Simulations of surface muon production in graphite targets

In this paper we present the results of GEANT4 simulations of the production of surface muons as a function of energy of the incident protons on a graphite target. A validation of the GEANT4 hadronic physics models has been performed by comparing the results with experimental data from the Lawrence Radiation Laboratory, United States. Considering the ISIS muon target as a reference, simulations have been performed to optimize the pion and muon production. Of particular significance, we predict that optimal surface muon production occurs at a relatively modest proton energy of 500 MeV. This will be of importance for the development of future $\mu \mathrm{SR}$ facilities.

Figure 1

Layout of the ISIS facility at the Rutherford Laboratory. The muon target (G) is situated 20 m upstream of the neutron target (I). The second neutron target is also shown (F).

Figure 2

Picture of the ISIS muon target. There are three targets on a rack which is lowered in the proton beam path during experiments.

Figure 3

Double differential cross section for positive pion production at 15, 45, 90, and 135 degrees with respect to the proton beam. Simulations using three physics lists (QGSP-BERT, QGSP-BIC, QGSP-INCL-ABLA) and experimental data are compared.

Figure 4

Pion momentum spectra predicted by three hadronic models, Bertini, Binary, and INCL-ABLA. Detectors are placed diagonally opposed at 45 and 135 degrees with respect to the proton beam.

Figure 5

Proton transmission through the muon target as a function of the proton beam energy.

Figure 6

Target thickness for 96% proton transmission through the muon target as a function of proton beam energy.

Figure 7

Variation of pion yield with proton energy.

Figure 8

Pion momentum and energy spectra for incident proton energy of 750 MeV.

Figure 9

Pion momentum and energy spectra for incident proton energy of 1 GeV.

Figure 10

Pion momentum distributions at various incident proton energies.

Figure 11

Variation of muon yield with proton energy.

Figure 12

Normalization to the incident proton energy.

Figure 13

Normalization to the number of protons interacting in the target.

Figure 14

Variation of muon yield with proton energy at higher energies.

Figure 15

Normalization of the muon yield to the proton energy.

Figure 16

Surface muon momentum distributions for various incident proton energies.