Abstract

The precision physics needs at TeV-scale linear electron-positron colliders (ILC and CLIC) require a vertex-detector system with excellent flavour-tagging capabilities through a measurement of displaced vertices. This is essential, for example, for an explicit measurement of the Higgs decays to pairs of b-quarks, c-quarks and gluons. Efficient identification of top quarks in the decay t → Wb will give access to the ttH-coupling measurement. In addition to those requirements driven by physics arguments, the CLIC bunch structure calls for hit timing at the few-ns level. As a result, the CLIC vertex-detector system needs to have excellent spatial resolution, full geometrical coverage extending to low polar angles, extremely low material budget, low occupancy facilitated by time-tagging, and sufficient heat removal from sensors and readout. These considerations challenge current technological limits. A detector concept based on hybrid pixel-detector technology is under development for the CLIC vertex detector. It comprises fast, low-power and small-pitch readout ASICs implemented in 65 nm CMOS technology (CLICpix) coupled to ultra-thin planar or active HV-CMOS sensors via low-mass interconnects. The power dissipation of the readout chips is reduced by means of power pulsing, allowing for a cooling system based on forced gas flow. This contribution reviews the requirements and design optimisation for the CLIC vertex detector and gives an overview of recent R&D achievements in the domains of sensors, readout and detector integration.

Highlights

  • Vertex-detector requirementsThe primary purpose of the CLIC vertex detector is to allow for efficient tagging of heavy quarks through a precise determination of displaced vertices

  • The precision physics needs at TeV-scale linear electron-positron colliders (ILC and CLIC) require a vertex-detector system with excellent flavour-tagging capabilities through a measurement of displaced vertices

  • In order to meet the vertex-detector requirements discussed in section 2, hybrid-pixel-detector systems are under study, combining fast charge collection through drift in high-field sensors with high-performance readout ASICs

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Summary

Vertex-detector requirements

The primary purpose of the CLIC vertex detector is to allow for efficient tagging of heavy quarks through a precise determination of displaced vertices. Where p is the momentum of the particle and θ is the polar angle with respect to the beam axis These requirements can be met with multi-layer barrel and endcap pixel detectors with an inner radius of approximately 30 mm, operating in a magnetic field of 4-5 T and using sensors with a single-point resolution of ≈ 3μm and a material budget of ≈ 0.2% of a radiation length (X0) for the beam-pipe and for each of the detection layers. The material-budget target corresponds to a thickness equivalent to less than 200 μm of silicon, shared by the active material, the readout, the support and the cooling infrastructure This implies that no active cooling elements can be placed inside the vertex detector. Such low power consumption can be achieved by means of power pulsing, i.e. turning off most components on the readout chips during the 20 ms gaps between bunch trains

Flavour-tagging performance
Measurement of the top Yukawa coupling
Impact of detector geometry on flavour-tagging
Impact of flavour-tagging on physics performance
Hybrid detector-readout technology
Thin-sensor assemblies
CLICpix readout chip
Active sensors with capacitive coupling
Detector integration
Findings
Conclusions
Full Text
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