1 downstream scraping and detector sizes rikard sandström university of geneva mice collaboration...
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Downstream scraping and detector sizes
Rikard SandströmUniversity of Geneva
MICE collaboration meeting2007-02-24 CERN
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Introduction
• Study A– Full phase space beam approach.– Radial positions measured at
• cryostat end• thick iron shield surfaces• TOF2• thin iron shield surfaces• calorimeter layer 0 surfaces• calorimeter center and end.
• Study B– Matched beam approach.
• 140 MeV/c, 200 MeV/c
– Radial positions measured at same z as in Study A.
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Setup, study A
• Geometry:– MICE stage6, with updated positions and iron shields.
• Iron shields not physically present in simulation, but using Virtual detectors at their surfaces.
– Now with cryostats physically present.– Empty absorbers.
• Field:– Holger’s empty channel, beta 42 cm, 200 MeV/c
field. http://mice.iit.edu/software/bfield/holger/FieldMaps24-01-07/CoilconfigWangNMRironshield200MeVbeta42emptychannel.g4mice
– RF field OFF
• Beam:– The same “full phase space beam” as was used
before.
4There are no good events going through the cryostat!
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Outside calorimeter (air)
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Again…The large radius events are all low momentum,Hence, setting a minimum → pz fixing maximum rho !
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Setup, study B
• Geometry:– MICE stage6, with updated positions and iron shields.
• Iron shields not physically present in simulation, but using Virtual detectors at their surfaces.
– Now with cryostats physically present.– 4.2 mm diffuser for 140 MeV/c, 7.6 mm diffuser for 200
MeV/c.– Empty absorbers.
• Field:– Holger’s empty channel, beta 42 cm, 140 MeV/c and
200 MeV/c fields respectively. http://mice.iit.edu/software/bfield/holger/FieldMaps24-01-07/CoilconfigWangNMRironshield140MeVbeta42emptychannel.g4mice
– RF field OFF.• Beam:
– Matched 140 MeV/c beam.
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Matched 200 MeV/c, thick shield
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Matched 200 MeV/c, TOF2
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Matched 200 MeV/c, thin shield
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Matched 200 MeV/c, EMCal0
Outside calorimeter (air)
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This beam uses the same field map as the full phase space beam, hence the same dependency on momentum
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Matched 140 MeV/c, thick shield
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Matched 140 MeV/c, TOF2
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Matched 140 MeV/c, thin shield
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Matched 140 MeV/c, EMCal0
Few muons make it through the preshower layer.
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Same tendency as before, but shifted w.r.t. pz
due to different field map.
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Emittance
• Typically it is the high amplitude particles which are missing the detectors.– High bias on emittance measurement.
• However, MICE will measure change of emittance!– If no change of emittance between upstream and
downstream, losing events does not affect the change of emittance measurement.
• This simulation contains no RF field, and empty absorbers, so bias on change of emittance as a function of TOF2 radius not meaningful here.– Instead, quoting bias on emittance measurement.
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Emittance
• Using no field approximation at TOF2 exit to calculate emittances:– ε = sqrt(x
2px2-xpx
2)/m
pz [MeV/c] εx εy
140 6.596 6.618
200 6.923 6.955
pz [MeV/c] R [cm] dεx/ εx dεy/ εy
140 42 -0.70 ppm -0.80 ppm
200 30 -0.63 ppm -0.80 ppm
• Requiring dε/ ε < 1 ppm, gives minimum radiuses
• Typically 1 ppm is at radius where 0.1 ppm is lost.
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Conclusions
• The cryostat is no longer an issue.• Setting TOF2 radius to
– 25 cm, start losing events pz<225 MeV/c– 30 cm, start losing events pz<169 MeV/c– 35 cm, start losing events pz<129 MeV/c
• According to no field approximation, minimum radius of TOF2 should be 42 cm to achieve dε/ ε < 1 ppm.– 30 cm for 200 MeV/c settings.– Usually 0.1 ppm loss radially is barely acceptable.