R. Settles

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.

The ALEPH minivertex detector

Abstract Vertex detectors allow high precision reconstruction of particle tracks and therefore make possible the investigation of the decay topology of short-lived particles in collider experiments. In the ALEPH experiment at LEP a minivertex detector will be installed. It consists of silicon microstrip detectors arranged on two concentric “cylindrical” surfaces around the interaction point. With this geometry it will be possible to measure the r − ϕ − z coordinates of particles traversing the detector. The expected position resolution is 10 μm in r − ϕ and 20 μm in r − z . For optimum signal processing monolithic CMOS readout electronics are under development. Each chip consists of 60 charge sensitive preamplifiers, multiplexed into one output channel. Fast power switching will reduce heat dissipation. Details about construction and expected device performance will be described.

Readout of double-sided silicon strip detectors with high density detectors with high density integrated electronics

The authors describe the readout system that has been developed for the ALEPH minivertex detector at LEP. The design makes use of capacitively coupled double-sided silicon strip detectors and custom-designated low-noise VLSI CMOS electronics, mounted on ceramic carriers which simultaneously serve as mechanical support and substrates for thick-film hybrid circuitry. The amplification of as many as 1536 analog channels of information using only 30 input/output lines is realized. The detector system with its peripheral driving and readout electronics is described, and first test results with a light source and a particle beam are given. >

New developments in double sided silicon strip detectors

A new type of double-sided silicon strip detector has been built and tested using high-density VLSI readout electronics connected to both sides. Capacitive coupling of the strips to the readout electronics has been achieved by integrating the capacitors into the detector design, which was made possible by introducing a new detector biasing concept. Schemes to simplify the technology of the fabrication of the detectors are discussed. The static performance properties of the devices as well as implications of the sue of VLSI electronics in their readout are described. Prototype detectors of the described design equipped with high-density readout electronics have been installed in the ALEPH detector at LEP (Large Electron Positron Collider). Test results on the performance are given. >

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.

Gating in the ALEPH Time Projection Chamber

The ALEPH TPC at LEP will use a gating grid to prevent distortions caused by space charge buildup in its 2.2 m drift region. Sets of measurements have demonstrated the feasibility of a “synchronous ion trapping” mode of gating, which reduces the positive ion flux through the grid by more than two orders of magnitude. A novel mode of gating will be discussed which would permit static operation of the gate, thereby avoiding the complexity of switching between the open and closed states of the gate. This mode would rely on the dissimilar gate penetration properties of electrons and ions in the presence of a magnetic field, and it may also provide a way to partially compensate for the E × B effect at the sense wires. A combination of these different modes is proposed for the ALEPH TPC.

TPC90, a test model for the ALEPH time projection chamber☆

Abstract A test model has been built to study the performance of prototypes for the ALEPH Time Projection Chamber. The device consists of a solenoid magnet providing a magnetic field up to 1.2 T inside a cylindric field cage of 75 cm diameter and 1.3 m length. It has been used to test two chambers of different design. We describe the setup and present results from measurements with these prototype chambers using laser beams and cosmic ray particles.

Influence of the magnetic field on the gating of a time projection chamber

A large cylindrical time projection chamber (TPC 90), 60 cm in diameter, a driftlength of 130 cm, as well as a smaller test-chamber of 30 × 30 × 15 cm3 have been used to investigate the effects of the magnetic field on the operation of a gated grid. The magnetic field is found to affect strongly the drifting electrons, but not for the positive ions. The results can be well explained by the specific configuration of the combined EandB fields near the gating grid wires and in the region of the proportional wires.

A new measurement of the magnetic moment of the Δ-hyperon

SummaryThe magnetic moment of the Δ-hyperon has been measured by observing the precession of the polarization vector of Δ-particles in a transverse pulsed magnetic field of 20 T (= 200 kG). The hyperons were produced in a polyethylene target by the reaction π−+p→+Δ+K0 at a pion momentum of 1.05 GeV/c; their decays were detected in stacks of nuclear emulsion at a distance of 11 em from the centre of the target. The angular distribution of the decay products in the rest frame of the Δ was used to determine the direction of the polarization at the time of the decay, and hence the magnetic moment. About 1300 Δ decays have been analysed, giving the resultn