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First kaonic atoms from SIDDHARTA-2 on DAΦNE

On July the 19th has successfully been concluded the first data taking of the SIDDHARTA-2 experiment at DAΦNE.

SIDDHARTA-2 is an international collaboration, among 12 institutions from 7 countries, aiming at studying strong interaction measuring the X-rays emitted in the transitions from different energy levels of kaonic-atoms. A kaonic atom is formed when one of the orbital electrons is replaced by a negative charge kaon produced by the DAΦNE collider. The experiment uses forefront technologies, in particular new silicon spectroscopic detectors (Silicon Drift Detectors) to detect X-rays and a complex veto system to cut down the background.


The first SIDDHARTA-2 run has been performed with SIDDHARTINO, a subset version of SIDDHARTA-2, intended to measure the first kaonic-atoms during the tuning of the DAΦNE accelerator.

After the lockdown that stopped the activity of the accelerator for about 10 months, DAΦNE was re-started on February 2021 with the goal to provide beams of kaons to SIDDHARTINO minimizing the background of X-rays coming out from spurious hits.

The DAΦNE accelerator complex is intended to realize collisions between electron and positron beams extremely focused and with high intensities that result in the production of an intense flux of low energy kaons. Kaons with these characteristics are practically unique in the world and are ideal to study strong interaction at threshold.

It is worth to mention, that the originality and the scientific relevance of DAΦNE are represented by a new collision scheme called “crab-waist”. This, designed and built for the first time in Frascati, has nowadays become a fundamental element not only for the design of new accelerators, but also for enhancing the performance of existing lepton colliders.

During these months, the parameters of the colliding beams have been suitably tuned and, starting from May 2021, SIDDHARTINO began the data taking with a maximum luminosity of about 8×1031 cm-2s-1, a deliberately moderate value to favor a progressive understanding of the new apparatus. This phase was also fundamental to understand the most effective parameters to reduce the background which, at the end of this working period, was more than halved.

In this context SIDDHARTINO measured X-rays corresponding to transitions to the 2p level of kaonic-Helium4 with different configurations of the detector and two different densities of Helium. These studies will help in getting a better understanding of the atomic cascade, and in the study of the kaonic-Helium itself for which is expected a precision on the measurement of the energy of the X-rays compatible with the best measurements done up-to-now.

During Summer, the SIDDHARTA-2 collaboration will install on DAΦNE the full apparatus to be ready for the measurement of the kaonic-deuterium that will start in Autumn.

This result has been reachable, thanks to the enthusiasm and to the perfect cooperation between the group of technicians, engineers and researchers that works for DAΦNE with the SIDDHARTA-2 people together with the constant support of all the laboratory.