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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.