Semiconductor Tracker Research Articles

Alignment of the Pixel and SCT Modules for the 2004 ATLAS Combined Test Beam

A small set of final prototypes of the ATLAS Inner Detector silicon tracking system (Pixel Detector and SemiConductor Tracker), were used to take data during the 2004 Combined Test Beam. Data were collected from runs with beams of different flavour (electrons, pions, muons and photons) with a momentum range of 2 to 180 GeV/c. Four independent methods were used to align the silicon modules. The corrections obtained were validated using the known momenta of the beam particles and were shown to yield consistent results among the different alignment approaches. From the residual distributions, it is concluded that the precision attained in the alignment of the silicon modules is of the order of 5 μm in their most precise coordinate.

Combined performance tests before installation of the ATLAS Semiconductor and Transition Radiation Tracking Detectors

The ATLAS (A Toroidal LHC ApparatuS) Inner Detector provides charged particle tracking in thecentre of the ATLAS experiment at the Large Hadron Collider (LHC). TheInner Detector consists of three subdetectors: the Pixel Detector,the Semiconductor Tracker (SCT), and the Transition Radiation Tracker(TRT). This paper summarizes the tests that were carried out at thefinal stage of SCT+TRT integration prior to their installation inATLAS. The combined operation and performance of the SCT and TRTbarrel and endcap detectors was investigated through a series of noisetests, and by recording the tracks of cosmic rays. This was acrucial test of hardware and software of the combined tracker detectorsystems. The results of noise and cross-talk tests on the SCT and TRT intheir final assembled configuration, using final readout and supplyhardware and software, are reported. The reconstruction and analysis ofthe recorded cosmic tracks allowed testing of the offline analysischain and verification of basic tracker performance parameters, such as efficiencyand spatial resolution, in combined operation before installation.

Semiconductor tracker final integration and commissioning in the ATLAS detector

The SemiConductor Tracker (SCT) is part of the Inner Detector of the ATLAS experiment at the LHC. It is located between the Pixel detector and the Transition Radiation Tracker (TRT). During 2006 and 2007, the SCT was installed in its final position inside the ATLAS detector. The SCT barrel was lowered in 2006 and was tested for connectivity and noise. Common tests with the TRT to look for pick-up noise and grounding issues were also performed. The SCT end-caps were installed during summer 2007 and will undergo similar checks. The results from the various tests done before and after installation will be presented here.

The ATLAS TRT electronics

The ATLAS inner detector consists of three sub-systems: the pixel detector spanning the radius range 4cm-20cm, the semiconductor tracker at radii from 30 to 52 cm, and the transition radiation tracker (TRT), tracking from 56 to 107 cm. The TRT provides a combination of continuous tracking with many projective measurements based on individual drift tubes (or straws) and of electron identification based on transition radiation from fibres or foils interleaved between the straws themselves. This paper describes the on and off detector electronics for the TRT as well as the TRT portion of the data acquisition (DAQ) system.

Engineering for the ATLAS SemiConductor Tracker (SCT) End-cap

The ATLAS SemiConductor Tracker (SCT) is a silicon-strip tracking detector which forms part of the ATLAS inner detector. The SCT is designed to track charged particles produced in proton-proton collisions at the Large Hadron Collider (LHC) at CERN at an energy of 14 TeV. The tracker is made up of a central barrel and two identical end-caps. The barrel contains 2112 silicon modules, while each end-cap contains 988 modules. The overall tracking performance depends not only on the intrinsic measurement precision of the modules but also on the characteristics of the whole assembly, in particular, the stability and the total material budget. This paper describes the engineering design and construction of the SCT end-caps, which are required to support mechanically the silicon modules, supply services to them and provide a suitable environment within the inner detector. Critical engineering choices are highlighted and innovative solutions are presented – these will be of interest to other builders of large-scale tracking detectors.The SCT end-caps will be fully connected at the start of 2008. Furthercommissioning will continue, to be ready for proton-proton collisiondata in 2008.

The detector control system of the ATLAS SemiConductor Tracker during macro-assembly and integration

The ATLAS SemiConductor Tracker (SCT) is one of the largestexisting semiconductor detectors. It is situated between the Pixeldetector and the Transition Radiation Tracker at one of the fourinteraction points of the Large Hadron Collider (LHC). During2006-2007 the detector was lowered into the ATLAS cavern and installedin its final position.For the assembly, integration and commissioning phase, a completeDetector Control System (DCS) was developed to ensure the safeoperation of the tracker. This included control of the individualpowering of the silicon modules, a bi-phase cooling system and varioustypes of sensors monitoring the SCT environment and the surroundingtest enclosure. The DCS software architecture, performance andoperational experience will be presented in the view of a validationof the DCS for the final SCT installation and operation phase.

The ATLAS TRT Barrel Detector

The ATLAS TRT barrel is a tracking drift chamber using52,544 individual tubular drift tubes. It is one part of the ATLASInner Detector, which consists of three sub-systems: the pixeldetector spanning the radius range 4 to 20 cm, the semiconductortracker (SCT) from 30 to 52 cm, and the transition radiation tracker(TRT) from 56 to 108 cm. The TRT barrel covers the centralpseudo-rapidity region |η|< 1, and the TRT while endcaps coverthe forward and backward eta regions. These TRT systems provide acombination of continuous tracking with many measurements inindividual drift tubes (or straws) and of electron identificationbased on transition radiation from fibers or foils interleaved betweenthe straws themselves. This paper describes the recently-completedconstruction of the TRT Barrel detector, including the quality controlprocedures used in the fabrication of the detector.

The data acquisition and calibration system for the ATLAS Semiconductor Tracker

The SemiConductor Tracker (SCT) data acquisition (DAQ)system will calibrate, configure, and control the approximately sixmillion front-end channels of the ATLAS silicon strip detector. Itwill provide a synchronized bunch-crossing clock to the front-endmodules, communicate first-level triggers to the front-end chips, andtransfer information about hit strips to the ATLAS high-level triggersystem. The system has been used extensively for calibration andquality assurance during SCT barrel and endcap assembly and forperformance confirmation tests after transport of the barrels andendcaps to CERN. Operating in data-taking mode, the DAQ has recordednearly twenty million synchronously-triggered events duringcommissioning tests including almost a million cosmic ray triggeredevents. In this paper we describe the components of the dataacquisition system, discuss its operation in calibration anddata-taking modes and present some detector performance results fromthese tests

The Semiconductor Tracker performance in the ATLAS Combined Testbeam 2004

The performance of the Semiconductor Tracker in the ATLAS Combined Testbeam 2004 is presented. The setup and DAQ system, data quality and software framework are described. Results of spatial resolution, efficiency and noise occupancy are shown.

Pitch adaptors of the ATLAS-SCT Endcap detector modules

Interconnection between detectors and electronics in modern High Energy Physics has become an issue of difficult solution due to the need to integrate both parts in the same module and the need for a low mass, simple connection. The Endcap section of the Semiconductor Tracker (SCT) of the ATLAS experiment at CERN has adopted the solution of using interface devices called pitch adaptors or fan-ins that, mounted on the modules, and using automatic wire bonding, connect the detector's multiple channels to the front-end electronics, adapting their different designs (pad pitch, dimensions, position). This paper describes the characteristics of these devices, the qualification tests that they have been submitted to, and the final results of their fabrication including quality assurance procedures.

The optical links of the ATLAS SemiConductor Tracker

Optical links are used for the readout of the 4088 silicon microstrip modules that make up the SemiConductor Tracker of the ATLAS experiment at the CERN Large Hadron Collider (LHC). The optical link requirements are reviewed, with particular emphasis on the very demanding environment at the LHC. The on-detector components have to operate in high radiation levels for 10 years, with no maintenance, and there are very strict requirements on power consumption, material and space. A novel concept for the packaging of the on-detector optoelectronics has been developed to meet these requirements. The system architecture, including its redundancy features, is explained and the critical on-detector components are described. The results of the extensive Quality Assurance performed during all steps of the assembly are discussed.

The ATLAS transition radiation tracker (TRT) from construction to installation

This paper shows the evolutions of the TRT construction during the last two years. After a presentation of the TRT and a description of its front-end electronics, the tests for this electronics are described. These tests have shown that 99% of the channels are functional. Some results concerning the tests of the services are also given. In 2006, the ATLAS SemiConductor Tracker (SCT) has been inserted inside the TRT. The barrel and one of the two endcaps have been tested in a SCT + TRT combined cosmic test. Some results from this combined test are presented. Finally, some noise measurements done after the successful installation of the TRT barrel in the ATLAS cavern are given.

Commissioning of the ATLAS Semiconductor Tracker with cosmic rays

This paper presents the results of the tests with cosmic rays of the ATLAS Semiconductor Tracker (SCT) as well as operational experience of running the fully integrated silicon detector during the commissioning of the completed SCT. Prior to inserting into ATLAS, the barrel part of the SCT has been integrated with the Transition Radiation Tracker (TRT) barrel and tested with cosmic rays. A sector of 468 SCT modules has been powered and read simultaneously with TRT modules in physics mode. In total 500 thousand events were recorded during cosmic runs and processed with the ATLAS off-line reconstruction software. The SCT performance was measured in terms of the average noise occupancy per channel ( 4.5 × 10 - 5 ) and the overall efficiency ( > 99 % ) . The tests with cosmic rays proved full functionality of the complex Detector Control System (DCS) which provides control, monitoring and safety functions for the detector electronics.

Alignment strategy for the ATLAS tracker

ATLAS is a general purpose spectrometer in preparation to take data on the Large Hadron Collider at CERN. It will start its operation in autumn 2007. Charged particle tracking is realised by the Inner Detector (ID). It consists of two silicon subsystems: Pixel Detector and Semiconductor Tracker, complemented by straw proportional gas chambers. In order to exploit the excellent intrinsic resolution of the precision tracking devices a high accuracy alignment is required. In this report the strategy to align silicon detectors of the ATLAS ID will be reviewed together with the current status of preparation.

Status and experience with construction and integration of the ATLAS SemiConductor Tracker for the CERN LHC

This paper describes some of the essential features of the SemiConductor Tracker (SCT) of the ATLAS experiment at the CERN Large Hadron Collider (LHC), and the September 2006 status and experience with its construction and integration.

Anomolous IV behavior of ATLAS SCT microstrip sensors

We observe deteriorated IV, leakage-to-voltage, characteristics when the ATLAS SemiConductor Tracker (SCT) silicon microstrip detector is biased at a fixed voltage Vk for a long period. The leakage current is nearly halved at voltages below Vk. The noise figure is deteriorated and signal charge spreads to neighboring strips. The detector performance is, however, not degraded when biased at or above Vk. We characterize the observed phenomena in detail in this article.

Serial powering of silicon strip detectors at SLHC

Serial powering is a technique to power a large numbers of detector modules using a single power cable and a constant current source. Module power is derived using local shunt regulators. Serial powering is of great interest for large-scale silicon tracking detectors for particle physics with many thousands of densely packed detector modules. We have been operating six ATLAS Semiconductor Tracker (SCT) modules using both serial powering and conventional independent powering. The modules operated stably with no indication of any extra noise sources. We present selected results and discuss the system aspects of serial powering.

Radiation hardness studies of VCSELs and PINs for the opto-links of the Atlas SemiConductor Tracker

We study the radiation hardness of the Vertical Cavity Surface Emitting Laser diodes (VCSELs) and the epitaxial silicon PIN diodes that will be used for the Atlas SemiConductor Tracker at the CERN Large Hadron Collider. The tests were conducted with 200 MeV protons to a fluence of 4 × 10 14 p / cm 2 and with 20 MeV (average energy) neutrons to 7.7 × 10 14 n / cm 2 . The radiation damage of the VCSELs and PINs and the annealing characteristics are presented.

Status of the ATLAS SCT

The ATLAS Semiconductor Tracker (SCT) is approaching completion at CERN, and will be ready to take data at the Large Hadron Collider (LHC) at the end of 2007. We review the development of the SCT and give an overview of the SCT design. The integration and commissioning is now in its final stages, and is described in detail for barrel and end caps (ECs). Results are presented on modules, sub-assemblies and the entire barrel and EC systems.

ATLAS tracking at the super-LHC

Replacement of the ATLAS tracker is necessitated by the plans to extend LHC running and to greatly increase the luminosity after a long shutdown starting in the middle of the next decade. The proposed luminosity upgrade will require replacement of the tracker to achieve the higher granularity and greatly increased radiation hardness that an order of magnitude more collisions per beam crossing will imply. Not only will this render the current straw-tube-based tracker at outer radii (the TRT) inoperable, it will also require use of even more advanced radiation hard technologies than in the current semiconductor tracker (SCT). The use of an all-silicon tracker is regarded by most as the only viable solution using new advances in substrate technology and lower temperature operation as appropriate. Additionally, the upgrade will require minimal disturbance to the rest of the experiment and be obliged to use much of the existing services infrastructure. The many challenges posed by both the extreme environment and the severe constraints coming from the very tight tracker construction timescale are discussed in this paper.