The SPY/Na56 (Secondary Particle Yields) experiment was performed using the H6 proton beam from the previous Na52 experiment, with the Na52 Spectrometer at CERN. The primary proton beam of 450 Gev/c, with typical intensities of the order of 1013 protons struck the beryllium target. The experiment sought to measure the production rates of pions and kaons from this setup.
Besides its general interest, the measurement of secondary particle fluxes was motivated by the planning of neutrino oscillation experiments. The calculation of the flux and energy spectra of a high energy neutrino beam is based on the knowledge of pion and kaon yeilds obtained by the incidence of a proton beam on the target material of low atomic number. Moreover, the measurement of muon neutrino to electron neutrino oscillations is carried out by searching for an excess of electron neutrino induced events with respect to what we would expect due to contamination of the beam by the decay of Kaons into 3 electrons. Prior to this experiment, there was no direct measurement of pion and kaon yields at energies below about 60 GeV/c. This necessitated the use of extrapolations from the (then) existing data, and Monte Carlo calculations instead. The uncertainty in kaon/pion productions was the major source of error in both these cases.
This experiment resulted in a measurement of Kaon/pion production ratios to an accuracy of about 3%. Charged particle (pion, anti-pion, kaon, anti-kaon, proton and anti-proton) production rates were measured to an accuracy of 5-10% depending on beam momentum. Additional results, obtained with targets of different thickness and shape with respect to the standard 100mm plate target were obtained. Using the experimentally determined target thickness dependence, data have been extrapolated to zero thickness, giving a model independent determination of invariant cross sections in the forward direction.
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