Influence of proton beam emittances on particle production off a muon collider target

A free-mercury-jet or a free-gallium-jet is considered for the pion-production target at a Muon Collider or Neutrino Factory. We previously optimized the geometric parameters of the beam and target to maximize particle production by incoming protons with kinetic energies (KE) between 2 and 16 GeV, using the MARS15 code, assuming a parallel proton beam with Gaussian transverse profile. In this paper, we extend our optimization to focused proton beams with various transverse emittances. For the special cases of proton beams with geometric emittances of 2.5, 5 or 10 μm-rad and a kinetic energy of 8 GeV, we optimized the geometric parameters of the target: The radius of the proton beam, the radius of the liquid jet, the crossing angle between the jet and the proton beam, and the incoming proton beam angle. We also studied the influence of a shift of the beam focal point relative to the intersection point of the beam and the jet.