See the HARP publication http://arxiv.org/abs/0706.1600, the goal is to replicate figure 30 in a simulation.
The graph shows yield of π+ and π− integrated over three different regions:
Incident proton momenta used in the graph are 3, 5, 8 and 12 GeV/c.
Simulations were made in MARS for each of these cases with at least 1 million incident protons and the yield of pions integrated over the above ranges. Incoming beam was assumed to be a pencil beam (no spatial or angular spread) with a 1% RMS Gaussian spread in momentum around the nominal value.
Dimensions for the 5% interaction length tantalum target were taken from http://pppa.group.shef.ac.uk/harp/ta5.html. The simulations used a cylinder of length 5.6 mm (nominal) and radius 15.07063 mm (average of measured values).
|Table 1. Integrals of pion yield in the three regions.|
|Proton momentum (GeV/c)||Incident protons simulated||π+ per proton||π− per proton|
|3||3.453 × 106||0.006589||0.00424||0.002244||0.006466||0.003875||0.001728|
|5||1 × 106||0.015915||0.011591||0.005759||0.016632||0.011557||0.005354|
|8||1 × 106||0.024146||0.018304||0.0089||0.025517||0.018929||0.009239|
|12||1 × 106||0.027387||0.020883||0.010101||0.030978||0.022904||0.01094|
Note that the three integration regions are listed left-to-right in decreasing order of size in these tables. In figure 1 it should be clear which are which, as with the graph it is based on.
|Table 2. Integrals of pion "efficiency", i.e. yield divided by kinetic energy of the incident protons, in the three regions.|
|Proton momentum (GeV/c)||π+ per proton.GeV||π− per proton.GeV|
I suspect the "arbitrary units" in the HARP publication's figure 30 are in fact units of 10-4 of the ones used here. It would be helpful to compare the absolute numbers here if they are available.
|Figure 1. Data for both pion signs over each of three integration regions, plotted in the same way as the HARP paper.|