ATLAS Transition Radiation Tracker

1. ATLAS Transition Radiation Tracker End-cap Quality Control and the Characterization of Straw Deformations Michael Kagan University of Michigan Supervisor: Mar Capeans CERN REU 2004

2. Outline • ATLAS and the Transition Radiation Tracker (TRT) • Quality Control and Commissioning End-Cap Acceptance Tests • Straw Eccentricity and Ellipticity Distortions • Conclusions • Acknowledgements Michael Kagan

3. ATLAS Inner Detector Inner Detector: pixel, silicon and straw tubes Combination of Central Tracker and TR for electron identification ATLAS Experiment Michael Kagan

4. The TRT Detector Barrel End-caps Detecting element Straw Tube 4 mm O.D. 30 mm W/Au wire Michael Kagan

5. TRT Barrel & End-cap C-fiber shell Radiator Straws Tension plate Detecting element: straw tube 4 mm diam., 30 mm W/Au wire Robust operation conditions: safe and fast gas Xe/CO2/O2 (70/27/3) End-cap Layers of straws & radiators End-cap HV & signal readout Michael Kagan

6. Transition Radiation Transition radiation is produced when a charged ultra-relativistic particle crosses the interface between different media, PP (fibres or foils) & air for the TRT. TR photons are emitted at very small angle with respect to the parent-particle trajectory. Energy deposition in the TRT is the sum of ionization losses of charged particles (~2 keV) and the larger deposition due to TR photon absorption (> 5 keV) TR threshold – electron/pion separation 5.5 keV 0.2 keV e- e- MIP threshold – precise tracking/drift time determination Radiator Foil Straw tube Michael Kagan

7. End-cap production & QC steps Straw installation Gas leak tightness Wiring Wheel transfer Wire crimping Wire tension & HV Wheel sealing Gas leak tightness & HV Wheel Test Wire eccentricity Michael Kagan

8. End-Cap Acceptance Tests • At assembly sites and after reception at CERN: • Gas tightness • HV • Wire Tension • Wire eccentricity Wheel Test Station Precise measurement of gas gain (1% accuracy) to derive eccentricity value per straw • 6 points of measurements along each straw • Slow control ( T, P, H, HV) • Monitoring straws (6 points of monitoring) • Electronics calibration • Online/Offline analysis • 4-plane wheel (3000 ch) characterization takes ~ 13 h Michael Kagan

9. Geometric Deformations The straw tube signal amplitude spectrum from a point ionization depends on the wire offset with respect to the straw center (eccentricity) and on the straw wall shape deformation (ellipticity). Field lines in a straw tube with no wire offset Field lines in a straw tube with 500 μm offset Field lines in an elliptically deformed straw tube Michael Kagan

10. Experimental Setup Precision magnetic support arms and a clock gauge were used to bend and squeeze the straw with a 10 micron accuracy. Michael Kagan

11. Eccentricity Results For straw eccentricities greater than 400 microns, the straw operation is observed to be unstable. However, we can not directly measure the wire offset. Thus, one must use measurable parameters in order to examine the quality of a straw, such as the signal amplitude and the straw tube resolution. These two parameters change considerably with eccentricity. The change in signal amplitude for various eccentricities. By 400 micron eccentricity, the amplitude has clearly increased by nearly 10%. The resolution is the width of the pulse height distribution from Fe 55 X-rays as they are converted in the straw tube. Michael Kagan

12. Eccentricity Results Continued To find bent straws, acceptance tests will record amplitude and resolution using Fe 55 X-rays at six point along the length of the straw. This profile can then be analyzed in order to determine the quality of the straw. For this reason, a controlled straw deformation has been performed and the resulting signal amplitudes for 13 points along the straw have been recorded and analyzed. Michael Kagan

13. Ellipticity Results While eccentric wires are a more common problem, it is important that straws with deformed wall shapes can also be recognized and examined. Thus straw tubes were elliptically deformed, and the signal amplitude and straw resolution were recorded for 11 points along the length of the straw. These profiles could then be used to characterize possible deformations encountered during acceptance tests. Michael Kagan

14. Conclusions Using multiple data samples, one can create a reproducible relationship between amplitude variations and resolution changes for both eccentric and elliptic deformations. These relations can be used when searching for deformed straws and assessing straw quality. Note that the elliptic data is still under analysis. Summer Conclusion on Hardware Experiments: I was told to expect 90% set-up, 10% data acquisition and analysis Are these statistics accurate? Of 45 days, it took 2 days for data collection, and 3 days for data analysis. So ~11% of my time was spent retrieving and analyzing data. Most days were spent building the equipment, and debugging hardware in order to create a working and usable experiment. Michael Kagan

15. Acknowledgements • Mar Capeans and Peter Cwetanski • Xavier Pons, Neil Dixon and Andreas Ekstroem • Jean Krish, Homer Neal, and Jeremy Birnholtz • CERN Summer Student Program, University of Michigan CERN REU, and NSF Michael Kagan

16. Questions? Michael Kagan