Takashi Matsushita [email protected] Imperial College T. Matsushita 1 Tracker performance Vacuum/helium/air
Feb 05, 2016
Takashi Matsushita
Imperial College
T. Matsushita 1
Tracker performance
Vacuum/helium/air
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
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
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)
T. Matsushita 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
T. Matsushita 6
Event selection
Select number of points used for track fit = 5 Reject if reconstructed value(s) <= -9999.
Selection efficiency is about 90%
T. Matsushita 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
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
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) =
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
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
T. Matsushita 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