A NEW MEASUREMENT OF THE KAONIC HELIUM L-LINES WITH SIDDHARTA-2 AT DAΦNE

The ultimate goal of the SIDDHARTA-2 experiment at the LNF-INFN is to perform the first ever measurement, via X-ray spectroscopy, of the width and shift induced by the strong interaction to the 2p → 1s energy transition of kaonic deuterium. Such a measurement has not been performed yet due to its high difficulty level; in fact, this transition exhibits an extremely low X-ray yield. For this reason, before starting the kaonic deuterium data taking campaign, an accurate and thorough characterisation of the experimental apparatus is of primary importance to gauge its performance. To finalize such a task the best candidate is Helium-4, since the 3d → 2p transition of kaonic helium-4 exhibits a much higher yield of X-rays. This work reports the results of the characterisation of the SIDDHARTA-2 apparatus in preparation for the kaonic deuterium measurement. This is done by measuring the shift and width for the 3d → 2p transition of kaonic helium-4. The measured values are ε2p = 2.0 ± 1.2(stat) ± 1.5(syst) eV and Γ2p = 1.9 ± 5.7(stat) ± 0.7(syst) eV. The result shows a net enhancement of the performance of the apparatus when compared to the previous measurement done by the SIDDHARTA experiment ε2p = 0 ± 6(stat) ± 2(syst) eV, thus providing strong evidence of the potential to perform the kaonic deuterium measurement.