Transcript Slide 1
Muon-raying the ATLAS Detector Rosemarie Aben Supervisor: Peter Kluit Track: Particle and Astroparticle Physics 1 Amsterdam Master of Physics Symposium, 16 April 2010 Outline • LHC and ATLAS • The muon spectrometer of ATLAS • Precision measurements • Sagitta Analysis • Sagitta Resolutions • ATLAS Now 2 Standard Model & Higgs Solution: ? Energy per Collision 14 TeV Protons per bunch 1011 Detection of Higgs decay: Bunches per ring H ZZ 4µ “Golden Channel”Design Luminosity Circumference Collisions per bunch 2835 1034 cm-2 s-1 27 Km 25 3 Exotic physics and ATLAS 4 Layout of the Muon spectrometer • Trigger chambers: trigger on muons • Precision chambers: Reconstruction of muon tracks Small and Large muon stations Three layers of muon stations Sector, containing 12 Measurement towers 5 Monitored Drift Tube (MDT) Chambers Tube diameter 30 mm Diameter Sense wire 50 μm # Tubes per chamber Up to 432 Length MDTs 1-6 m # MDT chambers 1150 6 Precision Measurements and Sagitta Needed accuracy MDT chamber: 10% for 1 TeV muons Knowledge about the precision of the chambers is extremely important. Contributions to precision: alignment and calibration. Reconstructed Track Sagitta Misalignment Outer Middle Inner Sagitta: measure for the precision of the MDT chambers. 7 Sagitta Distribution # Tracks Distribution of the sagittas for all barrel sectors. Sagitta [mm] 8 Sagitta Distribution Improvements Old alignment Improved alignment Misalignment was seen in certain towers: shifts and extra peaks. With this knowledge improvements have been made. New analysis shows good alignment! 9 Sagitta Resolution Fit Resolution: necessary to monitor the performance of the muon chambers in measuring momentum and position. Sagitta resolution is a measure for the accuracy of the chambers depending on alignment + calibration + chamber geometry + chamber deformations+ ... 10-20 GeV 20-40 GeV Slices up to 350 GeV. 40-70 GeV 70-110 GeV Each slice is fitted with a double Gauss fit and the standard deviation of the smaller Gauss is taken to do the final fit, using: σ (sagitta) = √( P1² + P2²/momentum²) • P1 = intrinsic resolution term: gives the sagitta resolution • P2 = multiple scattering term 10 Sagitta Resolution from Cosmic Data Latest results Large sectors Small sectors Intrinsic term Multiple Scattering term Sagitta resolution: 101 ± 6 μm Sagitta resolution: 143 ± 16 μm Last November the sagitta resolutions were still around 200 μm…. But, is this as expected? Look to simulated cosmic muons! 11 Sagitta Resolution from Simulated Cosmics Large sectors Sagitta resolution: 63 ± 2 μm Simulation Small sectors Sagitta resolution: 102 ± 5 μm Comparison with data: 101 μm for Large sectors and 153 μm for Small sectors. Difference between data and simulation due to effects not yet corrected for. But accuracy is already good enough for the muons coming from latest collisions. Muons ready to be reconstructed in ATLAS! 12 13 14 Time for questions. 15 BACK UP Summary and Conclusions • The sagitta is a good measure to study the achieved precision of the MDT chambers with respect to alignment and calibration; • The sagitta resolution is a measure for the accuracy of the chambers; • Sagitta resolution: - Resolutions for large sectors, data vs. MC: 101 μm vs. 63 μm. - Resolutions for small sectors, data vs. MC: 143 μm vs. 102 μm. The MDT chambers are ready for analysis of the 7 TeV Data!!! 16