Search

The most important information still missing in the field of the low-energy antikaon-nucleon inter actions studies is the experimental determination of the hadronic energy shift and width of kaonic deuterium. This measurement will be performed by the SIDDHARTA-2 experiment, installed at the DAΦNE collider and presently in data taking campaign. The precise measurement of the shift and width of the 1s level with respect to the purely electromagnetic calculated values, generated by the presence of the strong interaction, through the measurement of the X-ray transitions to this level, in kaonic hydrogen, was performed by the SIDDHARTA collaboration, the kaonic deuterium is underway by SIDDHARTA-2. These measurement will allow the first precise experimental extraction of the isospin dependent antikaon-nucleon scattering lengths, funda mental quantities for understanding low-energy QCD in the strangeness sector. The experimental challenge of the kaonic deuterium measurement is the very small X-rays yield, the even larger width (compared to kaonic hy drogen), and the difficulty to perform X-rays spectroscopy with weak signals in the high radiation environment of DAΦNE. It was, therefore, crucial to develop a new apparatus involving large-area X-rays detector system, to optimize the signal and to control and by improve the signal-to-background ratio by gaining in solid angle, increasing the timing capability, and as well implementing additional charge particle tracking veto systems.

KAMEO (Kaonic Atoms Measuring Nuclear Resonance Effects Ob-servables) is a proposal for an experiment aiming to perform the first consistent measurement of the E2 nuclear resonance effects in kaonic molybdenum A=94,96,98,100 isotopes. The E2 nuclear resonance mixes atomic states, due to the electrical quadrupole excitation of nuclear rotational states. It occurs in atoms having the energy of a nuclear excitation state closely matching an atomic de-excitation state energy, and affects the rates of X-ray atomic transitions matching the energy of the resonance. The measurement E2 nuclear resonance effect in KMO isotopes allows the study of the strong kaon-nucleus interaction in a rotational excited nuclear state. Moreover, the effect enables the K- to access an inner atomic level not easily reachable by the kaon normal cascade, due to the nuclear absorption. The KAMEO proposed apparatus consists of 4 enriched Mo A=94,96,98,100 isotope strips, exposed to the kaons produced by the DAφNE collider, for kaonic atoms formation, with a high-purity germanium detector, cooled with liquid nitrogen, used to measure the X-ray atomic transitions. The DAφNE collider is located at the National Laboratories of Frascati (LNF-INFN), in Italy. It is already suited for kaonic atoms measurement by the SIDDHARTA-2 collaboration.

The E2 nuclear resonance effect in kaonic atoms occurs when the energy of atomic de-excitation closely matches the energy of nuclear excitation, leading to the attenuation of some X-ray lines in the resonant isotope target. This phenomenon provides crucial information on the strong interaction between kaons and nuclei. The only nuclear E2 resonance effect observed so far was in the K− −9842Mo isotope, measured by G. L. Goldfrey, G-K. Lum, and C. E. Wiegand at Lawrence Berkeley Laboratory in 1975. However, the 25 hours of data taking were not sufficient to yield conclusive results. In four kaonic Molybdenum isotopes (9442Mo, 9642Mo, 9842and Mo, and 10042Mo), the nuclear E2 resonance effect is expected to occur at the same transition with similar energy values. To investigate this, the KAMEO (Kaonic Atoms Measuring Nuclear Resonance Effects Observables) experiment plans to conduct research on kaonic Molybdenum isotopes at the DAΦNE e+e− collider during the SIDDHARTA-2 experiment. The experimental strategy involves exposing four solid strip targets, each enriched with one Molybdenum isotope, to negatively charged kaons and using a germanium detector to measure X-ray transitions. In addition, a non-resonant 9242Mo isotope solid strip target will be used as a reference for standard non-resonant transitions.

Light kaonic atoms spectroscopy provides a unique approach to study the low-energy strong interaction in the strangeness sector. Precise measurements of X-ray emission from light kaonic atoms provide valuable information on kaon-nucleus interaction at threshold without the need for extrapolation as required in scattering experiments. The SIDDHARTA-2 experiment at the DAΦNE collider of INFN-LNF is now poised to perform the challenging measurements of the K−- d 2p → 1s transition to extract the isospin-dependent antikaonnucleon scattering lengths. To achieve this goal, the background reduction is a crucial factor. This paper provides an overview of the SIDDHARTA-2 Veto-1 system, which uses scintillators outside the vacuum chamber to detect charged particles produced by K− absorption by the nucleus. The arrival time of these particles is correlated with the position where the kaonic atom has been created inside the setup, allowing for the rejection of kaons stopped outside the target cell, which is a critical component for reducing the background and improve the accuracy of the measurement.

The SIDDHARTA-2 experiment aims to perform the first measurement of the kaonic deuterium 2p → 1s x-ray transition energy. Such measurement, together with the measurement of kaonic hydrogen 2p → 1s x-ray energy transition performed by the SIDDHARTA experiment in 2011, allows the determination of kaon proton and kaon neutron scattering lengths and represents a fundamental input for the low energies QCD in the strangeness sector theory. The SIDDHARTA-2 experiment is presently installed at the DAΦNE electronpositron collider at the National Laboratories of Frascati, in Italy. In May 2022, the kaonic 4He x-ray transitions measurement was performed by the complete SIDDHARTA-2 setup, by using a gaseous target. The result of this measurement is presented in this paper, with a specific focus on the background rejection performed by the kaon trigger system.

In this paper, an overview of kaonic atoms studies from the late 90s to nowadays at the DAΦNE collider at INFN-LNF is presented. Experiments on kaonic atoms are an important tool to test and optimize phenomenological models on the low-energy strong interaction. Since its construction, the DAΦNE collider has represented an ideal machine to perform kaonic atoms measurements, thanks to the unique beam of kaons coming from the øs produced in the collider decays. The DEAR and SIDDHARTA experiments achieved the precise evaluation of the shift and width of the 2p → 1s transition in kaonic hydrogen due to the strong interaction, and thus provided a measurement strictly linked to isospin-dependent antikaon--nucleon scattering lengths. To fully disentangle the iso-scalar and iso-vector scattering lengths, the measurement of kaonic deuterium is necessary as well. The SIDDHARTA-2 experiment is now taking data at the DAΦNE collider with the aim to fulfill the need of this measurement, and therefore provide important information to the various phenomenological models on low-energy strong interactions with strangeness. The SIDDHARTA-2 Collaboration is also exploring the possibility to perform future kaonic atoms experiments, developing X-ray detector systems beyond the current state-of-art. These measurements are crucial for a deeper understanding of the kaon interactions with nuclei and for solving the kaon mass "puzzle". [ABSTRACT FROM AUTHOR]

The SIDDHARTA-2 collaboration has developed a novel X-ray detection system based on cadmium-zinc-telluride (CZT, CdZnTe), marking the first application of this technology at the DAΦNE electron-positron collider at INFN-LNF. This work aims to demonstrate the stability of the detectors' performance in terms of linearity and resolution over short and long periods, thereby establishing their suitability for precise spectroscopic measurements within a collider environment. A reference calibration spectrum is presented in association with findings from assessments of linearity and resolution stability. Additionally, this study introduces a validated model of the response function of the detector. The relative deviations from the nominal values for the source transitions, obtained by fitting the entire spectrum with a background function and the previously introduced response function, are reported. Finally, a comparison of the calibration performance with and without beams circulating in the collider's rings is presented. These promising results pave the way for applying CZT detectors in kaonic atom studies and, more generally, in particle and nuclear physics spectroscopy.

Kaonic atom X-ray spectroscopy is a consolidated technique for investigations on the physics of strong kaon-nucleus/nucleon interaction. Several experiments have been conducted regarding the measurement of soft X-ray emission (<20 keV) from light kaonic atoms (hydrogen, deuterium, and helium). Currently, there have been new research activities within the framework of the SIDDHARTA-2 experiment and EXCALIBUR proposal focusing on performing precise and accurate measurements of hard X-rays (>20 keV) from intermediate kaonic atoms (carbon, aluminum, and sulfur). In this context, we investigated cadmium-zinc-telluride (CdZnTe or CZT) detectors, which have recently demonstrated high-resolution capabilities for hard X-ray and gamma-ray detection. A demonstrator prototype based on a new cadmium-zinc-telluride quasi-hemispherical detector and custom digital pulse processing electronics was developed. The detector covered a detection area of 1 cm 2 with a single readout channel and interesting room-temperature performance with energy resolution of 4.4% (2.6 keV), 3% (3.7 keV), and 1.4% (9.3 keV) FWHM at 59.5, 122.1, and 662 keV, respectively. The results from X-ray measurements at the DAΦNE collider at the INFN National Laboratories of Frascati (Italy) are also presented with particular attention to the effects and rejection of electromagnetic and hadronic background.