Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 1
Triggering CMSWesley H. Smith
U. Wisconsin – MadisonCMS Trigger Coordinator
Seminar, Texas A&MApril 20, 2011
Outline:
Introduction to CMS Trigger Challenges & ArchitectureLevel -1 Trigger Implementation & PerformanceHigher Level Trigger Algorithms & PerformanceThe Future: SLHC Trigger
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 2
LHC Collisions
with every bunch crossing23 Minimum Bias events
with ~1725 particles produced
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 3
LHC Physics & Event RatesAt design L = 1034cm-2s-1
• 23 pp events/25 ns xing•~ 1 GHz input rate•“Good” events contain ~ 20 bkg. events
• 1 kHz W events• 10 Hz top events• < 104 detectable Higgs
decays/yearCan store ~ 300 Hz eventsSelect in stages
• Level-1 Triggers•1 GHz to 100 kHz
• High Level Triggers•100 kHz to 300 Hz
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 4
Collisions (p-p) at LHC
Event size: ~1 MByte Processing Power: ~X TFlop
All charged tracks with pt > 2 GeV
Reconstructed tracks with pt > 25 GeV
Operating conditions:one “good” event (e.g Higgs in 4 muons )
+ ~20 minimum bias events)Event rate
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 5
CMS Detector Design
MUON BARREL
CALORIMETERS
PixelsSilicon Microstrips210 m2 of silicon sensors9.6M channels
ECAL76k scintillating PbWO4 crystals
Cathode Strip Chambers (CSC)Resistive Plate Chambers (RPC)
Drift Tube Chambers (DT)
Resistive Plate Chambers (RPC)
Superconducting Coil, 4 Tesla
IRON YOKE
TRACKER
MUONENDCAPS
HCALPlastic scintillator/brasssandwich
Today:RPC |η| < 1.6 instead of 2.1 & 4th endcap layer missing
Level-1 Trigger Output• Today: 50 kHz
(instead of 100)
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
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 9
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
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 10
CMS Level-1 Trigger & DAQOverall Trigger & DAQ Architecture: 2 Levels:Level-1 Trigger:
• 25 ns input• 3.2 μs latency
Interaction rate: 1 GHz
Bunch Crossing rate: 40 MHz
Level 1 Output: 100 kHz (50 initial)
Output to Storage: 100 Hz
Average Event Size: 1 MB
Data production 1 TB/day
UXC
U
SC
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 11
CMS Calorimeter Geometry
EB, EE, HB, HE map to 18 RCT cratesProvide e/γ and jet, τ, ET triggers
1 trigger tower (.087η✕ .087φ) = 5 ✕ 5 ECAL xtals = 1 HCAL tower
2 HF calorimeters map on to 18 RCT crates
Trigger towers:Δη = Δϕ = 0.087
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 12
ECAL Endcap GeometryMap non-projective x-y trigger crystal geometry
onto projective trigger towers:Individualcrystal
5 x 5 ECAL xtals ≠ 1 HCAL tower in detail
+ZEndcap
-ZEndcap
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 13
Calorimeter Trig. Processing
Trigger Tower
25 Xtals (TT)
TCC(LLR)
CCS(CERN)
SRP(CEADAPNIA)
DCC(LIP)
TCSTTC
Trigger primitives
@800 Mbits/s
OD
DAQ
@100 kHz
L1
Global TRIGGER
RegionalCaloTRIGGER
Trigger Tower Flags (TTF)
Selective Readout Flags (SRF)
SLB (LIP)
Data path
@100KHz (Xtal Datas)
Trigger Concentrator Card
Synchronisation & Link Board
Clock & Control System
Selective Readout Processor
Data Concentrator Card
Timing, Trigger & Control
Trigger Control System
Level 1 Trigger (L1A)
From : R. Alemany LIP
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 14
Calorimeter Trig.Overview(located in underground counting room)
CalorimeterElectronicsInterface
RegionalCalorimeter
Trigger
ReceiverElectron Isolation
Jet/Summary
Global Cal. TriggerSorting, ET
Miss, ΣET
GlobalTriggerProcessor
Global Muon TriggerIso Mu MinIon Tag
Lumi-nosity Info.
4K 1.2 Gbaud serial links w/2 x (8 bits E/H/FCAL Energy+ fine grain structure bit) + 5 bits error detection codeper 25 ns crossingUS CMS HCAL:BU/FNAL/Maryland/Princeton
CMS ECAL:Lisbon/Palaiseau
US CMS:Wisconsin
Bristol/CERN/Imperial/LANL
CMS:Vienna
72 φ ✕ 60 η H/ECALTowers (.087φ ✕.087η for η < 2.2 & .174-.195η, η>2.2)HF: 2✕(12 φ ✕ 12 η)
Copper 80 MHz Parallel4 Highest ET:Isolated & non-isol. e/γCentral, forward, τ jets,Ex, Ey from each crate
MinIon & QuietTags for each 4φ ✕ 4η region
GCT Matrix μ + Q bitsIC/LANL/UW
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 15
ECAL Trigger Primitives
Test beam results (45 MeV per xtal):
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 16
CMS Electron/Photon Algorithm
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 17
CMS τ / Jet Algorithm
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 18
L1 Cal. Trigger SynchronizationBX ID Efficiency – e/γ & Jets
• Sample of min bias events, triggered by BSC coincidence, with good vertex and no scraping
• Fraction of candidates that are in time with bunch-crossing (BPTX) trigger as function of L1 assigned ET
• Anomalous signals from ECAL, HF removed
• Noise pollutes BX ID efficiency at low ET values
e/γ
Jet/τ Forward Jet
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 19
L1 efficiency for electrons• Sample of ECAL Activity HLT triggers
(seeded by L1 ZeroBias)• Anomalous ECAL signals removed
using standard cuts• EG trigger efficiency for electrons
from conversions• Standard loose electron isolation & ID• Conversion ID (inverse of conversion
rejection cuts) to select electron-like objects
• Efficiency shown w.r.t ET of the electron supercluster, for L1 threshold of 5 GeV (top), 8 GeV (bottom)
• Two η ranges shown:• Barrel (black), endcaps (red)
L1_EG5
L1_EG8
With RCT Correction
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 20
Jet Trigger Efficiency
minimum-bias trigger jet energy correction: online / offline match turn-on curves steeper
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 21
Reduced RE system|η| < 1.6
1.6
ME4/1
MB1
MB2
MB3
MB4
ME1ME2 ME3
*Double Layer
*RPC
Single Layer
CMS Muon Chambers
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 22
Muon Trigger Overview|η| < 1.2 |η| < 2.40.8 < |η| |η| < 2.1
|η| < 1.6 in 2009
Cav
ern:
UX
C55
Cou
ntin
g R
oom
: US
C55
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)
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 30
High Level Trigger Strategy
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 31
All processing beyond Level-1 performed in the Filter FarmPartial event reconstruction “on demand” using full detector resolution
High-Level Trig. Implementation
8 “slices”
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 32
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
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 33
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
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 34
“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
Muon HLT & L1 EfficiencyBoth isolated & non-isolated muon trigger shown
• Efficiency loss is at Level-1, mostly at high-ηImprovement over these curves already done
• Optimization of DT/CSC overlap & high-η regions
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 36
Jet HLT EfficiencyJet efficiencies calculated
• Relative to a lower threshold trigger• Relative to an independent trigger
Jet efficiencies plotted vs. corrected offline recoAnti-kT jet energy
• Plots are from 2011 run 161312
HLT_Jet370
BarrelEndcap All
HLT_Jet240
BarrelEndcap All
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 37
Summary of Current Physics Menu(5E32) by Primary Dataset
JetSingle Jet, DiJetAve,MultiJetQuadJet, ForwardJets, Jets+Taus
HTMisc. hadronic SUSY triggers
METBtag• MET triggers, Btag POG triggers
SingleMu• Single mu triggers (no had. requirement)
DoubleMu• Double mu trigger (no had. requirement)
SingleElectron• Single e triggers (no had. requirement)
DoubleElectron• Double e triggers (no had requirement)
PhotonPhotons (no had. requirement)
MuEGMu+photon or ele (no had. requirement)
ElectronHadelectrons + had. activity
PhotonHadPhotons + had. activity
MuHadMuons + had. activity
TauSingle and Double taus
TauPlusXX-triggers with taus
MuOniaJ/psi, upsilon+ Commisioning, Cosmics, MinimumBias
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
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 39
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
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 41
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
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 42
Extension-1 of HLT Farm – 2011
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 43
Future HLT Upgrade Options
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 44
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
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 46
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
Example: strategy for Phase 1 Calorimeter Trigger (operating 2016+):• Present L1 algorithms inadequate above 1034 or 1034 w/ 50 ns spacing
• Pileup degrades object isolation• More sophisticated clustering & isolation deal w/more busy events
• 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
• Particle Cluster Finder• Applies tower thresholds to Calorimeter• Creates overlapped 2x2 clusters
• Cluster Overlap Filter• Removes overlap between clusters• Identifies local maxima• Prunes low energy clusters
• Cluster Isolation and Particle ID• Applied to local maxima• Calculates isolation deposits around 2x2,2x3
clusters• Identifies particles
• Jet reconstruction• Applied on filtered clusters• Groups clusters to jets
• Particle Sorter• Sorts particles & outputs the most energetic ones
• MET,HT,MHT Calculation• Calculates Et Sums, Missing Et from clusters
ECA
LHCAL Δη x Δφ=0.087x0.087
e/γ
ECA
L
HCAL
τ
ECA
L
HCAL
jet
ηφ
η
φ
η
φ
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 48
Upgrade Algorithm Performance:Factor of 2 for Phase I
Factor of 2 rate reduction
Higher Efficiency
Isolated electrons Taus
Effic
ienc
yQ
CD
Rat
e (k
Hz)
Isolated electrons
Taus
EfficiencyQ
CD
Rate (kH
z)
Phase 1 Algorithm
PresentAlgorithm
PresentAlgorithm
PresentAlgorithm
PresentAlgorithm
Phase 1 Algorithm
Phase 1 Algorithm
Phase 1 Algorithm
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 49
uTCA Calorimeter Trigger Demonstrators
processing cards with 160 Gb/s input & 100 Gb/s output using 5 Gb/s optical links.
four trigger prototype
cards integrated in a
backplane fabric to
demonstrate running & data
exchange of calorimeter
trigger algorithms
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 50
CMS CSC Trigger UpgradesImprove redundancy
• Add station ME-4/2 covering η=1.1-1.8• Critical for momentum resolution
Upgrade electronics to sustain higher rates
• New Front End boards for station ME-1/1
• Forces upgrade of downstream EMU electronics• Particularly Trigger & DAQ Mother
Boards• Upgrade Muon Port Card and CSC
Track Finder to handle higher stub rate
Extend CSC Efficiency into η=2.1-2.4 region
• Robust operation requires TMB upgrade, unganging strips in ME-1a, new FEBs, upgrade CSCTF+MPC
ME
4/2
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 51
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
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 55
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
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 56
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
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 58
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°
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 60
CMS L1 Trigger StagesCurrent for LHC:
TPG RCT GCT GTProposed for SLHC (with tracking added):
TPG Clustering Correlator SelectorTrigger Primitives
Regional Correlation, Selection, Sorting
Jet Clustering Seeded Track ReadoutMissing ET
Global Trigger, Event Selection Manager
e /γ /τ/jet clustering2x2, φ-strip ‘TPG’
µ track finderDT, CSC / RPC
Tracker L1 Front End
Regional Track Generator
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 61
CMS Level-1 LatencyPresent CMS Latency of 3.2 μsec = 128 crossings @ 40MHz
• Limitation from post-L1 buffer size of tracker & preshower• Assume rebuild of tracking & preshower electronics will store
more than this number of samplesDo we need more?
• Not all crossings used for trigger processing (70/128)• It’s the cables!
• Parts of trigger already using higher frequencyHow much more? Justification?
• Combination with tracking logic• Increased algorithm complexity• Asynchronous links or FPGA-integrated deserialization require
more latency• Finer result granularity may require more processing time• ECAL digital pipeline memory is 256 40 MHz samples = 6.4 μsec
• Propose this as CMS SLHC Level-1 Latency baseline
Wesley Smith, U. Wisconsin, April 20, 2011 Texas A&M Seminar: Triggering CMS - 62
CMS Trigger SummaryLevel 1 Trigger
• Select 100 kHz interactions from 1 GHz (10 GHz at SLHC)• Processing is synchronous & pipelined• Decision latency is 3 μs
• Algorithms run on local, coarse data from Cal., Muons• Processed by custom electronics using ASICs & FPGAs
Higher Level Triggers: hierarchy of algorithms• Level 2: refine using calorimeter & muon system info.
• Full resolution data• Level 3: Use Tracking information
• Leading to full reconstructionThe Future: SLHC
• Refined higher precision algorithms for Phase 1• Use Tracking in Level-1 in Phase 2