Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 1 Calibration of L1Calo L1Calo Calibration Overview L1Calo Calibration Overview Calibration

Alan WatsonAlan Watson Atlas Trigger Workshop, Amsterdam, Atlas Trigger Workshop, Amsterdam,

18-22/10/1018-22/10/10

11

Calibration of L1CaloCalibration of L1Calo

• L1Calo L1Calo Calibration Calibration OverviewOverview

•Calibration Calibration Status & Status & RefinementsRefinements

•Hardware Hardware ProblemsProblems

• Longer-term Longer-term QuestionsQuestions


18-22/10/1018-22/10/10

22

Overview of L1Calo SignalsOverview of L1Calo Signals


18-22/10/1018-22/10/10

33

Main Elements of L1Calo Main Elements of L1Calo

CalibrationCalibrationTimingTiming Optimum calibration requires ADC

timing to < 2-3 ns. Measure tower-by-tower in beam

data. Receiver gainsReceiver gains Set ADCs to uniform 250 MeV EM

scale Based on pulsers, check with beamFilter & LUT SlopeFilter & LUT Slope Filter improve S/N, ET calibration,

Bunch Crossing ID performance LUT “slope” is the final calibration

adjustment


18-22/10/1018-22/10/10

44

Main Elements of L1Calo Main Elements of L1Calo

CalibrationCalibrationTimingTiming Optimum calibration requires ADC

timing to < 2-3 ns. Measure tower-by-tower in beam

data. Receiver gainsReceiver gains Set ADCs to uniform 250 MeV EM

scale Based on pulsers, check with beamFilter & LUT SlopeFilter & LUT Slope Filter improve S/N, ET calibration,

Bunch Crossing ID performance LUT “slope” is the final calibration

adjustment

Output:Output: Uniform towertower

calibration ~1 GeV

deposited ET per count, EM scale


18-22/10/1018-22/10/10

55

Also Affecting Trigger Also Affecting Trigger

CalibrationCalibrationTower calibration ≠ trigger calibrationTower calibration ≠ trigger calibrationNoise cutsNoise cuts One-sided – towers below threshold are zeroed. Triggers combining many low-ET towers can be

sensitive.BCID efficiency turn-onBCID efficiency turn-on Only use “in-time” towers. Full efficiency reached

between 2-3 GeV. Performance not critically sensitive to filter coefficients

Trigger ThresholdsTrigger Thresholds Set to produce desired turn-onWhat you compare againstWhat you compare against Offline algorithm & calibration


18-22/10/1018-22/10/10

66

Calibration HistoryCalibration History TWiki: TWiki: L1CaloCommissioningChangesL1CaloCommissioningChanges


18-22/10/1018-22/10/10

77


Last significant

calibration

change


18-22/10/1018-22/10/10

88


Last significant

calibration

changeStable Stable

throughout > throughout >

98% of 2010 98% of 2010

data-takingdata-taking


18-22/10/1018-22/10/10

99

Originally reliant on pulsersOriginally reliant on pulsers Provide signals with controllable ET, good statistics for

all channels But expected to have systematic differences in pulse shape &

timing

Calibration using collision dataCalibration using collision data

Calibration using Physics EventsCalibration using Physics Events

Timing by fitting pulse shapes Needs events with ET >> noise in

all channels

Tower ET by comparison with

corresponding cell sums Requires wide range of ET in each

tower

Only recently had necessary statistics for these studies


18-22/10/1018-22/10/10

1010

Trigger Tower TimingTrigger Tower TimingQuite stable:Quite stable: Luminosity now sufficient to

gather data for timing fit quickly One good run will do most

channels Some low-activity channels need

longer

Most channels within ±3ns Further improvement desirable,

but effects on calibration will be small

Will need ongoing checks Two global timing changes this

summer

EM, run 160530

Global 2ns clock phase change made in RF2TTC module 1 day after these data were collected!


18-22/10/1018-22/10/10

1111

Receiver gains & ADC CalibrationReceiver gains & ADC CalibrationGenerally good Generally good correlation with cell correlation with cell readoutreadout Most detector partitions Across full ET range

Exception: EMEC Exception: EMEC 1.5<1.5<<1.8<1.8

Incorrect PS weight in tower sum affects pulser calibration

Effect understood, can be corrected.


18-22/10/1018-22/10/10

1212

Corrections to ADC scalesCorrections to ADC scales

FCAL 2/3 gains:FCAL 2/3 gains: FCAL 2/3 “towers” are added

in pairs before digitization. Believe gain variations between

pair likely cause of deviation

Physics signal scales:Physics signal scales: Pulser and physics signals

not identical. Observe differences of the order

of 2% Corrections being calculated


18-22/10/1018-22/10/10

1313

Corrections to Final ET ScaleCorrections to Final ET ScaleLUT slopes:LUT slopes: LUT slopes are sensitive to the

physics pulse shape, which differs from the calibration pulses. Shifts scale relative to ADC calibration Can now measure effect and apply

corrections

LUT filling:LUT filling: LUT filling scheme causes slight

tendency towards underestimation of some pulse ET values A small bias, visible mainly at low ET. Can correct with online software change


18-22/10/1018-22/10/10

1414

EM Transition RegionEM Transition RegionOne Trigger Tower spans transitionOne Trigger Tower spans transition Need to combine signals in receivers in USA15 Analogue summation before L1Calo electronics.

Timings need to be measured and cables cut to length O(45ns) difference between EMB and EMEC timings Measurement with data – pulser timing different Hence different partial towers in this region in some periods

Cutting cables is a one-shot operationStatusStatus Data collected and timings estimated A few problematic towers identified

Spread within one cable (4 TT) a bit large Should be able to reduce using Tower Builder Board settings


18-22/10/1018-22/10/10

1515

Applying CorrectionsApplying CorrectionsOptimisation vs StabilityOptimisation vs Stability Priority was to keep calibration stable for 2010 pp run Rather than apply quick fixes as each effect understood

Most can be applied for HI run FCAL 2/3 gains most difficult on that timescale

EM scale calibration will not be complete until after transition towers connected Expect this to be 2011 Will require some further work to understand signals once

connected.


18-22/10/1018-22/10/10

1616

HV TripsHV TripsEffects varyEffects vary PS trips: small loss of signal Tile: drawer off, towers dead Accordion: 50% signal lossFlagging statusFlagging status Performed by detector groupsDifficult area: accordion tripsDifficult area: accordion trips Reduced gain can be corrected offline Hence data usable for physics

But L1Calo and HLT both affected Trying to correct at L1 would be “messy”


18-22/10/1018-22/10/10

1717

Calibration Strategy for 2011 Calibration Strategy for 2011

RunRunPriority: Establish an understood EM scalePriority: Establish an understood EM scale Corrections to ADC, LUT scales to to match calibration to

readout Mostly few % effects

Corrections for long-term reduced HV, endcap PS weights Larger, but localised

Finalise timings Connect up and calibrate transition towersWill bad towers be fixed in shutdown?Will bad towers be fixed in shutdown? Dead OTX or Tile drawers, for example If so, will need to establish calibration for these towersConclusion: start 2011 with EM scale Conclusion: start 2011 with EM scale

calibration calibration


18-22/10/1018-22/10/10

1818

Calibration Strategy for 2011 Calibration Strategy for 2011

RunRunAre there other changes which might Are there other changes which might improve performance?improve performance? Reduce trigger tower noise cuts? Rather promising in MC. In reality…?

Eta-dependent corrections? e.g. for material effects?

Trigger threshold tuning? Will be needed if we do either of the above


18-22/10/1018-22/10/10

1919

Trigger RefinementsTrigger Refinements

Effects of any changes Effects of any changes must be studied using must be studied using

real datareal data

(Old MC plots used to (Old MC plots used to illustrate points in following illustrate points in following

slides)slides)


18-22/10/1018-22/10/10

2020

Noise Cut TuningNoise Cut TuningMC: lower cuts improve MC: lower cuts improve performanceperformance Sharper turn-on for jet, MET Reduced ET-dependence of

L1 jet responseTests with data-taking Tests with data-taking in early 2009 less in early 2009 less positivepositive Very modest effects seen Data had other imperfections, e.g.

timing, not present in MC. Did these mask effects?

Would larger reductions help more?

Study effects with recorded dataStudy effects with recorded data ESD contains ADC data, so can simulate effect of reduced

cuts


18-22/10/1018-22/10/10

2121

Material CorrectionsMaterial CorrectionsTrigger response varies Trigger response varies

with with Material effects a major factorCan tower calibration Can tower calibration

compensate?compensate? In principle, to some extent,

but with caveats: Corrections should depend on object

and ET. Tower-based corrections

cannot take this into account. Over-correction results in hot spots,

increased rate. Region where corrections largest

still partially-connected, not understood.

“EM scale”

“LUT Calib”

MC electrons, pT > 25

GeV


18-22/10/1018-22/10/10

2222

Investigating Material Investigating Material

CorrectionsCorrectionsPossible approachPossible approach Study LUT-based corrections Keep ADC data on EM scale for

reference, monitoring Digital correction, can be

studied reliably in data analysis

Base on electron response

(15-40 GeV pT?) Simpler to define & understand

than jets Less sensitive to other

parameters which may change

Don’t change overall ET

scale Mid-barrel response as reference

ConstraintsConstraints Need fully understood EM

scale first Can start investigation sooner,

but not conclude

Transition region incomplete Currently would have to exclude

Noise cut changes would affect results Mostly for jets, low-ET e/.

Reason not to tune for these

Need to understand effects

on all triggers, ET ranges


18-22/10/1018-22/10/10

2323

An Alternative ApproachAn Alternative ApproachA purely personal suggestion:A purely personal suggestion:

I don’t suppose that the next slide will I don’t suppose that the next slide will make me popular, but wanted all options make me popular, but wanted all options to be on the table…to be on the table…


18-22/10/1018-22/10/10

2424

Modulating Trigger Thresholds Modulating Trigger Thresholds

with with Modules span fixed Modules span fixed rangesranges

Can load different threshold values into different modules Modulate threshold value with

Could use to make turn-on more uniform, improve overall sharpness

Corrections depend on object ET

Questions/DrawbacksQuestions/Drawbacks Complicates threshold setting Does not help MET Is module eta granularity

enough?


18-22/10/1018-22/10/10

2525

Modulating Trigger Thresholds Modulating Trigger Thresholds

with with Modules span fixed Modules span fixed rangesranges

Can load different threshold values into different modules Modulate threshold value with

Could use to make turn-on more uniform, improve overall sharpness

Corrections depend on object ET

Questions/DrawbacksQuestions/Drawbacks Complicates threshold setting Does not help MET Is module eta granularity

enough?


18-22/10/1018-22/10/10

2626

Changing Conditions: PileupChanging Conditions: Pileup Place-holder – not much to say: main thing is what’s observed

about different effects in first crossing of train and subsequent

Note that we have jet element thresholds that can be applied to JEM triggers – may be useful to stabilise TE if luminosity variation within a fill becomes an issue.

Don’t so far see a need to raise tower thresholds etc, but keep under review. Currently out-of-time pileup actually reduces signal levels, which would favour opposite


18-22/10/1018-22/10/10

2727

SummarySummaryAnother place-holder, but points to coverAnother place-holder, but points to cover Status not at all bad: timing within couple of ns, most scales

good to few % Work to do to finish EM scale, but we know what the steps are.

Could have done most of them sooner, can do most quickly Still a few odd channels, such as transition, where we will need

a bit longer to get the calibration finalised and understood Accordion HV trips problematic for us. May be a small effect on

physics so far, but it’s a potential complication Are some ideas to investigate for improving trigger

performance. We have the tools to do the studies, but at least any calibration adjustments should start from good EM scale (noise cuts less so)

Documents

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 1 Calibration of L1Calo L1Calo Calibration Overview L1Calo Calibration Overview Calibration