Hadron Production for the Neutrino Factory and for the Atmospheric Neutrino Flux

The HARP experiment carries out, at the CERN PS, a programme of measurements of secondary hadron production, over the full solid angle, produced on thin and thick nuclear targets by beams of protons and pions with momenta in the range 2 to 15~\GeVc. The first aim of this experiment is to acquire adequate knowledge of pion yields for an optimal design of the proton driver of the Neutrino Factory. The second aim is to reduce substantially the existing $\sim 30$\% uncertainty in the calculation of absolute atmospheric neutrino fluxes and the $\sim 7$\% uncertainty in the ratio of neutrino flavours, required for a refined interpretation of the evidence for neutrino oscillation from the study of atmospheric neutrinos in present and forthcoming experiments. The HARP experiment comprises a large-acceptance charged-particle magnetic spectrometer of conventional design, located in the East Hall of the CERN PS and using the T9 tagged charged-particle beam. The main detector is a cylindrical TPC inside a solenoid magnet which surrounds the target. Downstream, the TPC is complemented by a forward spectrometer with a dipole magnet. The TPC, together with the forward spectrometer, ensures nearly full 4$\pi$ coverage for momentum measurement. The identification of charged secondary particles is achieved by d$E$/d$x$ in the TPC, by time-of-flight, by a threshold Cherenkov detector, and by an electromagnetic calorimeter.