In this work, new measurements of absolute X-ray yields for several transitions in kaonic copper and, for the first time, in kaonic fluorine are reported. The data were collected by the SIDDHARTA-2 collaboration at the DAΦNE collider using a novel room-temperature Cadmium Zinc Telluride (CZT) detection system. Detection efficiencies were evaluated through a dedicated Geant4 Monte Carlo simulation of the full experimental setup, enabling the extraction of absolute yields per stopped kaon. The measured yields exhibit a systematic dependence on the principal quantum number, reflecting the interplay between radiative transitions, Auger de-excitation, and strong-interaction-induced nuclear capture. In kaonic fluorine, a suppression of the 4→3 transition yield relative to higher-n transitions is observed, providing evidence for the onset of strong-interaction effects already at the n=4 level. From this behaviour, a conservative lower limit on the corresponding strong-interaction width is derived. These results provide new quantitative constraints for cascade models of exotic atoms and extend experimental access to intermediate atomic levels where strong-interaction effects are not directly observable via level shifts and widths. They also establish CZT-based detection as a powerful and versatile approach for high-resolution X-ray spectroscopy of kaonic atoms in collider environments.

Biophotons are non-thermal and non-bioluminescent ultraweak photon emissions, first hypothesised by Gurwitsch as a regulatory mechanism in cell division, and then experimentally observed in living organisms. Today, two main hypotheses explain their origin: stochastic decay of excited molecules and coherent electromagnetic fields produced in biochemical processes. Recent interest focuses on the role of biophotons in cellular communication and disease monitoring. This study presents the first campaign of biophoton emission measurements from cultured astrocytes and glioblastoma cells, conducted at Fondazione Pisana per la Scienza (FPS) using two ultra-sensitive setups developed in collaboration between the National Laboratories of Frascati (LNF-INFN) and the University of Rome II Tor Vergata. The statistical analyses of the collected data revealed a clear separation between cellular signals and dark noise, confirming the high sensitivity of the apparatus. The Diffusion Entropy Analysis (DEA) was applied to the data to uncover dynamic patterns, revealing anomalous diffusion and long-range memory effects that may be related to intercellular signaling and cellular communication. These findings support the hypothesis that biophoton emissions encode rich information beyond intensity, reflecting metabolic and pathological states. The differences revealed by applying the Diffusion Entropy Analysis to the biophotonic signals of Astrocytes and Glioblastoma are highlighted and discussed in the paper. This work lays the groundwork for future studies on neuronal cultures and proposes biophoton dynamics as a promising tool for non-invasive diagnostics and the study of cellular communication.

The study of the strong interaction among hadrons at low energies remains one of the key challenges in fundamental physics because of its non-perturbative nature, which makes theoretical descriptions strongly dependent on experimental input. Although substantial progress has been made for systems involving up and down quarks, theoretical models in the strangeness sector continue to face limitations due to the lack of experimental data. Kaonic atoms provide a powerful tool to study the low-energy strong interaction with strangeness through the energy shifts and widths induced on their lowest atomic levels. In this context, kaonic deuterium X-ray spectroscopy has long represented one of the major open challenges in hadronic-atom physics because of its extremely low X-ray yield. This measurement is particularly important because it gives access to the experimentally inaccessible K^-n interaction at threshold energy. Here, we report the first observation of kaonic deuterium X-ray transitions, performed with the SIDDHARTA-2 experiment at the DAΦNE collider. We determine the strong-interaction shift and width of the 1s level to be ε_1s=-810.9±24.5 (stat)±2.1 (syst) eV and Γ_1s=812±97 (stat)±33 (syst) eV, respectively. This measurement constitutes the most precise experimental determination of the K^-d strong interaction at threshold and allows discrimination among competing theoretical models. Combined with the kaonic hydrogen measurement, this result provides the experimental input required to determine the isospin-dependent K^-N scattering lengths, with implications for the description of the nature of the first predicted hadronic molecular state, the Λ(1405), and neutron-rich matter.

Kaonic atoms provide a unique laboratory to investigate the interplay between atomic, nuclear, and strong-interaction physics. In heavy nuclei, atomic transitions can couple to low-lying collective nuclear excitations via the electric quadrupole interaction. When the energy difference between two kaonic atomic levels approaches that of a nuclear 2^+ excitation, a resonant configuration mixing may occur, known as the E2 nuclear resonance effect. In this work, we investigate the conditions for E2 resonance in kaonic molybdenum isotopes. We describe the mixing using state-of-the-art Dirac-Fock calculations combined with updated nuclear structure inputs, including recent electric quadrupole transition strength values and excitation energies. We evaluate the sensitivity of the effect to key parameters, assess its observability in future experiments such as the EXKALIBUR program, and discuss its impact on cascade dynamics. Our results demonstrate the potential of kaonic atoms as a probe of nuclear structure, complementary to conventional nuclear spectroscopy.

Abstract In this work, new measurements of absolute x-ray yields for several transitions in kaonic copper and, for the first time, in kaonic fluorine are reported. The data were collected by the SIDDHARTA-2 collaboration at the DA Φ NE collider using a novel room-temperature cadmium zinc telluride (CZT) detection system. Detection efficiencies were evaluated through a dedicated Geant4 Monte Carlo simulation of the full experimental setup, enabling the extraction of absolute yields per stopped kaon. The measured yields exhibit a systematic dependence on the principal quantum number, reflecting the interplay between radiative transitions, Auger de-excitation, and strong-interaction-induced nuclear capture. In kaonic fluorine, a suppression of the 4 → 3 transition yield relative to higher- n transitions is observed, providing evidence for the onset of strong-interaction effects already at the n = 4 level. From this behaviour, a conservative lower limit on the corresponding strong-interaction width is derived. These results provide new quantitative constraints for cascade models of exotic atoms and extend experimental access to intermediate atomic levels where strong-interaction effects are not directly observable via level shifts and widths. They also establish CZT-based detection as a powerful and versatile approach for high-resolution x-ray spectroscopy of kaonic atoms in collider environments.

This work presents the results of a time-based event selection for the search of x-ray signals from kaonic atom transitions using a quasi-hemispherical Cadmium-Zinc-Telluride (CZT) detector at the DA Phi NE collider. To mitigate the high background level in the measured x-ray spectra, a dedicated event selection strategy was developed, exploiting the precise timing correlation between e+e- collisions and detector signals. This approach enabled, for the first time, the observation of two characteristic x-ray transitions from kaonic aluminum atoms with a CZT detector. For the 5-4 transition at 50 keV, 362 +/- 41 (stat.) +/- 20 (sys.) signal events were observed over 1698 +/- 197 (stat.) +/- 25 (sys.) background events within +/- 5 sigma, with an energy resolution of 9.2% FWHM. For the 4-3 transition at 106 keV, 295 +/- 50 (stat.) +/- 20 (sys.) signal events were measured over 2939 +/- 500 (stat.) +/- 16 (sys.) background events, with an energy resolution of 6.6% FWHM. A background suppression of approximately 95% of the triggered data was achieved through this time-based selection. The demonstrated timing capability of the CZT detector proved highly effective in isolating time-correlated events within an 80 ns window, setting an important benchmark for the application of compound semiconductors in timing-based x-ray spectroscopy. These results highlight the potential of CZT-based detection systems for future precision measurements in high-radiation environments, paving the way for compact, room-temperature x-ray and gamma-ray spectrometers in fundamental physics and related fields.

The SIDDHARTA-2 experiment at the DA Phi NE collider of INFN-LNF performs high precision light kaonic atoms x-ray spectroscopy to investigate the kaon-nucleon(s) strong interaction in the low-energy (O(10 keV)) regime. A large area silicon drift detectors (SDDs) system has been developed to carry out these measurements. The collaboration aims to extend the measurements campaign to higher mass kaonic atoms, which exhibit transition lines at increased x-ray energies. In this context, the spectroscopic response of the SIDDHARTA-2 SDD system was investigated in terms of linearity and energy resolution up to 50 keV. An accuracy of the energy calibration procedure Delta E/E < 10 (-3) was achieved.

The SIDDHARTA-2 collaboration is performing research in the field of kaonic atoms spectroscopy. In this work, following an introduction on kaonic atoms and their importance for the development of low-energy strong interaction theories, the first result of the experiment (kaonic helium) is presented. This measurement was promising in the view of the main goal of the experiment, i.e. the first measurement of the kaonic deuterium transitions to the 1s level, important to model the kaon-nucleon interaction. In the last part of the paper future plans of the collaboration to measure new key quantities in kaonic atoms with beyond stat-of-the-art radiation detectors are also presented.

The VIP collaboration operates a Broad Energy Germanium detector at the Gran Sasso National Laboratory to measure radiation in the few keV to 100 keV range, aiming to search for spontaneous collapse induced radiation and atomic transitions that violate the Pauli Exclusion Principle. Here we present a machine learning based upgrade for the BEGe detector using an event selection strategy aimed at improving the efficiency in detecting low energy events down to 10 keV. The method employs a denoising autoencoder to suppress electronic and microphonic noises and to reconstruct pulse shapes, followed by a convolutional neural network that classifies waveforms as normal single site or events with anomalies. The workflow was validated on a dataset comprising more than 20000 waveforms recorded in 2021. The classifier achieves a receiver operating characteristic curve with an area under the curve of 0.99 and an accuracy of 95 percent. Applying this procedure lowers the minimum detectable energy of the final spectrum to approximately 10 keV. It also yields a measurable enhancement in spectral quality, including an improvement of about 14 percent in the signal to background ratio and a reduction of the energy resolution for the characteristic Pb and Bi gamma lines. These developments enhance the sensitivity of the BEGe detector to rare low energy signals and provide a scalable framework for future precision tests of quantum foundations in low background environments.

Cadmium zinc telluride (CZT) detectors offer excellent room-temperature energy resolution, making them well suited for X- and γ-ray spectroscopy in challenging environments. Within the SIDDHARTA-2 program at the DAΦNE collider, a new CZT-based detection system has been developed to enable precision measurements of kaonic atom transitions in the intermediate mass range. In this work, we report the results of a calibration campaign performed with the collider operating, aimed at assessing the detector performance. A dedicated setup, including an array of quasi-hemispherical CZT sensors and a ^152Eu source, was used to characterize the spectral response. The reconstructed emission lines were fitted with a model accounting for Gaussian response and incomplete charge recollection tails, and the detector linearity was evaluated by comparing the measured peak positions with their nominal energies. The results demonstrate that the CZT detector exhibits excellent linearity and stable operation with the collider on, confirming its suitability for future kaonic-atom spectroscopy at DAΦNE.

VOXES is a Von Hamos X-ray spectrometer developed at the INFN National Laboratories of Frascati for high-resolution laboratory X-ray spectroscopy in the 5–20 keV range. It uses curved mosaic crystals and motorized positioning stages to perform wavelength-dispersive X-ray fluorescence (WD-XRF) with sub-10 eV tunable resolution for extended and dilute samples. Recent developments include the integration of an energy-dispersive X-ray fluorescence (ED-XRF) line based on a silicon pin-diode detector, which enables flux monitoring and simultaneous ED and WD measurements. In addition, a dedicated liquid-sample holder has been introduced, and a Y-shaped support geometry, crucial for switching to a transmission layout, provides mechanical compatibility with laboratory XAS, now under implementation. These upgrades expand the versatility and automation of VOXES, strengthening its role as a table-top platform for laboratory X-ray spectroscopy.

The spin-statistics theorem leads to Pauli’s Exclusion Principle (PEP), the basis of the stability of matter and many other phenomena relevant to physics, astrophysics, cosmology, and even biology. Possible violations of the PEP (PEPV) have been searched for since its inception; they may come from various Beyond Standard Model descriptions, including Non-Commutative Quantum Gravity models and extensions of the Quantum Field Theory, which must follow the Messiah-Greenberg Super-Selection (MGSS) rule and lead to the Quon description of the spin-statistic symmetries: the parastatstics. Efforts to search for a PEPV are not new; however, they have typically measured those cases without respecting MGSS. VIP (VIolation of the Pauli exclusion principle) first and its successor VIP-2, both sited in the “Gran Sasso underground laboratory,” aimed to set the most stringent limit for the non-Paulian transition following the MGSS rule. After two years of data with VIP-2 and better modeling of the electron-atom interaction, we present the most stringent upper limit of the probability of PEP violation for this case ([Formula: see text]), thus completing the state-of-the-art of all possible PEPV cases, and the consequent constraint to the Quon description: [Formula: see text].

The high-precision kaonic neon X-ray transitions measurement performed by the SIDDHARTA-2 collaboration at the DAΦNE collider is reported. Both the X-ray energies and yields for high-n transitions were measured, demonstrating the feasibility of sub-eV Xray spectroscopy for kaonic atoms using low-Z gaseous targets. The measurement provides valuable insights into the de-excitation processes in kaonic atoms, providing new input data for the refinement of the corresponding theoretical models, and a framework for testing Quantum Electrodynamics in strange exotic atoms.

Kaonic atoms, formed when a negatively charged kaon replaces an electron, provide a unique laboratory to test fundamental interactions at low energies. EXKALIBUR (EXtensive Kaonic Atoms research: from LIthium and Beryllium to URanium) is a program to perform systematic, high-precision X-ray spectroscopy of selected kaonic atoms across the periodic table at the DA Phi NE accelerator at the National Laboratory of Frascati. Here, we outline its detector-driven strategy: silicon drift detectors for 10-40 keV transitions in light targets (Li, Be, B, O), CdZnTe detectors for 40-300 keV lines in intermediate-Z systems (Mg, Al, Si, S), and a high-purity germanium detector for high-Z atoms (Se, Zr, Ta, Mo, W, Pb), complemented by VOXES, a high-resolution crystal spectrometer for sub-eV studies. EXKALIBUR plans to (i) reduce the charged-kaon mass uncertainty below 10 keV, (ii) produce a database of nuclear shifts and widths to constrain multi-nucleon K--nucleus interactions models, and (iii) provide precision data for testing bound-state quantum electrodynamics in strong fields. We summarize the planned measurements and expected sensitivities within DA Phi NE luminosities.

The SIDDHARTA-2 Collaboration aims to measure for the first time the shift and width induced on the 1s level of kaonic deuterium by the strong interaction. In the preliminary phase to the experiment, a test run using a Helium-4 target was performed to optimize the performance of the full experimental apparatus. This preliminary study highlighted the possibility to measure transition lines coming from intermediate-mass kaonic atoms, such as kaonic carbon and kaonic aluminum. In order to measure transitions where strong interaction is manifesting at higher energies, out of the energy range of the SIDDHARTA-2 apparatus, the collaboration is testing a new detector system which exploits a novel compound semiconductor, the cadmium-zinc-telluride. Tests are now running at DAFNE to study the performance of this detector, exploring the possibility to build a dedicated setup.

In this paper, an overview of kaonic atoms studies from the late 90s to nowadays at the DA Phi NE 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 DA Phi NE collider has represented an ideal machine to perform kaonic atoms measurements, thanks to the unique beam of kaons coming from the cis 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 DA Phi NE 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".