Hadron Production Experiment

Its goal was to systematically study hadron production on a wide variety of nuclear targets.

The data is used to help predict neutrino fluxes at experiments such as MiniBooNE and K2K, to understand the atmospheric neutrino flux, and to tune Monte Carlo simulations of particle production.

Protons of 1.5 to 15 GeV were directed at targets ranging from hydrogen to lead.

[1] Analysis of HARP data has been carried out by two independent groups, the second group calling itself HARP-CDP for "HARP-CERN-Dubna-Protvino".

This group split from the main collaboration over "a deep split of opinion over quality of work, working methods, and professional ethics"[2][3]