The Commissioning of the ATLAS Pixel Detector

Transcription

1 The Commissioning of the ATLAS Pixel Detector XCIV National Congress Italian Physical Society Genova, Settembre 2008 Nicoletta Garelli

2 Large Hadronic Collider MOTIVATION: Find Higgs Boson and New Physics Beyond the Standard Model Machi LHC is being built in a circular tunnel 27 km in ne circumference, m underground. LHC Aleph LHC CMS Alice Opal SPS Delphi ATLAS PS LHCb Ener gy Luminosity 14 TeV 1034 cm-2s-1 LHC Pb Pb 1027 cm-2s-1 Tevatron p antip e+ e- 5.5 TeV 2.0 TeV 200 GeV LEP 4 collision points L3 Bea ms pp 1032 cm-2s cm-2s-1 Beams inside continuous vacuum guided by superconducting magnets. Bunch cross every 25 ns 600 million collisions per2

3 SM Higgs Boson LEP direct search: mh>114.4 LEP Electroweak Fit Limit: mh<144 3

4 Higgs Mass Range Detector Requirements < MH < 130 GeV 130 < MH < 800 GeV Golden channel: H γ γ Golden channel: But small decay rate! H ZZ/ZZ* 4l QCD background. 800 < MH< 1000 GeV H WW lνjj ET missing Powerful inner tracking systems in magnetic field with high granularity and secondary vertex reconstruction capability. Crucial for background rejection. High granularity hadronic calorimeter with full coverage for good missing ET resolution, jet trigger and reconstruction. Electromagnetic calorimeter with good energy and spatial resolution, capability to separate γ /π 0. Efficient muon spectrometer for identification, trigger, and momentum measurement of high energetic muons. 4

5 ATLAS A Thoroidal LHC ApparatuS Cylindric al Onionlike Detector 5

6 The ATLAS Inner Detector PIXEL Technique: high granularity + low occupancy + 2D track measurement Geometry:3 Barrel layers (r = 5, 9, 12 cm) + 2 End-Caps with 3 Disks each 3 space points for η< 2.5 with resolution 16µm 115 µm 6

7 The Pixel Detector High multiplicity tracking detector: ~ 1200 tracks per bunch crossing high granularity (80 million channels!) High impact parameter resolution: ~ 12 μm vertex resolution secondary vertex reconstruction Low interaction length: ~10% χ0 High time resolution: 40 MHz bunch crossing rate High radiation dose tolerance: ~50 Mrad 7

8 The 10th September 2008 After ~20 years waiting finally beams circulating in LHC! Beams with injection energy of 450GeV. Pixel Detector OFF for safety reason. The way towards collisions and LHC stable operation is still long LHC Magnet Accident of th 8

9 Pixel Detector Milestones July 2007: Installation of pixel-package in the cavern. December 2007: Finished service connections. February April 2008: Sign-Off (=test on light transmission to and from detector, verify that analog and digital parts of the modules are powered, check the sensor) + Cooling Plant commissioning. August 2008: Cooling plant operative after 3 9

10 The Readout System 1 Module = ~50k pixels Detector = 1744 Modules Pixel PP0 connection Module Optoboard Bump bonds BOC ROD SBC TX RX ROBIN S-Link L1A S-link Optimize detector Wire bonds calibrate readout electronics, tune Signal: discriminator on-line and store results. decision on amplified charge deposition 16 FE response chips 10

11 The Calibration Procedure 1/2 Module Tuning. Motivation: Mean energy loss in pixels changes in time due to irradiation. Calibration Source: Directly inject charge (VCal) Calibration Procedure: Many! Vary VCal and determine distribution for the discriminator threshold, the noise (slope of signal rise), the Time-Over-Threshold (ToT, indirect charge deposit Tune link between measurement), for on-detector each pixel. Threshold Noise Optoboards and off-detector BackOf-Crate cards: Laser Power for the Optoboard (ViSet) Threshold at the BOC Delays at the BOC Find optimal values for individual module by varying the three parameters 57/1744 modules with optical communication problems RECENT OUTCOME 11 80/1744 (~5%) bad modules excluded from data taking

12 Calibration Procedures 2/2 The Software Challenge The Pixel Detector accesses an huge amount of information (# of channels and # of configuration parameters). Pixel Database Server handle in a fast and efficient way the configuration of the Pixel Detector caching mechanism The calibration procedures produce an huge amount of histograms, both on-line and off-line. Need to analyze data on-line in order to take decision about bad modules to disable during the data taking. Efficient on-line histogram dispatching system, Pixel Histo Server, using multi-threaded and distributed software. 12

13 Cosmic Runs Cosmic Trigger provided by Muon Chambers and Calorimeters 5K/ noisy pixels masked (occupancy >10-5) First Track! Event with 7 Pixel hits (overlapping L2 modules) and 16 SCT 13