G. Maehlum

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.

Experimental setup for very high resolution animal PET based on solid state detector

A very high resolution animal PET instrument was investigated using Monte Carlo simulations. The instrument consists of an outer cylindrical BGO scintillation detector surrounding an inner cylindrical solid state detector composed of 0.3 mm square silicon pads. The interaction point of gamma rays that scatter in the pad detector can be accurately localized in 3D to within the pad volume. Total energy is known from the summed energy in silicon and BGO detectors. Simulation results show 192 /spl mu/m spatial resolution for events in which both annihilation photons scatter in silicon detectors. We have constructed a prototype Compton PET instrument using two silicon detectors with 1.4 mm square pads, two CCDAQ data acquisition units that have digital signal processors, a source turntable, and a coincidence unit. Using this experimental setup the energy spectrum of photons from technetium (Tc-99m) was acquired with 2.45 keV energy resolution and the timing spectrum of annihilation photons from fluorine (F-18) was obtained with 1.9 ns timing resolution. This experimental, setup will be used to verify the simulation results for the high resolution PET that is expected to have a maximum resolution of 0.7 mm FWHM at the center of the field of view.

The DELPHI microvertex detector

The main characteristics of the DELPHI Microvertex Detector are presented. The performance in terms of impact parameter resolution, association efficiency, and ambiguity is evaluated after two years of data taking at LEP.