Konstantinos Nikolopoulos University of Athens / BNL ATLAS Cathode Strip Chambers Installation and Commissioning XXVI Workshop on Recent Developments in High Energy Physics and Cosmology Ancient Olympia, April 2008 ©CERN

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, ATLAS CMS LHC The ATLAS detector at LHC Current LHC Plan : 1 st June beam-pipe close and bake-out, 1 st injection ~mid-June, 1 st collisions ~end of summer, pilot physics run (10 TeV and 1.1x10 32 cm -2 s -1 ) looks possible for Muon Spectrometer Air-core toroid, Precision drift and Trigger chambers P T resolution:~10% at P T = 1 TeV (standalone) ~2.3% at P T = 50 GeV (combined) Hadron Calorimetry Fe/Sci + Cu/LAr  /E~60%/  E  3% E/M Calorimetry Pb/LAr  /E~10%/  E Inner Detector 2 T solenoid Si (Pixels + Strips) Transition Radiation Tracker ALICE LHCb ©CERN

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, SM Higgs → ZZ ( * ) → 4μ Acceptance Building a high-precision spectrometer is not enough. Good pseudorapidity (η) coverage also important! By extending the coverage from |η|<2 to |η|<2.7 the acceptance for a 150 GeV SM Higgs decaying to four muons increases by ~60%

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, Challenges in the high η coverage Besides muons from pp interactions, increased occupancy in the Muon Spectrometer due to Primary Background (e.g π/Κ decay in flight, punch through hadrons) and Radiation Background (mainly n/γ ~1 MeV) The Radiation Background is more severe for the forward region and especially for the Inner Station (>200 Hz/cm 2 ). The CSCs are Multi-Wire Proportional Chambers with a symmetric cell: 1.High rate capability. 2.High single layer spatial accuracy. 3.Good two-track separation (~40% of read-out pitch). 4.Insensitive to moderate gain variations. 5.Short electron drift time (max ~ 45ns) and good timing resolution (~3.5ns) 6.Low sensitivity to neutrals → ε n <10 -4, ε γ ~1%

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, Principle of Operation Spatial accuracy in the precision coordinate is in the 60 – 80 μm range, by measuring the induced charge on the segmented cathode by the avalanche formed in the anode wire. (Charge Interpolation) Relative measurement → important to know the cathode strips’ relative response. (Electronics Calibration) η = 2 CSCs are present in 27% of the Muon Spectrometer’s pseudorapidity coverage η = channels in total → 80% in precision coordinate

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, Pulse Shaping / Signal Reconstruction Only four samples of the bipolar waveform (20 MHz), mainly in its first half, available to reconstruct the signal. Bipolar signal shaping with relatively short peaking time (75ns) selected crude approach → parabola around the peak better approach → fit bipolar pulse using all samples Parabola Bipolar in progress Pulser input

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, Noise Correlation The electronic noise of the four samples is not totally independent → one amplifier shaper for whole pulse. Correlation pattern explained by bipolar shaping and peaking time. Covariance

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, Cosmic data studies relative layer rotation cluster charge effect on resolution

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, Channel-to-Channel Cross-talk Cross-talk appears in the pre-amplifiers due to parasitic capacitance → this affects several channels around the one with the main pulse Effect of cross-talk ~0.4% of main pulse amplitude, opposite polarity and higher frequency

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, Calibration/Electronics Linearity Equalization of strips’ response using calibration pulser (one for each layer) which provide 64 different pulse heights. The relative amplitudes of the different calibration levels, are understood at the 0.3% level. The calibration system cannot cover the lower part of the dynamic range → linearity of electronics is important Found deviations consistent with pulser understanding and well below the noise. the electronics are linear

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, Cathode Strip Chamber Installation The Cathode Strip Chambers are mounted on the Small Wheels, which are 10 m in height nevertheless! Contrary to ATLAS practice, the Small Wheels were fully assembled and commissioned on the surface ©CERN

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, Noise Levels are at the nominal values Large-Small Chamber Periodicity observed Structure within sectors also as expected Noise Performance Most Probable muon signal ~350 ADC counts

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, Calibration Pulser Runs Pulser runs used to test in detail the response of the precision strips to different pulse amplitudes and verify that the calibration system is fully operational. Only two sample distributions presented here. Bipolar Pulse Peaking Time Width of Bipolar Pulse

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, Cosmic Runs Strip response, HV connection and stability, gas and water circulation and the overall chamber condition. Unfortunately CSC’s preferred direction not favored by the setup + Trigger on cosmic ray induced particle showers (efficiency ~10%) = Low Rate + Low Data Quality SW – A : 10 days of cosmic runs. 24 h runs per sector pair. SW – C : 6 days of cosmic runs. Few hours of data taking per sector pair. Trigger Scintillators The chambers were found to be in good shape!

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, Hit Distribution : Precision Strips All layers have approximately the same number of hits, as expected Layer average

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, Lowering the Small Wheels to the cavern Small Wheel Side-C lowered in the cavern on 15 th of February. Small Wheel Side-A lowered in the cavern on 29 th of February. The last ATLAS pieces lowered in the cavern. ©CERN

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, CSCs at the ATLAS cavern Noise ratio with respect to surface tests. Work in progress! Small Wheels currently at the “Open” position, 7m of additional unshielded cable present → Not present during ATLAS data taking. Almost all services connected. Noise studies on-going. High Voltage tests to follow

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, Cooling system stability Due to high heat dissipation (~280W/chamber) cooling is needed → three water loops/chamber. Final leak-less cooling system functional for several weeks, without any problems. One sector switched off Controlled shut-down of two sectors ΔPedestal/ΔΤ ~-0.03 ADC/°C No cooling Cooling SW-C

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, Summary Detector/electronics level performance studies performed using final CSC electronics and data acquisition In parallel pre-commissioning of CSCs at the laboratory (Jul–Nov) installation/commissioning on Small Wheels (Sep–Jan). CSCs lowered at the cavern end of February → almost all services connected. Noise studies to understand new grounding configuration / interferences on-going. Preliminary results encouraging Looking forward to pp interactions!

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, Additional Slides

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, Muon Spectrometry in ATLAS The ATLAS Muon Spectrometer is designed to perform precise muon reconstruction up to P T =1 TeV. In order to achieve this goal, high spatial accuracy in the bending plane is required. This is implemented in a cost-effective way with the usage of Drift Chambers in most of Muon Spectrometer’s coverage. Oct 2005

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, Signal Reconstruction / Timing Totally channels in the CSCs → 80% in precision coordinate Implemented in the ATLAS software Bipolar fit has been implemented in the ATLAS software (currently under validation), taking into account reconstruction time issues → Don’t waste reconstruction time Data decoding only Bipolar Fit + Data decoding

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, X-Y strip charge correlation in cosmics Line Fit Q y = *Q x

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, ASM-I ASM-II CSC On-Chamber Electronics

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, CSC Commissioning Data taking and testing for SW-C finished end of November 2007, for SW-A just before CERN’s annual closure. The cathode strip chamber operation exhibits several levels of organization. Each one of them should be tested : 1) Chamber Level : LV, Gas, Water, Calibration Pulser 2) Layer Level : HV, Calibration Pulser 3) Groups of 24 channels 4) Groups of 12 channels 5) Single channel level : Disconnected or noisy channels Too complicated to intervene now, will have to live with them! The CSC chambers have been tested several times. The latest one was Jul – Nov at the laboratory (blg. 184), both using the calibration pulser and cosmic rays.

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, Hit Distribution : Transverse Strips

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17 th, Induced Charge Distribution