triggering in the atlas experiment thomas schörner-sadenius cern ep/atr desy zeuthen 15 january...

TRIGGERING IN THE ATLAS

EXPERIMENT

Thomas Schörner-SadeniusCERN EP/ATR

DESY Zeuthen

15 January 2003

DESY Zeuthen, 15 January 2003 TSS: Triggering in ATLAS 2

OVERVIEW

¶ INTRODUCTION • The Large Hadron Collider (LHC) – Why? • Physics at the LHC • The ATLAS Experiment • The ATLAS Trigger

¶ THE LEVEL1 TRIGGER (L1)

¶ THE HIGH-LEVEL TRIGGER (HLT)

¶ TRIGGER PERFOMANCE STUDIES


THE LHC - WHY?Standard-Model (SM) well confirmed, but incomplete !

LHC • Higgs bosons (SM/MSSM)• Supersymmetry• Large Extra Dimensions, Compositeness, new heavy gauge bosons• SM measurements, b physics

LEP, HERA,Tevatron …

+ SM precision measurements (QED, QCD, electroweak) -- EW symmetry breaking?-- 25 free parameters?-- Unification?-- Discrepancy at sin2eff etc?

… but openquestions:


PHYSICS AT THE LHC Ipp collisions with s = 14 TeV,L = 1034 cm-2s-1, f = 40 MHz

SM Higgs:

MSSM/SUSY:

SM Physics:

B0dK0*


PHYSICS AT THE LHC IIComparison of SM and ‘new physics’ processes

Small cross-sections for

‘new physics’processes

Understandingof SM processes

important

• Backgrounds for ‘discovery physics’: Wbb, ttbb, W/Z pairs…• Calibration, energy scale: Ze+e-,+-, J/e+e-,+-, Wjj…

At high luminosity~23 events overlaid

… for 2•1033cm-2s-1 usually only one event

… and small branching ratios (e.g. H).SM processes dominate.

Necessity of efficient trigger!


ATLAS TRIGGER MENU COVERAGE

Inclusive anddi-lepton

B physics

H

SUSY,leptoquarks

Resonances,compositeness

• Gauge boson pair production for study of anomalous couplings and behaviour of production at high energies • single and pair top production• direct Higgs production with HZZ*/WW*; associated SM Higgs production with WH, ZH, ttH• MSSM Higgs decays• Production of new gauge bosons with decays to leptons. • SUSY and leptoquark searches

• specialised, more exclusive menus

• 2EM15I at L1, 220i at L2. Also MSSM.

• High pT jets with/without ETmiss.

• High pT jets.

Triggering mostly with inclusive / di-leptons.


THE ATLAS EXPERIMENT - Length ~40 m- Diameter ~25 m- Weight ~7000 t- 108 channels (event ~2MB)

- ‘Inner (tracking) Detector’- calorimeters (energies)- muon detectors

- Barrel: solenoid around ID and toroid fields in muon system- Endcaps: toroid fields


THE ‘INNER DETECTOR’

Pixel Detector:

- 3 barrel layers - 2•4 end-discs - 140•106 channels- R=12m,z,R=~70m- || <2.5

Silicon Tracker:

- 4 barrel layers, || <1.4 - 2•9 end-discs, 1.4 < < 2.5- Area 60 m2

- 6.2•106 channels- R=16m, z,R=580m

Transition Radiation Tracker

- 0.42•106 channels- =170m per straw- || <2.5


THE CALORIMETERS

Hadronic Tile:

- 463000 scintillating tiles- 10000 PMTs- Granularity 0.1•0.1 - : <1.0, (0.8-1.7)- L=11.4 m, Rout=4.2 m

Hadronic LArEndcaps:

- steel absorbers- 4400 channels- 0.1•0.1 / 0.2•0.2- 1-5

EM LAr Accordeon:

- lead absorbers- 174000 channels- 0.025•0.025- : <2.5, <3.2

Forward LAr:

- 30000 rods of 1mm- cell size 2-5cm2 (4 rods)- : <3.1, <4.9- 1 copper, 2 tungsten

LAr Pre-Sampler

Against effects of energy losses in front

of calorimeters


THE MUON SYSTEM

Monitored Drift Tubes

- 3 cylinders at R=7, 7.5, 10m- 3 layers at z=7, 10, 14 m- 372000 tubes, 70-630 cm- space=80m, t=300ps (24-bit FADCs)

Cathode Strip Chambers

- 67000 wires- only for ||>2 in first layer- space=60m, t=7ns

Thin Gap Chambers

- 440000 channels- ~MWPCs

Resistive Plate Chambers

- 354000 channels- space=1cm- trigger signals in 1ns


THE ATLAS TRIGGER: OVERVIEWMulti-layer structure for rate reduction: 1 GHz 100 Hz.

} EF

- Full event- Best calibration- Offline algorithms- Latency ~seconds

} L1

- Hardware-based (FPGAs and ASICs)- Coarse granularity from calo/muon- 2s latency (pipelines)

} L2

- ‘Regions-of-Interest’- ‘Fast rejection’- Spec. algorithms- Latency ~10ms


OVERVIEW

¶ INTRODUCTION

¶ THE LEVEL1 TRIGGER (L1) • Overview • The Calorimeter and Muon Triggers • The CTP and the L1 Event Decision • Simulation (and Configuration)




THE LEVEL1-TRIGGERSelection based on high-pT objects from calo and muon.

Multiplicities

Regions-of-

InterestEvent decisionfor L1

Interface tofront-end

Muoncandidatesabove pT

thresholds

Interface to highertrigger levels/DAQ:objects with pT,,

Candidates forelectrons/photons,taus/hadrons,jetsabove pT thres-holds.

Energy sumsabove thresholds


THE CALORIMETER TRIGGER IComplex system with many modules to be developed.

digitisation,presumming to jet

elements with0.2•0.2 granularity

analog sums of EM/HA cells

7200 trigger towers(granularity 0.1•0.1)

cluster processor:Find e/ and /hadron

candidates in 6400trigger towers

(||<2.5)

jet/energy processor:- Find jet candidates in 30•32 jet elements for ||<3.2- Build total ET sum up to ||<4.9.


THE CALORIMETER TRIGGER II

Example: The /hadron trigger Example: The jet/energy trigger

• 2·2 jet EM+HA cluster (RoI) in 2·2 or 3·3 or 4·4 region (gives ET).

• 8 (4) (forward) jet ET thresholds.

• Total/missing ET from jets (sum of 0.2·0.2 jet elements to ·=0.4·0.2, conversion to Ex,Ey, then summation).

• Maximum of EM+HA ET in 2·2 ‘RoI’, isolation criteria (alternative core definitions?).

• Multiplicities for 8(8) e/ (/ hadron) ET thresholds.

Builds candidate objects (RoIs): electrons/photons, taus/hadrons, jets.Ideas about core definitions, isolation criteria not really finalised.


THE MUON TRIGGER

• ‘Roads’ can be defined for 6 different pT thresholds (for which multiplicity counts are delivered to the CTP).• BCID=1.5 ns.

Trigger chambers: • 3 RPC stations for ||<1.05• 3 TGC stations for 1.05<||<2.4. • 2 , layers per station (TGC 2/3)

pT information from hit coincidences in successive detector layers.

Procedure:• Put predefined ‘roads’ through all stations (width in ~ pT). • If hit coincidences in 2(3) stations muon candidate for pT threshold corresponding to ‘road’.

ATLAS quadrant in rz view

trigger chambers

precision chambers


THE MUON-TO-CTP INTERFACE208 RPC/TGC sectors deliver 1-2 RoIs combined by 16 MIOCTs.

MIBAK backplane builds RoImultiplicities for 6 pT thresholds.


THE L1 DECISIONDerived in the ‘Central Trigger Processor’ (CTP).

Multiplicitiesof objects above

pT thresholds

‘Conditions’:multiplicity

requirements

‘Items’: logicalcombinationsof ‘conditions’

L1 result as‘OR’ of all ‘items’

Inputs to HLT: L1 result and objects with pT,,.

CTP

calorimeter, muon


THE CENTRAL TRIGGER PROCESSOR

existing prototype1 9U VME module

final design~7 different modules

Combines calorimeter and muon information to L1 decision.

Lookup tables:‘conditions’

Programmabledevices: ‘items’

Dead time etc.

Combinationof ‘items’

One big FPGA

Interfaces todetectors,LHC

Input bits: multiplicities

To Level2 Number of items?


L1 SIMULATION: OVERVIEWMost developments originally for stand-alone applications.

Generation of MonteCarlo events for analysis purposes Rate/efficiency estimates Inputs for HLT tests Tests of L1 trigger hardware (~done for some compo- nents; just starting ‘slices’, configuration problem!)


L1 SIMULATION: ORGANISATION

Organisation Coordination: TSS Calorimeter trigger: London Muon trigger + MuCTPI: Tokyo, Rom, CERN CTP, RoIB, interfaces, configuration: TSS

Framework C++ Code LHCb framework Gaudi adapted to ATLAS-needs Athena (ATLAS Offline environment)

Status Complete simulation chain for calo trigger ready. Currently working on muon trigger integration. Also done: configuration code (sets up L1 trigger simulation software and hardware !) Successfully used for simulation of L1 result as input to HLT tests (important for HLT TDR).

Many contributors around the world.

Storageconcept

Specific concept for run/event-wise data persistency: StoreGate and DetectorStore for package communication: Objects are sent to predefined memory locations with ‘keys’.


L1 CONFIGURATIONBased on XML:

<TriggerThreshold name=“MU6” value=“6” bitstart=“3” bitlength=“3” etamin=“-5” …. />

<TriggerThreshold name=“JT90” value=“90” bitstart=“6” bitlength=“3” etamin=“-5” …. /> Calo and muon need to know

which multiplicity is to be delivered on which physical line.

• Simple definition of logical structures (better HTML).• Simple ‘parsing’ into instances of C++ classes.

<TriggerMenu> <TriggerItem> <AND> <TriggerCondition threshold=“MU6” multiplicity=“2” /> <TriggerCondition threshold=“JT90” multiplicity=“1” /> </AND> </TriggerItem></TriggerMenu>

Structure of L1 decision configures CTP.

Prevent from configuring logical structure that exceeds CTP’s abilities (number of inputs etc.).

Definition ofobjects to be

triggered:Trigger Menu

Def. of objectsfor which calo andmuon deliver multi-

plicity counts:thresholds

Description of hardware


<TriggerMenu> <TriggerItem> <AND> <TriggerCondition threshold=“MU6” multiplicity=“2” /> <TriggerCondition threshold=“JT90” multiplicity=“1” /> </AND> </TriggerItem></TriggerMenu>

L1 CONFIGURATION

Implementationin C++ classes

Logical tree structureof XML tags

Definitions oftrigger menu

“Parsing”


PROBLEM: HARDWARE CONFIGURATION

Idea: Runsimulation against

L1 hardware

Tests of hardware and software systems. Needs common input data. Needs unified configuration for simulation software and hardware.

Status First lookup table files successfully loaded. First (simple) VHDL code written. Translating and loading dangerous (damaging FPGA).

Have to generate lookup table files VHDL code for FPGAs. Have to be generated ‘on the fly’, from running configuration code.

Problem

TBV[0] = MIO[0] & MIO[1] & !MIO[2] & maskff[0] & !LOCADT[0] & !GLOBDT1[0] & !GLOBDT2[0] & !VETO


OVERVIEW

¶ INTRODUCTION


¶ THE HIGH-LEVEL TRIGGER (HLT) • Design of HLT and Selection Software • Selection Principles and Step-wise Procedure • HLT Decision • HLT Configuration



THE HIGH-LEVEL TRIGGER (HLT)Good example for solid software process.


HLT: DESIGN OVERVIEW

EventFilter (EF)

ClassificationSelection

~102 Hz

Hardware Implementation

LEVEL 2 (LVL2)

~1 kHzLevel1 (L1)

~102 kHz

Read-OutSubsystemModules

High-Level Trigger: Design

HIGH-LEVEL TRIGGER (HLT)

Offline

Simplified subsystem view

Event- Filter


HLT: SELECTION SOFTWARE

HLTSSW

Steering Monitoring Service

1..*

MetaData Service

1..*ROBDataCollector

DataManager HLTAlgorithms

Processing Task

EventDataModel

LVL2PU Application

<<import>>

Offline EventDataModel

Offline Reconstruction

Algorithms

<<import>>

StoreGateAthena/Gaudi

<<import>><<import>>

Interface

Dependency

Package

EventFilter

Level2

PESA Core Software

PESA Algorithms

Offline Architecture & Core Software

Offline Reconstruction

Running in Level2 Processing Units (L2PU)+EF.

Set-up by HLT configuration


HLT: SELECTION PRINCIPLES

‘Regions-of-Interest’ (RoI)

Step-wiseprocess and

‘Fast rejection’

Flexible L2/EF boundary

Use of offlinereconstruction

algorithms

PESA = ‘Physics- and Event Selection Architecture’

¶ Selection/Rejection starts with localized L1 objects (‘Regions-of-Interest’) limited data amount.¶ Then step-wise more and more correlated data from muon/calo and other detectors (e.g. cluster shapes, tracks for e/ separation).

¶ After every step: Check whether selection criteria still fulfilled optimal use of HLT processors.

¶ flexible distribution of load and use of resources.

¶ Use of common software architecture + algorithms understanding of trigger rates/efficiencies. ¶ Use of common ‘event data model’ (should be trivial ;-) ).


HLT DECISION (LEVEL2 AND EF)Overview of step-wise procedure with ‘dummy’ example Ze+e-

After every step: test + possibly rejection.

‘Physics Signature’: Ze+e- withpT>30 GeV

‘IntermediateSignature’


L1 result: 2 EM clusters

with pT>20 GeV


decision part algorithmic part


OVERVIEW

¶ INTRODUCTION



¶ TRIGGER PERFOMANCE STUDIES • Selection Planning • L1 Performance • L2 / HLT / Combined Performance


TRÍGGER STUDIES

Mostly done using full GEANT simulation of ATLAS detector and of trigger logic. Usually not full events used, but only parts (QCD jets, H processes etc.) Full dijet event ~1000s.

For jets and ETmiss studies only with fast parametrised simulation. Fast L1 trigger simulation for some purposes (large samples etc.).

Most studies have large uncertainties: LO MCs, computing time per event, costs, classification. Should be reduced with new L1 simulation + HLT software for HLT technical design report (5/2003).

Only rigidly done for L1+L2. EF should be ~100% efficient.Most studies from 1998 Trigger Performance Status Report.


LEVEL1 SELECTION: PLANNING

Selection 2·1033 cm-2s-1 1034 cm-2s-1

MU6(20?) (20) 23 (3?) 4.0

2MU6 --- (1?) 1.0

EM25i (30) 11 22.0

2EM15i (20) 2 5.0

J200 (290) 0.2 0.2

3J90 (130) 0.2 0.2

4J65 (90) 0.2 0.2

J60+xE60 (100) 0.4 0.5

TAU25+xE30 2.0 1.0

MU10+EM15i --- 0.4

others 5.0 5.0

total ~ 44 (25?) ~ 40

Rates in kHz; thresholds define 95% efficiencies.

No safety factors included (LO MonteCarlos etc.).

Muon triggerscontribute to

(di)lepton signatures.

Electron/photontriggers strong;

large backgrounds.

Low rate for jettriggers; difficult to

control backgrounds

New studies assume much reduced rate (~kHz).


HLT SELECTION: PLANNING

Selection 2·1033 cm-2s-1 1034 cm-2s-1 Rates (Hz, low lumi)

Electron e25i, 2e15i e30i, 2e20i ~40

Photon 60i, 220i 60i, 220i ~40

Muon 20, 210 20, 210 ~40

Jets j400, 3j165, 4j110 j590, 3j260, 4j150 ~25

jet+Etmiss j70+xE70 j100+xE100 ~20

tau+Etmiss 35+xE45 60+xE60 ~5

B physics 26 with mB/mJ/ 26 with mB ~20

Total ~200

Optimization of efficiency/rejection and CPU load / data volume.

Rate·Event size (1.6MB) needed band widths / storage volumeRate·CPU time number of processors (500?)


threshold ~30 GeV

Inclusive e/ triggerrate for high lumi

with/without isolation.

L1 e/ TRIGGER

SelectionThreshold[ET in GeV]

Rate[kHz]

1 e/ 17 / 26 11 / 21.5

2 e/ 12 / 15 1.4 / 5.2

Total rate 13 / 27

threshold ~20 GeV

e/ pair trigger ratefor high lumi with/without isolation.

EM isolation for e/jets

Tolerable rate dictates ET thresholds. Isolation criteria vital for rate control.


L1 /hadron TRIGGER

25 GeV threshold, but no single tau / hadron trigger planned for (hadr. decays HA calibration?).

Selection EM Isolation Rate

20 GeV 7 GeV 16 kHz

40 GeV 10 GeV 2.1 kHz

25 GeV+ETmiss 1-2 kHz

L1 tau/hadron efficiency as function of tau pT.

Problems:- Core definition (2•1,2•2,2•2+4•4 etc.)- isolation threshold definition.

For Z, W with additional lepton or ETmiss.


L1 JET TRIGGER: 1,3,4 JETS

Efficiency to flag a jet RoI at high lumi.How low can you go?

Type Low lumi High lumi

1 jet ET>180GeV ET>290GeV

3 jets ET>75GeV ET>130GeV

4 jets ET>55GeV ET>90GeV

Rate assigment defines thresholds and jet windows.

Performance depends on- window for ET determination,- jet element thresholds, - declustering procedure.

Njet=1

Njet=4180 GeV

55 GeV

Jet trigger rates (low lumi), assign 200Hz for 1,3,4 jet processes


L1 MUON TRIGGER PERFORMANCE

TGC efficiency for different thresholdssharp rise, good .

Type Barrel Endcap All Non-pp

6 GeV 10 13.2 23.2 >0.4

20 GeV 1 2.8 3.8 >0.026

Mainly want to trigger W/Z. Semilept.b,c is background (L2).

Fake rates from backgroundparticles about 10Hz/cm2? Newmuon studies assume less rate.

Muon trigger rates overview [kHz]


HLT: CALORIMETER TRIGGERS

Second sampling(0.025•0.025):

24X0

Back sampling(0.05•0.025): 2-12X0

• Main backgrounds in L1 sample: 0 and narrow hadronic jets.• Algorithms mainly based on ET, hadronic leakage, lateral shower shape and sub-structures in cluster (use of track veto possible).

Variables:- EM-ET in 3•7 cells E=wgl(wps*Eps+E1+E2+E3)- HA-ET

- lateral shape in 2. sampling: R = E3*7 / E7*7 >0.9 for e- lateral shape in 1. Sampling for narrow hadr. showers or jets with small Ehad

- Cuts tuned for >0.95 with large jet rejections

First sampling with finer cell granularity for 0 rejection

(0.003•0.1): 6X0


HLT TRIGGER: 40(60)i, 220i

2 peaks from0 / narrowhadronic shower

from jet BG(first sampling)

1 peak fromreal

Validation of L1 ET,, information (granularity, calibration) sharper cuts on ET + cluster shape analysis.

Efficiency for 20 GeV photons at high lumi.

Single photon efficiency > 90% (diphoton triggers >80%; f(ET)).

100 (600) Hz on L2 for triggers.Jet rejection of ~3000.


HLT ELECTRON: e25(30)i, 2e15(20)iSimilar to photons, but looser cuts. Track search in inner detector (reject neutrals, cuts on pT, shower shapes etc.).

L2 e/ triggerefficiency for

30 GeV electrons,(high lumi).

Electron triggers: rate of 100 (600) Hz after L2 selection.

Service crack betweenbarrel and endcap

Efficiency afterL1+L2 for single30GeV electrons

at high lumi.

Crack betweenbarrel halves


HLT JET TRIGGER: 1,3,4 JETS

L2 jet efficiency for50,100,150 GeV asfunction of threshold(cone, threshold fromtrigger jet).

L2/L1 reduction forlow lumi at 90(95)%

L2(L1) 1-jet efficiency(2 at 80 GeV).

Hard to suppress BG without inv. Mass cuts. Sum cells to 0.1•0.1; run jet algo on 1.0•1.0 window around RoI.

Type L1 [kHz] L2 [kHz]

J180 0.2 0.12

3J75 0.2 0.08

4J50 0.2 0.04 Rates for =95(90)% L1(L2).

Algorithms? Cell noise cut?Threshold definition? Window size?

L1 TT cut 1 GeV


• Get pT(MDTs), extrapolate track• Reduce L1 rate by ~100 (harder

cuts or more subdetectors)• Reduce BG from b-decays by factor 10 with high W/Z- 95%.

HLT MUON TRIGGER: 20, 210

L2 trigger algorithmefficiency in barrelfor two thresholds.

Efficiency >95% with r.m.s momentum resolution of 1-2 GeV (7% for 6 GeV)).

--- W,Z signal • b,c BG

Also ET criteriain calo cones

200(300) Hz L2 trigger rate for signatures (without B triggers with

exclusive requirements on masses).

Calo discriminatesW/Z vs. b,c.


SUMMARY

LHC/ATLAS• Necessary to complete Standard Model and to find extensions (SUSY etc.).• High event rates + small new physics cross-sections.• Multi-layer structure: Reduction 1 GHz 100 Hz.

L1 Trigger• Hardware-based with calo/muon inputs.• L1 decision in Central Trigger Processor (CTP).•(Offline) configuration and simulation ~ready.

HLT• HLT: Two software levels (Level2 and EventFilter)• HLT principles: Regions-of-Interest and step-wise decision procedure (‘fast rejection’).

Performance• Detailed studies for all trigger types based on old simulations (basically results from 1998, only L2). • New studies to be done for HLT TDR (5/2003) with new HLT selection and L1 simulation SW.• Large uncertainties (physics+computing)


AN ATLAS EVENT

H ZZ* e+e-+-

(mH = 130 GeV)

at high luminosity (1034 cm-2s-1)

The ‘hard’ Higgs event is overlaid with ~23‘minimum-bias’ and background events.


Backup Material


L1 SIMULATION: SUBSYSTEMSSimulation procedure; simplified view (only one storage instance).

RandomInputsData Files

Input zu HLT/DataFlow

ThresholdsTriggermenu

Hardware

Geant3 cells, test vectors


menu tableof step N

HLT CONFIGURATION PRINCIPLE

Comps. CN-2

at step N-2

Signature SN

at step N

Signature SN-1

at step N-1Comps. CN-1

at step N-1

Signature SN-2

at step N-2

Comps. CN

at step NSignature sN

at step NComps. cN

at step N

Comps. cN-1

at step N-1Signature sN-1

at step N-1menu tableof step N-1

menu tableof step N-2

algo algo

algo

sequence table of step N

sequence table of step N-1

sequence table of step N-2

Recursive algorithms derives all ‘lower-level’ signatures (=intermediate decisions) using top-level (physics) signatures (XML definition) and set of implemented sequences (algorithms+in/outputs).

algo

algo

L1 RoIs

L1 RoIs


HLT CONFIGURATION IMPLEMENTATION

Status

Well-tested software, used in many HLT applications. Currently: Development of ‘real-life’ algorithms which run on inputs of calo trigger simulation (HLT TDR!).

Code

Recursive algorithm implemented in C++ code in Athena framework (more complex than shown). Uses XML for definition of ‘Physics signatures und sequences. Embedded in HLT selection software (PESA steering code).

• One signature and one sequence

per step and ‘Physics Signatur’.

• One ‘Menu Table’ and one ‘Sequence Table’ per step.


HLT: CONFIGURATION‘Top-down’ approach: • Input 1: Signature ‘2e30i’

• Input 2: all known sequences (Algos+In/Outputs)

List of all ‘PhysicsSignatures’ = Trigger Menu e30iAlgo-1e30

3: Then next-lower signature clear: 2-times e30: 2e30

1: ‘Physics Signature’

and constituents(2-times e30i) 2: Sequence:

Outputs,Algorithm,

Inputs

4: Procedure recursively down to2EM20i signature.One signature and one sequence per step.5: Signatures of all

‘Physics Signatures’in one step:

Menu Table

6: Sequences of all ‘Physics Signatures’

in one step:

Sequence Table

triggering in the atlas experiment thomas schörner-sadenius cern ep/atr desy zeuthen 15 january...

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