Measurement of kaonic deuterium X-rays

The antikaon-nucleon (K-N) interactions close to threshold provide information to the interplay between spontaneous and explicit chiral symmetry breaking in low-energy QCD. We propose to measure the strong-interaction level shift and width of the kaonic deuterium 1s state with an accuracy of about 70 eV and 170 eV, respectively, in the SIDDHARTA-2 experiment. Together with the results of the shift and width of the kaonic hydrogen 1s state obtained by the SIDDHARTA experiment, it will be able to determine both the isospin I=0 and I=1 antikaon-nucleon scattering lengths, for the first time. Based on a first test measurement of kaonic deuterium in the SIDDHARTA experiment, new design of the experimental setup was developed in order to observe the kaonic deuterium X-rays with a good signal-to- background ratio. Compared to the data taken in the SIDDHARTA, detailed Monte Carlo studies were performed to investigate the background suppression factors in the new setup. The feasibility of the determination of shift and width of the kaonic deuterium 1s state was found. Although the importance of the kaonic deuterium X-ray spectroscopy in the field of low-energy antikaon-nucleon interactions has been well recognized, no experimental results were obtained up to now. SIDDHARTA-2 is a unique experiment of kaonic deuterium; no other proposals exist. The results of SIDDHARTA-2 provide the most stringent constraints on the antikaon-nucleon interaction, promising a breakthrough for this field. SMI will develop the target and veto systems used in the SIDDHARTA-2 experiment. The costs of these systems are requested to be funded by FWF.

The physics of strongly interacting particles hadrons is dealing with topics, which have profound consequences for the understanding of basic questions like the generation of the mass of the visible Universe or the structure of exotic objects e.g. neutron stars.To gain information on how strong interaction works, exotic atoms with strangeness provide a unique insight. Kaonic atoms are coulomb bound systems in which the heavier, negatively charged particle replaces an electron, for example a kaonic hydrogen (K-p) atom could be formed. Due to strong interaction the 1s ground state is shifted from his pure electromagnetic value and broadened. These observables (shift and width) can be related to the antikaon nucleon scattering lengths and will offer the unique opportunity to perform experiments equivalent to scattering experiments at vanishing energies (very close to threshold). The binding energies for antikaonic hydrogen are in the keV range, far below the lowest energies reached with scattering experiments, laying in the MeV range. Therefore, the antikaon-nucleus interaction at threshold is determined without the extrapolation to zero energy, which is still necessary in low-energy scattering experiments.The main challenge of kaonic atom experiments is that one has to detect a weak signal over a huge bremsstrahlung background. All this requires the use of numerous novel large area silicon drift detectors with excellent energy resolution and timing capabilities and of a pressurized low-weight cryogenic gaseous target.The K-p interaction is now well understood from the recent results of antikaonic hydrogen obtained from measurements in Japan (at the KEK accelerator complex) and Italy (at the DA?NE double annular storage ring) and the theoretical calculations based on these results.There is still one experiment missing, namely the antikaonic deuterium atom X-ray measurement, which will represent the most important experimental information missing in the field of low-energy antikaon-nucleon interactions today.With this proposal, using as input the experience gained with the antikaonic hydrogen experiments at the DA?NE storage ring, we have established the feasibility to measure the antikaonic deuterium X-ray spectrum at J-PARC (Japan) and DA?NE (Italy). The expected results, together with these of the antikaonic hydrogen experiment at DA?NE, will provide the most stringent constraints on the antikaon-nucleon interaction, promising a breakthrough in this field.