Speakers
Description
The High Luminosity LHC upgrade demands enhanced tracking, prompting a full replacement of ATLAS’s Inner Detector with the all-silicon Inner Tracker (ITk). Spanning 33–291 mm from the beam pipe, ITk will use hybrid pixel detectors with 65 nm CMOS chips. The inner region, facing extreme radiation, will feature 3D pixel sensors, while the outer regions use planar sensors. Testing in 2024–2025 evaluated two chip versions (v1 and v2) under high fluence. This talk presents tracking performance pre/post-irradiation, front-end electronics operability, and TOT-to-charge calibration, supported by results on IV characteristics, hit efficiency, and noise behaviour across operational settings.
Summary (500 words)
The High Luminosity upgrade of the Large Hadron Collider (HL-LHC) will significantly increase the demands on the ATLAS detector’s tracking system. To meet these challenges, the current Inner Detector will be entirely replaced with an all-silicon Inner Tracker (ITk). With the prototyping and pre-production phases completed, the project has now transitioned into full-scale component production.
The ITk hybrid pixel detectors will span a radial range from 33 mm to 291 mm relative to the beam pipe. These detectors will employ a 65 nm CMOS readout chip, hybridised to different sensor technologies to accommodate the varying radiation levels across the detector volume.
The innermost layer of the ITk will experience an extreme fluence of up to 1.7 × 1016 neq/cm2 over its operational lifetime. To withstand such conditions, 3D pixel sensors - known for their superior radiation tolerance - have been selected for this region. In the outer layers, where radiation levels are less severe, planar pixel sensors will be employed.
Extensive testing of sensor samples from both technologies was conducted throughout 2024 and 2025 at CERN’s test beam facilities, using 120 GeV pion beams. These samples have been assembled with two versions of the readout chip: v1 and v2. While both versions are functionally similar, v2 corrects a design flaw in v1 and introduces Time Over Threshold (TOT) readout capability. TOT provides an indirect measure of the charge deposited by traversing particles, playing a key role in improving spatial resolution.
This talk presents a twofold objective: firstly, to demonstrate the tracking performance of both 3D and planar sensors before and after irradiation at fluences ranging from 1.0×1016 to 1.7×1016 neq/cm2; and secondly, to evaluate the operability of the front-end electronics under similar irradiation, with a focus on TOT-to-charge calibration.
The presentation will include results on current-voltage (IV) characteristics, hit efficiency, and the occurrence of noisy pixels in the sensors. Additionally, the performance of the readout chips will be discussed across various working points, characterised by differing signal thresholds and TOT/charge calibrations.
