TAU/JET/E T MISS TRIGGERS IN ATLAS

1Francesca Sarri, INFN e Università di

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TAU/JET/ETAU/JET/ETTMISSMISS

TRIGGERS IN ATLASTRIGGERS IN ATLAS


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OUTLINEOUTLINE

Tau/Jet/ETMISS trigger description :

what is in the TDR and what is new.

An example of an analysis : optimization of tau and ET

MISS triggers for W at L=1031-32


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TAU/JET/ETAU/JET/ETTMISSMISS SOURCES AND SOURCES AND

INTEREST FOR PHYSICSINTEREST FOR PHYSICS• Standard Model:

– inclusive Wτν (Zττ) production – QCD.

• SM and MSSM Higgs: – 100-150 GeV SM Higgs: qqH(ττ)– A/H ττ– H+ τν (mH+ < mtop and mH+ > mtop)

• SUSY • Compositness


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The ATLAS triggerThe ATLAS trigger

Level 1 (hardware):Defines Regions of Interest (RoI).Uses Calo cells and Muon chambers with reduced granularity.e/, jet candidates.

Level 2 (software):Seeded by LVL1 RoI.Full granularity of the detectorPerforms calo-track matching

Event Filter (software):Offline-like algorithms.Refines LVL2 decisionFull event building

~200 Hz

~2 kHz

2s

10ms

1s

<75(100) kHz

Exe

cutio

n tim

e

TIER 0 mass storage

High Level Trigger


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LVL1 Trigger Rates LVL1 Trigger Rates Selection at 2x1033 cm-2 s-1 Rates (KHz)MU20 0.82MU6 0.2EM25I 12.02EM15I 4.0J200 0.23J90 0.24J65 0.2J60+xE60 0.4TAU25+xE30 2.0MU10+EM15I 0.1OTHERS (pre-Scales,calibration,…)

5.0

TOTAL 25


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HIGH LEVEL TRIGGER RATESHIGH LEVEL TRIGGER RATESSelection Physics coverage 2x1033 cm-2s-1 Rates

(Hz)

ElectronHiggs, new gauge bosons, extra dim., SUSY, W/Z, top

e25i, 2e15i ~40

Photon Higgs, SUSY, extra dim. 60i, 220i ~40

MuonHiggs, new gauge bosons, extra dim., SUSY, W/Z, top, B-Physics

m20i, 2m102m6 with mB /mJ/

~50

Jets SUSY, compositness, resonances j400, 3j165, 4j110 ~25

Jet & ETmiss SUSY, leptoquarks j70 + xE70 ~20

tau & ETmiss

Extended Higgs models (e.g. MSSM), SUSY

35 + xE45 ~5

Others pre-scales, calibration, … ~20

Total ~200

The rates for the HLT taken considering the EF performances equal to those one of the OFFLINE.


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LVL1 CALORIMETRIC SIGNAL PROCESSINGLVL1 CALORIMETRIC SIGNAL PROCESSING

TAU/JET/ETAU/JET/ETTMISSMISS triggers are calorimetric but they use triggers are calorimetric but they use

two different processorstwo different processors


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TAU TRIGGERTAU TRIGGER


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Hadronic Tau Trigger (I)Hadronic Tau Trigger (I) (ATL-COM-DAQ-2003-030)

LVL1 trigger: look at 4X4 matrix of calorimetric towers ( = 0.1 x 0.1 each trigger tower).ET threshold for the central core (EM+Had) and isolation thresholds between core and 12 external towers for e.m. and had. calorimeters.

+ track multiplicity in the RoI

second layer of EM calorimeter

LVL2 trigger: look at the shower shape in the 2nd layer of e.m. calorimeter and at the track multiplicity inside the RoI defined at LVL1.Cut on the ratio between ET contained in a 3x7 cell cluster and ET in a 7x7 cell cluster and on track multiplicity

For | |<2.5as in the TDR


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Hadronic Tau Trigger (II)Hadronic Tau Trigger (II) (ATL-COM-DAQ-2003-030)

LVL3 (Event Filter) :look at the complete event.The variables of the offline algorithms are used as an approximation of the LVL3 trigger five variables:number of reconstructed tracks, within R = 0.3 of the candidate calorimeter cluster, between 1 and 3; cut on isolation fraction, defined as the difference between the ET contained in a cone size of R=0.2 and 0.1 normalized to the total jet ET;cut on EM jet radius, an energy weighted radius calculated only in the e.m. calorimeter ;cut on EM energy fraction, defined as the fraction of the total jet energy in the e.m. calorimeter;threshold on the pT of the highest pT track.

as in the TDR


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EFFECT OF TRIGGER SELECTIONSEFFECT OF TRIGGER SELECTIONSET core EM iso HAD iso


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TAU TRIGGER EVOLUTIONTAU TRIGGER EVOLUTION

) from EMSamp2 Calo variables (more variables used than in the TDR)

Tracking(# of tracks, charge,…)

Final decision : matching of cluster and tracks, energy estimate

LVL2 : Calorimeter based approachPerform trackingand obtain

Calorimeter variables

Final decision : matching of cluster and tracks, energy estimate with energy flow

LVL2 :Tracking based approach

New:studied for Very Low

Lumi 1031 cm-2 s-1

Current approach

For the LVL1 different RoI sizes are under study (timing, resolution and efficiency,…)

Under developing an EF tracking based

algorithm.


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JET AND EJET AND ETTMISSMISS

TRIGGERTRIGGER


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• identify hadronic jets using calorimetric data;• classify them according to ET;• provide multiplicity of jets passing required threshold;• provide the coordinates of the candidates to the LVL2;• have an energy resolution as good as possible for high ET and low ET jets.

JET ELEMENT : = 0.2 x 0.2 (now only one sample in depth)

Algorithm :- 2x2 jet element cluster (0.4x0.4) to identify a jet RoI, it is a local ET maximum.- 4x4 jet element (or 3x3 or 2x2) trigger cluster to measure the jet ET.

Trigger cluster size : -big enough to have a good energy

resolution for high ET jets (containment)-not too big for low ET jets (noise and

pileup)RoI size and step size :

-spatial resolution and jet separation.

For | |<3.2

LVL1 JET TRIGGER LVL1 JET TRIGGER as in the TDR


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ROIROI

L2L2JetJet JetJet

Cone SizeCone Size

several iterations needed: several iterations needed: timing is an important timing is an important key.key.

LVL2 JET RECONSTRUCTION LVL2 JET RECONSTRUCTION LVL2 starts from LVL1 RoI information (, φ location) Iterative cone algorithm (R=0.4) to calculate weighted , φ energy center. Possible granularities : cell-based, LVL1 trigger towers,….

Jet calibration (energy scale and resolution) has an important effect on trigger efficiency.


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JETS AT THE EVENT FILTERJETS AT THE EVENT FILTER

Results of the study: Jet reconstruction is better with a higher size of RoI, Higher size of RoI requires more time, Topological clusters are faster than calorimeter towers but Towers reconstruct better pT of jets

Study of jet reconstruction at the EF : Size of Region of Interest (RoI):

16 (0.4x0.4), 32 (0.8x0.8), 64 (1.6x1.6) Different types of clusters:

topological clusters or calorimeter towers Algorithms:

Fast KT, Cone

Dijets samples with 35 GeV < PT < 1120 GeV


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EETTMISSMISS TRIGGER TRIGGER

ETMISS is a global variable.

LVL1 : Calorimeter energies summed into a map with a granularity = 0.2 x 0.2. Ex, Ey, ET, ET

MISS are computed.

ETMISS trigger is not a standalone trigger, but it will be

used in association with jet or tau trigger.

Rapidity coverage : critical for ETMISS trigger

performances.

For ||<5

Rapidity coverage

Mean value of ET

MISS

All 0.9 GeV|| < 5 5.6 GeV|| < 4 8.8 GeV|| < 3 12.5 GeV

as in the TDR

For QCD events :

trig

ger

rate

(KH

z)

ETMISS (GeV)


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LVL2 possible strategy:• Based on LVL1 Missing ET “ROI” (with scalar ET, ΣEx, ΣEy)• Based on LVL1 Jet ROIs - Use cell data for each RoI• Based on Trigger Towers: - Refine with better calibration and replace saturated

towers• For all the above, add muons

Possible Strategies for EPossible Strategies for ETTMISSMISS Trigger at Trigger at

LVL2 and EFLVL2 and EF

EF possible strategy:• Using FEB header ΣEX, ΣEY from RODs• Using full cell data.• For both of these, add muons.


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Algorithms for Tau/Jet/ETMISS triggers are still under

development : not a final decision taken.

ATLAS physics groups have started now to include trigger information in the simulations to perform analysis : a trigger part to perform a Trigger Aware Analysis has been added in the last releases of the ATLAS software.

The Tau Trigger slice is going to be added now : no analysis available with the “true” simulation of the tau trigger.

Trigger effects can be emulated : next slides will show an analysis.


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““Trigger aware analysis”Trigger aware analysis” from user perspectivefrom user perspective

Trigger Trigger optimizationoptimization and and prospectsprospects for W for W with 100 with 100 pbpb-1-1 (few weeks of data taking (few weeks of data taking at very low luminosity 10at very low luminosity 103131-10-103232 cm cm--

22ss-1-1 ) )Data samples:18 000 events W 124000 dijet events (J1-J2-J3)For topological studies ~10^8 events from fast simulation

Daniel Froidevaux and Elzbieta Richter-Was


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Why W Why W ? ? Extract signal for most abundant source of -leptons as early

as possible. This requires a performant and ETmiss trigger

from the very start! For L = 2 1033, baseline plan is to trigger on 25I + XE30 at

LVL1 (for a rate of about 2 kHz) and to raise the thresholds to 35i + xE45 at the HLT (for an output rate of about 5 Hz) .

Measurment of W / W e to confirm good understanding of trigger/reco/identification efficiencies

E/p measurement in single-prong decay for calorimeter calibration.

Assumed that trigger chain is fully operational and that the detector operates more or less as expected (especially in terms of ET

miss performance).

Expected rates for 100 pb-1

W hadron

W e Z hadron

.B (pb) 11200 17300 150030i + xE35

~ 15000 ~ 250000 ~ 1300

20i + xE25

~ 60000 ~ 560000 ~ 3500

Efficiencies of ~ 80% for the trigger and of ~ 50% for the id/reco of hadronic decays were assumed.


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Algorithm to “emulate” LVL1 Algorithm to “emulate” LVL1 triggertrigger

seed “RoI” with topo-clusters, accept if ET > 5 GeV

calculate energy in 2x2 and 4x4 towers of 0.1x0.1 (x)

noise subtraction not applied, cells with negative energy suppressed from enegy counting

energy in HAD (originaly at EM scale) multiplied by 1.25

remove overlapping “RoI” with iterative procedure, imposing separation by R > 0.3

missing energy taken from ”uncalibrated calo off-line”.


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More on LVL1-like RoI’sMore on LVL1-like RoI’sL1 towermultiplicity

multiplicity

<<> = 1.5

multiplicity<> = 0.78

Total QCD ET spectrum

signal

ET spectrum R between RoI’s

R between RoI’s


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Energy resolution for signal RoI and Energy resolution for signal RoI and threshold efficiency threshold efficiency

Threshold: 0.75 * 20 GeV90% efficient at ET

visible = 20 GeV

2x2 RoI

4x4 RoI


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Energy resolution for background RoI Energy resolution for background RoI anand d threshold efficiencythreshold efficiency

Threshold: 0.75 * 20 GeVFactor 10 rejection at ET

visible = 20 GeV

2x2 RoI

4x4 RoI

2x2 RoI


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Isolation for EMTau RoIIsolation for EMTau RoI

QCDsignal

1. ETL1otherEM/ET

L1core < 1.02. ET

L1otherHAD/ETL1core < 0.25

3. ETL1core/ET

L1tower > 0.54. ET

L1otherEM/ETL1coreEM < 1.0

5. ETL1otherHad/ET

L1coreHad < 1.0

L1core = 2x2L1tower = 4x4

Full cirles: with threshold ET

L1tower > 0.75 * 20 GeV

Isolation very loose .... Factor 5 rejection at 80% efficiency but almost no improvement if ET threshold added.


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More on EMore on ETTmissmiss : we have only off-line : we have only off-line

availableavailable

truth

off-lineAtlfast

ETmiss is calculated at EM scale, from calo only.

ETmiss, ET

MissFinal, ETTruthNonInt, ET

MissAtlfast


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LVL1 trigger: “ ET

L1tower 20 GeV Isol + ETmiss 20 GeV ”

( this means ETL1tower 0.75 * 20 GeV and isol_1+ isol_2 )

Rates: 0.02 Hz signal 2* 105 events for 100pb-1

60 Hz QCD bgd S/B ~ 0.0003

Concluding on LVL1-like selectionConcluding on LVL1-like selection

Isolation criteria rather weak. We use ET

miss from uncalibrated calo at EM scale...

L=10^31


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The LVL2 like selection:The LVL2 like selection:explore track-seeded reconstructionexplore track-seeded reconstruction

Algorithm for tauL2 : start from track with pT > 9 GeV accept if no more than 2 associated tracks in R < 0.2 and pT > 2 GeV store info on “track quality” of leading track for futher discrimination build energy from simplified Eflow (energy overestimated by 10%-20%

mostly because noise not suppressed) calo identification variables from EM2 or all EM calo Same definition for ET

MISS as at LVL1

Signal response < >

= 1.16 = 0.17

Bgd response < > = 0.86 = 0.18


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Concluding on LVL2-like selectionConcluding on LVL2-like selection

LVL2 trigger:“ET

L2tower 20 GeV + track quality + id EM2 + id all Cal + ETmissFinal 20

GeV”

Rates: 0.01 Hz signal 105 signal events “on tape”for 100pb-1 5 Hz QCD bgd S/B ~ 0.002

Loose triger selection, now we have to supress bgd in off-line analysis

L=10^31


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Off-line analysisOff-line analysis

~ 10^8 QCD events in fine pTbins

ETmiss > 60 GeV gives bgd: rejection 10^3, signal: accept

10% -> still 10^4 evt for 100pb-1, S/B ~ 0.2 without refined tau indentification

Results with only fast-sim offline, ETmiss has no instrumental tails !

~ LVL2 thresh.~ LVL2 thresh.

We start offline analysis with S/B ~ 0.002 and predicted ~10^5 signal events “on tape”Need rejection ~ 10^3 for effic ~ 50% or increase ET

miss

thresholdHow fast bgd is supressed with the off-line ET

miss threshold.


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Now we can go back to plot from page Now we can go back to plot from page 2525::

Atlfast

Off-line60 GeV


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Verify what off-line tauid rejection is possible.... since some discriminantion power already explored when accepting LVL2 (calo+tracks) candidates.

We take tauL2 candidate “on tape” (after LVL2 tauiD) and check efficiency for matching tau1P, tau3P identified with PDE-RS optimisation (one MVA technique among many)

tau1P tau3PdiscriPDERS > 0.85 68% 6.5% 46% 3.0% 0.90 50% 3.5% 23% 1.0% 0.95 40% 1.0% 4% 0.2%

signal bgd signal bgdpT = 20 – 40 GeV

Now we can go back to full-sim samplesNow we can go back to full-sim samples

After L2 track-based trigger, discrimination fairly flat as function of pT

tau1p (tau3p) ; track-based offline algorithm to identify 1-prong (3-prong) tau decay.


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SummarySummary:: LVL1 and LVL2 selection (calo+tracks) emulated for W analysis With rather soft selection ETmiss > 20 GeV + EMTauRoI > 20 GeV estimated for 10^31: 60 Hz after LVL1 5 Hz after LVL2 For off-line analysis start with S/B ~ 0.002 ~ 10^5 signal events accepted for 100pb-1 Increasing ET

MISS threshold helps in the background rejection: at 60 GeV threshold, supression 10^2-10^3 at 10% efficiency. Offline tau selection has to do the final work to extract the

signal.

Low luminosity provides unique opportunity to study low energy hadronic signatures in ATLAS (in view of SUSY) : important possibility to verify the understanding of tauID and ET

MISS reco before attacking “New Physcics”.


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BACKUP SLIDESBACKUP SLIDES


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Sistema calorimetrico di ATLAS

Tile Calorimeters

Electromagnetic Liquid Argon Calorimeters

Forward Liquid Argon Calorimeters

η=1.475 η=1.8

η=3.2

Hadronic Liquid Argon EndCap Calorimeters

EM LAr || < 3 :

Pb/LAr 24-26 X0

3 sezioni longitudinali 1.2 = 0.025 0.025 – 1% equal.Central Hadronic || < 1.7 :Fe(82%)/scintillatore(18%) 3 sezioni longitudinali 7.2 = 0.1 0.1 End Cap Hadronic 1.7 < < 3.2 :Cu/LAr – 4 sezioni longitudinali < 0.2 0.2Forward calorimeter 3 < < 4.9 :EM Cu/LAr – HAD W/LAr 3 sezioni longitudinali

EE8.1%8.1%9.41

E


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Tau Trigger RateTau Trigger Rate


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More on EMore on ETTmiss :miss : we have only off-line we have only off-line

availableavailable


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S.Levy, HCP session, July 2005


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Signal and background at 14 TeVSignal and background at 14 TeVcross-section (PYTHIA) signal ~ 10 x higher QCD bgd ~ 102-103 x higherthan in CDF. ( ERW, ATL-PHYS-2000-023)

<> = 16.6 GeV

<> = 22.6 GeV

<> = 18.4 GeV

spectrum rather softfor ET

miss, pTvis

signal

signal

signal

(ATL-PHYS-2000-023)


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Results from past studiesResults from past studies (ATLAS) (ATLAS) E/p measurements for calibration of hadronic calorimeters

C. BiscaratCOM-CAL-99-0003

Rejection 70 340 2

280Hz rates predicted after HTL at 10^33

.trigger-like: ETmiss > 35 GeV + pTjet > 20 GeVpreselection: veto iso lepton, veto iso photontau-jet selection: track with pT> 30 GeVsingle-track: veto if extra tracks pT>1 GeV in tau conenarrow-jet: calo isolation

total id rejection: 10^5

Events for 100 pb-1: | 5270 W | 3630 W | 320 QCD jets (bb)

total id effic: ~ 25%


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Off-line analysisWe don’t have enough events to continue with full-sim samples.We have move to fast-sim samples to study topological selection onlyand to estimate how much bgd suppression is possible:

~ 10^8 QCD events in fine pTbins


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Off-line analysis ~ 10^8 QCD events in fine pTbinsVetoying any other jet‘a la CDF’ gives 30% accept for signal 25% acept for bgd

We have looked at few more distribributions.... nothing obvious to optimise on...

We started offline analysis with S/B ~ 0.002 and predicted ~10^5 signal events “on tape”

Need rejection ~ 10^3 for effic ~ 50%or increase ET

miss threshold

TAU/JET/E T MISS TRIGGERS IN ATLAS

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