The BGO-OD experiment at the ELSA accelerator facility uses an energy tagged bremstrahlung photon beam to investigate the excitation structure of the nucleon. The setup consists of a highly segmented BGO calorimeter surrounding the target, with a particle tracking magnetic spectrometer at forward angles. BGO-OD is ideal for investigating low momentum transfer processes due to the acceptance and high momentum resolution at forward angles. In particular, this enables the investigation of strangeness photoproduction where t-channel exchange mechanisms play an important role. This also allows access to a kinematic region where extended, molecular structure may manifest in reaction mechanisms. The extensive strangeness photoproduction programme includes the photoproduction of neutral and charged kaons using both hydrogen and deuterium targets.

The AMADEUS collaboration studies low-energy K- interactions with light nuclei in order to clarify some aspects related to the behaviour of hadrons containing strangeness in nuclear medium. One of the main topics is the quest about the possible formation of Kaonic Nuclear Clusters (KNC), which depends on the strength of the anti-kaons interaction with nucleons. In kaonic absorption experiments, the search for KNC is strictly connected with the measurement of the yields of the so-called multi-nucleon absorption processes. In this paper, the study of Sigma(0) p correlated production from K- absorption in C-12, using the KLOE 2004-2005 data set, is reported. The yield of the two nucleon absorption (2NA), when the produced Sigma 0 and p particles are free from any final state interaction process, was measured for the first time. The contribution of a ppK(-) bound state was also tested. The best fit is obtained for a ppK(-) state with a binding energy of 45 MeV and a width of 30 MeV, but the statistical significance is at the level of 1 sigma only.

A new experiment is described to detect a permanent electric dipole moment of the proton with a sensitivity of 10(-29) e . cm by using polarized "magic" momentum 0.7 GeV/c protons in an all-electric storage ring. Systematic errors relevant to the experiment are discussed and techniques to address them are presented. The measurement is sensitive to new physics beyond the standard model at the scale of 3000 TeV. (C) 2016 Author(s).

The BGO Rugby Ball is a large solid angle electromagnetic calorimeter now installed in the ELSA Facility in Bonn. The BGO is operating in the BGO-OD experiment aiming to study meson photoproduction off proton and neutron induced by a Bremsstrahlung polarized gamma beam of energies from 0.2 to 3.2 GeV and an intensity of 5 x 10(7) photons per second. The scintillating material characteristics and the photomultiplier read-out make this detector particularly suited for the detection of medium energy photons and electrons with very good energy resolution. The detector has been equipped with a new electronics read-out system, consisting of 30 sampling ADC Wie-Ne-R modules which perform the off-line reconstruction of the signal start-time allowing for a good timing resolution. Performances in linearity, resolution and time response have been carefully tested at the Beam Test Facility of the INFN National Laboratories in Frascati by using a matrix of 7 BGO crystals coupled to photomultipliers and equipped with the Wie-Ne-R sampling ADCs.

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 DA Phi NE 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 kaonic He-3 and He-4 3d -> 2p transitions in gaseous targets were observed by the SIDDHARTA experiment. The X-ray energies of these transitions were measured with large-area silicon-drift detectors using the timing information of the K+K- pairs produced by the DA Phi NE e(+)e(-) collider. The strong-interaction shifts and widths both of the kaonic He-3 and He-4 2p states were determined, which are much smaller than the results obtained by the previous experiments. The "kaonic helium puzzle" (a discrepancy between theory and experiment) was now resolved. (C) 2012 Elsevier B.V. All rights reserved.

The X-ray transition yields of kaonic atoms produced in Kapton polyimide (C(22)HiON(2)O(5)) were measured for the first time in the SIDDHARTA experiment. X-ray yields of the kaonic atoms with low atomic numbers (Z = 6,7, and 8) and transitions with high principal quantum numbers (n = 5-8) were determined. The relative yields of the successive transitions in the same atoms and the yield ratios of carbon-to-nitrogen (C:N) and carbon-to-oxygen (C:O) for the same transitions were also determined. These X-ray yields provide important information for understanding the capture ratios and cascade mechanisms of kaonic atoms produced in a compound material, such as Kapton. (C) 2013 Elsevier B.V. All rights reserved.

Compton backscattering gamma ray beams are characterized by a high degree of linear and circular polarization with low unpolarized backgrounds and have proven to provide very precise measurements of polarization observables. Latest results from LEGS and GRAAL experiments on proton and deuteron targets are presented. The Sigma beam asymmetry for omega photoproduction has been measured by the GRAAL collaboration for both the omega -> pi(0)gamma and the omega -> pi(+)pi(+)pi(0) decay channels on the proton target; single and double polarization asymmetries have been provided also for the K photoproduction channel. E and G double polarization asymmetries for single pion photoproduction on the proton and deuteron have been measured at LEGS using a frozen spin HD target.

AMADEUS is an experiment planned to be performed at the DA Phi NE 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 nuclear clusters. The study of the absorption of antikaon by the nucleus will provide information concerning the (K) over barN 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 He-4 of the drift chamber from the KLOE experiment data.

The SIDDHARTA experiment measured the kaonic He-3 and He-4 3d -> 2p X-ray transitions using gaseous targets for the first time. The strong-interaction shift both of the kaonic He-3 and He-4 2p states was determined with a precision of a few eV. The shift of kaonic He-4 is much smaller than the values obtained in the experiments performed in 70's and 80's, while it is consistent with the recent result of the KEK E570 experiment, as well as the theoretical calculated values. Therefore, the problem on kaonic helium (the "kaonic helium puzzle") was definitely solved. The first observation of the kaonic He-3 X-rays was also achieved in the SIDDHARTA experiment. The shift both of kaonic He-3 and He-4 was found to be as small as a few eV.

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 (K) over barN interaction. (C) 2012 Elsevier B.V. All rights reserved.

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.

The AMADEUS collaboration is performing experimental investigations in the sector of the low energy strangeness hadron physics by taking advantage of the DA Phi NE 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, He-4, Be-9 and C-12, both at-rest and in-flight, are studied with the aim to determine the nature of the controversial Lambda ( 1405), the non-resonant hyperon pion formation amplitude below the (K) over barN 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 first observation of the kaonic (3)He 3d -> 2p transition was made, using slow K(-) mesons stopped in a gaseous (3)He target. The kaonic atom X-rays were detected with large-area silicon drift detectors using the timing information of the K(+)K(-) pairs of phi-meson decays produced by the DA Phi NE e(+)e(-) collider. The strong interaction shift of the kaonic (3)He 2p state was determined to be -2 +/- 2 (stat) +/- 4 (syst) eV. (c) 2011 Elsevier B.V. All rights reserved.

The (K) over barN 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 Is 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 +/- 36(stat) +/- 6(syst) eV and Gamma(1s) = 541 +/- 89(stat) +/- 22(syst) eV, respectively. The new values will provide vital constraints on the theoretical description of the low-energy (K) over barN interaction. (C) 2011 Elsevier B.V. All rights reserved.