for lead as function of target length

For a lead target of 10 to 15 cm length the pion yield at 2 GeV/c is about 10^-4 per pimary pion at 40 GeV/c. In this range a longer target is favoured, as the lepton background decreases. We still have to study the impact of increasing the the primary pion energy to 80 Gev/c and beyond. The production at T4 at this higher momenta is higher and therfor favoured and at the same time the impact on the use of H6 is such, that the momentum range is more flexible. Detailed information is shown in Figure.

The pion yield for higher primary momentum and a lead target of 25 cm is schown above. The background increases with higher momentum. Still reasonble is a choice of 25 cm length and 60 GeV/c primary momentum.

The application of a longer target using higher primary momentum does not improve the situation. Extending the lead target beyond one interaction length has no advantage.