Takashi Matsushita

t.matsushita@imperial.ac.uk

Imperial College

T. Matsushita 1

Tracker performance

Vacuum/helium/air

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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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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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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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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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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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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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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