Search

The ALICE experiment at LHC will implement a high-level trigger system for online event selection and/or data compression. The largest computing challenge is posed by the TPC detector, which requires real-time pattern recognition. The system entails a very large processing farm that is designed for an anticipated input data stream of 25 GB s⁻¹. In this paper, we present the architecture of the system and the current state of the tracking methods and data compression applications.

A charged-particle detector based on proportional tubes with cathode readout is described. The cathode is sectionalized into 2.2 × 2.2-cm pads. The detector was tested on high-energy particle beams. At an anode-to-cathode distance of 1.1 cm, the spatial resolution was 1.25 mm along the anode wire. A simulation model of the detector on the basis of the measured pad-response function was proposed, compared to the experimental data, and used to calculate the two-track resolution. The detector can be used in various experiments as a large-area multiparticle two-coordinate detector.

The properties of ferromagnetic Gd as a host for IMPAC measurements have been investigated. The transient and internal magnetic fields at Cd, Nd, Sm, Dy, Er, Yb and Hf nuclei recoil implanted into polarized Gd at 80 K have been studied by the IMPAC technique. All available experimental transient field data for Gd have been analysed in the framework of the Lindhard-Winther theory. Empirical values of the parametersvp andCionCatom have been deduced which give good agreement between experiments and theory. Internal magnetic fields at rare-earth nuclei in magnetized Gd at 80 K have been deduced. The results areHh.f. (NdGd)=-1370±440 kG,Hh.f.(SmGd)=-1440±120 kG,Hh.f.(DyGd)=1410±400 kG,Hh.f.(ErGd)=2310±420 kG andHh.f.(YbGd)=-216±32 kG. The signs of these fields are, except for Yb which is in a 2+ ionic state, consistent with a ferromagnetic coupling between the 4f spins of the implanted ion and the Gd host. The deduced internal field at Hf in Gd is -440±90 kG. The observed time-dependent interactions for rare-earth nuclei in ferromagnetic Gd are consistent with the Abragam-Pound theory. For the Cd isotopes,g-factors of the first 2+ states were deduced from the experiments. The results areg(110Cd)=0.49±0.11,g(114Cd)=0.34±0.09 andg(116Cd)=0.41±0.11. The use of transient magnetic fields forg-factor measurements on high-spin rotational states is discussed.

The structure of a shashlik calorimeter allows the insertion of tracking detectors within the longitudinal sampling to improve the accuracy in the determination of the direction of the showering particle and the eπseparation ability. The new forward calorimeter of the DELPHI detector has been equipped with two planes of silicon pad detectors respectively after 4 and 7.4 radiation lengths. The novelty of these silicon detectors is that to cope with the shashlik readout fibers, they had to incorporate 1.4 mm holes every cm2. The detector consists of circular strips with a radial pitch of 1.7 mm and an angular granularity of 22.5°, read out by means of the MX4 preamplifier. The preamplifier is located at 35 cm from the silicon detector and the signal is carried by Kapton cables bonded to the detector. The matching to the MX4 input pitch of 44 μm was made by a specially developed fanin hybrid.

The DELPHI STIC detector is a lead-scintillator sampling calorimeter with wavelength shifting optical fibers used for light collection. The main goal of the calorimeter at LEP100 is to measure the luminosity with an accuracy better than 0.1%. The detector has been in operation since the 1994 LEP run. Presented here is the performance measured during the 1994-1995 LEP runs, with the emphasis on the achieved energy and space resolution, the long-term stability and the efficiency of the detector. The new bunch-trains mode of LEP requires a rather sophisticated trigger and timing scheme which is also presented. To control the trigger efficiency and stability of the calorimeter channels, a LED-based monitoring system has been developed.

The research project RD24 is studying applications of the scalable coherent interface (IEEE-1596) standard for the Large Hadron Collider (LHC). First SCI node chips from Dolphin were used to demonstrate the use and functioning of SCI's packet protocols and to measure data rates. We present results from a first, two-node SCI ringlet at CERN, based on a R3000 RISC processor node and DMA node on a MC68040 processor bus. A diagnostic link analyzer monitors the SCI packet protocols up to full link bandwidth. In its second phase, RD24 will build a first implementation of a multi-ringlet SCI data merger.<>

The experimental data have been compared with the result of extensive compound nucleus calculations based on the statistical theory. The shapes and the absolute cross sections for the high energy parts of the proton- and a-spectra are reproduced with a level density parametera ? 0·11 A MeV-1 and a moment of inertiaJ?1·3Jrig. The same parameters fairly well reproduce the angular distributions corresponding to the high energy parts of the spectra whereas deviations between theory and experiment are observed for the lower energies where particles emitted by higher order processes contribute. The observed total cross section for emission of an a-particle is 500 mb or 1·7 times calculated value. For protons the corresponding numbers are 2313 mb and 3·0. The increase in cross section is ascribed to the process in which several particles are evaporated. Various methods are discussed for determination of the average orbital angular momentum of the emitted particle or the average spin of the daughter nucleus.

Highly excited compound nuclei of74Kr have been formed by bombardment of58Ni with 70 MeV16O ions. The spectra of protons and a-particles resulting from the decay of the compound nucleus (and several daughter nuclei) have been recorded at laboratory angles from 30° to 155°. The CM differential cross sections corresponding to definite energies for the particles emitted were calculated from the data. The charged particle spectra and the angular distributions show that evaporation processes are dominant. A study of spectral shapes and angular distributions has to some extent made it possible to distinguish primary particles from those evaporated after the emission of one or several particles.