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The X-ray measurements of kaonic atoms play an important role for understanding the low-energy QCD in the strangeness sector. The SIDDHARTA experiment studied the X-ray transitions of 4 light kaonic atoms (H, D, 3 He, and 4 He) using the DAFNE electron-positron collider at LNF (Italy). Most precise values of the shift and width of the kaonic hydrogen 1s state were determined, which have been now used as fundamental information for the low-energy K − p interaction in theoretical studies. An upper limit of the X-ray yield of kaonic deuterium was derived, important for future K − d experiments. The shifts and widths of the kaonic 3 He and 4 He 2p states were obtained, confirming the end of the "kaonic helium puzzle". In this contribution also the plans for new experiments of kaonic deuterium are being presented.

The DAΦNE electron-positron collider at the Laboratori Nazionali di Frascati of INFN, Italy has made available a unique quality low-energy negatively charged kaons "beam", which is used to unveil the secrets of the kaon-nucleon/nuclei interactions at low energies by the SIDDHARTA-2 and 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 plans to perform in the coming years precision measurements on kaon-nuclei interactions at low-energies, to study the possible formation of kaonic nuclei, of the Λ(1405) and of many other processes involving strangeness. © Owned by the authors, published by EDP Sciences, 2013.

The strong interaction of charged antikaons (K − ) with nucleons and nuclei in the low-energy regime is a fascinating topic. The antikaon plays a peculiar role in hadron physics due to the strong attraction antikaon-nucleon which is a key question for possible kaonic nuclear bound states. A rather direct experimental access to the antikaon- nucleon scattering lengths is provided by precision X-ray spectroscopy of transitions to low-lying states in light kaonic atoms like kaonic hydrogen and deuterium. After the successful completion of precision measurements on kaonic hydrogen and helium iso- topes by SIDDHARTA at DAΦNE/LNF, new X-ray studies with the focus on kaonic deuterium are in preparation (SIDDHARTA2). In the future with kaonic deuterium data the antikaon-nucleon isospin-dependent scattering lengths can be extracted for the first time. An overview of the experimental results of SIDDHARTA and an outlook to fu- ture perspectives in the SIDDHARTA2 experiments in this frontier research field will be given.

The SIDDHARTA experiment at the DAΦNE collider of LNF-INFN performed in 2009 high precision measurements of kaonic hydrogen and kaonic helium atomic transitions. To determine the KN isospin dependent scattering lenghts an important measurement, namely the kaonic deuterium one, is, however, still missing. Due to the very low expected yield of the kaonic deuterium Kα transition, a major improvement in the signal over background ratio is needed. To achieve a further background reduction, a second level trigger, based on the detection of charged pions produced by the K^− absorption on various materials, including the target gas nuclei, is planned to be implemented in the future SIDDHARTA-2 experiment. For shielding-related geometrical limitations, a single side of the scintillators can be accessed ; in order to reach a good time resolution and uniform efficiency, a both- end readout was then realized with complex multi-reflection light guides. In this work, the results of the tests made on a detector prototype, performed on the πM−1 beamline of the Paul Scherrer Institute (Switzerland), are presented. The tests had the goal to determine the efficiency and the time resolution for pions, which should comply with the minimum required values of 90% and 1 ns (FWHM) respectively. The obtained results, 96% efficiency and 750 ps FWHM for 170 MeV/c momentum pions, qualify the prototype as an excellent second level trigger for the SIDDHARTA-2 experiment. Similar results for 170 MeV/c momentum muons and electrons are also presented.

This work presents the SIDDHARTA experimental results on the kaonic hydrogen and helium atoms, reviewing some fundamental aspects of the physics case. After an introduction about the fundamental role played by these bound systems and their X-ray transitions measurements in testing the reliability of the Chiral Perturbation Theory as a realisation of Quantum Chromodynamics at low energies, a short review of the light kaonic atoms physics is given. The review, highlighting the experimental challenges, aims to better understand the SIDDHARTA performances to obtain the most precise spectroscopic X-ray measurements of these light kaonic atoms. A description of the SIDDHARTA apparatus is followed by the presentation of the results on kaonic hydrogen and helium, nowadays the most precise available in literature.

The Pauli exclusion principle (PEP) and, more generally, the spin-statistics connection, is at the very basis of our understanding of matter. The PEP spurs, presently, a lively debate on its possible limits, deeply rooted in the very foundations of Quantum Field Theory. Therefore, it is extremely important to test the limits of its validity. Quon theory provides a suitable mathematical framework of possible violation of PEP, where the q violation parameter translates into a probability of violating PEP. Experimentally, setting a bound on PEP violation means confining the q-parameter to a value very close to either 1 (for bosons) or -1 (for fermions). The VIP (Violation of the Pauli exclusion principle) experiment established a limit on the probability that PEP is violated by electrons, using the method of searching for PEP forbidden atomic transitions in copper. We describe the experimental method, the obtained results, both in terms of the q-parameter and as probability of PEP violation, we briefly discuss the results and present future plans to go beyond the actual limit by upgrading the experimental technique using vetoed new spectroscopic fast Silicon Drift Detectors. We mention as well the possibility of using a similar experimental technique to search for eventual X-rays generated as a signature of the spontaneous collapse of the wave function, predicted by continuous spontaneous localization type theories.

Kaonic Hydrogen and Helium X-ray measurements play nowadays a fundamental role in testing the reliability of the Chiral Perturbation Theory as a realisation of the Quantum Chromodynamics at low energies. Dictated by both electromagnetic and strong interaction, X-ray transitions at lower energy levels of these complex bound systems offer indeed the unique opportunity to perform a threshold measurements of zero-energy meson-nucleon scattering. Nowadays the SIDDHARTA experiment at DAFNE collider is the only apparatus which can provide such kind of measurements with the high precision needed to disentangle different theoretical calculation scenarios. In this work we present the SIDDHARTA experiment performances and results, with a focus on the main topics of light kaonic atom physics.

One of the fundamental rules of nature and a pillar in the foundation of quantum theory and thus of modern physics is represented by the Pauli Exclusion Principle. We know that this principle is extremely well fulfilled due to many observations. Numerous experiments were performed to search for tiny violation of this rule in various systems. The experiment VIP at the Gran Sasso underground laboratory is searching for possible small violations of the Pauli Exclusion Principle for electrons leading to forbidden X-ray transitions in copper atoms. VIP is aiming at a test of the Pauli Exclusion Principle for electrons with high accuracy, down to the level of 10$^{-29}$ - 10$^{-30}$, thus improving the previous limit by 3-4 orders of magnitude. The experimental method, results obtained so far and new developments within VIP2 (follow-up experiment at Gran Sasso, in preparation) to further increase the precision by 2 orders of magnitude will be presented., Proceedings DISCRETE 2012-Third Symposium on Prospects in the Physics of Discrete Symmetries, Lisbon, December 3-7, 2012

We are preparing Silicon Drift Detecters (SDDs) for a precision spectroscopy of kaonic helium-3 3d→2p x-rays (~6.2 keV) at J-PARC (E17, DAY-1). Since we need to operate SDDs and their preamplifiers in a cryogenic system, their low-temperature behavior was investigated. The optimal operational temperatures were found to be 110 - 130 K and over 270 K for SDDs and preamplifiers, respectively. In such condition, energy resolution is around 150 eV (FWHM) with 5.9 keV x-rays and time resolution is around 400 ns (FWHM). We also investigated the effect of different incident angles to verify our calibration method in E17. Although response function depends on incident angle, Mn Ka peak positions differ at most 0.5 eV equivalent. Further basic studies of SDDs are ongoing toward the physics run planned in 2011.

We will measure the Balmer-series x-rays of kaonic-3He atoms using large-area high-resolution silicon drift x-rays detectors in order to provide the crucial information of K−-nucleus strong interaction at the low energy limit. The strong interaction 2p level shift will be determined with a precision of a few eV. At the present status, the construction of all detectors is in progress. In February, 2009, the first tuning of K1.8BR beamline was performed by the secondary beam generated in J-PARC hadron facility. The data taking will be started soon.

The J-PARC E15 experiment will be performed to search for the simplest kaonic nuclear bound state, K− pp , by the in-flight 3 He(K − ,n) reaction. The exclusive measurement can be performed by a simultaneous measurement of the missing mass using the primary neutron and the invariant mass via the expected decay, K− pp → Λp → pπ− p . In this report, an overview of the experiment and the preparation status are presented.

The first measurement of the yields of three kaonic nitrogen X-ray transitions, using the DEAR (DAΦNE Exotic Atom Research) setup at the DAΦNE collider of Frascati, is reported. The yields are 41.5±8.7(stat.)±4.1(sys.)% for the n=7→6 transition, 55.0±3.9(stat.)±5.5(sys.)% for the n=6→5 transition and 57.4±15.2(stat.)±5.7(sys.)% for the n=5→4 transition at a density ρ=3.4ρNTP. By using the experimental yields in an atomic cascade calculation, a 1 to 3% K-shell electron population in the n=6 level was deduced.

Bragg spectroscopy is a consolidated experimental method for high energy resolution X-ray measurements. However, this technique is limited to the detection of photons produced from point-like or well collimated sources and becomes quite inefficient for photons generated in extended and diffused ones; also, the possibility to perform simultaneous measurements of several X-ray lines is of great benefit when low rate signals are expected and individual angular scans require long exposure times. We present a prototype of a high resolution Highly Annealed Pyrolytic Graphite (HAPG) mosaic crystals based X-ray spectrometer, developed by the VOXES (high resolution VOn hamos X-ray spectrometer using HAPG for extended sources) collaboration at INFN Laboratories of Frascati, able to work with extended (millimetric) and isotropic sources. The spectrometer has been tested in the energy range 6–19 keV, with the aim to deliver a cost effective system having an energy resolution (FWHM) at the level of few eV, able to perform sub-eV precision measurements of single and multielement targets in a broad energy range. In this paper, the working principle of the VOXES spectrometer is presented, including a detailed description of the geometry, of the calibration methods and of the spectral fitting functions. Results of X-ray tracing simulations are compared to the experiment. The main results achieved by our spectrometer regard the peak resolutions. In particular, we report values as low as 4.02 ± 0.08 eV and 3.60 ± 0.05 eV for the Fe(Kα1,2) and Cu(Kα1,2) lines; for larger dynamic ranges, we report single shot spectra with Cu(Kα1,2) Ni(Kβ) and Zn(Kα1,2) lines with best resolution values of 5.15 ± 0.13 eV, 6.02 ± 0.24 eV and 6.20 ± 0.34 eV, respectively. Finally, we explored the capabilities of our spectrometer for energies above 15 keV, obtaining for Mo(Kα1,2) and Nb(Kβ) lines resolution values of 19.44 ± 0.75 eV and 39.90 ± 1.48 eV, respectively. The proposed spectrometer has possible applications in several fields, going from fundamental physics, synchrotron radiation and X-FEL applications, medicine and industry to hadronic physics experiments, where its performances make it a fundamental tool for a series of measurements like the energies of kaonic atoms transitions, allowing to extract fundamental parameters in the low energy QCD in the strangeness sector.

The $\bar{K}N$ system at threshold is a sensitive testing ground for low energy QCD, especially for the explicit chiral symmetry breaking. Therefore, we have measured the $K$-series x rays of kaonic hydrogen atoms at the DA$\Phi$NE electron-positron collider of Laboratori Nazionali di Frascati, and have determined the most precise values of the strong-interaction energy-level shift and width of the $1s$ atomic state. As x-ray detectors, we used large-area silicon drift detectors having excellent energy and timing resolution, which were developed especially for the SIDDHARTA experiment. The shift and width were determined to be $\epsilon_{1s} = -283 \pm 36 \pm 6 {(syst)}$ eV and $\Gamma_{1s} = 541 \pm 89 {(stat)} \pm 22 {(syst)}$ eV, respectively. The new values will provide vital constraints on the theoretical description of the low-energy $\bar{K}N$ interaction., Comment: 5 figures, submitted to Physics Letters B

The AMADEUS experiment aims to perform dedicated precision studies in the sector of low-energy kaon-nuclei interaction at the DA NE collider at LNF-INFN. In particular, the experiment plans to perform measurements of the debated deeply bound kaonic nuclear states, to deepen our knowledge about the controversial state (1405) and to measure the low energy cross section of K on light nuclei. AMADEUS will exploit the process of stopped kaons in cryogenic gaseous targets, measuring both charged and neutral particles produced in a 4 geometry, so performing a full study of the various inter- action channels. Taking advantage of the fact that the KLOE drift chamber is mainly filled with 4 He (90% helium 10% isobutane) according to Monte Carlo simulations about 0.1% of kaons from DA NE should stop in the inner volume of the drift chamber; the analysis of the existing KLOE data (run from 2002 to 2005) is presently going on, searching for hadronic interactions of K in such an active target. The AMADEUS physics program and preliminary results from the analysis of KLOE data will be discussed.

The \(\overline{K}N\) system at rest plays a key role for the understanding of strong interaction of hadrons with strangeness involved. The experiment SIDDHARTA used X-ray spectroscopy of kaonic atoms to measure the strong interaction induced shift and width of the ground state. It was the first experiment on kaonic He3 and deuterium ever, kaonic hydrogen was measured with improved precision resulting in \(\epsilon_{1s} = -283 \pm 36 \mbox{(stat)} \pm 6 \mbox{(syst)}\) eV and \(\Gamma_{1s} = 541 \pm 89 \mbox{(stat)} \pm 22 \mbox{(syst)}\) eV. Additionally a scheme for an improved future experiment on kaonic deuterium is introduced in this contribution.

With precision X-ray spectroscopy of kaonic hydrogen at the DAΦNE electron-positron collider at Laboratori Nazionali di Frascati the chiral symmetry breaking scenario in the strangeness sector will be investigated by studying the K-p s-wave interaction at threshold. This is possible by observing the strong interaction induced shift and width of the 1s state in kaonic hydrogen atoms. The results of the first measurement at LNF with DEAR (DAΦNE Exotic Atom Research) will be given and the new SIDDHARTA (Silicon Drift Detector for Hadronic Atom Research with Timing Application) project will be described, which is aiming at a substantial improvement of the preceding DEAR result.

Recent results obtained by the AMADEUS Collaboration on the experimental investigation of the K− low-energy interaction with light nuclei are summarised. The step 0 of AMADEUS consists in the analysis of the data collected at the DAΦNE collider with the KLOE detector during the 2004/2005 data taking campaign. The low momentum K− particles (pK ∼ 127 MeV/c) are absorbed in the light nuclei contained in the detector setup (H, 4He, 9Be and 12C) and hyperon–pion/hyperon–nucleons, emitted in the final state, are reconstructed. From the study of Λπ− and Λp correlated production, important information on the KN¯ strong interaction in the non-perturbative QCD regime are extracted.

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 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 Silicon-Drift X-ray detectors. The measurement of kaonic deuterium will be realized in the near future by SIDDHARTA-2, a major upgrade of SIDDHARTA.