Speaker
Description
The High-Luminosity upgrade of the Large Hadron Collider (LHC) will push the ATLAS tracking system into an unprecedented experimental environment, with particle densities and radiation levels far beyond those faced by the current LHC configuration. To meet these challenges, ATLAS is replacing its tracking system with the all-silicon Inner Tracker, ITk. Following the successful completion of prototyping and pre-production, the project has now entered the full-scale production phase.
The ITk pixel detector will employ hybrid pixel modules. Different sensor technologies are used across the detector volume to match the expected radiation environment: highly radiation-tolerant 3D pixel sensors are selected for the innermost layer, where fluences up to $1.7\times10^{16}$\,n$_\mathrm{eq}$/cm$^2$ are expected; planar pixel sensors will instrument the outer layers.
Test-beam campaigns were carried out at CERN in 2025 and 2026 to qualify the module performance before and after irradiation. A key milestone was the first test-beam operation of an ITk pixel production module, equipped with the final readout chip that will be installed in the detector. It provides Time Over Threshold readout, enabling an indirect measurement of the charge deposited by traversing particles and playing a crucial role in optimising spatial resolution. This talk will present the tracking performance of 3D sensors assembled in production modules after irradiation to fluences between $1.0\times10^{16}$ and $1.7\times10^{16}$\,n$_\mathrm{eq}$/cm$^2$. It will also discuss the operability of the final front-end electronics under realistic irradiation conditions, with particular emphasis on Time-over-Threshold (ToT) to charge calibration. The results will include current–voltage characteristics, hit efficiency, noisy-pixel occupancy, and the performance of the readout electronics at different operating points, defined by threshold settings and ToT-to-charge calibrations. In addition to these laboratory characterisations, a simple Monte Carlo toy model has been developed to interpret charge sharing within the pixel cell, taking into account the experimental track-intercept resolution and non-perfectly perpendicular particle incidence.