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