Simulating the Effects of Wire Sag in ATLAS’s Monitored Drift Tubes

Ashley Thrall, Vassar College ‘04

Dan Levin, Mentor

REU Presentations August 5, 2004

Monitored Drift Tubes in ATLAS

½ length of a football field

8 Stories

~ 4-6 m

Why Muons?

• Decay products from other particles that are of interest:

H →Z Z*→ µ-µ+µ-µ+

• Can reconstruct a muon track to determine its momentum and therefore its invariant mass

• Can use its invariant mass to determine the mass of the parent particle

Drift Tube

Aluminum tube: rinner= 1.46 cm

router =1.5 cm

Gold-plated Tungsten wire

r = 25μm

V= 3080 V

Stretched by 350g

of tension

Gas Mixture:

93.0% Ar , 7% CO2

Pressure: 3 bar

Drift Tube

Tube Cross-Section

Muon Track

Electrons drifting toward wire

Aluminum tubeTungsten Wire

• Factors that influence the resolution of chambers through the time-space conversion:– Chemical:

• Temperature• Pressure• Gas Mixture• Contaminants

– Geometrical:• Tube/Wire• Position of Tube• Temperature• Wire Position in Tube: Wire Sag

– Electronics:• Electronics Response

Motivation?

• Gravitational Sag: ~470µm for 5.9m tube

• Electromagnetic Attraction: ~28µm for 5.9m tube with 3080V

• Sag destroys symmetry – not compensated for in Endcap chambers

The Problem: Wire Sag

T

LD

L

X

L

X 22

2

2

32

81.94

X= position along tube

L= length of tube

ρ = density of wire

D = diameter of wire

T= pre-stretched tension

• Distance electrons travel

• Electric Field

Factors Influenced by Sag

Goals

• Overall Objective: – to be able to parameterize the effects of wire sag in

ATLAS’s monitored drift tubes based on the position of the event along the tube

• Objective of this Project:– To simulate the effects of wire sag on muon drift time

spectra using the Garfield software program– To quantitatively measure these effects– To compare these results with cosmic ray data that

Divine analyzes

Preliminary Study: Horizontal vs. Vertical Tracks

Vertical Tracks with 472 µm Sag

Horizontal Tracks with 472 µm Sag

Drift Time Spectra

Drift Time (ns)

dN/d

t

Drift Time Spectra

Drift Time (ns)

dN/d

t

Drift Time Spectra

Drift Time (ns)

dN/d

t

Maximum Drift TimesRun Drift

Time 1 (ns)

Error Drift Time 2

(ns)

Error

No Sag 696.937 1.66387 --- ---

Vertical Tracks with 472 µm Sag

699.374 1.76805 --- ---

Horizontal Tracks with 472 µm Sag

650.476 4.80863 768.188 2.21768

Why the Double Tail?Impact Parameter Plot

Max

imum

Dri

ft T

ime

(µs)

Impact Parameter (cm)

Comparison with Cosmic Ray Data: No Sag

Drift Time (ns)

dN/d

t

Drift Time (ns)

dN/d

t

Garfield Data Cosmic Ray Data

Maximum Drift Time:

696.937 +/-1.66387

Maximum Drift Time:

671.215 +/- 1.21142

Comparison with Cosmic Ray Data: Middle of Tube (Max Sag)

Drift Time (ns)

dN/d

t

Drift Time (ns)

dN/d

t

Garfield Data:

Horizontal Tracks

472µm Sag

Cosmic Ray Data:

323 µm Sag

Maximum Drift Times:

650.476 +/-4.80863

768.188 +/-2.21768

Maximum Drift Times:

637.784 +/-1.93216

717.928 +/-1.9416

Conclusions

Future Work

• Wire sag has a significant effect on drift time spectra and maximum drift times for tracks oriented in particular directions with respect to sag

• Program Garfield to randomly sample from the distribution of cosmic rays

• Perform simulations that correspond to the positions at which data was taken

• Quantitatively compare these results to the cosmic ray data

Acknowledgements

• Dan Levin, Rachel Avramidou, Rob Veenhof, Divine Kumah

• National Science Foundation, University of Michigan REU Program, CERN Summer Student Program