atlas liquid argon calorimeter monitoring & data quality
DESCRIPTION
ATLAS Liquid Argon Calorimeter Monitoring & Data Quality. Jessica Lev ê que Centre de Physique des Particules de Marseille ATLAS Liquid Argon Calorimeter Group NEC, Varna, Bulgaria 7-11 th September 2009. Introduction: about ATLAS data. Raw data in ATLAS: 1.6 MByte per event - PowerPoint PPT PresentationTRANSCRIPT
ATLAS Liquid Argon Calorimeter
Monitoring &
Data Quality
Jessica LevêqueCentre de Physique des Particules de Marseille
ATLAS Liquid Argon Calorimeter Group
NEC, Varna, Bulgaria7-11th September 2009
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Introduction: about ATLAS dataRaw data in ATLAS:
1.6 MByte per eventAcquisition rate: 200 Hz1 day = 2 runs = 2*10 hours of data
~23 TBytes per day
Disk Buffer at Tier 0: 610 TBytesAfter migration of data on tape: 200 Hz readout rate
Consequences: Delay between data acquisition and data reconstruction should be less than 5 days Very efficient monitoring and Data Quality feedback loops are required
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ATLAS Data Processing Model
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The Liquid Argon Calorimeters
~ 182 000 readout channels
- Sampling Calorimeter- Active Medium : LAr- Absorber: lead in EM, copper in HEC, copper & tungsten in FCAL
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LAr Calorimeter Electronic
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LAr Calorimeter MonitoringDetector Control System:
To monitor variations of liquid argon purity, temperature High voltage, cooling plant, power supplies
Data Integrity: To monitor the electronic front-end boards, and the integrity of the readout data
Signal Peak positionTo monitor the detector timing
Misbehaving channels: to spot hot channels that might affect the physics objects reconstruction.
Physics objects (electrons, photons, jets…) not a “detector task”, therefore not presented here.
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Validation of monitoring tools Extensive use of cosmics data:
Experience daily detector operations Validation of the full data chain reconstructionTest and optimization of automatic data quality and monitoring tools
In the following: a few examples of calorimeter monitoring during ATLAS cosmics runs
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Detector Control SystemDetector fully operational during last cosmic campaign
Requirement for physics: detector coverage and behavior should be stable during a run (oa a luminosity block)
Data Quality Flag assessment: warning when the detector states changes during the run.
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Online Computation MonitoringFor all cells, the energy is computed online and sent to the central acquisition system.
For high energy cells (typically above few GeV) the individual digits in ADC counts are also readout
For these energetic cells, we recompute the energy offline from the digits and compare the result with the energy computed online
The plot illustrates the perfect reliability over ~ 40 000 events. The 1 MeV tails are within the expected accuracy.
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Signal Timing MonitoringThe digits are readout for each cell above a given threshold (typically above a few GeV)
For these very energetic cells,we average the pulse shapes per detector region
This allows to compare the timing between the different LAr detector parts
This check is also very important for ATLAS, as the LAr calorimeter is the subdetector with the largest time window (32 time samples, i.e 800ns). The plot above is used to align the timing between different trigger sources.
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Noise monitoringFor each calorimeter cell, the electronic noise is measured in random triggered events, and stored in a database
The electronic noise is used as a reference to spot channels with deviant behavior during physics runs
Monitoring individual noisy cells: number of events per cell, where the cell energy is above 3 times the expected noiseMonitoring global detector noise: number of cells per event, with energy above 3 times the expected noise With perfectly gaussian noise, we expect 0.27% of events/cells passing the cut.
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Global Detector Noise example
December 2007: O(10) events out of 3 000 in non-gaussian tailsFor these events, a large number of cells are fluctuating outside 3 at the same time
Expected Value: 0.27%
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insulation
HV cable 110m long
Origin of the Global Noise
Counting Room Detector Cryostat
1-2 volts difference
between cryostat ground
and HV module ground
degrading the filter box
performances
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CAPACITOR one per cable
HV cable 110m long
Fixing the Problem
Counting Room Detector Cryostat
improve the grounding
between HV filter box and
the cryostat by adding
capacitive link.
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Global Detector Noise: current status
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Individual cell noise example
October 2008 (blue line): large tails above 0.7%. This tail is populated by channels with unstable and noisy shapers, creating large noise pulses that triggered the event data taking.
April 2009 (red line): the tails vanished after a major campaign of FEB refurbishment, replacing the faulty preamplifiers.
Cosmic data triggered by a signal in LAr calorimeter Given the very low muon rate, physics signal does not bias the expected event rate (we still expect 0.27% of cells)
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Summary & Conclusions
Conclusion: we are ready and waiting for beam !
Liquid Argon Monitoring and Data Quality developed and tested with cosmics data since 2006
Monitoring extensively used to commission the detector and provide meaningful information to others ATLAS subdetectors
Liquid Argon detector fully operational and in a very good shape (99.8% channels active and calibrated)