Pawel Jalocha

The DELPHI Microvertex detector

The DELPHI Microvertex detector, which has been in operation since the start of the 1990 LEP run, consists of three layers of silicon microstrip detectors at average radii of 6.3, 9.0 and 11.0 cm. The 73728 readout strips, oriented along the beam, have a total active area of 0.42 m2. The strip pitch is 25 μm and every other strip is read out by low power charge amplifiers, giving a signal to noise ratio of 15:1 for minimum ionizing particles. On-line zero suppression results in an average data size of 4 kbyte for Z0 events. After a mechanical survey and an alignment with tracks, the impact parameter uncertainty as determined from hadronic Z0 decays is well described by (69pt)2 + 242 μm, with pt in GeV/c. For the 45 GeV/c tracks from Z0 → μ− decays we find an uncertainty of 21 μm for the impact parameter, which corresponds to a precision of 8 μm per point. The stability during the run is monitored using light spots and capacitive probes. An analysis of tracks through sector overlaps provides an additional check of the stability. The same analysis also results in a value of 6 μm for the intrinsic precision of the detector.

The DELPHI silicon strip microvertex detector with double sided readout

The silicon strip microvertex detector of the DELPHI experiment at the CERN LEP collider has been recently upgraded from two coordinates (RΦ only) to three coordinates reconstruction (RΦ and z). The new Microvertex detector consists of 125 952 readout channels, and uses novel techniques to obtain the third coordinate. These include the use of AC coupled double sided silicon detectors with strips orthogonal to each other on opposite sides of the detector wafer. The routing of signals from the z strips to the end of the detector modules is done with a second metal layer on the detector surface, thus keeping the material in the sensitive area to a minimum. Pairs of wafers are daisy chained, with the wafers within each pair flipped with respect to each other in order to minimize the load capacitance on the readout amplifiers. The design of the detector and its various components are described. Results on the performance of the new detector are presented, with special emphasis on alignment, intrinsic precision and impact parameter resolution. The new detector has been taking data since spring of 1994, performing up to design specifications.

Development of silicon pad detectors and readout electronics for a Compton camera

Abstract Applications in nuclear medicine and bio-medical engineering may profit using a Compton camera for imaging distributions of radio-isotope labelled tracers in organs and tissues. These applications require detection of photons using thick position-sensitive silicon sensors with the highest possible energy and good spatial resolution. In this paper, research and development on silicon pad sensors and associated readout electronics for a Compton camera are presented. First results with low-noise, self-triggering VATAGP ASICs are reported. The measured energy resolution was 1.1 keV FWHM at room temperature for the 241 Am photo-peak at 59.5 keV .

Beam test results from a prototype for the delphi microvertex detector

Abstract Results are presented from a test in the CERN SPS North Area of a prototype of the DELPHI microvertex detector. Full-sized modules built up from prototype ac-coupled detectors and VLSI readout electronics were used. The spatial resolution of the detectors equipped with prototype VLSI chips was measured to be 6.5 μm. The system aspects, including the readout, were found to work well. Extrapolating to the final components we expect to achieve a measurement precision of 5 μm with the DELPHI microvertex detector.

Double-sided silicon microstrip detectors and low noise self-triggering multichannel readout chips for imaging applications

Abstract Double-sided silicon microstrip detectors and CMOS low noise self-triggering 16-channel chips have successfully been tested with low energy X-rays and β-emitting sources for imaging of simple patterns. The noise slope of the chip is measured to 19.2 e − /pF. Also a 2 × 2 mm 2 diode has been used to measure the photon energy resolution in the range of 8–60 keV. With the diode the K-line from Cu (8.04 keV) is clearly visible. Two-dimensional images are shown.

Status of the DELPHI vertex detector: Alignment methods and geometrical resolution

Abstract Progress in the construction of the DELPHI silicon microstrip vertex detector is described and results obtained for the various components are presented. Problems related to the design, construction and survey of a system capable of maintaining in a collider environment the resolution achievable by microstrip detectors are discussed. Finally, some plans for the future are also reported.

A new 2-dimensional high resolution Si detector for β- and γ-radiography

Abstract A double-sided silicon microstrip detector read out by a CMOS low noise self-triggering 128-channel chip has successfully been tested with low energy γ- and X-rays and β-emitting sources for imaging of simple patterns. The readout chip is described in detail, as well as the detector, the ancillary electronics and the data acquisition. Images of the size of 6.4 × 6.4 mm 2 are presented. The readout pitch is 50 μm in both the x - and the y -direction. The energy resolution for the 44.23 keV K α -line from Tb is measured to 0.86 keV (240 e − rms). For β-patterns with 35 S, the spatial spread shows a good correlation with the range of the particles (130 μm).

Hybrid pixel detector development for the linear collider Vertex Tracker

In order to fully exploit the physics potential of the future high energy e+e− linear collider, a Vertex Tracker able to provide particle track extrapolation with very high resolution is needed. Hybrid Si pixel sensors constitute an attractive technology due to their fast read-out capabilities and radiation hardness. A novel pixel detector layout with interleaved cells has been developed to improve the single point resolution. Results of the characterisation of the first processed prototypes by electrostatic measurements and charge collection studies are discussed.