lowest experimentally accessible level (1s for H and D and 2p for He). Shift and width are connected to the real and imaginary part of the scattering length. To disentangle the isospin dependent scattering lengths of the antikaon-nucleon interaction, measurements of Kp and of Kd are needed. We report here on an exploratory deuterium measurement, from which a limit for the yield of the K-series transitions was derived: Y(K_tot), Accepted by Nuclear Physics A

The DAΦNE electron–positron collider at the Laboratori Nazionali di Frascati of INFN has made available a unique quality low-energy negative kaons “beam”, which is being used to unlock the secrets of the kaon–nucleon/nuclei interactions at low energies by the SIDDHARTA(-2) and the AMADEUS experiments. SIDDHARTA has already performed unprecedented precision measurements of kaonic atoms, and is being presently upgraded, as SIDDHARTA-2, to approach new frontiers. The AMADEUS experiment already started a data taking with a dedicated carbon target, plans to perform in the coming years precision measurements on kaon–nuclei interactions at low-energies, in particular to study the possible formation of kaonic nuclei and the Λ ( 1405 ) . The two experiments are briefly presented in this paper.

The SIDDHARTA collaboration measured kaonic 3 He and 4 He 3d → 2p X-rays with gaseous targets at the DAΦNE e + e − collider. The 2p -state strong-interaction shifts and widths were precisely determined by using 144 high-resolution silicon drift detectors. The shift of K −4 He is in good agreement with theoretical calculations and consistent with the recent experimental result of KEK-PS E570. The shift of K −3 He is also determined for the first time. The newly determined widths are in agreement with optical model calculations.

Kaonic hydrogen atoms provide a unique laboratory to probe the kaon-nucleon strong interaction at the energy threshold, allowing an investigation of the interplay between spontaneous and explicit chiral symmetry breaking in low-energy QCD. The SIDDHARTA Collaboration has measured the $K$-series X rays of kaonic hydrogen atoms at the DA$\Phi$NE electron-positron collider of Laboratori Nazionali di Frascati, and has determined the most precise values of the strong-interaction induced shift and width of the $1s$ atomic energy level. This result provides vital constraints on the theoretical description of the low-energy $\bar{K}N$ interaction., Comment: 11 pages, 7 figures, Nuclear Physics A (in press) Special Issue on Strangeness Nuclear Physics

The DAΦNE electron–positron collider of the Laboratori Nazionali di Frascati of INFN has made available a unique quality low-energy negatively charged kaons “beam”, which is being used to study the kaon–nucleon/nuclei interactions by the SIDDHARTA-2 experiment and the AMADEUS Collaboration. The dynamics of the strong interaction processes in the nonperturbative regime is approached by lattice calculations and effective field theories (ChPT) which are still lacking experimental results in the lowenergy regime, fundamental for their good understanding. The studies of kaonic atoms and of the kaonic nuclear processes performed by SIDDHARTA-2 and AMADEUS play in this context a key-role.

The SIDDHARTA experiment (SIlicon Drift Detector for Hadronic Atom Research by Timing Application) had the aim to perform kaonic atoms X-ray transitions measurements, to better understand aspects of the low-energy QCD in the strangeness sector. The experiment combined the excellent low-energy kaon beam generated at DAΦNE, allowing to use gaseous targets, with excellent fast X-rays detectors: Silicon Drift Detectors. SIDDHARTA was installed on DAΦNE in autumn 2008 and took data till late 2009. Apart of the kaonic hydrogen and kaonic deuterium measurements, we have performed the kaonic helium transitions to the 2p level ( L -lines) measurements: for the first time in a gaseous target for helium4 and for the first time ever for kaonic helium3. The interest for such type of measurement was rather high, being it triggered by two reasons: the so-called "kaonic helium puzzle" (even if this was solved by KEK-PS E570 experiment, but a cross-check was useful) and some theoretical predictions of possible high energy shift (at the level of 10 eV). In this paper the preliminary results for the measurements to the 2p level ( L -series) for kaonic helium4 and kaonic helium3 are presented.

AMADEUS is an experiment planned to be performed at the DAFNE e+e− collider of the Frascati National Laboratories (Italy) of INFN, to investigate the antikaon‐nuclei interaction at low energies. AMADEUS will perform, for the first time, full‐acceptance studies of antikaon interaction in light nuclei, including a complete experimental program for the case of the kaonic clusters. The study of the absorption of antikaon by the nucleus will provide information concerning the K̄N interaction and the modification of the kaon mass in the nuclear medium. The experiment is being preceded by the study of the hadronic interactions of K− in the 4He of the drift chamber from the KLOE experiment data.

The SIDDHARTA experiment aims a precise measurement of K -series kaonic hydrogen x-rays and the first-ever measurement of the kaonic deuterium x-rays to determine the strong-interaction energy-level shifts and widths of the lowest lying atomic states. These measurements offer a unique possibility to precisely determine the isospin-dependent kaon-nucleon ( KN ) scattering lengths [1] which are directly connected with the physics of the KN interaction. Kaonic Helium transitions to the 2p level ( L -lines) were as well measured. The experiment has been performed at the DAΦNE e+e- collider which produces the Φ-resonance. The resulting low energy negative charged kaons, coming from the Φ decay, are well suited to be stopped efficiently in a high density gas target for producing such kind of atoms. As x-ray detectors, we employed 144 Silicon Drift Detectors developed especially for this experiment, having good energy resolution of 140 eV FWHM at 6keV and time resolution of sub-micro seconds. The data taking was completed in November 2009. In this paper, an overview of this experiment and preliminary results are presented, together with future plans.

We have measured the K‐series x‐rays of kaonic hydrogen atoms to determine the strong‐interaction energy‐level shift and width of the 1s atomic state with significant improvements over the previous experiments. The measurement offers a unique possibility to precisely determine the complex K−p S‐wave scattering length. We have also measured kaonic x‐ray spectra with several gaseous targets : deuterium, helium‐3 and helium‐4. In this paper, we present an overview of this experiment and preliminary spectra of those kaonic x‐rays.

The SIDDHARTA (SIlicon Drift Detector for Hadronic Atom Research with Timing Application) collaboration performed X-ray spectroscopy measurement of kaonic atoms at the DAΦNE e+e−collider. Low energy negative kaons from DAΦNE -factory were stopped in gaseous targets to produce kaonic atoms. We employed specially designed Silicon Drift Detectors(SDDs) to detect the kaonic X-rays. Based on the energy of kaonic- 4He 3d → 2p transition, we determined a new value of the 2p level strong-interaction shift of kaonic- 4He: 0 ± 6 (stat.)± 2 (syst.) eV[1]. Together with the result of recent E570 experiment[2] at the KEK-PS, a small shift (if any) of kaonic- 4He 2p level has become well established.

The KN system at rest makes a sensitive testing ground for low energy QCD. At the DAΦNE electron‐positron collider of Laboratori Nazionali di Frascati we study kaonic atoms, taking advantage of the low‐energy kaons from Φ‐mesons decaying nearly at rest. The DEAR (DAΦNE Exotic Atom Research) experiment at LNF delivered the most precise data on kaonic hydrogen up to now. DEAR and its follow‐up experiment SIDDHARTA (Silicon Drift Detector for Hadronic Atom Research by Timing Application) are using X‐ray spectroscopy of kaonic atoms to measure the strong interaction induced shift and width of the ground state. SIDDHARTA is the first experiment on kaonic helium‐3 and deuterium ever, and kaonic hydrogen was remeasured with improved precision.

The SIDDHARTA experiment (SIlicon Drift Detector for Hadronic Atom Research by Timing Application) aims to perform a precise measurement of the X-ray K-series of kaonic hydrogen and the first-ever measurement of kaonic deuterium, to obtain the strong-interaction energy-level shifts and widths of the lowest lying atomic states. The measurements will allow the determination of the isospin-dependent kaon-nucleon (KN) scattering lengths, directly connected to the physics of the KN interaction. The experiment uses the low-energy kaon beam generated at DAΦNE collider, high-density cryogenic targets and fast, large area X-ray spectroscopic detectors. In addition to the kaonic hydrogen and kaonic deuterium, the collaboration performed measurements of the kaonic Helium transitions to the 2p level (L-lines). Kaonic Helium 4 was measured for the first time in a gaseous target while the kaonic Helium 3 was mesured for the first time ever.

The DAΦNE electron-positron collider at the Frascati National Laboratories has made available a unique “beam” of negative kaons providing unprecedented conditions for the study of the low-energy kaon-nucleon interaction, a field still largely unexplored. The DEAR (DAΦNE Exotic Atom Research) experiment at DAΦNE and its successor SIDDHARTA (SIlicon Drift Detector for Hadronic Atom Research by Timing Application) aim at a precision measurement of the strong interaction shift and width of the fundamental 1s level, via the measurement of the X-rays transitions to this level, for kaonic hydrogen and kaonic deuterium. The final aim is to extract the isospin dependent antikaon-nucleon scattering lengths which contribute to the understanding of aspects of chiral symmetry breaking in the strangeness sector. Other kaonic atoms transition measurements possible at DAΦNE are under study.

The DEAR experiment performed at the DAΦNE electron-positron collider (Frascati, Italy) studied the strong interaction shift and width of the 1s state in kaonic hydrogen using X-ray spectroscopy. The repulsive character of the kaon-proton interaction at threshold was confirmed and the most precise values of the shift and width were obtained. However, high precision data at the percent level are highly requested to further develop the theories and thus our understanding of the low-energy antikaon-nucleon interaction. Therefore, a new series of precision experiments on kaonic hydrogen and kaonic deuterium are planned at LNF.

Low-energy QCD is still lacking experimental results, fundamental for reaching a good understanding of the strangeness sector. The information provided by the low energy kaon- nucleon/nuclei interaction is accessible through the study of kaonic atoms and kaonic nuclear processes. The lightest atomic systems, namely the kaonic hydrogen and the kaonic deuterium, provide the isospin dependent kaon-nucleon scattering lengths by measuring the X-rays emitted during their de-excitation to the 1s level. The most precise kaonic hydrogen measurement to date, together with an exploratory measurement of kaonic deuterium and of upper-level transitions in kaonic helium 3 and kaonic helium 4 were carried out at the DA?NE collider by the SIDDHARTA collaboration. Presently, a significantly upgraded setup developped by the SIDDHARTA-2 collaboration is ready to perform a precise measurement of kaonic deuterium and, afterwards, of heavier exotic atoms. In parallel, the kaon-nuclei interaction at momenta below 130 MeV/c is studied by the AMADEUS collaboration, using the KLOE detector and a dedicated setup inserted in the central region, near the interaction point. Preliminary results of the study of charged antikaons interacting with nuclei are shown, including an analysis of the controversial ?(1405).