The EVA trigger: Transverse momentum selection in a solenoid

Abstract

A custom CMOS LSI and ECL PAL-based trigger system for a particle physics experiment is presented. The EVA apparatus at Brookhaven National Laboratory is designed to observe large angle scattering near the kinematic limit of P T for hadron-proton scattering with cross sections in the picobarn range and interaction rates of 100 MHz. The trigger selects events with high P T tracks in a solenoidal straw tube tracking magnetic spectrometer in three stages. An ECL PAL scintillation hodoscope pretrigger and timing mask is followed by P T reconstruction from three superlayers of straw tube drift chambers using custom CMOS LSI integrated circuits. The higher level CMOS trigger system is implemented on custom modules and functions at secondary trigger rates in excess of 1 MHz. A Motorola MC68000 microprocessor resides on each module and uses global information on the event to provide a third trigger level. The modules are interfaced to VMEbus, controlled by a single board VME computer.