The Commissioning The Commissioning of the ATLAS Pixel of the ATLAS Pixel

DetectorDetector

XCIV National Congress Italian Physical Society

Genova, 22-27 Settembre 2008

Nicoletta Garelli

Large Hadronic ColliderLarge Hadronic Collider

Opal

Delphi

SPS

PS

 

LHCAleph

L3

LHCb

Alice

ATLAS

CMS

MOTIVATION: Find Higgs Boson and New Physics Beyond the Standard Model

LHC is being built in a circular tunnel 27 km in circumference, 50-175 m underground.

Beams inside continuous vacuum guided by superconducting magnets.

Bunch cross every 25 ns 600 million collisions per second

4 collision points

Machine

Beams

Energy

Luminosity

LHC p p 14 TeV 1034 cm-2s-1

LHC Pb Pb 5.5 TeV

1027 cm-2s-1

Tevatron p anti-p

2.0 TeV

1032 cm-2s-1

LEP e+ e- 200 GeV

1032 cm-2s-1

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SM Higgs BosonSM Higgs Boson

LEP direct search: mH>114.4 GeV/c2

@95%CL

LEP Electroweak Fit Limit: mH<144 GeV/c2 @95%CL

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Higgs Mass Range – Detector Higgs Mass Range – Detector RequirementsRequirements

114.5 < MH < 130 GeVGolden channel: Hγ γ But small decay rate! QCD background.

130 < MH < 800 GeVGolden channel: HZZ/ZZ*4l

• 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 /π0 .

• Efficient muon spectrometer for identification, trigger, and momentum measurement of high energetic muons.

800 < MH< 1000 GeVHWWlνjjET missing

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ATLASATLAS A Thoroidal LHC ApparatuSA Thoroidal LHC ApparatuS

Cylindrical ‘Onion-like’ Detector

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The ATLAS Inner DetectorThe ATLAS Inner DetectorTechnique: high granularity + low occupancy + 2D track measurementGeometry: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

PIXEL

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The Pixel DetectorThe Pixel DetectorHigh multiplicity tracking detector:

~ 1200 tracks per bunch crossing high granularity (80 million ⇒channels!)

High radiation dose tolerance: ~50 Mrad

High impact parameterresolution: ~ 12 μm vertex resolution – secondary vertex reconstruction

High time resolution: 40 MHz bunch crossing rate

Low interaction length: ~10% χ0

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After ~20 years waiting… finally beams circulating in LHC!

• Beams with injection energy of 450GeV. •Pixel Detector OFF for safety reason.

The 10The 10thth September 2008 September 2008

•The way towards collisions and LHC stable operation is still long… •LHC Magnet Accident of 19th September 2008.

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Pixel Detector MilestonesPixel 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 months of accident recovery, finally cosmic runs and calibration procedure.

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The Readout SystemThe Readout System

Pixel Module Optoboard

BOC

TXRX

S-Link

ROD

L1A

SBC

ROBIN

S-link

Signal: discriminator decision on amplified charge deposition within the pixels.

1 Module = ~50k pixelsDetector = 1744 Modules

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16 FE chips

Bump bonds

PP0 connection

Wire bondsOptimize detector

response calibrate readout electronics, tune on-line and store results.

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 measurement), … for each pixel.Tune link between on-detector

Optoboards and off-detector Back-Of-Crate cards:Laser Power for the Optoboard (ViSet)Threshold at the BOC Delays at the BOCFind optimal values for individual module by varying the three parameters

The Calibration Procedure The Calibration Procedure 1/21/2

Threshold Noise

RECENT OUTCOME11

57/1744 modules with optical communication problems 80/1744 (~5%) bad modules excluded from data taking

Calibration Procedures 2/2

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.

The Software ChallengeThe 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

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Cosmic RunsCosmic Runs

First Track!First Track!Event with 7

Pixel hits (overlapping L2 modules) and 16 SCT

hits

Cosmic Trigger provided by Muon Chambers and Calorimeters5K/80·106 noisy pixels masked (occupancy >10-5)

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