MARS: A start detector system for the COSY time-of-flight spectrometer TOF

A start detector system (MARS) was developed for the time-of-flight spectrometer TOF at the external beam of the cooler synchrotron COSY. The start detector system is specially tailored to the measurement of the proton–proton bremsstrahlung, but it can also be used for the investigation of other reactions. The MARS detector system consists of two 16-fold segmented rings of plastic scintillators with 500 μm thickness embedded in specially formed hollow light guides. According to simulation calculations and test measurements the light transmission of these light guides amounts to about 40%. The time resolution for minimum ionizing particles was determined to be 0.5 ns (FWHM).