Axial Field Spectrometer Research Articles

The production of prompt positrons at low transverse momentum increases with the square of the associated charged multiplicity: Axial field spectrometer collaboration

We have measured the production of prompt positrons in pp collisions at √ s = 63 GeV and y = 0 in the p T interval 0.12< p T<1.0 GeV/c. The results indicate that the production of positrons at low p T (<0.4 GeV/ c) is proportional to the square of the mean multiplicity in the central region | y| < 1. Such a quadratic dependence is not expected from final-state sources such as hadronic bremsstrahlung or hadronic decays, but is natural in models where low mass electron pairs are produced by interactions of constituents created during the collision.

A highly segmented NaI(Tl) detector with vacuum photodiode readout for measuring electromagnetic showers at the CERN ISR

In this report we describe construction and performance of two identical units of electromagnetic shower counters which were installed in the axial-field spectrometer at the CERN-ISR in 1982 to provide improved detection of photons and electrons over a 1.3 sr solid angle of the AFS calorimeter. Thallium doped sodium-iodide in the form of small blocks served as an active shower material. Vacuum photodiodes and low-noise charge sensitive electronics were used for the deposited energy measurement and signal amplification. The stable performance of the detectors over a period of more than 18 months until the closure of the ISR has proven that vacuum photodiodes can reliably be utilized in highly modularized large scale detectors operating in a high magnetic field environment.

Effects of long-term low-level exposure to radiation as observed in acrylic scintillator: Cause and prevention of radiation disease in uranium calorimeters

The acrylic scintillator which was used for several years as the active medium in the Axial Field Spectrometer uranium calorimeter at the CERN Intersecting Storage Rings was found to be severely damaged. The observed light output has decreased on the average by a factor of 2, and the attenuation length by a factor of 3, causing a severe degradation of the energy resolution of the system for the detection of both electromagnetic and hadronic showers. It could be shown that the effects are due to the radiation induced by uranium decay. The fact that the integrated dose obtained from this process (50 Gy) is 2 orders of magnitude smaller than what was currently believed to be a safe level, strongly suggests that the dose rate is a dominating factor in these radiation damage problems. It could be shown that the radiation resistivity is improved by at least an order of magnitude if contact with oxygen is avoided.

Charged particle production and correlations at high transverse momentum at the CERN intersecting storage rings

We study the production of identified charged particles in pp collisions at a c.m. energy of 63 GeV in events with an identified high- p T trigger particle. The measurements were performed at the CERN Intersecting Storage Rings using the Axial Field Spectrometer. Production ratios are presented as a function of p T in the range 2.5 to 8 GeV/ c.

The search for glurballs in final state interactions

Models of confinement in QCD predict an isoscalar 0 ++ glueball usually below 1 GeV. We show conclusively that the pp → pp ππ axial field spectrometer experiment at the ISR designed to discover such a state finds nothing below 1.15 GeV that is not seen in ππ elastic scattering. Elastic unitarity leaves little room for a distinction between ππ production by glue or quark initial states.

Further evidence for jet production from the charged particles produced in pp collisions at [formula omitted] triggered on large transverse energy

The detailed shape of events triggered by a 1.7 sr hadron calorimeter is studied using charged track information in the Axial Field Spectrometer at the CERN ISR. With increasing transverse energy ( E T) a large fraction of the events are seen to have a limited transverse momentum relative to the trigger direction. A comparison of the circularity of the events with a prediction of a QCD-motivated Monte Carlo model shows that at high E T the events originate predominantly from two-constituent scattering.

The axial field spectrometer at the CERN ISR

The axial field spectrometer is being exploited in a wide-ranging programme to study pp and p p -collisions which are characterized by a large transverse momentum. A specially shaped magnet together with an “imaging” drift chamber is used for efficient detection and momentum analysis of high multiplicity events at interaction rates of up to 5 × 10 6 s. Particle identification is accomplished over 1 sr; an uranium/scintillator hadron calorimeter will cover more than 8 sr in 1982 to provide an unbiased energy measurement.

Performance of the AFS vertex detector at the CERN ISR

The central detector of the axial field spectrometer (AFS) is a cylindrical drift chamber using a “bicycle-wheel” geometry. It is design has been optimized for jet-like events with high track densities. This is accomplished through a high degree of azimuthal segmentation (4° sectors) with up to 42 space points per track, using measurements of drift time and charge division. Particle identification in the non-relativistic region is obtained by (d E/d x) sampling. The detector is operated in an inhomogeneous magnetic field at event rates of typically 5 × 10 5 collisions per second. Results will be presented on the detector performance after one year of operation at the ISR.

Controlled mixer for the gas to the drift chambers in the axial field spectrometer in the CERN intersecting storage rings

This report describes a continuous mixing system used to supply a very stable gas mixture to the central detector of the Axial Field Spectrometer. The way in which the mixture is measured and controlled is described. A particular feature of this system is the careful minimization of effects due to variations in atmospheric pressure, inlet pressure and inlet temperature.

The polar co-ordinate magnetic measuring system for the axial field spectrometer magnet at the ISR-CERN

A system for the measurement of three-dimensional magnetic fields with nearly axial symmetry is described. The apparatus, which was used for the mapping of the field volume in the axial field spectrometer magnet of the ISR, measures in polar co-ordinates. The choice of the co-ordinate system and its advantages over other possible configurations is explained with particular reference to the measured magnet. The design and operation of the measuring system is described in detail, and its performance is discussed.

Performance of the AFS-Vertex Detector at the CERN ISR

The central detector of the Axial Field Spectrometer (AFS) is a cylindrical drift chamber using a "bicycle-wheel" geometry. Its design has been optimized for jet-like events with high track densities. This is accomplished through a high degree of azimuthal segmentation (4° sectors) with up to 42 space points per track, using measurements of drift time and charge division. Particle identification in the non-relativistic region is obtained by (dE/dx) sampling. The detector is operated in an inhomogeneous magnetic field at event rates of typically > 5 × 105 collisions per second. Preliminary results will be presented on the detector performance achieved after the first months of operation at the ISR.

Operation of a drift chamber vertex detector at the ISR

A cylindrical drift chamber with “bicycle-wheel” geometry has been constructed as the central detector for the Axial Field Spectrometer (AFS) at the ISR. To permit particle separation in jet-like event at high events rates, a considerable degree of azimuthal segmentation was chosen together with up to 42 space points per track. These points are obtained from measurements to drift time and charge division. Some particle identification is achieved with ionization loss sampling (d E/d x). This contribution presents details on the construction and the operation of the drift chamber at the ISR and preliminary performance results.

The drift time and charge division electronics system for the axial field spectrometer vertex detector

The electronics system of the AFS vertex detector permits the unambiguous determination of space points by drift time and charge division measurement (more than 10 000 electronic channels). Facilities are included for re-ordering of the raw time and pulse height information for optimized preprocessing and off-line analysis. Programmable processors permit trigger decisions and spatial correlation with calorimeter information.

Panel on the Impact of Changing Computer Technology on Nuclear and Particle Physics

The large spectrometers which will play a major role at ISABELLE, with their many thousands of detector elements, can be expected to generate copious amounts of data. Considering also that some experiments may generate events at rates as high as 10/sup 6/ per second readily leads one to the conclusion that the data handling problems to be faced at ISABELLE will be quite formidable. In order to provide a basis for generating an appropriate model for computing at ISABELLE, the data handling group examined the needs of several possible detectors during the course of the 1978 summer study. The five devices chosen for study were small-angle detector, lepton detector, wide-angle detector, axial-field spectrometer, and large-aperture dipole spectrometer. Because of the high event rates, the process of selecting the events for full analysis occurs in several stages, with more time available in consecutive stages as the amount of data being handled decreases. It seems feasible to construct special function processors to act as triggers for fairly simple geometries. It is an open question as to the degree of generality which can be achieved with this approach. (RWR)