CLIC Muon Background Simulation Using BDSIM
This is an ongoing project to simulate the muon flux into the CLIC detector due to beam halo collimation. All data presented here are provisional.
Overview
BDSIM gmad files were generated from the v_09_04_01 MAD decks, including all apertures. Cross checks were performed using core electron and positron distibutions. A tunnel geometry was created including a tunnel floor, beam line offset, concrete walls and surrounding soil. A tapered spoiler geometry was created. Relevant physics processes were turned on and cross section biased to reduce required computing time. The simulation was run on the RHUL grid farm with 1.5 T eV electrons and positrons as the primary particles (halo distribution files generated by H. Burkhardt at CERN using htgen).
Data Files
Processes and biasing
At 1.5 T eV, the dominant process is gamma-> mu- mu+ and electron positron annihilation can be ignored. Therefore electrons incident and positrons incident produce similar numbers of muons.
The following cross section biasing was used:
gamma -> muons: 1e4
annihilation -> muons: 1e4
File formats
Format 1
x' y' z' x[mum] y[mum] z[m] charge[e] energy[GeV]
Energy is the energy of the particle in G eV. x and y are the positions of the particle from the reference trajectory in mum. x' y' and z' are the normalised components of the momentum vector along the three axes.
Format 2
Format 2 has two additional columns:
x' y' z' x[mum] y[mum] z[m] charge[e] energy[GeV] z0[m] weight
z0 is the position along the z axis of the last interaction of the particle. weight is the weight factor, which depends upon the cross section biasing factor of the process in which the particle was generated and the weight of the parent particle.
History
OldFiles - click here
Files 13 and 14 16th April 2010
The number of primaries used to generate this file was N_p = 30130
The number of muons/antimuons per primary halo particle hitting the sampler at QD0 is (5.56 +/- 0.01) X 10^(-5). Assuming 2 X 10^(10) particles per bunch, and a halo population factor of 10^(-3), there are 1113 +/- 2 muons/antimuons per bunch (here +/- is the statistical uncertainty in the estimate of the mean).
Files 15 and 16 27th April 2010
Swapped layout.
The number of primaries used to generate this file was N_p = 12059
The number of muons/antimuons per primary halo particle hitting the sampler at QD0 is (2.274 +/- 0.09) X 10^(-5). Assuming 2 X 10^(10) particles per bunch, and a halo population factor of 10^(-3), there are 455 +/- 2 muons/antimuons per bunch (here +/- is the statistical uncertainty in the estimate of the mean). This is a 41% reduction compared to file 13.
NOTE
A bug meant that in all the previous files a sample of only a few hundred halo electrons was used. This has now been fixed and 37500 halo electrons are used in the files below.
Current files
Files 17 and 18 2nd February 2011
These files were generated using the same simulation as files 13 and 14. The statistics are increased, and a sample of 37500 halo electrons was used, instead of just a few hundred. The muons were recorded at a plane at the exit of QF1.
The number of primaries used to generate this file was N_p = 7.65E5 by repeating a sample of 3.75E4 halo electrons.
The number of muons/antimuons per primary halo particle hitting the sampler at the exit of QF1 is (4.96 +/- 0.12)E-5. Assuming 2E10 particles per bunch, and a halo population factor of 1E-3, there are 991 +/- 24 muons/antimuons per bunch (here +/- is the statistical uncertainty in the estimate of the mean).
Files 19 and 20 2nd February 2011
Here, the spoiler geometries are updated to the latest designs, as presented in
WEPEB046
, "Optimisation of the CLIC baseline collimation system", in the Proceedings of IPAC '10, Kyoto, Japan. The magnet settings, however, remain unchanged. Work is ongoing to include the optics optimisation in the simulation.
The number of primaries used to generate this file was N_p = 7.6E5 by repeating a sample of 3.75E4 halo muons.
The number of muons/antimuons per primary halo particle hitting the sampler at the exit of QF1 is (4.86 +/- 0.11)E-5. Assuming 2E10 particles per bunch, and a halo population factor of 1E-3, there are 972 +/- 21 muons/antimuons per bunch (here +/- is the statistical uncertainty in the estimate of the mean).
Files 21 and 22 31st May 2011
Muon spoilers and a tunnel filler were added. Factor 15 fewer muons hit the detector than files 19 and 20 above. For details see outline file below.
- outline.dat: Outline of BDS with muon spoilers and a tunnel filler.
Files 23 and 24 15th June 2011
Muon spoilers only. Factor 10 fewer muons than files 19 and 20. For details see outline file below.
Note - results are preliminary and subject to change