An asynchronous version of a binary pixel readabout circuit has been implemented in an array with 16 columns at 500 mu m pitch and 63 rows at 75 mu m pitch. This readabout chip has been bonded with solder bumps to a silicon detector with matching pixel elements. Event information in a pixel can be strobed into a local memory by a trigger signal and subsequently read out. Without a strobe the information is continuously cleared. The complete hybrid detector has been successfully tested with ionizing particles from a radioactive source. Three such devices have been put in the CERN heavy-ion experiment WA94 in the Omega spectrometer, where they recorded particle tracks from high-multiplicity /sup 32/S interactions. Preliminary data indicate a noise of approximately 60 e/sup -/ and a threshold spread of approximately 500 e/sup -/. The timing characteristics are adequate for a fixed-target experiment.<>

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Disclaimer/Complaints regulations If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible.

Disclaimer/Complaints regulations If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible.

The investigation of CVD-diamond as a new detector material for applications in heavy-ion physics is described. Pulse-height and time spectra for various projectiles, measured with diamond samples of different thicknesses, are discussed.

A prototype Pestov Spark Counter with two-dimensional position resolution has been developed. The position resolution is 0.32 mm and <2 mm in transverse and longitudinal direction, respectively. Beam tests yielded both the time resolution and the efficiency in accordance with earlier results obtained at BNIP Novosibirsk. A long-term stability test has been performed and stable behaviour for more than 3 month was observed.

The performance of a new ALICE prototype of the Pestov spark counter was measured both in a dedicated test beam as well as in a high multiplicity heavy-ion environment. Results in terms of time resolution and background behaviour are presented.

A multi-chip, large area hybrid silicon pixel detector has been integrated in a particle physics experiment for the first time. The plane had 72K 75 μm × 500 μm sensor elements, covering a total area of about 30 cm2. It was constructed and characterized in a collaboration between heavy-ion experiment WA97 and R&D project RD19. Several such planes will be incorporated in a hyperon telescope, in order to improve tracking in the high multiplicity environment of central lead-lead collisions at the SPS. Results on the characterization of this detector in a proton beam at the Omega spectrometer at CERN are presented and discussed.

A second version of the Omega pixel readout chip has been developed in order to make it compatible with large area coverage. Specific features of the new chip include a reset which can be applied immediately following a “false” trigger, an improved minimum strobe time of ∼ 100 ns, a readout clock rate of ∼ 20 MHz and tri-state buffers on the output data lines. The excellent performance figures of the first chip for noise (100 e rms without detector and 170 e rms with detector) and power consumption (30 μW/pixel) have been maintained. We demonstrate how with solder bump-bonding we can create hybrid “ladders” which hermetically cover an area of ∼ 5 mm × 50 mm. Potential problems of electrical matching and yield have been addressed and procedures are in place for selecting only “good” readout chips for mounting.

Successive versions of high speed, active silicon pixel detectors with integrated readout electronics have been developed for particle physics experiments using monolithic and hybrid technologies. Various matrices with binary output as well as a linear detector with analog output have been made. The hybrid binary matrix with 1024 cells (dimension 75 μm×500 μm) can capture events at ∼5 MHz and a selected event can then be read out in < 10 μs. In different beam tests at CERN a precision of 25 μm has been achieved and the efficiency was better than 99.2%. Detector thicknesses of 300 μm and 150 μm of silicon have been used. In a test with a 109Cd source a noise level of 170 e− r.m.s. (1.4 keV fwhm) has been measured with a threshold non-uniformity of 750 e− r.m.s. Objectives of the development work are the increase of the size of detecting area without loss of efficiency, the design of an appropriate readout architecture for collider operation, the reduction of material thickness in the detector, understanding of the threshold non-uniformity, study of the sensitivity of the pixel matrices to light and low energy electrons for scintillating fiber detector readout and last but not least, the optimization of cost and yield of the pixel detectors in production.

We have studied the four-fermion processes ee → eeee, eeμμ, eeττ, μμμμ, μμττ, eeqq and μμqq with the L3 detector at LEP. For an integrated luminosity of 36 pb−, corresponding to 960 000 hadronic Z decays, we find a total of 67 candidate events. The rate and kinematical distributions are found to be consistent with first order Monte Carlo calculations based on the Standard Model. No significant structure is seen in the dilepton invariant or recoil mass spectra.