Tracker performance
description
Transcript of Tracker performance
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Takashi Matsushita
Imperial College
T. Matsushita 1
Tracker performance
Vacuum/helium/air
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T. Matsushita 2
Purpose
Requested to check the tracker performance with tracker volume filled by air at the tracker review meeting on 21 Apr 2006
This study is to answer the request
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T. Matsushita 3
Material Three different materials compared; Vacuum/Helium/Air
Density Vacuum: 1.e-25 g/cm^3; defined as universe_mean_density
in CLHEP/Units/PhysicalConstants.href; 5e-11 Torr => 8e-17 g/cm^3
He: 0.166 mg/cm^3 @ 293.15K, 1 atm; Air: 1.205 mg/cm^3 @ 293.15K, 1 atm; N:0.7, O:0.3
Radiation length @ 293.15K, 1 atm. x/X0 (x=1m) Helium gas; 5671m 1.76e-4 Air; 304m 3.29e-3
ref; http://pdg.lbl.gov/AtomicNuclearProperties
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T. Matsushita 4
Multiple Coulomb scattering 0=13.6MeV/cp z(x/X0)1/2 [1+0.038 log(x/ X0 )]
accurate to 11% or better for 10-3 < x/ X0 < 100; PDG
yplane (rms) = 1/sqrt(3) x0
plane(rms) = 0
For 200MeV/c muon
plane(rms) yplane (rms) x/ X0
He gas; 4.7e-4 1.3e-4 0.88e-4 (x=0.5m) Air; 2.4e-3 6.8e-4 1.65e-3 (x=0.5m) A station; 4.1e-3 4.5e-6 4.5e-3 (x=1.9mm)
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Setup
Simulation setup Input beam;
matched 2.5 pi mm rad. data10k events
G4MICE;Malcolm-demo-T20050208
Performance checked with upstream tracker
Baseline spacing;45-35-20-10 cm for stations 12, 23, 34, 45
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Event selection
Select number of points used for track fit = 5 Reject if reconstructed value(s) <= -9999.
Selection efficiency is about 90%
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Residual - Pt
RMS of residual distributions
All rangevac: 5.6hel: 8.5air: 5.9
|Pt|<200vac: 1.9hel: 1.9air: 1.8
Not much difference
vacuum
helium
air
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T. Matsushita 8
Residual - Pz
RMS of residual distributions
All rangevac: 9.5hel: 8.0air: 9.1
|Pz|<100vac: 7.2hel: 6.7air: 7.9
Not much difference
vacuum
helium
air
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T. Matsushita 9
RMS parameterisation
From error propagation formulae, parameterise RMS of residual in terms of Pt and Pz
(Pz) = / Pt(true) (Pz) = *
Pz(true)^2 (Pt) =
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T. Matsushita 10
RMS(Pt) vs Pt(true), Pz(true) RMS(Pt) in terms of Pt/Pz is
parameterised by (constant)
RMS(Pt) = (Pt) RMS(pt) = (Pz)
(Pt)vac: 1.8hel: 1.8air: 1.8
(Pz)vac: 1.8hel: 1.8air: 1.8
Not much difference, although parameterisation is not perfect
vacuum
helium
air
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T. Matsushita 11
RMS(Pz) vs Pt(true), Pz(true) RMS(Pz) in terms of Pt/Pz is
parametrised by
RMS(Pz) = /Pt(true) RMS(pz) = *Pz(true)^2
vac: 103.1hel: 99.1air: 110.8
vac: 0.18E-3hel: 0.16E-3air: 0.19E-3
Not much difference, although parametrisation is not perfect
vacuum
helium
air
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Summary
Analysis with G4MICE show little difference on tracker performance with tracker volume filled by vacuum/helium/air for the default spacing; 45-30-20-10 cm
Probably we need to redo the analysis after fixing the spacing. With the current spacing, 4 mrad deflection caused by a station has 2.25mm lateral displacement between station 1 and 2! (for 200MeV/c muon)
Question still remains; do we want to use air instead of helium?
By the way, I would like to try the G4MICE version used for MICE-NOTE90 analysis, which is known to be newer than the one I am currently using