LHC Days in Split 10 Oct. 2002 Claudia-Elisabeth Wulz Institute for High Energy Physics, Vienna The...

LHC Days in Split10 Oct. 2002

Claudia-Elisabeth WulzInstitute for High Energy Physics, Vienna

The CMS Trigger

C.-E. Wulz 2 Split, Oct. 2002

Cross Sections and Rates

Cross sections for different processes vary by many orders of magnitude

• inelastic: 109 Hz• W l: 100 Hz• tt: 10 Hz• Higgs (100 GeV): 0.1 Hz• Higgs (600 GeV): 0.01 Hz

Required selectivity 1 : 10 10 - 11

TriggerTrigger

-

C.-E. Wulz


Event typeProperties of the measured trigger objects

Event accepted?T( ) YES

NO

Depends on

Trigger objectsTrigger objects (candidates): e/, , hadronic jets,-Jets, missing energy, total energy

Trigger conditions:Trigger conditions: according to physics and technical priorities

Successive steps

Principle of Triggering


CMS Detector (Compact Muon Solenoid)


Trigger Levels in CMS

Level-1 TriggerMacrogranular information from calorimters and muon system (e, , Jets, ET

missing)Threshold and topology conditions possibleLatency: 3.2 sInput rate: 40 MHzOutput rate: up to 100 kHzCustom designed electronics system

High Level Trigger (several steps)More precise information from calorimeters, muon system, pixel detector and trackerThreshold, topology, mass, … criteria possible as well as matching with other detectors Latency: between 10 ms and 1 sInput rate: up to 100 kHzOuput (data acquisition) rate: approx. 100 HzIndustral processors and switching network


Conventional Concept with 3 Steps

Investment inspecialized processors,control


Investment inband width andcommercial components

Advantages:Fewer components, scalable

CMS Concept with 2 Steps


Evolution of Trigger Requirements

ATLAS/CMS:ATLAS/CMS: Rather high rates and large event sizes

Interaction rates:Interaction rates: ~ Factor 1000 larger than at LEP,~ Factor 10 larger than at Tevatron

8 Split, Oct. 2002


Level-1 TriggerLevel-1 Trigger

Only calorimeters and muon system involvedOnly calorimeters and muon system involvedReason: no complex pattern recognition as in tracker required (appr. 1000 tracks at 1034 cm-2s-1 luminosity), lower data volumeTrigger is based on:Trigger is based on:Cluster search in the calorimetersTrack search in muon system


Architecture of the Level-1 Trigger

GLOBAL TRIGGER

Local CalorimeterTrigger

Local DT Trigger

Local CSCTrigger

Regional CSCTrigger

RPCTrigger

CSC Hits RPC HitsDT HitsCalorimetercell energies

Global CalorimeterTrigger Global Muon Trigger

Regional DTTrigger

Regional CalorimeterTrigger


Strategy of the Level-1 TriggerLocalLocal

• Energy measurement in single calorimeter cells or groups of cells (towers) • Determination of hits or track segments in muon detectors

RegionalRegional• Identification of particle signature• Measurement of pT/ET (e/, , hadron jets, -jets)• Determination of location coordinates (,) and quality

GlobalGlobal• Sorting of candidates by pT/ET, quality and retaining of the best 4 of each type together with location and quality information• Determination of ET, HT, ET

missing, Njets for different thresholds and ranges• Algorithm logic

• thresholds (pT/ET, NJets)• geometric correlations

- e.g. back-to-back events, forward tagging jets- more detailed topological requirements optional- location information for HLT- diagnostics


Level-1 Calorimeter Trigger

GoalsGoalsIdentify electron / photon candidatesIdentify electron / photon candidatesIdentify jet / Identify jet / -jet candidates-jet candidatesMeasure transverse energies (objects, sums, missing EMeasure transverse energies (objects, sums, missing ETT))

Measure locationMeasure locationProvide MIP/isolation information to muon triggerProvide MIP/isolation information to muon trigger


Local / Regional Electron/Photon Trigger

Trigger primitive generator (local) Trigger primitive generator (local) Flag max of 4 combinations Flag max of 4 combinations

(“Fine Grain Bit”)(“Fine Grain Bit”)

Hit +max of > EHit +max of > ETT threshold threshold

Regional calorimeter trigger Regional calorimeter trigger

EETT cut cut

Longitundinal cut hadr./electromagn. ELongitundinal cut hadr./electromagn. ET T // < 0.05 < 0.05

Hadronic and electromagnetic isolation < 2 GeV Hadronic and electromagnetic isolation < 2 GeV

One of < 1 GeVOne of < 1 GeV

Electron / photonElectron / photon

JetJet

e/e/


Typical e/ Level-1 Rates and Efficiencies

• Single isolated e/ rate at 25 GeV threshold: 1.9 kHz • 95% efficiency at 31 GeV


Jet / Trigger

{

Jet EJet ETT is obtained from energy sum of 3 x 3 regions - is obtained from energy sum of 3 x 3 regions -

sliding window technique, seamless coverage up to |sliding window technique, seamless coverage up to || < 5| < 5 Up to |Up to || < 3 (HCAL barrel and endcap) the regions are 4 x 4 trigger towers| < 3 (HCAL barrel and endcap) the regions are 4 x 4 trigger towers

Narrow jets are tagged as -jets in tracker acceptance (|| < 2.5) if ET deposit matches any of these patterns


Typical Level-1 Jet Rates and Efficiencies

• Single jet rate at 120 GeV threshold: 2.2 kHz, 95% efficiency at 143 GeV• Dijet rate at 90 GeV: 2.1 kHz 95% efficiency at 113 GeV• Single -jet rate at 80 GeV threshold: 6.1 kHz



HT Trigger

HT, which is the sum of scalar ET of all high ET objects in the event is more useful than total scalar ET for the discovery or study of heavy particles (SUSY sparticles, top):

• Total scalar ET integrates too much noise and is not easily calibrated– At Level-1 tower-by-tower ET

calibration is not available• However, jet calibration is

available as f(ET, , )• Implemented in Global

Calorimeter Trigger

• Rate with cutoff at 400 GeV: 0.7 kHz, 95% efficiency at 470 GeV


Muon Trigger Detectors

Drift Tube Chambers and Cathode Strip Chambers are used for precision measurements and for triggering.

Resistive Plate Chambers (RPC’s) are dedicated trigger chambers.


Cathode StripChambers

Local Muon Trigger

6 hit stripsform track segment

Vector of 4 hit cells

Correlator combines vectors to track segment

Comparators allow resolution of 1/2 strip width

Superlayer

Station

Drift TubeChambers


Regional DT/CSC Muon Trigger (Track Finder)

Trigger relies on track segments pointing to the vertex and correlation of Trigger relies on track segments pointing to the vertex and correlation of several detector planesseveral detector planes

• Tracks with small pT often do not point to the vertex (multiple scattering, magnetic deflection)• Tracks from decays and punchthrough do not point to vertex in general• Punchthrough and sailthrough particles seldom transverse all muon detector planes


Regional DT/CSC Muon Trigger (Track Finder)

Drift Tube Trigger(CSC Trigger similar)

Track Segment and direction of extrapolation

Bendingplane

Longitudinalplane


Regional RPC Muon Trigger

RPC-Trigger is based on strip hits matched to precalculated patterns according to pT and charge.

For improved noise reduction algorithm requiring conincidence of at least 4/6 hit planes has been designed. Number of patterns is high. FPGA solution (previously ASICs) seems feasible, but currently expensive. Solutions to reduce number of patterns under study.

4/4

3/4High

pT

LowpT

3/4

4/4


Global Muon TriggerDR/CSC/RPC: combined in Global Muon TriggerDR/CSC/RPC: combined in Global Muon Trigger

Optimized algorithm (no simple AND/OR) with respect to• efficiency• rates• ghost suppression

-> Make use of geometry + quality


|| < 2.1Trigger rates in kHz

L1 Single & Di-Muon Trigger Rates

20, 5;5W =82.3 %Z =99.7 %Bs=15.1 %

25, 4;4W =74.2 %Z =99.5 %Bs=18.4 %

14, -;-W =89.6 %Z =99.8 %Bs=27.1 %

L = 1034cm-2s-1L = 2x1033cm-2s-1

working points compatible with current L1 pT binning

18, 8;8W =84.9 %Z =99.7 %Bs= 7.2 %


Global/Central Trigger within ATLAS and CMS

Thresholds already set in calorimeters and muon system. The Central Trigger Processor receives object multiplicities. It does not receive location information, therefore topological conditions are impossible. Separate RoI electronics for the Level-2 Trigger is necessary.

Thresolds set in Global Trigger. The processor receives objects with location information, therefore topological conditions are possible. Special HLT algorithms or lower thresholds can be used for selected event categories. Sorting needs some time, however.

Algorithmbits

Algorithmbits


Global Trigger

The trigger decisiontrigger decision is taken according to similar criteria as in data analysis:

• Logic combinations of trigger objects sent by the Global Calorimeter Trigger and the Global Muon Trigger Best 4 isolated electrons/photons ET, , Best 4 non-isolated electrons/photons ET, , Best 4 jets in forward regions ET, , Best 4 jets in central region ET, , Best 4 -Jets ET, , Total ET ET

Total ET of all good jets HT

Missing ET ETmissing, (ET

missing) 12 jet multiplicities Njets (different ET thresholds and -regions) Best 4 muons pT, charge, , , quality, MIP, isolation

• Thresholds (pT, ET, NJets)

• Optional topological and other conditions (geometry, isolation, charge, quality)


Algorithm Logic in Global Trigger

Logical CombinationsObject Conditions

128 flexible parallel running algorithms implemented in FPGA’s.Trigger decision (Level-1-Accept) is a function of the 128 trigger algorithm bits (for physics). 64 more technical algorithms possible.

eis.(1)

eis.(2)

ET(1) > ET(1)threshold

ET(2) > ET(2)threshold

0o ≤ φ(1) < 360o

0o ≤ φ(2) < 360o

170o ≤ |φ(1) - φ(2)| < 190o

+(1)

μ-(2)

pT(1) > pT(1)threshold

pT(2) > pT(2)threshold

0o ≤ φ(1) < 360o

0o ≤ φ(2) < 360o

170o ≤ |φ(1) - φ(2)| < 190o

ISO(1) = 1, ISO(2) = 1MIP(1) = 1, MIP(2) = 1SGN (1) = 1, SGN(2) = -1

ETmissing

OR

Particle Condition formissing ET

Particle Conditions for muons

Particle Conditions for isolated electrons

ET(eis.) > ET(eis.)threshold pT(μ) > pT(μ)thresholdET

missing > ETthreshold

OR

ALGORITHM AND-OR

ANDAND

eis .

ETmiss ing

eis . μ


Bs -> : Example of Topological Trigger

similar.

Can ask foropposite charges in addition.

- distributions


Bs -> : Example of Topological Trigger

Topological conditions: < 1.5, < 2 rad, opposite muon charges

Gain by topological conditions and requiring no threshold on second muon with respect to working point 20; 5,5: 1 kHz rate, 7.8%efficiency (15.1% without, 22.9% with cuts).


High Level Trigger Goals

•Validate Level-1 decisionValidate Level-1 decision

• Refine ERefine ETT/p/pTT thresholds thresholds

• Refine measurement of position and other parametersRefine measurement of position and other parameters

• Reject backgroundsReject backgrounds

• Perform first physics selectionPerform first physics selection

Detailed algorithms: see talks of A. Nikitenko (e/,jets), N. Neumeister () and other talks related to CMS physics and wait for DAQ/HLT TDR due Dec. 2002.


High Level Trigger Challenges

Rate reductionRate reductionDesign input rate: 100 kHz (50 kHz at startup with luminosity 2x1033 cm-2s-1), i.e. 1 event every 10 s. Safety factor of 3: 33 kHz (16.5 kHz).Output rate to tape: order of 100 Hz Reduction factor: 1:1000Example of allocation of input bandwidth to four categories of physics objects plus service triggers (1 or 0.5 kHz):- electrons/photons (8 or 4 kHz)- muons (8 or 4 kHz)- -jets (8 or 4 kHz)- jets + combined channels (8 or 4 kHz)

AlgorithmsAlgorithmsThe entire HLT is implemented in a processor farm. Algorithms can almost be as sophisticated as in the off-line analysis. In principle continuum of steps possible. Current practice: level-2 (calo + muons), level-2.5 (pixels), level-3 (tracker), full reconstruction.


High Level Trigger and DAQ ChallengesProcessing timeProcessing timeEstimated processing time: up to 1 s for certain events, average 50 msAbout 1000 processors needed.

Interconnection of processors and frontendInterconnection of processors and frontendFrontend has O(1000) modules -> necessity for large switching network.

BandwidthBandwidth Average event size 1 MB -> For maximum L1 rate need 100 GByte/s capacity.


Conclusions• CMS has designed a Trigger capable of fulfilling physics and technical requirements at LHC. • The Trigger consists of 2 distinct levels. Level-1 is custom designed, the HLT is implemented with industrial components.• Prototypes of many Level-1 electronics boards exist.• Integration and synchronization tests are scheduled for 2003/2004.• The HLT/DAQ Technical Design Report is finalized and due to be ready at the end of 2002.

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AcknowledgmentsAcknowledgments - my colleagues in CMS and at HEPHY Vienna, especially P. Chumney, my colleagues in CMS and at HEPHY Vienna, especially P. Chumney, J. Erö, S. Dasu, N. Neumeister, H. Sakulin, W. Smith, G. Wrochna, J. Erö, S. Dasu, N. Neumeister, H. Sakulin, W. Smith, G. Wrochna, A. Taurok.A. Taurok.

- to the Organizing Committee of LHC Days in Split for the invitation and to the Organizing Committee of LHC Days in Split for the invitation and the enjoyable conference.the enjoyable conference.

LHC Days in Split 10 Oct. 2002 Claudia-Elisabeth Wulz Institute for High Energy Physics, Vienna The...

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