Abstract: The inner tracking system of the ATLAS experiment will be upgraded to a full silicon detector in 2030 for HL-LHC. The new tracking system is called ITk, the Inner Tracker. The ITk requirements include operational efficiency higher than 99% and noise hit occupancy smaller than 0.1%. During the pre-production phase of the ITk project, many short-strip modules were observed to exhibit so-called “Cold Noise (CN)”, wherein clusters of strips displayed very high noise when the modules were operated at temperatures below-35 degrees C. To investigate the CN impact and ensure the quality of module production, huge amount of effort have been put in by the collaboration. This paper focuses on the impact of CN on the tracking performance by examining two short strip modules that exhibit CN: one is non-irradiated, while the other one has been irradiated to the maximum expected end-of-lifetime fluence. For each module, the global and single strip tracking performance are evaluated. The global performance study shows that the non-irradiated module can be operated within specifications with a threshold around 1fC, but it is not possible to operate the irradiated module as required. In the single strip analysis, it was found that while CN does not affect the charge collection, it reduces the operating window and leaves less margin for detector operation. In the non-irradiated module, less than 3% of strips fail the detector requirements in the CN regions. For the irradiated module, about 20% of strips fail the requirements in the low CN region and around 52% fail in the high CN region. The fraction of strips that cannot operate due to CN throughout their lifetime can be predicted according to the measured noise at the required noise occupancy level and its expected median collected charge. In cases when the noise hit occupancy caused by CN is kept below 1% with a threshold smaller than 0.45 fC, at least 60% of strips could meet the operating requirements by the end of detector's lifetime. Thus, the module is likely to satisfy the operating requirements in terms of global efficiency and global noise occupancy.

Abstract: We present an approach to construct position-sensitive silicon detectors with an integrated cooling circuit. Tests on samples demonstrate that a very modest liquid flow very effectively cool the devices up to a power dissipation of over 10 W/cm(2). The liquid flow is found to have a negligible impact on the mechanical stability. A finite-element simulation predicts the cooling performance to an accuracy of approximately 10%.

Abstract: The ATLAS inner detector comprises three different sub-detectors: the pixel detector, the silicon strip tracker, and the transition-radiation drift-tube tracker. The Insertable B-Layer, a new innermost pixel layer, was installed during the shutdown period in 2014, together with modifications to the layout of the cables and support structures of the existing pixel detector. The material in the inner detector is studied with several methods, using a low-luminosity root s = 13 TeV pp collision sample corresponding to around 2.0 nb(-1) collected in 2015 with the ATLAS experiment at the LHC. In this paper, the material within the innermost barrel region is studied using reconstructed hadronic interaction and photon conversion vertices. For the forward rapidity region, the material is probed by a measurement of the efficiency with which single tracks reconstructed from pixel detector hits alone can be extended with hits on the track in the strip layers. The results of these studies have been taken into account in an improved description of the material in the ATLAS inner detector simulation, resulting in a reduction in the uncertainties associated with the charged-particle reconstruction efficiency determined from simulation.

Abstract: Pixel sensors in 3D technology equip the outer ends of the staves of the Insertable B Layer (IBL), the innermost layer of the ATLAS Pixel Detector, which was installed before the start of LHC Run 2 in 2015. 3D pixel sensors are expected to exhibit more tolerance to radiation damage and are the technology of choice for the innermost layer in the ATLAS tracker upgrade for the HL-LHC programme. While the LHC has delivered an integrated luminosity of similar or equal to 235 fb(-1) since the start of Run 2, the 3D sensors have received a non-ionising energy deposition corresponding to a fluence of similar or equal to 8.5 x 10(14) 1MeV neutron-equivalent cm(-2) averaged over the sensor area. This paper presents results of measurements of the 3D pixel sensors' response during Run 2 and the first two years of Run 3, with predictions of its evolution until the end of Run 3 in 2025. Data are compared with radiation damage simulations, based on detailed maps of the electric field in the Si substrate, at various fluence levels and bias voltage values. These results illustrate the potential of 3D technology for pixel applications in high-radiation environments.

Abstract: The momentum measurement capability of the ATLAS muon spectrometer relies fundamentally on the intrinsic single-hit spatial resolution of the monitored drift tube precision tracking chambers. Optimal resolution is achieved with a dedicated calibration program that addresses the specific operating conditions of the 354 000 high-pressure drift tubes in the spectrometer. The calibrations consist of a set of timing offsets and drift time to drift distance transfer relations, and result in chamber resolution functions. This paper describes novel algorithms to obtain precision calibrations from data collected by ATLAS in LHC Run 2 and from a gas monitoring chamber, deployed in a dedicated gas facility. The algorithm output consists of a pair of correction constants per chamber which are applied to baseline calibrations, and determined to be valid for the entire ATLAS Run 2. The final single-hit spatial resolution, averaged over 1172 monitored drift tube chambers, is 81.7 +/- 2.2 μm.