M.G. Catanesi

LHC1: A semiconductor pixel detector readout chip with internal, tunable delay providing a binary pattern of selected events

The Omega3/LHC1 pixel detector readout chip comprises a matrix of 128 × 16 readout cells of 50 μm × 500 μm and peripheral functions with 4 distinct modes of initialization and operation, together more than 800 000 transistors. Each cell contains a complete chain of amplifier, discriminator with adjustable threshold and fast-OR output, a globally adjustable delay with local fine-tuning, coincidence logic and memory. Every cell can be individually addressed for electrical test and masking. First results have been obtained from electrical tests of a chip without detector as well as from source measurements. The electronic noise without detector is ∼ 100 e− rms. The lowest threshold setting is close to 2000 e− and non-uniformity has been measured to be better than 450 e− rms at 5000 e− threshold. A timewalk of < 10 ns and a precision of < 6 ns rms on a delay of 2 μs have been measured. The results may be improved by further optimization.

First operation of a 72-k element hybrid silicon micropattern pixel detector array

Abstract We have constructed and tested silicon pixel detector arrays of 96 × 378 (36 288) sensor elements with 75 μm × 500 μm area. The low-noise signal processing circuit associated with each element occupies an identical area on a bump-bonded readout chip. The pixel cell response for ionizing particles is binary with an adjustable threshold between 4000 e − and 15 000 e − . Single chips, the array of 6 ladders and a double array have been characterized in particle test beams and in the Omega experiment WA97 at CERN. The two arrays together, staggered by ∼ 4 mm cover hermetically a 53 mm × 55 mm area with 72 576 pixels. The proportion of properly functioning pixels was 98% in the first 36 k pixel array and 80% in the second one. The ∼ 1% “always-on” pixels could be masked electronically. After masking the rate of “spurious noise hits” was −8 of the identified particle hits while with beam off no hits at all were recorded With a beam trigger most events consisted of a single cluster with a single hit. At the 8000 e − threshold an efficiency > 99% was measured. Tracks were reconstructed with a precision of 22 μm. The proportion of double hits (∼ 11%) depends only slightly on threshold and detector bias voltage, and for these double hits a precision of 10 μm on the particle position was obtained.

Measurement of charm production in neutrino charged-current interactions

The nuclear emulsion target of the CHORUS detector was exposed to the wide-band neutrino beam of the CERN SPS of 27 GeV average neutrino energy from 1994 to 1997. In total, about 100 000 charged-current (CC) neutrino interactions with at least one identified muon were located in the emulsion target and fully reconstructed, using newly developed automated scanning systems. Charmed particles were searched for by a program recognizing particle decays. The observation of the decay in nuclear emulsion makes it possible to select a sample with very low background and minimal kinematical bias. In all, 2013 CC interactions with a charmed hadron candidate in the final state were selected and confirmed through visual inspection. The charm production rate induced by neutrinos relative to the CC cross-section is measured to be σ(νμN→μ−CX)/σ(CC)=(5.75 ± 0.32(stat)±0.30(syst))%. The charm production cross-section as a function of neutrino energy is also obtained. The results are in good agreement with previous measurements. The charm-quark hadronization produces the following charmed hadrons with relative fractions (in %): fD0=43.7±4.5, fΛc+=19.2±4.2, fD+=25.3±4.2 and fDs+=11.8±4.7.

Performance of a limited streamer tube hadron calorimeter

The energy response and the resolution of a hadron calorimeter test module prepared by the ALEPH collaboration at LEP have been studied between 5 and 50 GeV. The energy resolution for pions follows a 0.78√E law for orthogonally incident particles. Effects of different incident polar angles (θ = 90°, 60°, 50°) are studied. The wire readout and the trigger capability are also discussed.

Experience with a 30 cm2 silicon pixel plane in CERN experiment WA97

Abstract 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 μ m × 500 μ m sensor elements, covering a total area of about 30 cm 2 . 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.

Hadron, electron and muon response of a uranium-scintillator calorimeter

Abstract A hadron calorimeter comprising 10 mm depleted uranium plates and 5 mm plastic scintillator was exposed to electrons, hadrons and muons in the energy range 5–210 GeV. The measured ratios of sampling fractions are 0.8 for e/π and 0.6 for e/mip. The addition of a fine grained electromagnetic calorimeter with 1.6 mm depleted uranium plates and 4 mm plastic scintillator in front of the hadron calorimeter leads to a slightly worse hadronic energy resolution. Results on the longitudinal shower development and energy containment for hadron showers are given.

A hybrid silicon pixel telescope tested in a heavy-ion experiment

Abstract Specific features of the OMEGA-ION pixel detector are the adjustable delay with external trigger capability and the detector leakage current compensation. A row of pixels can be used for testing the electrical performance of the amplifier and comparator circuits. Detailed results of these electrical tests are presented. A telescope made of three OMEGA-ION hybrid silicon pixel detectors has been successfully tested in the heavy-ion experiment WA94. Each plane consisted of a single detector with 1006 active pixels (500 μm×75 μm), each one being bump-bonded to the readout chip, and arranged in 16 columns and 63 rows respectively. With a sensitive area as small as 8000 × 4725 μm 2 several million events with at least one track originating from the sulphur-sulphur interaction have been recorded in a few hours. Results on target reconstruction, tracking accuracy and efficiency are presented.

The production of beauty particles in π−-U interactions at 320 GeV energy

Abstract B B production in π − -uranium interactions has been observed at 320 GeV beam energy looking at events with three muons in the final state. The cross section is found to be σ B B = 4.5±1.4±1.4 nb per nucleon (for a linear A -dependence) or σ B B = 17.6±5.5±5.5 nb per nucleon (assuming A 0.75 dependence). An estimate of x F distribution is given.

A Hybrid Experiment to Search for Beauty Particles

We give here a detailed description of experiment WA75, which was performed at CERN to search for beauty particles. Events containing at least one muon with a high momentum transverse to the beam direction were selected; then the primary interactions and decay vertices, located in stacks of nuclear research emulsions, were examined and analysed. The various parts of the apparatus are described and the off-line analysis and search in emulsion are discussed. An estimate is made of the sensitivity of the experiment to beauty- and charmed-particle production.

K/π production ratios from 450 GeV/c protons on beryllium

Abstract This paper reports on the charged K / π production ratios and on the shape of the p T distributions of π fluxes measured by the SPY/NA56 experiment for 450 GeV/c proton interactions on beryllium targets. The present data cover a secondary momentum range from 7 GeV/c to 135 GeV/c in the forward direction and with p T values up to 600 MeV/c. An experimental accuracy of about 3% has been achieved. These results will reduce the uncertainty on the estimation of the ν e component of neutrino beams.