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In this paper we present the results of a new kaonic helium-4 measurement with a 1.37 g/l gaseous target by the SIDDHARTA-2 experiment at the DA{\Phi}NE collider. We measured, for the first time, the energies and yields of three transitions belonging to the Mseries. Moreover, we improved by a factor about three, the statistical precision of the 2p level energy shift and width induced by the strong interaction, obtaining the most precise measurement for gaseous kaonic helium, and measured the yield of the L{\alpha} transition at the employed density, providing a new experimental input to investigate the density dependence of kaonic atoms transitions yield., Comment: 12 pages, 5 figures, 3 tables

In this work, we present novel Machine Learning and Differentiable Programming enhanced calibration techniques used to improve the energy resolution of the Silicon Drift Detectors (SDDs) of the VIP-2 underground experiment at the Gran Sasso National Laboratory (LNGS). We achieve for the first time a Full Width at Half Maximum (FWHM) in VIP-2 below 180 eV at 8 keV, improving around 10 eV on the previous state-of-the-art. SDDs energy resolution is a key parameter in the VIP-2 experiment, which is dedicated to searches for physics beyond the standard quantum theory, targeting Pauli Exclusion Principle (PEP) violating atomic transitions. Additionally, we show that this method can correct for potential miscalibrations, requiring less fine-tuning with respect to standard methods., Comment: Submitted to Measurement Science and Technology

The SIDDHARTA-2 experiment installed at the DA$\mathrm{\Phi}$NE collider of INFN-LNF performed, for the first time, measurements of high-n transitions in intermediate mass kaonic atoms during the data taking campaigns of 2021 and 2022. Kaonic carbon, oxygen, nitrogen and aluminium transitions, which occur in the setup materials, were measured by using the kaons stopped in the gaseous helium target cell with aluminium frames and Kapton walls, and are reported in this paper. These new kaonic atoms measurements add valuable input to the kaonic atoms transitions data base, which is used as a reference for theories and models of the low-energy strong interaction between antikaon and nuclei. Moreover, these results pave the way for future dedicated kaonic atoms measurements through the whole periodic table and to a new era for the antikaon-nuclei studies at low energy., Comment: 8 pages, 7 figures

We present a new measurement of the $^4_\Lambda$H hypernuclear lifetime using in-flight $K^-$ + $^4$He $\rightarrow$ $^4_\Lambda$H + $\pi^0$ reaction at the J-PARC hadron facility. We demonstrate, for the first time, the effective selection of the hypernuclear bound state using only the $\gamma$-ray energy decayed from $\pi^0$. This opens the possibility for a systematic study of isospin partner hypernuclei through comparison with data from ($K^-$, $\pi^-$) reaction. As the first application of this method, our result for the $^4_\Lambda$H lifetime, $\tau(^4_\Lambda \mathrm{H}) = 206 \pm 8 (\mathrm{stat.}) \pm 12 (\mathrm{syst.})\ \mathrm{ps}$, is one of the most precise measurements to date. We are also preparing to measure the lifetime of the hypertriton ($^3_\Lambda$H) using the same setup in the near future.

We present the tests performed by the SIDDHARTA-2 collaboration at the DA{\Phi}NE collider with a quasi-hemispherical CdZnTe detector. The very good room-temperature energy resolution and efficiency in a wide energy range show that this detector technology is ideal for studying radiative transitions in intermediate and heavy-mass kaonic atoms. The CdZnTe detector was installed for the first time in an accelerator environment to perform tests on the background rejection capabilities, which were achieved by exploiting the SIDDHARTA-2 Luminosity Monitor. A spectrum with an $^{241}Am$ source has been acquired, with beams circulating in the main rings, and peak resolutions of 6% at 60 keV and of 2.2% at 511 keV have been achieved. The background suppression factor, which turned out to be of the order of $\simeq10^{5-6}$, opens the possibility to plan for future kaonic atom measurements with CdZnTe detectors.

The SIDDHARTA-2 experiment at the DA$\Phi$NE collider aims to perform precision measurements of kaonic atoms X-ray spectroscopy for the investigation of the antikaon-nucleon strong interaction. To achieve this goal, novel large-area Silicon Drift Detectors (SDDs) have been developed. These devices have special geometry, field configuration and readout electronics that ensure excellent performance in terms of linearity and stability. The paper presents preliminary results for the linearity determination and stability monitoring of the SDDs system during the measurement of kaonic deuterium carried out in the summer of 2022.

In this paper, we present the first tests performed after the full installation of the SIDDHARTA-2 experimental apparatus on the Interaction Region of the DA{\Phi}NE collider at the INFN National Laboratories of Frascati. Before starting the first measurement of the kaonic deuterium 2p{\rightarrow}1s transition, accurate evaluation of the background rejection. mainly achieved with the Kaon Trigger system, was required. This run, performed in the period 04-26/05/2022 with a 4 He gaseous target, confirmed the 10^5 rejection factor obtained with a reduced version of the setup and different machine conditions in 2021. This important outcome motivated the filling of the target cell with deuterium and the starting of the measurement campaign of the kaonic deuterium 2p{\rightarrow}1s transition.

The SIDDHARTA-2 experiment at the DA$\Phi$NE collider aims to perform the first kaonic deuterium X-ray transitions to the fundamental level measurement, with a systematic error at the level of a few eV. To achieve this challenging goal the experimental apparatus is equipped with 384 Silicon Drift Detectors (SDDs) distributed around its cryogenic gaseous target. The SDDs developed by the SIDDHARTA-2 collaboration are suitable for high precision kaonic atoms spectroscopy, thanks to their high energy and time resolutions combined with their radiation hardness. The energy response of each detector must be calibrated and monitored to keep the systematic error, due to processes such as gain fluctuations, at the level of 2-3 eV. This paper presents the SIDDHARTA-2 calibration method which was optimized during the preliminary phase of the experiment in the real background conditions of the DA$\Phi$NE collider, which is a fundamental tool to guarantee the high precision spectroscopic performances of the system over long periods of data taking, as that required for the kaonic deuterium measurement.

Kaonic atoms are a unique tool to explore quantum chromodynamics in the strangeness sector at low energy, with implications reaching neutron stars and dark matter. Precision X-ray spectroscopy can fully unlock the at-threshold isospin dependent antikaon-nucleon scattering lengths, via the atomic transitions to the fundamental level. While the SIDDHARTA experiment at the INFN-LNF DA$\Phi$NE collider successfully measured kaonic hydrogen, its successor SIDDHARTA-2 is starting now its data taking campaign aiming to finally fully disentangle the isoscalar and isovector scattering lengths via the measurement of kaonic deuterium. An overview of the first experimental results from a preparatory run for the SIDDAHARTA-2 experiment is presented., Comment: 13 pages, 7 figures, to be sumbitted to Phys. Scr. - Focus on New Frontiers in Physics - Selected Papers from ICNFP 2021

The SIDDHARTINO experiment at the DA{\Phi}NE Collider of INFN-LNF, the pilot run for the SIDDHARTA-2 experiment which aims to perform the measurement of kaonic deuterium transitions to the fundamental level, has successfully been concluded. The paper reports the main results of this run, including the optimization of various components of the apparatus, among which the degrader needed to maximize the fraction of kaons stopped inside the target, through measurements of kaonic helium transitions to the 2p level. The obtained shift and width values are {\epsilon}_2p = E_exp-E_e.m = 0.2 {\pm} 2.5(stat) {\pm} 2(syst) eV and {\Gamma}_2p = 8 {\pm} 10 eV (stat), respectively. This new measurement of the shift, in particular, represents the most precise one for a gaseous target and is expected to contribute to a better understanding of the kaon-nuclei interaction at low energy.

The VOXES collaboration at INFN National Laboratories of Frascati developed a prototype of a high resolution Von Hamos X-ray spectrometer using HAPG (Highly Annealed Pyrolytic Graphite) mosaic crystals. This technology allows the employment of extended isotropic sources and could find application in several physics fields. The capability of the spectrometer to reach energy precision and resolution below 1 and 10 eV, respectively, when used with wide sources have been already demonstrated. Recently, the response of this device, for a $\rho$ = 206.7 mm cylindrically bent HAPG crystal using $CuK\alpha_{1,2}$ and $FeK\alpha_{1,2}$ XRF lines, has been investigated in terms of reflection efficiency by a dedicated ray-tracing simulation. Details of the simulation procedure and the comparison with the experimental results are presented. This study is crucial in order to retrieve information on the spectrometer signal collection efficiency, especially in the energy range in which the standard calibration procedures cannot be applied.

$\bar K$-nuclear bound systems, kaonic nuclei, have been widely discussed as products of the strongly attractive $\bar K N$ interaction in $I = 0$ channels. Recently, we demonstrated that kaonic nuclei can be produced via in-flight $(K^-,N)$ reactions using the low-momentum DC kaon beam at the J-PARC E15 experiment. We observed the simplest kaonic nuclei, $K^-pp$, having a much deeper binding energy than normal nuclei. For further studies, we have proposed a series of experimental programs for the systematic investigation of light kaonic nuclei, from $\bar K N$ ($\Lambda(1405)$) to $\bar K NNNN$. In the new experiment approved as J-PARC E80, we will measure the $\bar K NNN$ ($A=3$) system as a first step toward a comprehensive study., Comment: 10 pages, 5 figures, proceedings of the 8th Asia-Pacific Conference on Few-Body Problems in Physics (APFB2020), accepted for publication in Fwe-Body Systems

A luminosity monitor, based on plastic scintillator detectors, has been developed for the SIDDHARTA-2 experiment aiming to perform high precision measurements of kaonic atoms and was installed in 2020 on the DAFNE $e^+e^-$ collider at LNF (Laboratori Nazionali di Frascati, INFN). The main goal of this system is to provide the~instantaneous and integrated luminosity of the DAFNE facility by measuring the rate of $K^+K^-$ correlated pairs emitted by the phi meson decay. This task requires an accurate timing of the DAQ signals, as well as timing resolution below 1ns, in order to disentangle the $K^\pm$ signals from the background minimum ionizing particles (MIPs) produced during the $e^+e^-$ collisions at DAFNE. In this paper the luminosity monitor concept as well as its laboratory characterization and the first results inside DAFNE are presented., Comment: Published in JINST

Bragg spectroscopy is one of the best established experimental methods for high energy resolution X-ray measurements; however, this technique is limited to the measurement of photons producedfrom well collimated (tens of microns) or point-like sources and becomes quite inefficient for photonscoming from extended and diffused sources. The possibility to perform simultaneous measurementsof several energies is strongly demanded when low rate signals are expected and single angular scansrequire long exposure times. A prototype of a high resolution and high precision X-ray spectrometerworking also with extended isotropic sources, has been developed by the VOXES collaboration atINFN Laboratories of Frascati, using Highly Annealed Pyrolitic Graphite (HAPG) crystals in a semi- Von Hamos configuration, in which the position detector is rotated with respect to thestandard Von Hamos one, to increase the dynamic energy range. The aim is to deliver a cost effectivesystem having an energy resolution at the level of eV for X-ray energies from about 2 keV up to tensof keV, able to perform sub-eV precision measurements with non point-like sources. The proposedspectrometer has possible applications in several fields, going from fundamental physics to quantummechanics tests, synchrotron radiation and X-FEL applications, astronomy, medicine and industry.In particular, this technique is fundamental for a series of nuclear physics measurements like, forexample, the energies of the exotic atoms radiative transitions which allow to extract fundamentalparameters in the low energy QCD in the strangeness sector. In this work, the working principleof the spectrometer is presented, together with the tests and the results, in terms of resolution andsource, size obtained for Fe(K\alpha1,2), Cu(K\alpha1,2), Ni(K\beta), Zn(K\alpha1,2), Mo(K\alpha1,2) and Nb(K\beta)lines.

The VIP2 experiment tests the Pauli Exclusion Principle with high sensitivity, by searching for Pauli-forbidden atomic transitions from the 2p to the 1s shell in copper at about 8keV. The transition energy of Pauli-forbidden K X-rays is shifted by about 300 eV with respect to the normal allowed K line. This energy difference can be resolved using Silicon Drift Detectors. The data for this experiment is taken in the Gran Sasso underground laboratory (LNGS), which provides shielding from cosmic radiation. An overview of the detection system of the VIP2 experiment will be given. This includes the Silicon Drift Detectors used as X-ray detectors which provide an energy resolution of around 150 eV at 6 keV and timing information for active shielding. Furthermore, the low maintenance requirement makes them excellent X-ray detectors for the use in an underground laboratory. The VIP2 setup will be discussed which consists of a high current target system and a passive as well as an active shielding system using plastic scintillators read out by Silicon Photomultipliers.

The VIolation of Pauli exclusion principle -2 experiment, or VIP-2 experiment, at the Laboratori Nazionali del Gran Sasso searches for x-rays from copper atomic transition that are prohibited by the Pauli Exclusion Principle. Candidate direct violation events come from the transition of a $2p$ electron to the ground state that is already occupied by two electrons. From the first data taking campaign in 2016 of VIP-2 experiment, we determined a best upper limit of 3.4 $\times$ 10$^{-29}$ for the probability that such a violation exists. Significant improvement in the control of the experimental systematics was also achieved, although not explicitly reflected in the improved upper limit. By introducing a simultaneous spectral fit of the signal and background data in the analysis, we succeeded in taking into account systematic errors that could not be evaluated previously in this type of measurements., Comment: 18 pages, 10 figures, 2 tables, accepted by EPJ C on 12th April 2018

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 setup, SIDDHARTA-2, is being realized to reach this goal. In this paper, the results obtained in 2009 and the proposed SIDDHARTA-2 upgrades are presented.

Bragg spectroscopy is one of the best established experimental methods for high energy resolution X-ray measurements and has been widely used in several fields, going from fundamental physics to quantum mechanics tests, synchrotron radiation and X-FEL applications, astronomy, medicine and industry. However, this technique is limited to the measurement of photons produced from well collimated or point-like sources and becomes quite inefficient for photons coming from extended and diffused sources like those,for example, emitted in the exotic atoms radiative transitions. The VOXES project's goal is to realise a prototype of a high resolution and high precision X-ray spectrometer, using Highly Annealed Pyrolitic Graphite (HAPG) crystals in the Von Hamos configuration, working also for extended sources. The aim is to deliver a cost effective system having an energy resolution at the level of eV for X rays energies from about 2 keV up to tens of keV, able to perform sub-eV precision measurements with non point-like sources. In this paper, the working principle of VOXES, together with first results, are presented., Comment: arXiv admin note: text overlap with arXiv:1709.06503

The VOXES project's goal is to realize the first prototype of a high resolution and high precision X-ray spectrometer for diffused sources, using Highly Annealed Pyrolitic Graphite (HAPG) crystals combined with precision position detectors. The aim is to deliver a cost effective and easy to handle system having an energy resolution at the level of few eV for X-ray energies from about 2 keV up to tens of keV. There are many applications of the proposed spectrometer, going from fundamental physics (precision measurements of exotic atoms at DA$\Phi$NE collider and J-PARC, precision measurement of the $K^-$ mass solving the existing puzzle, quantum mechanics tests) to synchrotron radiation and applications (X-FEL), astronomy, medicine and industry. Here, the basic concept of such a spectrometer and the first results from a measurement of the characteristic Cu $K_{\alpha 1}$ and $K_{\alpha 2}$ X-ray lines are presented., Comment: 7 pages, 2 figures, Presented at 2 nd Jagiellonian Symposium on Fundamental and Applied Subatomic Physics