K. H. Becks

The ATLAS Silicon Pixel Sensors

Prototype sensors for the ATLAS silicon pixel detector have been developed. The design of the sensors is guided by the need to operate them in the severe LHC radiation environment at up to several hundred volts while maintaining a good signal-to-noise ratio, small cell size, and minimal multiple scattering. The ability to be operated under full bias for electrical characterization prior to attachment of the readout integrated circuit electronics is also desired.

A measurement of Lorentz angle and spatial resolution of radiation hard silicon pixel sensors

Silicon pixel sensors developed by the ATLAS collaboration to meet LHC requirements and to withstand hadronic irradiation to fluences of up to

Electrical characteristics of silicon pixel detectors

10^{15} n_eq/cm^{2}

The DELPHI very forward tracker for LEP200

have been evaluated using a test beam facility at CERN providing a magnetic field. The Lorentz angle was measured and found to alter from 9.0 deg. before irradiation, when the detectors operated at 150 V bias at B=1.48 T, to 3.1 deg after irradiation and operating at 600 V bias at 1.01 T. In addition to the effect due to magnetic field variation, this change is explained by the variation of the electric field inside the detectors arising from the different bias conditions. The depletion depths of irradiated sensors at various bias voltages were also measured. At 600 V bias 280 micron thick sensors depleted to ~200 micron after irradiation at the design fluence of 1 10^{15} 1 MeV n_eq/cm2 and were almost fully depleted at a fluence of 0.5 * 10^{15} 1 MeV n_eq/cm2. The spatial resolution was measured for angles of incidence between 0 deg and 30 deg. The optimal value was found to be better than 5.3 micron before irradiation and 7.4 micron after irradiation.

B-quark tagging using neural networks and multivariate statistical methods A comparison of both techniques

Prototype sensors for the ATLAS silicon pixel detector have been electrically characterized. The current and voltage characteristics, charge-collection efficiencies, and resolutions have been examined. Devices were fabricated on oxygenated and standard detector-grade silicon wafers. Results from prototypes which examine p-stop and standard and moderated p-spray isolation are presented for a variety of geometrical options. Some of the comparisons relate unirradiated sensors with those that have received fluences relevant to LHC operation.

The power supply system for the ATLAS pixel detector

Abstract The design of a new silicon tracker detector for the forward region in the DELPHI experiment is presented. It consists of two layers of macropixel and two layers of ministrip detectors in both the forward directions. The motivations and the requirements for this detector will be shown together with test beam results.

First experiences with the ATLAS pixel detector control system at the combined test beam 2004

Abstract We have studied the b-quark tagging problem from Z 0 decays as measured in the DELPHI experiment at LEP using artificial neural networks and conventional multivariate statistical methods. Contrary to the classical approaches we used as input to the neural network very simple variables, closely related to the directly measured particle momenta. The results of the methods are compared and tested for possible complementation.

Measurement of the thermal resistance of VCSEL devices

The innermost part of the ATLAS (A Toroidal LHC Apparatus) experiment at the LHC (Large Hadron Collider), CERN (Conseil Eurpeenne pour la Recherche Nucleaire), will be a pixel detector, which is presently under construction. To operate the approx. 1700 detector modules and their related readout electronics a sophisticated power supply system is required. Its design constraints are the high power density and the sensitivity of the read out chips developed in deep sub-micron technology. A high granularity of the system is desired to allow individual adjustment and to minimize the number of elements out of service. We describe the layout of the full power supply system and concentrate on the components designed in-house: the supply system for the optical link, which offers the possibility of handling a high number of channels at a reasonable price and the remotely-programmable regulator stations, which protect the sensitive front end electronics.

The control system for the ATLAS pixel detector

Abstract Detector control systems (DCS) include the readout, control and supervision of hardware devices as well as the monitoring of external systems like cooling system and the processing of control data. The implementation of such a system in the final experiment also has to provide the communication with the trigger and data acquisition system (TDAQ). In addition, conditions data which describe the status of the pixel detector modules and their environment must be logged and stored in a common LHC wide database system. At the combined test beam all ATLAS subdetectors were operated together for the first time over a longer period. To ensure the functionality of the pixel detector, a control system was set up. We describe the architecture chosen for the pixel DCS, the interfaces to hardware devices, the interfaces to the users and the performance of our system. The embedding of the DCS in the common infrastructure of the combined test beam and also its communication with surrounding systems will be discussed in some detail.

System Tests of the ATLAS Pixel Detector

In the context of particle physics detector development, the environmental conditions will change with the increasing capabilities of the accelerators to deliver more particles at higher energies. Since currently the increase of energy above the 14 TeV the LHC is designed for will not be the priority, the increase of luminosity will dominantly change the conditions in which particle detectors will be operated. A higher number and therefore flux of particles per collision through the detectors leads to higher radiation dosages the components must withstand. To operate and read out even the innermost detectors under these conditions electronics and optical components must be developed accordingly. For semiconductor lasers, on which we will concentrate here, it has been found, that an inner temperature increase has direct impact on the light power emitted by the device. It has been found that the effects of radiation on the behavior of semiconductor lasers are convolved with those of temperature. An optimized coupling to the cooling of the laser device reduces the thermal effects in the material. Therefore, a test stand to qualify the effect of heat in the device and the adoption of the heat sink has been realized. In this paper we present first measurements to prove the functionality of the setup.