1Malcolm Ellis - G4 Physics Validation Meeting - 17th July 2006 MuScat Validation of G4  Muon Scattering (MuScat) Experiment u Motivation: Ionisation Cooling requires maximising dE/dx and minimising multiple scattering of ~200 MeV/c muons. u Uncertainty over multiple scattering of muons in region of interest, and extrapolations from other experiments, suggested larger rates of scatters to high angles (unwanted for cooling) than predictions by Moliere. u Dedicated experiment approved at TRIUMF, ran in 2003 measuring a range of solid targets and liquid hydrogen with a collimated 172 +/- 2 MeV/c muon beam. u Scattered muons were tracked with a scintillating fibre tracker, and Time of Flight and NaI calorimeter were used to select a pure (> 99.2%) sample of muons. u Results of MuScat analysis have been accepted for publication in NIM and the preprint can be found on the web: s

2Malcolm Ellis - G4 Physics Validation Meeting - 17th July 2006 MuScat Layout & Targets

3Malcolm Ellis - G4 Physics Validation Meeting - 17th July 2006 Comparison with G4  In the MuScat paper, the analysis was performed using G4 7.0.p01.  The empty target and thick steel target data was used to tune the Monte Carlo model of the incoming beam and response of the detector.  The scattering distributions were obtained from the raw data by performing a deconvolution that subtracts the effects of background particles, the small contamination from pions and the response and efficiency of the detector from the measured projected scattering distribution in the target.  The deconvolution is achieved using MINUIT and the requirement of symmetry about  = 0 was imposed.

4Malcolm Ellis - G4 Physics Validation Meeting - 17th July 2006 No Target and Thick Fe Data Comparison with G4.7.0.p01

5Malcolm Ellis - G4 Physics Validation Meeting - 17th July 2006 Scattering Distributions Comparison with G4.7.0.p01

6Malcolm Ellis - G4 Physics Validation Meeting - 17th July 2006 More Distributions Comparison with G4.7.0.p01

7Malcolm Ellis - G4 Physics Validation Meeting - 17th July 2006 Comparison with G4.8.1  No change to real data (results of analysis as before).  New simulations performed using GEANT4 8.0 and 8.1  G4.8.0 similar to version 7  G4 8.1 shows an improvement in agreement, especially in high angle scattering.  G4 8.1 prediction for LH2 now in much better agreement with data and ELMS simulation.  Still see a strong effect when changing the maximum step size in the target (original simulations used a max step of 10  m).

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18Malcolm Ellis - G4 Physics Validation Meeting - 17th July 2006 Conclusions  For thick, higher Z targets (e.g. Al & Fe) G4 version 7 gave a reasonable description and this is still the case for versions 8.0 and 8.1.  There is still a tendency to over-estimate the rate of scattering to higher angles, however.  For lower Z targets (e.g. LH2, Li, Be) G4 versions 7.x and 8.0 would frequently over-estimate the rate of high angle scattering (by factors of 3 or 4).  G4 version 8.1 gives a much better agreement with both the MuScat data and the ELMS model for LH2.  There is still a strong effect seen on the simulated scattering distribution when changing the maximum step size (always << the target thickness) that is not understood. Is this a problem in G4, or with the way that we are using it?