We wish to measure the total + p cross-section at 20 GeV incident momentum. We build

We wish to measure the total π⁺p cross-section at 20 GeV incident momentum. We build a liquid hydrogen target (ρ = 60 kg m^-3) that is l = 1 m long. We measure the flux before and after the target with two scintillation counters. Measurements are made with the target empty and with the target full. By normalising the fluxes after the target to the same incident flux we obtain in the two cases N₀ = 7.5 × 10⁵ an N_H = 6.9 × 10⁵ respectively. Find the cross-section and its statistical error (ignoring the uncertainty of the normalisation).