lhc days in split 10 oct. 2002 claudia-elisabeth wulz institute for high energy physics, vienna the...
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LHC Days in Split10 Oct. 2002
Claudia-Elisabeth WulzInstitute for High Energy Physics, Vienna
The CMS Trigger
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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
-
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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
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CMS Detector (Compact Muon Solenoid)
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Triggerstufen in CMS
Level-1 TriggerMakrogranulare Information aus Kalorimetern und Müonsystem (e, , Jets, ET
missing)Schwellwert- und Topologiebedingungen möglichEntscheidungszeit: 3,2 sEingangsrate: 40 MHz Ausgangsrate: bis zu 100 kHzSpeziell entwickelte Elektronik
High Level Trigger (mehrere Stufen)Genauere Informationen aus Kalorimetern, Müonsystem und TrackerSchwellwert-, Topologie-, Massenbedingungen u.a. sowie Vergleiche mit anderen Detektoren möglichEntscheidungszeit: zwischen 10 ms und 1 sEingangsrate: bis zu 100 kHzAusgangsrate (Datenakquisition): ca. 100 HzIndustrielle Prozessoren und Switching-Netzwerk
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Conventional Concept with 3 Steps
Investment inspecialized processors,control
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CMS Concept with 2 Steps
Investment inband width andcommercial components
Advantages:Fewer components, scalable
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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
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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
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Architecture of the Level-1 Trigger
GLOBALER TRIGGER
LokalerKalorimetertrigger
LokalerDT-Trigger
LokalerCSC-Trigger
Regionaler CSC-Trigger
RPCTrigger
CSCHits
RPCHits
DTHits
Kalorimeter-Energie
Globaler Kalorimetertrigger Globaler Müontrigger
Regionaler DT-Trigger
Regionaler Kalorimetertrigger
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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
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Level-1 Calorimeter Trigger
GoalsGoalsIdentify electron / photon candidatesIdentify electron / photon candidatesIdentify jet / Identify jet / -jet candidates-jet candidatesMeasure transverse energies Measure transverse energies
(objects, sums, missing E(objects, sums, missing ETT))
Measure locationMeasure locationProvide MIP/isolation information to Provide MIP/isolation information to
muon triggermuon trigger
JetJet
e/e/
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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
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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
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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
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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.
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Cathode StripChambers
Drift TubeChambers
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
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Regional DT/CSC Muon Trigger (Track Finder)
Trigger relies on track segments Trigger relies on track segments pointing to the vertex and pointing to the vertex and correlation of several detector correlation of several detector planesplanes• Spuren mit kleinem pSpuren mit kleinem pTT zeigen nicht zeigen nicht zum Vertex (Vielfachstreuung,zum Vertex (Vielfachstreuung, Ablenkung im Magnetfeld)Ablenkung im Magnetfeld)• Spuren aus Zerfällen undSpuren aus Zerfällen und Punchthrough zeigen meist Punchthrough zeigen meist auch nicht zum Vertexauch nicht zum Vertex• Punchthrough / Sailthrough-TeilchenPunchthrough / Sailthrough-Teilchen durchqueren selten mehreredurchqueren selten mehrere Detektorebenen Detektorebenen
Drift Tube Trigger(CSC Trigger similar)
ETA track Finder!!
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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
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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
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L1 single & di-muon trigger rates
20, 6;6W =82.3 %Z =99.6 %Bs= 9.9 %
25, 5;5W =74.1 %Z =99.5 %Bs=14.3 %
12, 8;8W =91.4 %Z =99.7 %Bs=14.5 %
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
|| < 2.1Trigger rates in kHz 100 kHz DAQ 8 kHz for
50 kHz DAQ4 kHz for
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Global Trigger
Physics requirementsPhysics requirements
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)
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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
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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.
Algorithm-bits
Algorithmand
input bits
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Standardmodell-HiggsDas Standardmodell beschreibt bis jetzt die Natur sehr gut, es hat aber einige theoretische Unzulänglichkeiten, darunter:• keine echte Vereinigung aller Kräfte (W aus Experiment, keine Gravitation etc.)• Problem der Massen nicht gelöst, nur auf Higgsmechanismus verschoben • Natürlichkeit: Strahlungskorrekturen zur Higgsmasse der O(mH)
Bei LEP (√s ≤ 209 GeV) wurden mögliche Higgskandidaten gefunden. Offizielles Resultat:
mH > 114.1 GeV
Suchstrategie bei LHC je nach Higgsmasse: 80 GeV < mH < 140 GeV H -> , H -> bb130 GeV < mH < 700 GeV H -> ZZ(*) -> 4 l (l = e,)500 GeV < mH < 1000 GeV H -> ZZ -> 2 l + 2 Jets500 GeV < mH < 1000 GeV H -> ZZ -> 2 l + 2 800 GeV < mH < 1000 GeV H -> WW-> l + + Jets800 GeV < mH < 1000 GeV H -> ZZ-> 2 l + 2 Jets
-
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H -
mmHH = 130 GeV = 130 GeV
HiggssignalHiggssignal
Ere
ign
isse
/ 5
00
MeV
fü
r 10
0 fb
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MeV
fü
r 10
0 fb
-1-1
mm
Analyse-Ereignisselektion:2 isolierte elektromagnetische Cluster, keine passenden Spuren im Tracker
Mögliche L1-Triggerselektion:2 isolierte “e/”
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H -> ZZ(*) - 4 Leptonen
Ere
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/ 2
Ge
VE
reig
nis
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2 G
eV
m(4m(4ll) / GeV) / GeV
Mögliche L1-Triggerselektion:2 oder mehr isolierte “e/” oder
mmHH = 150 GeV = 150 GeV
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H - Leptonen, Neutrinos, Jets
mmHH = 800 GeV = 800 GeV m(2m(2ll, 2 Jets) / GeV, 2 Jets) / GeV
Ere
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/ 2
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GeV
Ere
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/ 2
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GeV
SignalSignalUntergrundUntergrund
Mögliche L1-Triggerselektion:2 “e/” oder 2 1 oder 2 Jets
Andere Kanäle: 1 oder mehr Leptonen, fehlende Energie, Jets
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H -> WW -> l + lfür mH ~ 2mW
Für mH = 170 GeV ist das Verzweigungsverhältnis ca. 100 mal größer als für H->ZZ*->4l. Durch Ausnützung von W+W- -Spinkorrelationen kann man “irreduziblen” Untergrund unterdrücken. Man sucht nach l+l- - Paaren mit kleinem Öff-nungswinkel.
Mögliche L1-Triggerselektion:2 “e/” oder 2 Option: || < 450
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Supersymmetrische Higgs-Teilchen
Im minimalen supersymmetrischen Standardmodell (MSSM) gibt es 5 Higgs-Bosonen: h0, H0, A0 and H±. Man braucht 2 Parameter zur Bestimmung der Eigenschaften: mA, tan. Bei großem mA sind die Kopplungen des h0 ähnlich wie im SM. Die Kopplungen von A und H an Quarks mit Ladung 1/3 und Leptonen sind für großes tanerhöht. A koppelt nicht an WW, ZZ. Kopplungen von H an WW und ZZ für große mA und tansind unterdrückt. Die folgenden Zerfallskanäle sind wie für das SM-Higgs zu behandeln:h, A -> (für mA < 2 mt wegen des Verzweigungsverhältnisses), h -> bbh, H -> ZZ* (kein H -> ZZ bei großer Masse, da Verzw.verh. zu klein)Die folgenden Zerfallskanäle öffnen sich:H, A -> (-Kanäle im Vergleich zum SM wichtig für große tan)A -> tt; (H, A -> hh; A -> Zh) A, H -> supersymmetrische TeilchenH± -> , tbVektorbosonfusionskanäle qq -> qqHiggs ebenfalls möglich: mit h, H -> ; H -> ; h, H -> WW -> ll; h -> 00
-
-
~ ~
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h0, HSM -> bb-
mmHH = 115 GeV = 115 GeV
Ere
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/ 1
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eVE
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se /
10
GeV
mminvinv (Jet, Jet) /GeV (Jet, Jet) /GeV
Nur assoziierte Produktionaufgrund von Problemen mit Trigger und Untergrund!
Analyse-Ereignisselektion:1 isoliertes e or 1 isoliertes e or , 6 Jets von , 6 Jets von denen mindestens 4 ein b-tag denen mindestens 4 ein b-tag haben müssen. Rekonstruktion haben müssen. Rekonstruktion beider t’s durch kinematischen beider t’s durch kinematischen Fit nötig um kombinatorischen Fit nötig um kombinatorischen Untergrund zu unterdrücken.Untergrund zu unterdrücken. Resultat für mH = 115 GeV:S/√B = 5.3, m/mH = 3.8%
Mögliche L1-Triggerselektion:1 isoliertes Lepton und mehrere Jets
tth(H) -> l±qqbbbb-- --
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H, A - Aufgrund der hohen Rate überspannt dieser Kanal einen weiten Parameterbereich.
Zugängliche Endzustände: (-> ee) (-> ) (-> h± 0’s ) (-> ll) (-> h± 0’s ) (-> hm 0’s )
Mögliche L1-Triggerselektion:1 e/ oder 1 -JetFehlende Energie
Ere
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eV
10 fb-1 bei 1033cm-2s-1
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Squarks, Gluinos
Supersymmetrische Teilchen können spektakuläre Signaturen durch Kaskadenzerfälle aufweisen.
Mögliche L1-Triggerselektion:Mehrere Leptonen: “e/” oder (beliebige Kombinationen)Mehrere JetsFehlende Energie je nach Zerfallskanal
pp -> qq~~
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Charginos, Neutralinos, Sleptonen
Mögliche L1-Triggerselektion:Mehrere Leptonen: “e/” oder (2 oder 3, beliebige Kombination)Fehlende Energie Jetveto
Ere
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SM-SM-UntergrundUntergrund
Endzustand mit 3l + fehlender Energie, keine Jets
~ ~Beispiel für Drell-Yan-Produktion von 1± 2
0:qq -> W* -> 1
± 20 -> 1
0 l± + 10 l+l-
20 -> l±lm -> 1
0 l+l-
oder
20 -> 1
0 l+l-
~~ ~
~ ~
~ ~ ~ ~
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Raten und Algorithmen
• Ausgangsrate maximal 100 kHz (25 bis 30 kHz mit Sicherheitsfaktor) - Aufsetzen der Triggertabelle - gleichzeitige Festlegung der Schwellwerte
Niedrige Luminosität: 1033 cm-2 s-1
Hohe Luminosität: 1034 cm-2 s-1
Schwellwerte in GeV
Algorithmus e ee j jj jj jjjj .Niedrige Lum 24 18 95 75 150 115 95 75
.Hohe Lum 35 20 180 110 285 225 125 105Algorithmus +e +j e ET
miss +e ETmiss +j ETmiss ( . .)e n isol ( . .)ee n isol ET
.Niedrige Lum 80,14 125,14 275 12,175 65,175 24 18 1000 .Hohe Lum 125,20 165,20 350 18,250 95,250 58 28 1500
Algorithmus e +j +ET +ETmiss Gesamtrate
.Niedrige Lum 10 3 4,12 4,80 4,80 4,600 4,140 25kHz .Hohe Lum 25 8,5 5,32 5,140 5,155 5,800 5,200 25kHz
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Zeitliche Anforderungen
• Triggerentscheidung durch globalen Trigger alle 25 ns - jede Strahlkreuzung muß betrachtet werden
- Level-1-Accept je nach Triggerregeln (Registrierung der Totzeit, < 1%)
• Rechenzeit klein im Vergleich zur gesamten Level-1-Latenzzeit (3,2s) - 200 ns (8 Strahlkreuzungsintervalle)
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Technische Anforderungen
• Technische Trigger zusätzlich zu Physiktriggern - Kalibration, Synchronisation, Tests• Effizienzen für jeden Triggeralgorithmus müssen bestimmbar sein - durch überlappende Trigger (niedrigere Schwellen, Unterdrückung von Korrelationen etc.) - Kontrolle durch Monte-Carlo• Triggerung von Prozessen mit hohen Raten mit Skalenfaktor• Physikalische und technische Überwachung durch on-line und off-line Monitoring • Triggerentscheidung muß nachvollziehbar sein - Aufzeichnung der Triggerdaten jedes Ereignisses - Aufzeichnung von Ereignissen, die nicht triggern würden (optionell) - Aufzeichnung von Ereignissen vor und nach der Trigger-Strahlkreuzung (optionell)
(i+1)-te Kreuzung n n-1 n-2 … n-126 n-127(i+2)-te Kreuzung n+1 n n-1 … n-125 n-126… … … … … … …(i+127)-te Kreuzung n+126 n+125 n+124 … n n-1 (Triggerentscheidung)(i+128)-te Kreuzung n+127 n+126 n+125 … n+1 n
Effizienzen fuer mu kein Problem, jedoch evtl. fuer Jets aus mSUGRA fuer hohe Lumi
Effizienzen fuer mu kein Problem, jedoch evtl. fuer Jets aus mSUGRA fuer hohe Lumi
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Die Umgebung des globalen Triggers
Für die Physikdatennahme verwendet der globale Trigger nur Information der Kalorimeter und des Müonsystems. Sie besteht aus speziellen makrogranularen Triggerdaten. Die volle Information steht erst dem Higher Level Trigger zur Verfügung. Spezielle Signale von allen Subsystemen können für Kalibrations-, Synchronisations- und Prüfzwecke verwendet werden (technische Trigger). Das TTC-System ist ein optisches Verteilernetzwerk, das zur Übertragung des Level-1-Accept- Signals (L1A) und von Zeitinformation (LHC clock etc.) zwischen dem Trigger und der Detektorelektronik dient. Das Triggersteuersystem steuert die Ausgabe von L1A-Signalen und “Bunch Crossing Zero” sowie “Bunch Counter Reset” Befehlen. Die Möglichkeit der Reduzierung der Triggerrate im Fall von imminenter Speicherüberbelegung ist vorgesehen. Der “Event Manager” steuert den High Level Trigger und die Datenakquisition.
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Zusammenfassung• Konzept des Level-1-Triggers und insbesondere des globalen Triggers von CMS vorgestellt
• Der globale Trigger eignet sich zur Selektion der physikalisch interessanten Ereignisse
• Durch sein spezielles Design, das komplexe Triggerbedingungen erlaubt, ermöglicht er die Auszeichnung besonders interessanter Ereignisse bei gleichzeitiger Unterdrückung von Untergrund • Protokollauszug der Sitzung des Large Hadron Collider Committee (LHCC) vom 21.-22. März 2001: http://committees.web.cern.ch/Committees/LHCC/LHCC51.html
““The concept of the L1 trigger built around the topological association of The concept of the L1 trigger built around the topological association of predefined elements associated with leptons, photons, jets and missing predefined elements associated with leptons, photons, jets and missing energy is well suited to the challenge of triggering in a flexible and energy is well suited to the challenge of triggering in a flexible and responsive manner.”responsive manner.”
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High Level Trigger Goals
Validate Level-1 decisionValidate Level-1 decision
Refine thresholdsRefine thresholds
Refine measurement of position and other parametersRefine measurement of position and other parameters
Reject backgroundsReject backgrounds
Perform physics selectionPerform physics selection
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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: 1:1000Allocation 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.
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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.
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Electron/Photon HLT Algorithms““Level-2.0”Level-2.0”Only calorimeter information used. Algorithm based on clustering of energy deposits in crystals (barrel) and crystals / 3X0 preshower (endcaps) and subsequent estimation of ET and position. Energy corrections for unrecovered bremsstrahlung are applied (also already at L1).““Level-2.5”Level-2.5”Matching with pixel detector hits. Separate streams for electrons and photons.Lower ET thresholds for electrons than photons.
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Electron/Photon HLT Algorithms““Level-3”Level-3”Include full tracker information, starting from Level-2.5 pixel seeds. E/p matching for electrons. Check on hadronic energy vs em. energy depositions. At high luminosity isolation cuts are used to reject background from jets. Track isolation less sensitive to pileup than calorimeter isolation.
Table with efficiencies for W and H -> ggTOBEDONE
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HLT Algorithms for Jets and -like Objects““Level-2”Level-2”xxx
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HLT Algorithms for ’s““Level-2”Level-2”xxx
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HLT Algorithms for ’s““Level-2”Level-2”xxx
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Conclusions““Level-2”Level-2”xxx
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AcknowledgmentsAcknowledgments - my colleagues in CMS and at HEPHY Vienna, especially D. Acosta, J. Erö,my colleagues in CMS and at HEPHY Vienna, especially D. Acosta, J. Erö, S. Dasu, N. Neumeister, H. Sakulin, W. Smith, G. Wrochna, A. Taurok.S. Dasu, N. Neumeister, H. Sakulin, W. Smith, G. Wrochna, 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 workshop.the enjoyable workshop.