Kaonic atoms measurements at the DAΦNE collider : the SIDDHARTA-2 experiment

The X-ray spectroscopy measurements of light kaonic atoms’ deexcitation towards the fundamental level provide unique information on the low-energy Quantum ChromoDynamics (QCD) in the strangeness sector, being a direct probe of the kaon/nucleon interaction at threshold, unobtainable through the scattering experiments. In this framework, the SIDDHARTA-2 collaboration is going to perform the first kaonic deuterium 2p $\to$ 1s transition measurement at the DAΦNE collider of Istituto Nazionale di Fisica Nucleare – Laboratori Nazionali di Frascati. Combining this measurement with the kaonic hydrogen one performed by SIDDHARTA in 2009 it will be possible to obtain, in a model-independent way, the isospin-dependent antikaon-nucleon scattering lengths. The paper introduces the SIDDHARTA-2 setup, an upgraded version with respect to the one used for the kaonic hydrogen measurement, dedicated to the ambitious kaonic deuterium measurement, together with the preliminary results obtained during the kaonic helium run, preparatory for the SIDDHARTA-2 data taking campaign

Main features of the SIDDHARTA-2 apparatus for kaonic deuterium X-ray measurements

The low-energy, non-perturbative regime of QCD can be studied directly by X-ray spectroscopy of light kaonic atoms. The SIDDHARTA-2 experiment, located at the DAΦNE collider, aims to measure the 2p $\to$ 1s transition in kaonic deuterium for the first time to extract the antikaon-nucleon scattering lengths. This measurement is impeded, inter alia, by the low K$^{-}$d X-ray yield. Hence, several updates have been implemented on the apparatus to increase the signal-to-background ratio, which are discussed in detail in this paper: a lightweight gas target cell, novel Silicon Drift Detectors for the X-ray detection with excellent performance, and a veto system for active background suppression. The experiment has undergone a first preparatory run during DAΦNE’s commissioning phase in 2021, concluding with a successful kaonic helium measurement

probing strong interaction with siddharta 2

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A charged particle veto detection system for kaonic deuterium measurements at DAΦNE

Im nicht-perturbativen, niederenergetischen Bereich der QCD wirft die Wechselwirkung zwischen Antikaonen und Nukleonen noch immer viele ungelöste Fragen auf und wird daher intensiv erforscht. Das Studium dieser Antikaon-N-Interaktionen bietet Einsicht in die komplexen Prozesse der chiralen Symmetriebrechung und führt zu einem besseren Verständnis von fundamentalen Konzepten in der Hadronenphysik, wie etwa die Herkunft der Hadronenmassen. Röntgenspektroskopie von kaonischen Atomen hat sich als vielseitiges Werkzeug zur Untersuchung der starken Wechselwirkung bei niedrigen Energien erwiesen, da sie eine direkte Beobachtung des Einflusses derselben auf den Grundzustand kaonischer Atome ermöglicht. Das SIDDHARTA-2-Experiment, das derzeit am DAΦNE-Beschleunigerkomplex im italienischen Frascati gebaut wird, hat die Bestimmung der Energieverschiebung und der Breite des 1s-Zustandes in kaonischem Deuterium mit einer Präzision von 30 eV beziehungsweise 75 eV zum Ziel. Diese Messung wird jedoch durch die für kaonisches Deuterium erwartete niedrige Röntgenausbeute bedeutend erschwert. Daher ist eine Verbesserung des Signal/Hintergrund-Verhältnisses um mindestens eine Größenordnung im Vergleich zu den vorhergehenden Messungen mit kaonischem Wasserstoff (SIDDHARTA) unbedingt erforderlich. Diese Verbesserung in SIDDHARTA-2 basiert auf der Implementierung dreier Updates: eines leichten, kryogenischen Targets, eines neuentwickelten großflächigen Röntgendetektionssystems bestehend aus Siliziumdriftdetektoren und eines Vetosystems zur Hintergrundunterdrückung. Dieses setzt sich aus einem äußeren Vetosystem (Veto-1) zur aktiven Abschirmung und einem inneren Vetosystem (Veto-2) zusammen. Letzteres ist neben der aktiven Abschirmung auch für die Unterdrückung von signalkorreliertem Hintergrund, bestehend aus geladenen Teilchen, verantwortlich. Für beide Vetosysteme ist eine hervorragende Zeitauflösung essentiell. Das Veto-2-System wurde am Stefan-Meyer-Institut gefertigt, getestet und optimiert. Seine Zeitauflösung, Nachweisempfindlichkeit sowie sein Verhalten in einem breiten Temperaturbereich wurden untersucht und zufriedenstellende Ergebnisse konnten erzielt werden. Ein erster Teil der Veto-2-Detektoreinheiten wurde im SIDDHARTA-2-Aufbau in Frascati installiert.In the non-perturbative, low-energetic regime of QCD, the interaction between antikaons and nucleons close to threshold still poses many unresolved questions and is thus the subject of extensive research. The study of the antikaon-N interaction allows to gain insight in the complex processes of chiral symmetry breaking, leading to a better understanding of fundamental concepts in hadron physics like the origin of the hadron masses. X-ray spectroscopy of kaonic atoms provides a versatile tool to study the strong interaction at low relative energies via a direct observation of its influence on the ground state of kaonic atoms. The SIDDHARTA-2 experiment, currently under construction at the DAΦNE collider complex in Frascati, Italy, aims to determine the energy shift and width of the kaonic deuterium 1s state induced by the strong interaction with precisions of 30 eV and 75 eV, respectively. However, this measurement is severely aggravated by the low kaonic deuterium X-ray yield. Due to this challenge, an improvement of the signal-to-background ratio by at least one order of magnitude compared to the previously performed kaonic hydrogen measurement (SIDDHARTA) is crucial. This increase will be achieved in SIDDHARTA-2 through the implementation of three updates: a lightweight, cryogenic target, a newly developed large-area X-ray detection system consisting of Silicon Drift Detectors, and a dedicated veto system for background suppression. The veto system consists of an outer veto system (Veto-1) for active shielding and an inner veto system (Veto-2) for active shielding as well as the suppression of signal-correlated background in the form of charged particles. Excellent timing properties are required for both veto detectors. The Veto-2 system was constructed, tested and optimised at the Stefan Meyer Institute. The time resolution, detection effciency and its performance within a broad temperature range were studied and satisfying results were obtained. The first detector units of the Veto-2 system were installed in the SIDDHARTA-2 setup in Frascati

Kaonic atoms measurements at the DAΦNE collider: the SIDDHARTA-2 experiment

The X-ray spectroscopy measurements of light kaonic atoms’ deexcitation towards the fundamental level provide unique information on the low-energy Quantum ChromoDynamics (QCD) in the strangeness sector, being a direct probe of the kaon/nucleon interaction at threshold, unobtainable through the scattering experiments. In this framework, the SIDDHARTA-2 collaboration is going to perform the first kaonic deuterium 2p → 1s transition measurement at the DAΦNE collider of Istituto Nazionale di Fisica Nucleare – Laboratori Nazionali di Frascati. Combining this measurement with the kaonic hydrogen one performed by SIDDHARTA in 2009 it will be possible to obtain, in a model-independent way, the isospin-dependent antikaon-nucleon scattering lengths. The paper introduces the SIDDHARTA-2 setup, an upgraded version with respect to the one used for the kaonic hydrogen measurement, dedicated to the ambitious kaonic deuterium measurement, together with the preliminary results obtained during the kaonic helium run, preparatory for the SIDDHARTA-2 data taking campaign

Kaonic Atoms to Investigate Global Symmetry Breaking

Kaonic atoms measure the antikaon-nucleus interaction at almost zero relative energy, allowing one to determine basic low-energy quantum chromodynamics (QCD) quantities, namely, the antikaon-nucleon (K ¯ N) scattering lengths. The latter are important for extracting the sigma terms which are built on the symmetry breaking part of the Hamiltonian, thereby providing a measure of chiral and SU(3) symmetries breaking. After discussing the sigma terms and their relations to the kaonic atoms, we describe the most precise measurement in the literature of kaonic hydrogen, performed at LNF-INFN by the SIDDHARTA experiment. Kaonic deuterium is still to be measured, and two experiments are planned. The first, SIDDHARTA-2 at LNF-INFN was installed on DAΦNE in spring 2019 and will collect data in 2020. The second, E57 at J-PARC, will become operative in 2021

Studies of kaonic atoms at the DAΦNE collider: from SIDDHARTA to SIDDHARTA-2

The DAΦNE electron-positron collider of the Laboratori Nazionali di Frascati of INFN is a worldwide unique low-energy kaon source and for this reason is suitable for low-energy kaon physics like kaonic atoms and kaon-nucleons/nuclei interaction studies. Kaonic atoms are atomic systems where an electron is replaced by a negatively charged kaon, containing the strange quark, which interacts in the lowest orbits with the nucleus also by the strong interaction. As a result, their study offers the unique opportunity to perform experiments equivalent to scattering at vanishing relative energy. This allows to study the strong interaction between the antikaon and the nucleon or the nucleus “at threshold”, without the need of ad hoc extrapolation to zero energy, as in scattering experiments. 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

Main Features of the SIDDHARTA-2 Apparatus for Kaonic Deuterium X-Ray Measurements

The low-energy, non-perturbative regime of QCD can be studied directly by X-ray spectroscopy of light kaonic atoms. The SIDDHARTA-2 experiment, located at the DAΦNE collider, aims to measure the 2p → 1s transition in kaonic deuterium for the first time to extract the antikaon-nucleon scattering lengths. This measurement is impeded, inter alia, by the low K−d X-ray yield. Hence, several updates have been implemented on the apparatus to increase the signal-to-background ratio, which are discussed in detail in this paper: a lightweight gas target cell, novel Silicon Drift Detectors for the X-ray detection with excellent performance, and a veto system for active background suppression. The experiment has undergone a first preparatory run during DAΦNE’s commissioning phase in 2021, concluding with a successful kaonic helium measurement