F. Riccardi

Construction and test of calorimeter modules for the CHORUS experiment

Abstract The construction of modules and the assembly of the calorimeter for CHORUS, an experiment that searches for ν μ ↔ ν τ oscillation, have been completed. Within the experiment, the calorimeter is required to measure the energy of hadronic showers produced in neutrino interactions with a resolution of /∼30%/√ E (GeV). To achieve this performance, the technique, developed in recent years, of embedding scintillating fibers of 1 mm diameter into a lead matrix has been adopted for the most upstream part of the calorimeter. A more conventional system, of alternating layers of lead and scintillator strips, was used for the rest. Details of module construction as well as results obtained when modules were exposed to electron and muon beams are presented.

The CHORUS scintillating fiber tracker and opto-electronic readout system

Abstract A scintillating fiber tracker system consisting of more than one million fibers has been successfully constructed and made operational for the CERN WA95/CHORUS experiment. The design and construction of the tracker system as well as its opto-electronic readout are described. The performance of the detector with high-energy muons is presented.

Scintillating fiber trackers with optoelectronic readout for the CHORUS neutrino experiment

Abstract The CERN WA95/CHORUS collaboration has been constructing a hybrid detector to search for ( ν μ - ν τ )-oscillations. An essential component of the detector is a scintillating fiber tracking system for precise track reconstruction of particles. The physics motivation is explained, and the detector layout, the tracker design, its optoelectronic readout and test beam results are presented.

Experimental results from a large volume active target made of glass capillaries and liquid scintillator

We are investigating the feasibility of high-resolution tracking with an active target made of glass capillaries filled with organic liquid scintillator. This technique allows real time detection of short-lived particle decays. In this paper, we report on experimental results obtained from an active target having 2 × 2 cm2 cross section and 180 cm length, installed in front of the CHORUS detector and exposed to the CERN Wide Band Neutrino Beam. The detector consists of 5.1 × 105 capillaries with 20 μm inner diameter, read out by a single optoelectronic chain and a Megapixel CCD. Details on tests in the neutrino beam will be reported. First neutrino interactions have been detected.

The Data Acquisition System of the CHORUS Experiment

Abstract In the years 1994–1998 the CHORUS Collaboration has recorded data in the CERN WA95 experiment. Here we describe the data acquisition system that has been used, featuring concurrent hierarchical state machines, a remote operating system, a buffer manager, a dispatcher, a control panel and a supervisor.

Charged-particle tracking with high spatial and temporal resolution using capillary arrays filled with liquid scintillator

We abstract developed a new technique that allows the trajectories of ionizing particles to be imaged with very high spatial and temporal resolution. This technique, developed for future experiments in high-energy physics, may also be applied in other field. Central to the technique is a detector consisting of a bundle of thin, glass capillaries filled with a liquid scintillator of high refractive index. These liquid-core scintillating fibers act simultaneously as a detector of charged particles and as an image guide. Track images seen at the readout end of the capillary bundle are amplified by an optoelectronic chain consisting of a set of image- intensifier tubes and read by a photosensitive CCD camera. We report here on results obtained with detector prototypes. A spatial resolution of 6-14 micrometers , dependent on image magnification prior to readout, has been obtained with 16 micrometers capillaries. The high scintillation efficiency of the liquid scintillator used and a large light attenuation length-- approximately 3 m for 20 micrometers capillaries--result in hit densities along the track of a minimum-ionizing particle of 8.5 mm-1 and 3.5 mm-1 at distances from the readout window of approximately 2 cm and approximately 1 m respectively. The radiation resistance of the detector is an order of magnitude greater than that of other types of tracking device of comparable performance. To complement the detector we have been developing a new readout system based around a gateable vacuum image pipeline (VIP) and an electron- bombarded CCD camera. These increase the spatial and temporal resolution obtained with detector and render it particlarly attractive as a microvertex detector for the observation of short-lived particles in high-energy physics experiments performed with evelated interaction rates.

CHORUS scintillating fiber tracker and optoelectronics readout system

An essential component of the CERN WA95/CHORUS experiment is a scintillating fiber tracker system made up of more than one million scintillating fibers, for the precise track reconstruction of particles. The design and construction of the tracker system as well as its opto-electronics readout are discussed. Performances of the detector are presented.

The CHORUS calorimeter: test results

Abstract In the framework of the CHORUS experiment for the search of v μ ↔ v τ oscillations at CERN, we have built the high resolution calorimeter, intended for the measurement of the energy of hadronic showers produced in neutrino interactions. The calorimeter consists of three parts. The first two are made of lead and plastic scintillating fibers in the volume ratio 4 : 1, such as to achieve compensation. The third is a sandwich of lead plates and scintillator strips in the same volume ratio. The techniques used for the construction of the calorimeter are described, as well as its performance in shower and muon detection. We used electron, pion and muon beams in the energy range 2–100 GeV for this purpose.

An instrument for the high-statistics measurement of plastic scintillating fibers

There is today widespread use of plastic scintillating fibers in particle physics, mainly for calorimetric and tracking applications. In the case of calorimeters, we have to cope with very massive detectors and a large quantity of scintillating fibers. The CHORUS Collaboration has built a new detector to search for νμ-ντ oscillations in the CERN neutrino beam. A crucial task of the detector is ruled by the high-energy resolution calorimeter. For its construction more than 400000 scintillating plastic fibers have been used. In this paper we report on the design and performance of a new instrument for the high-statistics measurement of the fiber properties, in terms of light yield and light attenuation length. The instrument has been successfully used to test about 3% of the total number of fibers before the construction of the calorimeter.

A fast constant-fraction discriminator for eπ separation with a lead/scintillating-fiber calorimeter

Abstract In a lead/scintillating-fiber calorimeter with fibers oriented in the direction of the incident particles, the different longitudinal development of the showers generated by electrons and pions results in a different time structure of the signals. We have designed a constant-fraction discriminator, which allows the achievement, on-line, of the electron/pion ( e π ) separation needed for trigger purposes. The fast signals from the calorimeter, of 10–20 ns duration, demand a circuit able to operate in the high frequency domain. We tested the performance of the circuit with signals produced by a prototype calorimeter constructed by the LAA-SPACAL collaboration at CERN. The circuit allows triggering on electrons with an efficiency higher than 99% with about 6% of the pions faking electrons in the dynamic range from 0.2 V to more than 2 V. The decision time is shorter than 60 ns and the typical time resolution is better than 100 ps.