P. Martinengo

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.

Final tests of the CsI-based Ring Imaging Detector for the ALICE experiment

We report on the final tests performed on a CsI-based RICH detector equipped with 2 C6F14 radiator trays and 4 photocathodes, each of 6438 cm 2 area. The overall performance of the detector is described, using different gas mixtures, in view of optimizing the photoelectron yield and the pad occupancy. Test results under magnetic field up to 0.9 T, photocathode homogeneity and stability are presented.

Measurements of charmed-meson production in interactions between 350 GeV/c π− particles and nuclei

Abstract Charmed-meson production by 350 GeV/c π − particles incident on copper and tungsten targets has been studied in the WA92 experiment, performed at the CERN Ω′ spectrometer. Results obtained are reported and discussed. Reconstruction of decays from the set D 0 → K − π + D 0 → K − π − π + π + , D s + → φπ + and charge conjugates has yielded a sample of 7280 ± 108 charmed mesons, produced with χ F > 0, ( χ F ) = 0.18 and〈 p T 2 〉 = 1.86 ( GeV / c ) 2 . Assuming a relationship σ = σ 0 A α between the cross section, σ, per nucleus of mass A and the nucleonic cross section, σ 0 the α value found for the detected charmed particles is 0.95 ± 0.06 ± 0.03. Taking α = 1, the measured cross sections per nucleon for χ F > 0 production are 7.78 ± 0.14 ± 0.52 μ b for D 0 / D 0 , 3.28 ± 0.08 ± 0.29 μ b for D + /D − and 1.29 ± 0.16 ± 0.33 μ b for D s + /D s − . Differential cross sections with respect to χ F and p T 2 have been determined for the various types of charmed meson, and particle-antiparticle asymmetries have been analysed.

The CsI based Ring Imaging Detector for the ALICE experiment: Technical description of a large prototype

We report on the design and construction of a CsI-RICH detector composed of four CsI photocathodes of 64]40 cm2 each, and two C 6 F 14 radiator trays of 133]41 cm2. A detailed description of the novel elements is given and the performance of the detector is illustrated with some basic results obtained during the tests at the beam. ( 1999 Elsevier Science B.V. All rights reserved.

Performance of large area CsI-RICH prototypes for ALICE at LHC

Abstract We present the performances of large area CsI-RICH prototypes obtained in single-particle events. The differential quantum efficiency of the photocathodes has been deduced from Cherenkov rings by means of two different procedures: a direct measurement with a thin NaF radiator and a Monte Carlo-based estimation for a C 6 F 14 radiator. A factor of merit of 45 cm −1 has been found for the typical detector configuration. Two angle reconstruction algorithms have been used and the different errors affecting the Cherenkov angle resolution have been estimated combining the analytical treatment and the Monte Carlo simulation. Also the dependence on radiator thickness, Cherenkov ring radius, chamber voltage and particle incidence angle has been studied.

A partial wave analysis of the centrally produced

A partial wave analysis of the centrally produced K+K- and K0K0 channels has been performed in pp collisions using an incident beam momentum of 450 GeV/c. An unambiguous physical solution has been found in each channel. The striking feature is the observation of peaks in the S-wave corresponding to the f0(1500) and fJ(1710) with J = 0. The D-wave shows evidence for the f2(1270)/a2(1320), the f2(1525) and the f2(2150) but there is no evidence for a statistically significant contribution in the D-wave in the 1.7 GeV mass region.A partial wave analysis of the centrally produced K+K- and K0K0 channels has been performed in pp collisions using an incident beam momentum of 450 GeV/c. An unambiguous physical solution has been found in each channel. The striking feature is the observation of peaks in the S-wave corresponding to the f0(1500) and fJ(1710) with J = 0. The D-wave shows evidence for the f2(1270)/a2(1320), the f2(1525) and the f2(2150) but there is no evidence for a statistically significant contribution in the D-wave in the 1.7 GeV mass region.

K^{+}K^{-}

The paper summarizes our latest progress in the development of newly introduced micro-pattern gaseous detectors with resistive electrodes. These resistive electrodes protect the detector and the front-end electronics in case of occasional discharges and thus make the detectors very robust and reliable in operation. As an example, we describe in greater detail a recently developed GEM-like detector, fully spark-protected with electrodes made of resistive kapton. We discovered that all resistive layers used in these studies (including kapton) that are coated with photosensitive layers, such as CsI, can be used as efficient photocathodes for detectors operating in a pulse counting mode. There is a description of the first applications of such detectors combined with CsI or SbCs photocathodes for the detection of UV photons at room and cryogenic temperatures.

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We have developed and tested several prototypes of GEM-like detectors with electrodes coated with resistive layers or completely made of resistive materials. These detectors can operate stably at gains close to 105. The resistive layers limit the energy of discharges appearing at higher gains thus making the detectors very robust. We demonstrated that the cathodes of some of these detectors could be coated by CsI or SbCs layers to enhance the detection efficiency for the UV and visible photons. We also discovered that such detectors can operate stably in the cascade mode and high overall gains (~106) are reachable. Applications in several areas, for example in RICH or in noble liquid TPCs are therefore possible. The first results from the detection of UV photons at room and cryogenic temperatures will be given.