S. Marti i Garcia

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 six million front-end channels of the ATLAS silicon strip detector. It will provide a synchronized bunch-crossing clock to the front-end modules, communicate first-level triggers to the front-end chips, and transfer information about hit strips to the ATLAS high-level trigger system. The system has been used extensively for calibration and quality assurance during SCT barrel and endcap assembly and for performance confirmation tests after transport of the barrels and endcaps to CERN. Operating in data-taking mode, the DAQ has recorded nearly twenty million synchronously-triggered events during commissioning tests including almost a million cosmic ray triggered events. In this paper we describe the components of the data acquisition system, discuss its operation in calibration and data-taking modes and present some detector performance results from these tests

A model of charge collection for irradiated p+n detectors

Abstract The charge collection in irradiated p + n silicon detectors was studied as a function of the reverse bias voltage. Oxygenated and non-oxygenated devices were irradiated beyond type inversion with 24 GeV /c protons. The charge collection is successfully described with a model based on the hypothesis that the charge trapping depends on the carriers velocity. With this model, values for the full depletion voltage are extracted which show good agreement with those measured using the CV technique. The model allows a quantitative understanding of why although oxygenation of p + n devices improves substantially the full depletion voltage, much less improvement is observed in the charge collection efficiency.

Charge collection efficiency studies with irradiated silicon detectors

Abstract Small area (1×1 cm 2 ) microstrip detectors, made with a p+-n diode structure on FZ silicon substrates, both with and without oxygen enrichment, have been irradiated with 24 GeV /c protons to fluences of 1.9, 2.9 and 5.1×10 14 p/cm 2 . Their charge collection properties have been studied using a 106 Ru beta-source with a wide bandwidth current amplifier and compared with those for a non-irradiated device. The integrated charge collected at different times (10, 25, 40 and 80 ns ) has been used to estimate the effect of ballistic deficit. Predictions for the reduction in charge collection efficiency expected at fluences as high as 10 15 cm −2 are presented using a parameterization described in earlier work which also fits this data well.

Annealing effects on irradiated n+n silicon detectors

The performance of ATLAS forward region full-sized n+n prototype silicon micro-strip detectors has been studied after irradiation with 2×1014 protons/cm2 and 52 days annealing at 20°C. The signal-to-noise ratio measured at −10°C with LHC speed read-out was found to be degraded primarily due to increased noise. The reduction in the reverse current and the changes in the voltage needed for maximum charge collection have both been studied as a function of annealing time. Above the depletion voltage, no effect on the charge collection efficiency has been observed during this annealing period.

Charge collection efficiency of irradiated n+n wedge silicon microstrip detectors for ATLAS

Abstract The charge collection efficiency of the n + n silicon microstrip detectors for the ATLAS forward tracking has been evaluated for detectors irradiated with 24 GeV/c protons. The charge collection efficiency is found to be 99±1% after a fluence of 2×10 14 protons/cm 2 and 81±2% after 4×10 14 protons/cm 2 . Furthermore, the charge collection efficiency of the detector irradiated with the lower dose does not show any dependence on the isothermal annealing up to 52 days at 20°C, as it remains constant through the whole annealing cycle.

Experimental studies of QCD using flavour tagged jets from DELPHI

Identified bb¯g and qq¯γ events from DELPHI are used to measure the ratio of the mean charged particle multiplicity distribution between gluon and quark jets. The dependence of this ratio with the jet energy is established using about three million Z0 decays. Results from all other detectors are discussed and compared. A nice agreement is found among all them. The ratio between the normalized total three-jet cross sections of bb¯g and qq¯γ, q ≡ u, d, s events is also determined. The preliminary value obtained indicates that b quarks are experimentaly seen to radiate less than light quarks due to their higher mass. The suggested experimental error is ∼300 MeV for the b mass determination at the MZ scale.

Radiation hardness of oxygenated microstrip detectors read out with LHC speed electronics

Full-size and miniature Large Hadron Collider (LHC) detectors fabricated on 4- and 6-in wafers have been processed using oxygenated and nonoxygenated substrates. After irradiation to 3/spl times/10/sup 14//cm/sup 2/ with 24-GeV/c protons and short-term annealing, these detectors have been studied in terms of their charge collection as a function of depletion voltage with LHC-speed analog electronics. Results are presented indicating the degree of improvement seen in terms of the main operationally significant parameter, namely, the bias voltage needed for a given signal read out with fast electronics.

Studies on charge collection of p-type silicon detectors under neutron irradiation expected for Super-LHC

The existing technology used in the ATLAS Tracker is at the limit for performances of 10 years of running at a LHC peak luminosity of 1034 cm-2s-1. The operation under an upgraded luminosity of 1035 cm-2s-1 (Super-LHC) will imply a corresponding increase of the radiation dose. The expected dose for the inner detector tracker at the Super-LHC is up to 1 × 1016 equivalent neutron cm-2 in comparison with a dose of 1 × 1015 equivalent neutron cm-2 at the LHC after the envisaged 10 years of operation. So, the classic concept of p-on-n silicon microstrip detector as used in the current Semiconductor Tracker (SCT) in ATLAS needs to be abandoned for the Super-LHC. Investigations with n-on-p silicon sensors are showing arguments in favor of implementing these technologies in harsh radiation environment as the Super-LHC. This paper reports about studies with p-type sensors undergoing high radiation doses of neutrons in terms of their charge collection efficiency. A significant contribution to the radiation damage to the sensors in the tracker volume is due to backscattered neutrons so it is important to know the sensor performance under this kind of irradiation. Microstrip sensors from two different suppliers have been tested and a new analogue acquisition system called ALIBAVA system has been used to carry out the measurements.

Performance, high voltage operation and radiation hardness of full-size ATLAS charge division silicon detectors with LHC electronics

ATLAS silicon detectors designed for charge division read-out were produced during 1995 and have been extensively studied both in the laboratory and test beam at the CERN SPS. Data have been taken with the analogue read-out FELIX-128 chip and studies simulating other read-out architectures under consideration by ATLAS have been performed. To evaluate survival in the harsh environment of the LHC, detectors have been tested to high voltage, both before and after radiation damage by protons exceeding the expected charged hadron dose after 10 years of LHC operation. These tests have all employed analogue read-out to be sensitive to changes in noise and charge collection efficiency as a function of the detector damage.

Silicon detectors for forward tracking in ATLAS

Abstract A 12 cm long silicon microstrip detector module with a fan geometry has been designed and constructed. The performance of the detector has been studied in a test beam at CERN. Results are presented on the hit efficiency and the position resolution as a function of position along the strips. With a hit efficiency of 99.5% and a spatial resolution of typically 35 μm the performance of these detectors exceeds that of other candidate technologies for the precision forward tracker of the ATLAS inner detector.