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Abstract
Knowledge of the material in the ATLAS inner tracking detector is crucial in understanding the reconstruction of charged-particle tracks, the performance of algorithms that identify jets containing b-hadrons and is also essential to reduce background in searches for exotic particles that can decay within the inner detector volume. Interactions of primary hadrons produced in pp collisions with the material in the inner detector are used to map the location and amount of this material. The hadronic interactions of primary particles may result in secondary vertices, which in this analysis are reconstructed by an inclusive vertex-finding algorithm. Data were collected using minimum-bias triggers by the ATLAS detector operating at the LHC during 2010 at centre-of-mass energy √s = 7 TeV, and correspond to an integrated luminosity of 19 nb−1. Kinematic properties of these secondary vertices are used to study the validity of the modelling of hadronic interactions in simulation. Secondary-vertex yields are compared between data and simulation over a volume of about 0.7 m3 around the interaction point, and agreement is found within overall uncertainties.
Highlights
A measurement of material in the ATLAS tracker using secondary hadronic interactions in 7 TeV pp collisions
The hadronic interactions of primary particles may result in secondary vertices, which in this analysis are reconstructed by an inclusive vertex-finding algorithm
Kinematic variables that are mainly dependent on details of the hadronic interactions are compared, e.g., the total momentum of tracks emerging from the secondary vertex, the fraction of the total momentum carried by the highest-momentum secondary track, and the opening angle between the tracks
Summary
The ATLAS detector consists of an inner tracking detector, electromagnetic and hadron calorimeters, a muon spectrometer, and three magnet systems [1]. The pixel detector is located at r < 150 mm, and provides precision measurements from 80.4 million sensors It consists of three barrel layers with |z| < 400 mm and six disks in the end-cap region, which extend out to |z| ∼ 660 mm. The SCT detector has four barrel layers extending from r ∼ 250 mm to 550 mm with |z| < 750 mm, and 18 disks in the end-cap region with |z| < 2710 mm; it consists of ∼ 6.3 million readout strips. The data are compared to simulation, which includes an improved description of the ID geometry, e.g., the position of the beam pipe, the implementation of a slight shift of the pixel barrel layers, and the amount of material in the end-region of the pixel barrel. The simulated events were weighted such that the mean and width of the z-coordinate distribution of the PV position matched the data
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