Results from the HARP Experiment

The HARP experiment at CERN performed extensive measurements of hadronic cross‐sections and secondary particle yields in the momentum range 1.5–15 GeV/c aiming at full angular covarage and full particle identification. We report about the double‐differential production cross‐section for positive pions, for incident protons of 12.9 GeV/c momentum hitting an aluminum target of 5% nuclear interaction length. The measurement of this cross‐section has direct application to the prediction of the neutrino flux of K2K experiment and in particular on the far‐near neutrino flux ratio.