H. Beker

Strangeness enhancement at mid-rapidity in Pb Pb collisions at 158-A-GeV/c

We study the influence of lexical subsumption on the semantic proximity of terms. By studying the semantic relation between lexically subsumed terms in an existing controlled vocabulary and those in a corpus, we formulate hypotheses on the underlying specific relations. These hypotheses enable us to propose an ordering of term variants found in the corpus, by probability of decreasing semantic proximity. Results from our experiment show that surface indices like the presence of proper names, compounds and the number of added words in a term variant are criteria for ordering the variants of the same term. The ranking obtained will enable us to form more semantically-cohesive clusters. Applications targeted are text mining, question-answering and science and technology watch.

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.

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.

LAMBDA , XI AND OMEGA PRODUCTION AT MID-RAPIDITY IN PB-PB AND P-PB COLLISIONS AT 158 A GEV/C

Λ, Ξ and Ω yields and transverse mass spectra measured at central rapidity in Pb-Pb and p-Pb collisions at 158 A GeV/c are presented. The yields in Pb-Pb interactions are given as a function of the collision centrality and compared with those obtained from p-Pb collisions. The dependence of hyperon yields on the centrality of the impact and on the strangeness content of the hyperon are discussed.

Construction and characterization of a 117 cm/sup 2/ silicon pixel detector

A silicon pixel detector, developed in RD19, and consisting of 4 planes, /spl sim/30 cm/sup 2/ each, is operating for the first time in the lead ion experiment WA97 at CERN. The 288 CMOS readout chips are bump-bonded to 48 Si detector matrices, assembled in 8 identical arrays. The total number of pixel cells is nearly 300000 and each cell, 75 /spl mu/m/spl times/500 /spl mu/m, contains a complete signal processing chain. Overall dead area is less than 3%. >

Performance of 0.5 × 106 sensitive elements pixel telescope in the WA97 heavy ion experiment at CERN

Abstract A silicon pixel telescope, consisting of seven planes for a total of about 0.5 M sensor elements with size of 75 μ m × 500 μ m, was successfully employed in the WA97 experiment at CERN. We describe here the overall performance of the detector; we also report some early results from PbPb and p-Pb runs, showing the powerful capability to measure particle momenta and the effective mass of hyperons with a good resolution.

Test-beam performance of a tracking TRD prototype

Abstract A tracking transition radiation detector prototype has been constructed and tested. It consists of 192 straw tubes, 4 mm in diameter, embedded in a polyethylene block acting as radiator. Its performance has been studied as an electron identifier as well as a tracking device for minimum-ionizing particles.

Silicon pixel detectors for tracking in NA57

Abstract In this paper, after recalling the main features of the NA57 experiment, we describe its silicon pixel tracker.

DI-V

The first results on V0-V0 pairs, namely invariant masses and HBT correlations, obtained by the WA97 experiment in Pb-Pb collisions are presented. There is no evidence for any resonance signal.