[Paper Review] Extended X-ray energy characterization of SIDDHARTA-2 large-area Silicon Drift Detectors up to 50 keV

F. Clozza, Francesco Sgaramella+39 more|arXiv (Cornell University)|Feb 20, 2026

Particle Detector Development and Performance0 citations

TL;DR

The paper characterizes the SIDDHARTA-2 large-area Silicon Drift Detectors up to 50 keV, demonstrating linear energy response with ΔE/E < 1e-3 and evaluating energy resolution for future kaonic-atom measurements.

ABSTRACT

The SIDDHARTA-2 experiment at the DA$Φ$NE collider of INFN-LNF performs high precision light kaonic atoms X-ray spectroscopy to investigate the kaon-nucleon(s) strong interaction in the low-energy (O(10 keV)) regime. A large area Silicon Drift Detectors (SDDs) system has been developed to carry out these measurements. The collaboration aims to extend the measurements campaign to higher mass kaonic atoms, which exhibit transition lines at increased X-ray energies. In this context, the spectroscopic response of the SIDDHARTA-2 SDD system was investigated in terms of linearity and energy resolution up to 50 keV. An accuracy of the energy calibration procedure $ΔE/E &lt; 10^{-3}$ was achieved.

Motivation & Objective

• Motivate extending kaonic-atom X-ray measurements to higher energies (15–50 keV) beyond the initial 4–12 keV range.
• Quantify the SDDs' linearity, calibration accuracy, and energy resolution up to 50 keV.
• Validate calibration accuracy for the EXKALIBUR program targeting heavier kaonic atoms.

Proposed method

• Use fluorescence lines from Bi, Pd, Ag, Ba, and Tm to perform linear energy calibration up to 50 keV.
• Fit each detector’s spectrum with Gaussian peaks plus tail function to extract peak centroids and FWHM.
• Model FWHM as FWHM(E)=2√(2ln2)·√(εFE+ (N/(2ln2))^2) to extract ε, F, N from data.
• Sum spectra from all SDDs after individual calibrations to obtain an aggregated calibrated spectrum.
• Assess calibration linearity via residuals ΔE = E_meas − E_th for multiple lines and energies.

Figure 1: Above: Picture of an SDDs array used by the SIDDHARTA-2 experiment. Below: schematic representation of the SDD and of the charge collection process.

Experimental results

Research questions

• RQ1 What is the linearity and calibration accuracy of SIDDHARTA-2 SDDs in the 10–50 keV range?
• RQ2 What is the achievable energy resolution (FWHM) of the SDDs up to 50 keV?
• RQ3 Are the SDD performance metrics sufficient to measure strong-interaction-induced shifts and widths in heavier kaonic atoms (Li, Be, B) within EXKALIBUR energy ranges?

Key findings

• SDDs show a linear energy response in the 10–50 keV range with relative precision ΔE/E < 1e-3.
• Calibration using Bi Lα, Pd Kα, and Ag Kα achieves high accuracy across the extended energy range.
• Residuals for key lines are within a few tens of eV, with Ba α1 and Tm lines having larger uncertainties due to statistics.
• Best-fit F and N are 0.116579(68) and 172(29) eV, respectively, describing the FWHM energy dependence.
• Measured FWHM values span from about 236 eV to 446 eV across the lines tested (e.g., BiLα 235.5 eV, TmKα2 446 eV).
• Energy-resolution performance supports resolving strong-interaction widths in kaonic-atom transitions up to 50 keV.

Figure 2: Above: fit of the energy spectrum for the run in beams collision mode, obtained by summing up all the SDDs’ calibrated spectra. Below: fit of the calibrated energy spectrum obtained with a 169 Tm target.