Abstract
The semiconductor tracker is a silicon microstrip detector forming part of the inner tracking system of the ATLAS experiment at the LHC. The operation and performance of the semiconductor tracker during the first years of LHC running are described. More than 99% of the detector modules were operational during this period, with an average intrinsic hit efficiency of (99.74±0.04)%. The evolution of the noise occupancy is discussed, and measurements of the Lorentz angle, δ-ray production and energy loss presented. The alignment of the detector is found to be stable at the few-micron level over long periods of time. Radiation damage measurements, which include the evolution of detector leakage currents, are found to be consistent with predictions and are used in the verification of radiation background simulations.
Highlights
The ATLAS detector [1] is a multi-purpose apparatus designed to study a wide range of physics processes at the Large Hadron Collider (LHC) [2] at CERN
In the absence of stable beam conditions at the LHC, the semiconductor tracker (SCT) modules are biased at a reduced high voltage of 50 V to ensure that the silicon sensors are only partially depleted; in the unlikely event of a significant beam loss, this ensures that a maximum of 50 V is applied temporarily across the strip oxides, which is not enough to cause electrical breakdown
Once the LHC declares stable beam conditions, the SCT is automatically switched on if the LHC collimators are at their nominal positions for physics, if the background rates measured in beam conditions monitor (BCM), beam loss monitor (BLM) and the ATLAS forward detectors are low enough, and if the SCT hit occupancy with 50 V is consistent with the expected luminosity
Summary
The ATLAS detector [1] is a multi-purpose apparatus designed to study a wide range of physics processes at the Large Hadron Collider (LHC) [2] at CERN. In addition to measurements of Standard Model processes such as vector-boson and top-quark production, the properties of the newly discovered Higgs boson [3, 4] are being investigated and searches are being carried out for as yet undiscovered particles such as those predicted by theories including supersymmetry All of these studies rely heavily on the excellent performance of the ATLAS inner detector tracking system. A high-precision toroid-field muon spectrometer surrounds electromagnetic and hadronic calorimeters, which in turn surround the inner detector This comprises three complementary subdetectors: a silicon pixel detector covering radial distances between 50.5 mm and 150 mm, the SCT covering radial distances from 299 mm to 560 mm and a transition radiation tracker (TRT) covering radial distances from 563 mm to 1066 mm.
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