TARGET – THE SIDDHARTA-2 EXPERIMENT

SIDDHARTINO — The Target

The target cell is a cylinder of 144 mm in diameter and 125 mm in height, made of high-purity aluminium bars and 150 μm thick two-kapton walls. It is placed inside the vacuum chamber above the beam pipe, has a 125 μm entrance window, a 100 μm thick Ti top window, and is surrounded by 8 SDD arrays (64 SDD cells), with a dedicated thermal contact to keep them stable at the 170 K working temperature [1,2].
For the optimization of the degrader, the SIDDHARTINO target cell has been filled with ⁴He gas at a temperature of 25 K and pressure of 1 bar, which corresponds to 1.5% of Liquid Helium Density (LHeD). The high yield of the 3d → 2p transition of kaonic helium-4 (K-⁴He) allowed to appreciate variations in the number of signal events at the level of 2% in a few hours of data-taking. The final period of the SIDDHARTINO data taking in June 2021 was dedicated to the measurement of K^––⁴He(3d → 2p) transitions at lower density, namely 0.4 bar, corresponding to 0.73% LHeD. The analysis was performed on the summed spectra of 16.5 pb−1 and 9.5 pb−1 for the 1.5% and 0.73% LHeD runs, respectively, for a total integrated luminosity of 26 pb−1 collected in about 20 days of data-taking with the SIDDHARTINO apparatus [3,4]. Results can be found in this page. Below, several pictures of the cylindrical target are shown and, in the end, a schematic reconstruction of the SIDDHARTINO apparatus is provided.

The SIDDHARTINO cylindrical target cell with part of the SDD arrays mounted.

Left part of the SIDDHARTINO target.

Right part of the SIDDHARTINO target.

The SIDDHARTINO cylindrical target cell with part of the SDD arrays mounted.

Schematic reconstruction of the SIDDHARTINO apparatus installed in January 2021 at there DAΦNE collider, in Italy.

References

- [1]. L. De Paolis et al., Trigger rejection factor in the first kaonic helium run with the complete SIDDHARTA-2 setup, EPJ Web of Conferences 270, 00028 (2022).
- [2]. F. Sgaramella et al., The SIDDHARTA-2 calibration method for high precision kaonic atoms x-ray spectroscopy measurements, Physica Scripta 97, 11 (2022).
- [3]. D. L. Sirghi et al., A new kaonic helium measurement in gas by SIDDHARTINO at the DAΦNE collider, J. Phys. G: Nucl. Part. Phys. 49, 055106 (2022).
- [4]. D. L. Sirghi et al. , A New measurements of kaonic helium-4 L-series X-rays yields in gas with the SIDDHARTINO setup, Nucl. Phys. A 1029, 122567 (2023).