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: r inner = 1.46 cm r outer =1.5 cm Gold-plated Tungsten wire r = 25μm V= 3080 V Stretched by 350g of tension Gas Mixture: 93.0% Ar, 7% CO 2 Pressure: 3 bar

Drift Tube Tube Cross-Section Muon Track Electrons drifting toward wire Aluminum tube Tungsten 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 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/dt

Drift Time Spectra Drift Time (ns) dN/dt

Drift Time Spectra Drift Time (ns) dN/dt

Maximum Drift Times RunDrift Time 1 (ns) ErrorDrift Time 2 (ns) Error No Sag Vertical Tracks with 472 µm Sag Horizontal Tracks with 472 µm Sag

Why the Double Tail? Impact Parameter Plot Maximum Drift Time ( µ s) Impact Parameter (cm)

Cosmic Ray Data: Experimental Setup Tube Length = 4.9m Data collected at three points along the tubes: X=0 Sag =0 X=1.5 Sag = 274µm X=2.45 Sag = 323µm These diagrams are courtesy of Divine Kumah

Comparison with Cosmic Ray Data: No Sag Drift Time (ns) dN/dt Drift Time (ns) dN/dt Garfield DataCosmic Ray Data Maximum Drift Time: / Maximum Drift Time: /

Comparison with Cosmic Ray Data: Middle of Tube (Max Sag) Drift Time (ns) dN/dt Drift Time (ns) dN/dt Garfield Data: Horizontal Tracks 472µm Sag Cosmic Ray Data: 323 µm Sag Maximum Drift Times: / / Maximum Drift Times: / /

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