Monitoring of L1Calo EM Trigger Items:

Overview & Midterm ResultsHardeep Bansil

University of Birmingham

Birmingham ATLAS Weekly Meeting11/11/2010

Contents• Trigger and L1Calo• Analysis• Efficiencies– Bump at Low Transverse Energies– Missing Trigger Events

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ATLAS Trigger• Divided into three levels (L1

hardware based, L2 & EF software based)

• Reduces 40 MHz bunch-crossing rate to ≈200 Hz for recording while keeping events containing physics processes of interest

• Level-1 has three sub-systems: – Calorimeter Trigger– Muon Trigger– Central Trigger (CTP)

• L1 identifies Regions of Interest (RoIs) to send to L2

• L2 looks around RoI with full detector info, EF looks at whole event in detail using same algorithms as used in offline reconstruction

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Level-1 Calorimeter Trigger (L1Calo)

• Summed analogue signals sent to USA15 in Trigger Towers (0.1x0.1)• Signals digitised and sent to specific modules to identify electrons, photons,

taus and jets as well as total and missing energy• Event level result sent to L1 CTP, if passed get L1A and data readout to DAQ

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Cluster Processor• Birmingham responsibility• 4-crate system, each crate covers one

quadrant with 14 modules in each crate

• Receives trigger tower info up to |η| < 2.5 to identify e/γ/τ/h

• Uses 4x4 sliding window algorithm– The EM cluster (e/γ) or HAD cluster

(τ/hadron) must have ET greater than the electromagnetic or hadronic threshold under consideration.

– The ET in the EM isolation ring must be less than the electromagnetic isolation threshold.

– The ET in the HAD isolation ring must be less than the hadronic isolation threshold.

– For EM clusters, the total ET in the hadronic inner core must be less than a threshold.

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data10 Analysis• Used AthenaProduction-15.6.12.2 with ESDs on grid with

TrigT1CaloAnalysisExamples package• Using MinBias stream events pass L1_MBTS_1 || L1_MBTS_2 items• Using JetTauEtmiss stream events pass L1_J*, EM cluster under study

must have ΔR > 0.4 from jet ROI which triggered event (tag & probe)• eγ Good Runs Lists / Lumi block selection• Require ≥ 1 vertex with ≥ 3 associated tracks• Remove photon conversions based on eγ code• Remove crack region between barrel and end-cap & OTX cuts• ΔR < 0.15 for matching RoIs to clusters of offline electrons / photons• Started from calibrated eγ candidates from egClusterCollection

(reconstructed using sliding window algorithm)• … recalculate raw cluster ET, η, φ using energy weighting of CaloCells that

make up CaloCluster• Done with period E data () for electron and photon candidates with no isEm

requirement better statistics but poor jet rejection6

Efficiencies

• EM2, EM3, EM5 Combined Efficiency Plot (MinBias stream)– Generally agrees well with public results– Dips in efficiencies in plateau more noticeable for public results– Bump present at low ET in efficiencies, significant for EM2 and less

conspicuous for higher energy thresholds– In my results there is a contribution to bump in Monte Carlo for EM2

but very little for EM3 and EM5

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Efficiencies• EM10, EM14 Combined Efficiency Plot (MinBias stream)

– No bump at these energies– Relative to EM2, EM3, EM5 turn on starts a little earlier– General shape features for EMx thresholds in terms of cluster ET

raw:• x+1.0 : ε ≈ 0.2 – 0.4 (L1Calo just able to see energy to trigger)• x+2.5 : ε > 0.9 (Getting there!)• x+5.0 : ε = 1 (Plateau of turn-on curve takes a little while to reach)• Fit Fermi function to curves as better way to describe this in future?

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Efficiencies• EM5 Turn On Curve – MBTS to JET trigger comparison

– To show that it does not matter which independent trigger is used– MBTS uses MinBias stream, JET uses JetTauEtmiss stream– Plotted without Monte Carlo– Overall shapes look very similar– JET tag and probe estimates slightly higher efficiencies at low ET but in

plateau results are similar important for physics analyses

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Bump• See a bump at low ET (also in public results) • Causes for bump were studied originally by

looking at all objects within an event (text dump) and trying to classify them

• One cluster matched to one RoI– Noise and miscalibration (dominant effect)

• Raw cluster has ET < 3 GeV than this but this is enough to make a 3 GeV RoI (Energies in L1Calo are normally rounded down but with slight miscalibrations in trigger, noise, … it is possible)

• Signals from LAr to L1Calo could add up to 500 MeV in noise but would not explain some raw clusters triggering with less than 2 GeV some other effect present? Dodgy offline reconstruction?

– Offline cluster calibration• The offline calibration produces a big difference

between the raw and calibrated energies of the cluster with calibrated energy much less than the raw energy.

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Bump• Two or more clusters matched to one RoI

– Bad matching to RoI (thought to be dominant)• One cluster with low energy matches to another one nearby

with a much higher energy artefact of trigger tower granularity and ΔR<0.15 matching requirement, get RoI ET > 3 GeV

– Offline reconstruction of clusters• One cluster from an electron and one cluster from a photon

with energy less than 3 GeV. Energies and positions are almost identical or at least very close – both objects were reconstructed from the same cluster so RoI sees enough energy to make a 3 GeV RoI Subset of Noise and miscalibration effect

– Two or more clusters combined to make RoI• 2 clusters nearby each other with very different energies add

up together so that the trigger tower sees enough energy for a 3+ GeV RoI

• Based on common features of objects in these events, an algorithm was developed to automatically classify them

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Bump• Why is there a difference between the data and Monte

Carlo for EM3 and EM5?

• For Monte Carlo, noise effect dominates which contributes to a bump in EM2

• Cluster combination and bad matching only have small effects so nothing for EM3 & EM5

• Monte Carlo (MC09) has not got an ideal response in this case, need to see if MC10 will be better

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Effect Data MCNoise & Miscal. 59.83 ± 0.35 97.61 ± 1.34Bad Matching 20.65 ± 0.18 1.20 ± 0.11Off. Recon. 3.39 ± 0.07 0.29 ± 0.05Cl. Calibration 0.13 ± 0.01 0.23 ± 0.05Cl. Combination 16.00 ± 0.15 0.67 ± 0.08

Bump• Contributions as a function of ET

raw

• Noise effect dominates in all ET bins• Comparable results for cluster

combination and bad matching• Any good ideas for y-axis title?

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Effect Data

Noise & Miscal. 59.83 ± 0.35

Bad Matching 20.65 ± 0.18

Off. Recon. 3.39 ± 0.07

Cl. Calibration 0.13 ± 0.01

Cl. Combination 16.00 ± 0.15

Bump• Asked why we see a ‘bump’ and not a ‘shoulder’• Mainly due to electron and photon reconstruction• Based on sliding window algorithm which searches for seed

clusters with at least 2.5 GeV in second layer• Fraction that trigger is higher around 1-2 GeV than 0-1 and 2-

3 GeV giving a bump

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• Why should reconstruction produce clusters with raw ET less than 2.5 GeV then?– Will need to

understand this– Papers only give

details above 2.5 GeV

Missing Trigger Events• The turn-on curves calculated for the energy thresholds

indicate that there are some candidates for which no EmTau RoI was produced

• If no energy produced then there was a lack of energy seen in the PPr many stages lead up to this so many reasons for it

• Killed trigger tower (for being too noisy/faulty electronics)• Dead trigger tower (signal lost before receivers)• BCID calculates that object out of time with LHC beam• Shower spread over many trigger towers so no single trigger

tower sees enough energy (either from early shower in Inner Detector or actually part of a jet)

• In the transition region, the summation of trigger towers was difficult so either the barrel or endcap towers were deliberately masked (again causing a lack of energy seen)

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Missing Trigger Events• η-φ efficiency map for EM3 (JET triggers) with OTX cuts for

offline clusters with raw ET > 5 GeV– Done in offline coordinates, φ shift from L1Calo coordinates– Areas with reduced efficiency are identified and problems (attempted

to be) understood many understood to some level, many not– Need to do with respect to RoI coordinates problems clearer

16Transition Region

Missing Trigger Events• η-φ efficiency map for EM3 (JET triggers) with OTX cuts for

offline clusters with raw ET > 5 GeV– Done in offline coordinates, φ shift from L1Calo coordinates– Areas with reduced efficiency are identified and problems (attempted

to be) understood many understood to some level, many not– Need to do with respect to RoI coordinates problems clearer

17Transition Region

HV ProblemHV Problem

Loose cableLAr miscabling

Know L1Calo sees less energy, not

sure why

Dead towerDead tower

Dead towerKilled tower

Results• η-φ efficiency map for EM3 (JET triggers) with/without OTX

cuts for clusters with raw ET > 5 GeV– Where OTX problem is in second layer, eγ reconstruction poor and

trigger tower efficiency drops– In other places, OTX cuts are conservative– Would prefer not to use OTX cuts what is best way to adjust this

without reducing the areas where efficiency will be very bad?

18Without OTX CutsWith OTX cuts

Next stepsFOR L1CALO MONITORING• Submit midterm today!• Migrate code to latest version of

TrigT1CaloAnalysisExamples package• Run over more recent data (period F-H/I)• Improve understanding of offline reconstruction• Work out the best way to get statistics in the future• Look at bump on TT level?• Clever things with fits of Fermi functions?• Dead material corrections• Algorithm to identify cause of missing trigger events

FOR OTHER TOPICS• Start diffractive charm physics

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