1. ATLAS Muon Spectrometer Calibration
Ethan Cannaert, August 2017
UM REU Symposium

2. Muon Spectrometer
Measures the momentum and trajectories of Muons created in pp collisions
Comprised of 4000 chambers of 4 different technologies
Thin Gap Chambers (TGC) – trigger chamber for endcap
Resistive Plate Chambers (RPC) – trigger chamber for barrel
Cathode Strip Chambers (CSC), res. ~60 μm/muon cluster
Monitored Drift Tubes (MDT), res. ~80 μm/tube

3. Monitored Drift Tubes 354,240 tubes in 1,171 MDT chambers
MDT chambers are made of drift tubes:
Diameter of mm
Filled with Ar/CO2 (93/7) gas at 3 bars
Tungsten-rhenium wire, diameter 50 μm
Tubes in each chamber are arranged in 2 multi- layers
Trigger system selects 100 most interesting events per second out of ~1 billion

4. MDT Chamber Layout in Muon Spectrometer

5. MDT’s
Muons pass through chambers in bent trajectories, ionizing electrons that then drift to wire and deposit charges that are detected as chamber hits.
Computer program analyzes these raw chamber hits and matches appropriate hits to create muon particle trajectories.
Matched hits are called “track” hits.

6. Data Analysis & Calibration
Enormous amounts of data are collected and sent out for analysis to many computing centers worldwide
Arrives to me in statistics text files and 18 types of plots/histograms
Goal is to find and report malfunctioning chambers by finding irregularities in data and plots

7. The TDC (drift time) Spectrum
Good TDC spectrum
Abnormal TDC spectra
-Asymmetry in ML’s
-Irregular shape
-Few hits

8. ADC (charge) (ML)
Good
Bad
-Asymmetry in ML’s
-Few hits

9. Drift Radius (ML)
Good
Bad
-Asymmetry in ML’s

10. Muon Hit Occupancy
Good
Bad

11. Identifying Problems
Chamber has far fewer hits than its azimuthal neighbors
Indicative of trigger problems, usually affects linked inner, middle, and outer chambers (ie. BIL4A03, BML4A03, BOL4A03)
Sudden drops in hits between runs
Bad electronics, trigger
Inconsistent ML ratios
Problem with electronics, triggers
High Tmax slope/deformed Tmax fit in TDC
A sign of sagging wires
Most prominent in completely horizontal chambers

12. The Usual Suspects Few hits High Tmax slope Geometric Cutoff
BIS8, BME, BOE,BxS4A16, BOG, BMG, BMF
Due to location, small chamber size, cutouts
High Tmax slope
Bxxxx05, Bxxxx13, horizontal endcap chambers
Wires sag in horizontal chambers
Geometric Cutoff
EIL4, EMx5, EOx6, EIS2, Bxx6, EEL2
Manifests itself in low ML ratios

13. Calibration Procedure
Manual skimming
Look for unusual histogram shapes/features
Look at how shapes compare among azimuthal neighbors
Look for consistency among trigger linked chambers
Analysis Program
Good for finding high/low Tmax/T0 slopes
Good at finding histograms with bad Tmax ranges
Much, much faster than manually analyzing

14. Summary
Great introduction to analysis work, High Energy Physics, and the ATLAS experiment
Gained valuable programming skills
Will be continuing work with ATLAS next year on the Gas Monitor system and testing/calibration of the BMG chambers
Thanks to Professor Bing Zhou, Edward Diehl, and anyone else that helped me this summer

15. Citations
"The ATLAS Experiment at the CERN Large Hadron Collider." Institute of Physics Publishing and SISSA, 14 Aug
Wotschack, Joerg. "ATLAS Muon Chamber Construction Parameters for CSC, MDT, and RPC chambers." CERN, 17 Apr