glast lat project july 19, 2005 e. do couto e silva 1/17 science verification analysis and...

GLAST LAT Project July 19, 2005

E. do Couto e Silva 1/17

Science Verification Analysis and Calibration

GLAST Large Area Telescope Eduardo do Couto e Silva

SLAC Jul 19, 2005



Science Verification Analysis and CalibrationScience Verification Analysis and Calibration

• Objectives– Calibrate the LAT and characterize its performance prior to launch

– Maximize science return by optimizing instrument capabilities– Understand systematic effects to extend science reach

– Provide input to Instrument Science Operations Center– Develop calibration, monitoring and diagnostics tools to be exercised on-orbit

– Strengthen collaboration ties and disseminate knowledge across teams– Instrument analysis workshops ( 5th meeting scheduled for Aug 29)

• Data – Cosmic ray secondaries and low energy photons

– Collected at several stages of the LAT integration

– Particle beam tests – spare LAT modules (after instrument delivery)

– Sophisticated Monte Carlo simulations– Comprehensive description of detector geometry and physics processes

• Data Analysis– Probe a large parameter space of the Large Area Telescope

– Search for hardware failures– Debug software– Learn about the operational characteristics of the instrument



Secondary Cosmic Ray ShowersSecondary Cosmic Ray Showers

Muon candidates Work from Anders Borgland (SLAC)



Instrumental Capabilities Instrumental Capabilities

• Energy Resolution requirements

– Calibrate Energy Scales– Beam test

– Calibrate out non-linear effects

• Pointing accuracy requirements

– Inter and Intra tower alignment



Calibrate Energy ScalesCalibrate Energy Scales

• Muon candidates – 11.2 MeV peak in CAL crystals

• We are able to probe effects at the 2% level – improved offline software

DataDataMCMC

Work from David Smith (Bordeaux, France)



Intra Tower AlignmentIntra Tower Alignment

the ideal tower

a horizontal shift

a vertical shift

a rotation

the real tower

Work from Michael Kuss (Pisa, Italy)



Horizontal and Vertical AlignmentHorizontal and Vertical Alignment

Aligns:• horizontal ( to strips)• vertical

X4

X3

X2

X1

X0

realposition

idealposition

res = x + z · cot(θ)

θ

horizontal displacement: 157m

vertical displacement: 81m



Calibrations Work!Calibrations Work!

• Effect is calibrated out for all planes



• Objective– Measure and monitor trigger

efficiencies – includes effects from

» Gap between Silicon wafers» dead strips» insensitive area» alignment» timing

• Select muon candidates with TKR– Define a track using 4 layers

– 3 top and 1 bottom

– Test intermediate layers– Measure efficiency

– Compare with MC simulations– Direction and position

measured by TKR» See next slide

TKR EfficienciesTKR Efficiencies

Work from Tsunefumi Mizuno et al (Hiroshima, Japan)

Tower



Good agreement between MC and Data within 1% for all 6 towers

Tower in Pos#8 Tower in Pos#9

TKR Efficiencies: Data/MC SimulationTKR Efficiencies: Data/MC Simulation



Timing of Integrated SystemsTiming of Integrated Systems

• Need to align TKR/CAL/ACD

– To trigger efficiently

• Need to align TKR/CAL/ACD

– To latch data efficiently

• On-orbit Operations

– Trigger alignment knobs are controllable remotely

– We are currently acquiring experience on the ground



Minimizing the Effects of Trigger JitterMinimizing the Effects of Trigger Jitter

• Mainly caused by pulse height differences with respect to the trigger threshold

– TKR– Large signals from CNO

– CAL– Large variation in energy

• Time-in of towers – Optimize performance– Uniformity across towers

Work from Martin Kocian and Su Dong (SLAC)



Time Between Events: Baseline RunTime Between Events: Baseline Run

Expect 26.5 sGood agreement!

Work from Warren Focke and Anders Borgland

(SLAC)



Probing Several Instrument Configurations Probing Several Instrument Configurations

• We designed a series of tests in which we change only one parameter in the instrument and– Collect cosmic rays– Select muon candidates– Verify the behavior is not affected by parameter changes

• Example of parameters– Read TKR from “right” or “left” cables only– Change Voltage of Power Distribution Unit – Overlay a source of high rate triggers on the top of existing

cosmic ray triggers


E. do Couto e Silva 15/17Plane

●Baseline●Min●Max

Bottom Plane = 0Top plane = 35

From Stefano and Claudia (Perugia, Italy)

No major discrepancies found so far…No major discrepancies found so far…

Change voltage

From Monica Brigida (Bari, Italy)

Baseline (read from both sides)

Right Readout onlyLeft Readout only



Cosmic Ray Secondaries: Photon CandidatesCosmic Ray Secondaries: Photon Candidates

Work from Leon Rochester (SLAC)

and William Atwood (UCSC)



Summary and OutlookSummary and Outlook

• Summary of SVAC activities– Focus on improving and updating calibrations– Explore on-orbit operational aspects of the instrument

– As well as we can simulate on the ground

– Not part of PASS/FAIL testing– Longer term feedback on instrument characterization– Propose special tests as needed

• Timeline– Environmental Tests

– Data will be delivered to SLAC for offline analysis– Focus on correlating housekeeping with science data– Environmental dependencies of calibrations

– Spacecraft Integration – On-orbit checkout– First year of operation

glast lat project july 19, 2005 e. do couto e silva 1/17 science verification analysis and...

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