Production, Calibration and Performance of the Scintillation Detectors for the IceCube Surface Array Enhancement

The IceCube Surface Array Enhancement (SAE) represents a significant upgrade to the IceCube Neutrino Observatory’s surface cosmic-ray detection capabilities, targeting the energy region in the cosmic-ray spectrum around the knee (PeV energies). This work covers the production, calibration, and on-ice commissioning of the scintillation detectors equipped with temperature-sensitive Silicon Photomultipliers (SiPMs). As part of the detector preparation, a dedicated pre-calibration framework was developed to ensure uniform detector performance, including natural radioactive background suppression and energy response validation. Following this, the first final-configuration station (Station 0) was deployed at the South Pole in early 2023 with fully updated scintillation modules and readout electronics, expanding the observable dynamic range and improving data acquisition fidelity.

During commissioning, a robust SiPM gain calibration across the three gain channels covering the entire South Pole temperature range enabled reliable conversion of raw ADC data into physical Minimum Ionizing Particle (MIP) units. Post-deployment studies confirmed excellent detector uniformity and nanosecond-level timing precision, critical for accurate reconstruction of the air-shower front and effective background suppression. ... mehrA scalable data processing pipeline was established to integrate scintillator data with coincident IceTop and radio detector events, enabling unified hybrid event reconstruction.

Furthermore, a data-driven air-shower reconstruction approach was developed, incorporating temporal pulse cleaning and a L2 reconstruction that leverages IceTop’s core position estimates to overcome single-station limitations. A realistic zenith-dependent signal variance model reflecting near-Poisson fluctuations was introduced, improving signal weighting in Lateral Distribution Function (LDF) fits. For the single-station setup, the reconstruction achieved a space-angle resolution of 2.3° overall with Station 0, improving to 1.2° for showers with cores near the station, which is particularly relevant for studies of lower-energy cosmic-rays. Timing resolution studies further demonstrated excellent performance with zenith-dependent timing behaviour and a reconstructed shower front resolution of approximately 7\,ns for scintillation pairs separated by 5\,m.

Preliminary comparisons of the reconstructed shower size, $S_{125}$, between scintillators and IceTop revealed a factor of $\approx3$ pointing to the difference in the two detectors' response due to the scintillation detector's lower energy threshold and higher sensitivity to the electromagnetic component of the air-showers. Preliminary seasonal analyses with measured signals suggest evolving detector response linked to snow accumulation effects, highlighting the need for ongoing calibration improvements.

Collectively, these results demonstrate the technical readiness and scientific potential of the SAE scintillator modules for long-term cosmic-ray observations at the South Pole. The enhanced surface array promises improved sensitivity and precision for probing the astrophysical origins and acceleration mechanisms of high-energy cosmic rays, particularly in the crucial knee region of the spectrum.