M. Steinacher

THE NEW INNER-TEC TRIGGER OF THE L3 EXPERIMENT USING A HADWIRED NEURAL NETWORK PROCESSOR

Abstract A new first-level trigger for the L3 experiment at LEP (CERN) is presented. It is using the inner time expansion chamber of the detector. The event selection is based on identifying sectors containing genuine tracks originating from the interaction point. The sector identification uses a neural network algorithm tuned to identify single tracks in a sector (hadronic jets are also selected). The hardware for this trigger is built around existing custom made neural network digital modules. The decision time is less than 100xa0ns and the final rate of accepted events is 1–5xa0Hz depending on the beam luminosity.

What is the mechanism for three-nucleon absorption of pions in 3He?

Abstract Experimental data for 3 He(π + , pp)p at T π =120 MeV in a kinematical region dominated by three-nucleon absorption, where all three protons have obtained an appreciable amount of energy, are analyzed by means of variables specifically sensitive to different reaction mechanisms. The data are compared with predictions for two-step mechanisms and a genuine three-nucleon absorption mechanism. No evidence is found for such two-step processes as scattering or charge exchange preceding a two-nucleon absorption or as two-nucleon absorption followed by “Hard FSI”. The results, however, agree with a genuine three-nucleon absorption process, consistent with the recently measured phase-space-like behavior of this process.

Three-nucleon processes and the total pion absorption cross section in 3He

Abstract Pion absorption processes involving three nucleons have been investigated in 3 He with positive and negative pions of 64, 119, 162 and 206 MeV kinetic energy. The most important of these processes is characterized by a constant phase-space density and has comparable integrated cross sections for π + and π − with a Δ-resonance-like dependence on the pion energy. This process constitutes up to one third of the total absorption cross section. The total absorption cross section has been determined by adding up the measured cross sections for all the observed absorption channels.

Pion absorption in flight on 4He

Abstract We have measured double and triple coincidences following π + and π − absorption on 4 He at various pion energies. Differential and integrated cross sections are determined for all possible absorption channels. We study and compare the two-nucleon absorption on nucleon pairs with isospin I = 0 and I = 1. In the dNN final-state two absorption mechanisms are identified, one with only one spectator nucleon and one with phase-space behavior. The existence of a three-nucleon absorption component with a spectator nucleon is established and a four nucleon phase-space-like contribution is also identified and found to be small. The total absorption cross section is directly determined by adding the integrated cross sections of all measured reaction channels.

Hardware realization of a fast neural network algorithm for real-time tracking in HEP experiments

Abstract A fast pattern recognition system for HEP experiments, based on artificial neural network algorithms (ANN), has been realized with standard electronics. The multiplicity and location of tracks in an event are determined in less than 75 ns. Hardware modules of this first level trigger were extensively tested for performance and reliability with data from the CPLEAR experiment.

Two-nucleon absorption of π+ and π− on 3He across the Δ-resonance region☆

Abstract The angular distributions of nucleons from a kinematically complete measurement of pions absorbed in 3He on nucleon pairs with isospin T = 0 and T = 1 at incident pion energies of 64, 119, 162 and 206 MeV are presented. The T = 0 data are quite similar to pion absorption data in deuterium but scale with the number of nucleon pairs. The T = 1 cross sections are an order of magnitude smaller and the angular distributions show a significant asymmetry. This asymmetry together with the measured energy dependence indicates interference effects between amplitudes with and without Δ isobars in the intermediate states.

The neural network first level trigger for the DIRAC experiment

Abstract The neural network first level trigger for the DIRAC experiment at CERN is presented. Both the neural network algorithm used and its actual hardware implementation are described. The system uses the fast plastic scintillator information of the DIRAC spectrometer. In 210 ns it selects events with two particles having low relative momentum; such events are selected with an efficiency of more than 0.94. The corresponding rate reduction for background events is a factor of 2.5.

A position-sensitive detector system with subnanosecond timing and its utilization in the measurement of pion absorption

A complex position-sensitive, time-of-flight detector was designed at the SIN to be used in the kinematically complete measurements of pion absorption in light nuclei, for the detection of both neutrons and charged particles. Design parameters and TOF properties resulting from the computer calculations and suitable test measurements are given for the system consisting of 200 × 10 × 5 cm3 NE 102A scintillator bars, XP 2230 photomultipliers and discriminator. Position dependence of the timing parameters of the 2 m long NE 102A bar viewed from the ends by photomultipliers has been clearly revealed in our model and experimentally verified.

Neural network real time event selection for the DIRAC experiment

The neural network first level trigger for the DIRAC experiment at CERN is presented. Both the neural network algorithm used and its actual hardware implementation are described. The system uses the fast plastic scintillator information of the DIRAC spectrometer. In 210 ns it selects events with two particles having low relative momentum. Such events are selected with an efficiency of more than 0.94. The corresponding rate reduction for background events is a factor of 2.5.

A fast beam position monitor based on arrays of secondary emission monitors

Abstract We describe an instrument for a fast determination of the beam position of a rastered high-energy electron beam with an intensity as low as 10xa0nA. Two arrays of stripes of thin metal foils, one in the horizontal and one in the vertical direction, are inserted into the beam. They work as a position-sensitive Secondary Emission Monitor (SEM) with a resolution of 1xa0mm. The charges from the stripes are amplified and converted into position signals using electronics providing a low vibration sensitivity and a fast beam position measurement. At a beam intensity of 10xa0nA a measurement can be carried out with an integration time of only 130xa0μs.