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Tracker performance

Tracker performance. Vacuum/helium/air. 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. Material. Three different materials compared; Vacuum/Helium/Air Density

vaughan-johns
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Tracker performance

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  1. Tracker performance Vacuum/helium/air

  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

  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

  4. Multiple Coulomb scattering • q0=13.6MeV/bcp 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) xq0 • qplane(rms) = q0 • For 200MeV/c muon qplane(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)

  5. 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

  6. Event selection • Select number of points used for track fit = 5 • Reject if reconstructed value(s) <= -9999. • Selection efficiency is about 90%

  7. 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

  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

  9. RMS parameterisation • From error propagation formulae, parameterise RMS of residual in terms of Pt and Pz • s(Pz) = a / Pt(true) • s(Pz) = b * Pz(true)^2 • s(Pt) = g

  10. RMS(Pt) vs Pt(true), Pz(true) • RMS(Pt) in terms of Pt/Pz is parameterised by g (constant) • RMS(Pt) = g(Pt) • RMS(pt) = g(Pz) • g(Pt)vac: 1.8hel: 1.8air: 1.8 • g(Pz)vac: 1.8hel: 1.8air: 1.8 • Not much difference, although parameterisation is not perfect vacuum helium air

  11. RMS(Pz) vs Pt(true), Pz(true) • RMS(Pz) in terms of Pt/Pz is parametrised by a, b • RMS(Pz) = a/Pt(true) • RMS(pz) = b*Pz(true)^2 • avac: 103.1hel: 99.1air: 110.8 • bvac: 0.18E-3hel: 0.16E-3air: 0.19E-3 • Not much difference, although parametrisation is not perfect vacuum helium air

  12. 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

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