Measuring the masses of the charged hadrons using a RICH as a precision velocity spectrometer

The Selex experiment measured several billion charged hadron tracks with a high precision magnetic momentum spectrometer and high precision RICH velocity spectrometer. We have analysed these data to simultaneously measure the masses of all the long lived charged hadrons and anti-hadrons from the π to the Ω using the same detector and technique. The statistical precision achievable with this data sample is more than adequate for 0.1% mass measurements. e used these measurements to develop and understand the systematic effects in using a RICH as a precision velocity spectrometer with the goal of measuring 10 masses with precision ranging from 100 KeV for the lightest to 1000 KeV for the heaviest. This requires controlling the radius measurement of RICH rings to the ∼ 10 − 4 level. Progress in the mass measurements and the required RICH analysis techniques developed are discussed.