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Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 1
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 6
LHC Trigger & DAQ Challenges
Computing Services
16 Million channels
Charge Time Pattern
40 MHz COLLISION RATE
100 - 50 kHz 1 MB EVENT DATA
1 Terabit/s READOUT
50,000 data channels
200 GB buffers ~ 400 Readout memories
3 Gigacell buffers
500 Gigabit/s
5 TeraIPS
~ 400 CPU farms
Gigabit/s SERVICE LAN
Petabyte ARCHIVE
Energy Tracks
300 HzFILTERED
EVENT
EVENT BUILDER. A large switching network (400+400 ports) with total throughput ~ 400Gbit/s forms the interconnection between the sources (deep buffers) and the destinations (buffers before farm CPUs).
EVENT FILTER. A set of high performance commercial processors organized into many farms convenient for on-line and off-line applications.
SWITCH NETWORK
LEVEL-1TRIGGER
DETECTOR CHANNELS
Challenges:1 GHz of Input InteractionsBeam-crossing every 25 ns with ~ 23 interactions produces over 1 MB of dataArchival Storage at about 300 Hz of 1 MB events
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 7
Level 1 Trigger Operation
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 8
CMS Trigger Levels
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L1 Trigger LocationsUnderground Counting Room•Central rows of racks fortrigger•Connections via high-speed copper links to adjacent rows of ECAL & HCAL readout racks with trigger primitive circuitry•Connections via opticalfiber to muon trigger primitive generatorson the detector•Optical fibersconnected via“tunnels” to detector(~90m fiber lengths)
Rows of Racks containing trigger & readout
electronics
7m thickshielding
wall
USC55
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Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 23
CMS Muon Trigger Primitives
Memory to store patterns
Fast logic for matching
FPGAs are ideal
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 24
CMS Muon TriggerTrack Finders
Memory to store patterns
Fast logic for matching
FPGAs are ideal Sort based on PT, Quality - keep loc.
Combine at next level - match
Sort again - Isolate?
Top 4 highest PT and quality muons with location coord.
Match with RPCImprove efficiency and quality
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 25
DT
L1 Muon Trigger SynchronizationBX ID Efficiency – CSC, DT, RPC
All muon trigger timing within ± 2 ns, most better & being improved
RPC
CSC
Log Plot
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 26
L1 Muon Efficiency vs. pT
01/04/2011
Barrel
EndCap
OverLap
L1_Mu7L1_Mu10L1_Mu12L1_Mu20
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CMS Global Trigger
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 28
Global L1 Trigger Algorithms
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 29
“Δelta” or “correlation” conditions
Unique Topological Capability of CMS L1 Trigger• separate objects in η & Φ:• Δ ≥ 2 hardware indices• ϕ: Δ ≥ 20 .. 40 degrees
Present Use:• eγ / jet separation to avoid
triggering twice on the same object in a correlation trigger
• objects to be separated by one empty sector (20 degrees)
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High Level Trigger Strategy
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All processing beyond Level-1 performed in the Filter FarmPartial event reconstruction “on demand” using full detector resolution
High-Level Trig. Implementation
8 “slices”
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Start with L1 Trigger Objects Electrons, Photons, τ-jets, Jets, Missing ET, Muons
• HLT refines L1 objects (no volunteers)Goal
• Keep L1T thresholds for electro-weak symmetry breaking physics• However, reduce the dominant QCD background
• From 100 kHz down to 100 Hz nominallyQCD background reduction
• Fake reduction: e±, γ, τ• Improved resolution and isolation: μ• Exploit event topology: Jets• Association with other objects: Missing ET• Sophisticated algorithms necessary
• Full reconstruction of the objects• Due to time constraints we avoid full reconstruction of the event - L1
seeded reconstruction of the objects only• Full reconstruction only for the HLT passed events
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Electron & Photon HLT“Level-2” electron:
• Search for match to Level-1 trigger• 1-tower margin around 4x4-tower trig. region
• Bremsstrahlung recovery “super-clustering”• Road along φ — in narrow η-window around seed• Collect all sub-clusters in road η “super-cluster”
• Select highest ET cluster• Calorimetric (ECAL+HCAL) isolation
“Level-3” Photons• Tight track isolation
“Level-3” Electrons• Electron track reconstruction• Spatial matching of ECAL cluster• and pixel track• Loose track isolation in
a “hollow” cone
basic cluster
super-cluster
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“Tag & probe” HLT Electron Efficiency
Use Z mass resonance to select electron pairs & probe efficiency of selection• Tag: lepton passing very tight selection with very low fake rate (<<1%)• Probe: lepton passing softer selection & pairing with Tag object such that invariant mass of tag & probe
combination is consistent with Z resonanceEfficiency = Npass/Nall
• Npass → number of probes passing the selection criteria• Nall → total number of probes counted using the resonance
Barrel Endcap
The efficiency of electron trigger paths in2010 data reaches 100% within errors
Electron (ET Thresh>17 GeV) with Tighter Calorimeter-basedElectron ID+Isolation at HLT
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 35
Expected rate of each PD is 15-30 Hz @ 5E32Writing a total of O(360) Hz. (Baseline is 300 Hz)
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 38
Trigger Rates in 2011Trigger rate predictions based mostly on data.
• Emulation of paths via OpenHLT working well for most of trigger tableData collected already w/ sizeable PU (L=2.5E32 → PU~7)
• Allows linear extrapolation to higher luminosity scenariosEmulated &Online Rates:
Agreement to 30%, ≲data-only check of measured ratevs. separate emulation
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Approx. evolution for some triggers
L=5E32• Single Iso Mu ET: 17 GeV• Single Iso elec ET: 27 GeV• Double Mu ET: 6, 6 GeV• Double Elec ET: 17, 8 GeV• e+mu ET: 17,8 & 8,17 GeV• Di-photon: 26, 18 GeV• e/mu + tau: 15, 20 GeV• HT: 440 GeV• HT+MHT: 520 GeV
L=2E33• Single Iso Mu ET: 30 GeV• Single Iso elec ET: 50 GeV• Double Mu ET: 10,10 GeV• Double Elec ET: 17, 8 GeV*• e+mu ET: 17,8 & 8,17 GeV*• Di-photon: 26, 18 GeV*• e/mu + tau: 20, 20-25 GeV• HT:• HT+MHT:
Targeted rate of each line is ~10-15 Hz.Overall menu has many cross triggers for signal and prescaled triggers for efficiencies and fake rate measurements as well* Tighter ID and Iso conditions, still rate and/or efficiency concerns
Possibly large uncertainty due
to pile-up
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 40
HLT at 1E33
Total is 400 Hz
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Prescale set used: 2E32 Hz/cm²Sample: MinBias L1-skim 5E32 Hz/cm² with 10 Pile-up
Unpacking of L1 information,early-rejection triggers,non-intensivetriggers
Mostly unpacking of calorimeter info.to form jets, & some muon triggers
Triggers with intensive tracking algorithms
Overflow: Triggers doing particle flow
reconstruction (esp. taus)
Total HLT Time Distribution
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Extension-1 of HLT Farm – 2011
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Future HLT Upgrade Options
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Requirements for LHC phases of the upgrades: ~2010-2020
Phase 1:• Goal of extended running in second half of the decade to
collect ~100s/fb• 80% of this luminosity in the last three years of this decade• About half the luminosity would be delivered at luminosities
above the original LHC design luminosity• Trigger & DAQ systems should be able to operate with a peak
luminosity of up to 2 x 1034
Phase 2:• Continued operation of the LHC beyond a few 100/fb will require
substantial modification of detector elements• The goal is to achieve 3000/fb in phase 2• Need to be able to integrate ~300/fb-yr• Will require new tracking detectors for ATLAS & CMS• Trigger & DAQ systems should be able to operate with a peak
luminosity of up to 5 x 1034
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 45
Detector Luminosity Effects H→ZZ → μμee, MH= 300 GeV for different luminosities in CMS
1032 cm-2s-1 1033 cm-2s-1
1034 cm-2s-1 1035 cm-2s-1
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CMS Upgrade Trigger StrategyConstraints
• Output rate at 100 kHz• Input rate increases x2/x10 (Phase 1/Phase 2) over LHC design (1034)
• Same x2 if crossing freq/2, e.g. 25 ns spacing → 50 ns at 1034
• Number of interactions in a crossing (Pileup) goes up by x4/x20• Thresholds remain ~ same as physics interest does
• Process with full granularity of calorimeter trigger information• Should suffice for x2 reduction in rate as shown with initial L1 Trigger studies
& CMS HLT studies with L2 algorithmsPotential new handles at L1 needed for x10 (Phase 2: 2020+)
• Tracking to eliminate fakes, use track isolation.• Vertexing to ensure that multiple trigger objects come from same interaction• Requires finer position resolution for calorimeter trigger objects for matching
(provided by use of full granularity cal. trig. info.)
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 47
Phase 1 Upgrade Cal. Trigger Algorithm Development
• Robust operation requires TMB upgrade, unganging strips in ME-1a, new FEBs, upgrade CSCTF+MPC
ME
4/2
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CMS Level-1 Trigger 5x1034
Occupancy• Degraded performance of algorithms
• Electrons: reduced rejection at fixed efficiency from isolation• Muons: increased background rates from accidental coincidences
• Larger event size to be read out• New Tracker: higher channel count & occupancy large factor• Reduces the max level-1 rate for fixed bandwidth readout.
Trigger Rates• Try to hold max L1 rate at 100 kHz by increasing readout bandwidth
• Avoid rebuilding front end electronics/readouts where possible• Limits: readout time (< 10 µs) and data size (total now 1 MB)
• Use buffers for increased latency for processing, not post-L1A• May need to increase L1 rate even with all improvements
• Greater burden on DAQ• Implies raising ET thresholds on electrons, photons, muons, jets and use of
multi-object triggers, unless we have new information Tracker at L1• Need to compensate for larger interaction rate & degradation in algorithm
performance due to occupancy
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 52
CMS Level-1 Trigger 5x1034
Occupancy• Degraded performance of algorithms
• Electrons: reduced rejection at fixed efficiency from isolation• Muons: increased background rates from accidental coincidences
• Larger event size to be read out• New Tracker: higher channel count & occupancy large factor• Reduces the max level-1 rate for fixed bandwidth readout.
Trigger Rates• Try to hold max L1 rate at 100 kHz by increasing readout bandwidth
• Avoid rebuilding front end electronics/readouts where possible• Limits: readout time (< 10 µs) and data size (total now 1 MB)
• Use buffers for increased latency for processing, not post-L1A• May need to increase L1 rate even with all improvements
• Greater burden on DAQ• Implies raising ET thresholds on electrons, photons, muons, jets and use of
multi-object triggers, unless we have new information Tracker at L1• Need to compensate for larger interaction rate & degradation in algorithm
performance due to occupancy
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 53
Tracking needed for L1 triggerMuon L1 trigger rate
Single electron trigger rate
Isolation criteria are insufficient to reduce rate at L = 1035 cm-2.s-1
5kHz @ 1035
L = 1034
L = 2x1033
MH
z
Standalone Muon trigger resolution insufficient
We need to get another x200 (x20)
reduction for single (double)
tau rate!
Amount of energy carried by tracks around tau/jet direction
(PU=100)
Cone 10o-30o
~dE T
/dco
sq τ
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 54
The Track Trigger Problem• Need to gather
information from 108 pixels in 200m2 of silicon at 40 MHz
• Power & bandwidth to send all data off-detector is prohibitive• Local filtering necessary• Smart pixels needed to
locally correlate hit Pt information
• Studying the use of 3D electronics to provide ability to locally correlate hits between two closely spaced layers
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3D InterconnectionKey to design is ability of a single IC to connect to both top & bottom sensorEnabled by “vertical interconnected” (3D) technologyA single chip on bottom tier can connect to both top and bottom sensors – locally correlate informationAnalog information from top sensor is passed to ROIC (readoutIC) through interposerOne layer of chips
No “horizontal” data transfer necessary – lower noise and power
Fine Z information is not necessary on top sensor – long (~1 cm vs ~1-2 mm) strips can be used to minimize via density in interposer
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Track Trigger ArchitectureReadout designed to send all hits with Pt>~2
GeV to trigger processor High throughput – micropipeline architecture Readout mixes trigger and event data Tracker organized into phi segments
• Limited FPGA interconnections• Robust against loss of single layer hits• Boundaries depend on pt cuts & tracker geometry
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 57
Tracking for electron triggerPresent CMS electron HLT
Factor of 10 rate reductionγ: only tracker handle: isolation
• Need knowledge of vertexlocation to avoid loss of efficiency
- C. Foudas & C. Seez
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Tracking for τ-jet isolationτ-lepton trigger: isolation from pixel tracks
outside signal cone & inside isolation cone
Factor of 10 reduction
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 59
CMS L1 Track Trigger for Muons
Combine with L1 μ trigger as is now done at HLT:•Attach tracker hits to improve PT assignment precision from 15% standalone muon measurement to 1.5% with the tracker•Improves sign determination & provides vertex constraints
•Find pixel tracks within cone around muon track and compute sum PT as an isolation criterion•Less sensitive to pile-up than calorimetric information if primary vertex of hard-scattering can be determined (~100 vertices total at SLHC!)
To do this requires η information on muons finer than the current 0.052.5°•No problem, since both are already available at 0.0125 and 0.015°
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CMS L1 Trigger StagesCurrent for LHC:
TPG RCT GCT GTProposed for SLHC (with tracking added):