G. Stefanini

Performance of the ALEPH Time Projection Chamber

Abstract The performance of the ALEPH Time Projection Chamber (TPC) has been studied using data taken during the LEP running periods in 1989 and 1990. After correction of residual distortions and optimisation of coordinate reconstruction algorithms, single coordinate resolutions of 173 μm in the azimuthal and 740 μm in the longitudinal direction are achieved. This results in a momentum resolution for the TPC of Δp / p 2 = 1.2 × 10 −3 (GeV/ c ) −1 . In combination with the ALEPH Inner Tracking Chamber (ITC), a total momentum resolution of Δp / p 2 = 0.8 × 10 −3 (GeV/ c ) −1 is obtained. With respect to particle identification, the detector achieves a resolution of 4.4% for the measurement of the ionisation energy loss.

Measurement of the magnetic birefringence of noble gases

The Cotton–Mouton constants of argon, krypton, and xenon have been measured relative to nitrogen at room temperature and ambient pressure for λ = 514.5 nm. Upper limits for helium and neon have been determined. The sensitivity of the apparatus was Δnmin = 0.8 × 10−14 for a measuring time of 1 sec.

Digital techniques applied to phase-sensitive detection

A phase-sensitive detector, based on digital techniques, has been designed and tested. The main features of this instrument are presented and compared with those of a commercial analogue device.

On a sensitive ellipsometer to detect the vacuum polarization induced by a magnetic field

SummaryAn ellipsometer able to measure ellipticities down to 10−11 is being developed. We present here results of measurements made in order to test the main parts of the apparatus. The feasibility and the limits of such an ellipsometer are discussed, in particular in view of measuring the polarization of the vacuum induced by a magnetic field (photon-photon interaction).RiassuntoIn questo articolo si presentano i risultati di misure fatte allo scopo di mettere a punto un ellipsometro capace di misurare ellitticità dell’ordine di 10−11. Il metodo descritto è stato sviluppato principalmente allo scopo di misurare la polarizzazione del vuoto indotta da un forte campo magnetico (interazione fotone-fotone).РезюмеПредлагается эллипсометр, позволяющий измерить эллиптичности вплоть до 10−11. Приводятся результаты измерений, проведенных с целью проверки основных частей аппаратуры. Обсуждаются осуществимость и ограничения такого эллипсометра, в частности, применительно для измерения поляризации вакуума, индуцированной магнитным полем (фотон-фотонное взаимодействие).

The Alice silicon pixel detector

CERN European Organization for Nuclear Research, CH-1211 Geneva 23, Switzerland Universita degli Studi di Padova, I-35131, Padova, Italy Dipartimento IA di Fisica e Sez. INFN di Bari, I-70126,Bari,Italy Comenius University, SK-84215 Bratislava, Slovakia NIKHEF, National Institute for Nuclear Physics and High Energy Physics, 1098 SJ Amsterdam, The Netherlands Slovak Academy of Sciences, SK-04353, Kosice, Slovakia Universita di Roma I, La Sapienza, I-00185, Roma, Italy

A HIGH STABILITY LIGHT EMITTING DIODE SYSTEM FOR MONITORING LEAD GLASS ELECTROMAGNETIC CALORIMETERS

Abstract We have designed, built and tested a high stability system based on blue light emitting diodes (LED) and current pulse generators for calibration and monitoring of lead-glass calorimeters. This apparatus is presently being used for the electromagnetic calorimeter of the WA96 (NOMAD) experiment at CERN. The system was developed to minimize the sensitivity to temperature variations, different loadings, and ageing effects. Tests performed both in the laboratory and in the experiment showed that the response of the lead-glass calorimeter modules to LED light pulses could be kept within the precision of ±1% for periods of several months.

Measurement of the magnetic birefringence in oxygen and nitrogen gases

Abstract The Cotton-Mouton constant for oxygen and nitrogen has been measured at room temperature and pressure using a laser with λ = 514.5 nm .

Magnetic birefringence measurement in hydrogen and deuterium gases

The first measurement of the magnetic birefringence (Cotton–Mouton effect) in molecular hydrogen and deuterium has been performed. The Cotton–Mouton constant of H2 and D2 has been measured at room temperature, atmospheric pressure, and for λ=514.5 nm. Comparison with theoretical calculations shows very good agreement in both cases.

The spatial resolution of the ALEPH TPC

The present understanding of the factors which limit the rφ measurement accuracy of the ALEPH time projection chamber is outlined. The resolution for high-momentum tracks is shown to be dominated by the E × B and angular affects.

ION TRAPPING PROPERTIES OF A SYNCHRONOUSLY GATED TIME PROJECTION CHAMBER

Abstract Studies have been made of the transmission of positive ions through the gating grid of a time projection chamber operated synchronously at a high rate. With a duty cycle of 25% (22 μs periodic wave form) it has been demonstrated that less than one positive ion in 7 × 10 −3 traverses the gating grid. This new gating technique can be used by a time projection chamber operating at the LEP e + e − collider.