1. CMS Trigger System J. Varela LIP/IST-Lisbon & CERN
on behalf of the CMS collaboration
HEP2005 International Europhysics Conference on High Energy Physics
July 21st-27th 2005, Lisboa, Portugal

2. Physics Selection at LHC
Formidable task: Trigger Rejection 4.105
Bunch crossing rate 40MHz  permanent storage rate O(102)Hz

3. The CMS Trigger Level 1 Trigger: Hardwired processors
High Level Triggers:
Farm of processors
Level-1 Trigger Requirements:
Output: 100 kHz (50 kHz for initial running)
Latency: 3 msec for collection, decision, propagation
HLT designed to output O(102)Hz
One of the more complex electronics systems ever built!

4. Level-1 Trigger Information from Calorimeters and Muon detectors
Electron/photon triggers
Jet and missing ET triggers
Muon triggers
Backgrounds are huge
Sophisticated trigger algorithms
Steep functions of thresholds
Synchronous and pipelined
Bunch crossing time = 25 ns
Time needed for decision (+its propagation) ≈ 3 s
Highly complex
Trigger primitives: ~5000 electronics boards of 7 types
Regional/Global: 45 crates, 630 boards, 32 board types
Large flexibility
Large number of electronics programmable parameters
Most algorithms implemented in re-programmable FPGAs

5. Level-1 Trigger DataflowHF
HCAL
ECAL
RPC
CSC DT
Pattern Comparator Trigger
Regional Calorimeter Trigger
4 m
4+4 m
4 m (with MIP/ISO bits)
MIP+ ISO bits
e, J, ET, HT, ETmiss
Calorimeter Trigger
Muon Trigger
max. 100 kHz L1 Accept
Global Trigger
Global Muon Trigger
Global Calorimeter Trigger
Local DT Trigger
Local CSC Trigger
DT Track Finder
CSC Track Finder
40 MHz pipeline, latency < 3.2 ms

6. Calorimeter Trigger Geometry   

7. L1 Electron/Photon Trigger
Issue is rejection of huge jet background
Electromagnetic trigger based on 3x3 trigger towers
Each tower is 5x5 crystals in ECAL (barrel; varies in end-cap)
Each tower is single readout tower in HCAL E
+ H/E
Electron/Photon
2-tower T E
+ H/E
Isolated Electron/Photon
Trigger threshold on sum of two towers
2x5-crystal strips>90%
energy in 5x5 (Fine Grain)
Neighbor EM + Had Quiet

8. L1 Jet and  Triggers
Issues are jet energy resolution and tau identification
Sliding window:
granularity is 4x4 towers = trigger region
jet ET summed in 3x3 regions , = 1.04
“-like” shapes identified for  trigger
Single, double, triple and quad thresholds possible
Possible also to cut on jet multiplicities
Also ETmiss, SET and SET(jets) triggers

9. Calorimeter Trigger Rates at 1034
Rates drop sharply with trigger Et cutoff
Provides ability to tune cuts to sustain rates during operation
Several cuts are available to optimize efficiency versus rate
QCD background rates are within target

10. Calorimeter Trigger Efficiency
0.2
0.4
0.6
0.8 1
0 2 3
0 4 5
0 6 7
0 8
0 9
MC e/ ET
Efficiency
>95% at PT =35 GeV
for e in top events
(incl. minbias)
For a 7kHz rate
e/
efficy
0.2
0.4
0.6
0.8 1 5
100
150
200
250
300
Efficiency
QCD
CMSIM 116 ORCA 4.2.0
(With minimum bias)
L = 10 34 cm -2 s -1
1-Jet E t
250 GeV
286.5
2-Jet E
200 GeV
232.5
3-Jet E
100 GeV
157.5
4-Jet E
80 GeV
106.5
QCD jet efficiency for | |<5
0.2
0.4
0.6
0.8 1 5
100
150
200
250
300
MC -jet ET
Efficiency
>95% at Pt =180 GeV
for  (incl. minbias)
for a 1 kHz rate
 efficy
Calibrated Hadron Level Jet E t
(GeV)
>95% at PT
=286, 232, 157, 106 GeV for
individual 1,2,3,4 jet triggers
(incl. minbias)
(~0.5 kHz rate each totaling ~2 kHz)

11. Calorimeter Trigger Primitives
1200 Synchronization and Link Boards: ECAL & HCAL Trigger Interface

12. Regional Calorimeter Trigger
SORT
ASICs
(w/heat sinks)
EISO
Bar Code
Input
DC-DC
Converters
Clock delay adjust
Clock Input
Oscillator
Adder
mezz
link
cards
BSCAN
PHASE
MLUs
Back
Front
Regional Calorimeter Trigger
Receiver Card: Electron Isolation & Clock: Jet/Summary:
Receiver
Mezz. Card
Sort
Phase
ASIC
Clock

13. Full Regional Cal. Trigger Crate
18 Such Crates make up the full RCT System covering |h|<5 & 0 < f < 2p.
Rear: Receiver Cards
Front: Electron, Jet, Clock Cards

14. Global Calorimeter Trigger
Input Module
Processor Module

15. Muons at LHC Issue is pT measurement of real muons |h| < 2.1
L = 1034 cm-2s-1
|h| < 2.1

16. L1 Muon trigger Level-1 m-trigger info from:
Dedicated trigger detector: RPCs (Resistive plate chambers)
Excellent time resolution
Muon chambers with accurate position resolution
Drift Tubes (DT) in barrel
Cathode Strip Chambers (CSC) in end-caps

17. L1 Muon Trigger Overview
|| < 1.2
0.8 < ||
|| < 2.4
|| < 2.1
Cavern: UXC55
Counting Room: USC55

18. Drift Tube Trigger Track Finder
Phi Track Finder
(Sector Processor)
Track Finder Processor
Pipeline logic running at 40MHz
(LHC bunch crossing frequency)
Implemented in programmable logic
devices
Based on extrapolation and pattern
matching methods
Drift Tubes

19. CSC Muon Trigger Overview
Muon Track-Finder Crate in underground counting room
Muon Port Card
Trig Motherboard
Clock Control Board M P C D B T O N R L E
Optical
Link
Peripheral Crate
on iron disk
Slow Control
1 of 5
Cathode Front-end Board
Start w/ wire & strip segment combinations:
Wires:25ns bunch xing
Strips: precision 
Form “Trigger Primitives”
Link into tracks
Assign pT, , and 
Send highest quality tracks to Global L1
CSC
CFEB
ALCT
1 of 24
1 of 2
LVDB
Anode Local Charged Track Board
LV Distribution Board 
Anode
Front-end
Board 

20. Global Muon Trigger Overview

21. Muon Trigger Rates vs. Pt at 1034

22. Muon Trigger Efficiency vs. Pt

23. Drift Tube Track Finder
Phi Track-Finder
Eta Track Finder
DCC

24. Drift Tube Muon Sorter
Wedge Sorter
Barrel Sorter

25. CSC Trigger Full Chain MPCCCB Track-Finder Crate: SP CCB MS 5 TMB
Fully Loaded Peripheral Crate

26. RPC Trigger Board

27. Global Muon Trigger Logic Board
Input board (4x4 m)
Logic Board
Logic fwd
Logic brl
ROP
MIP/ISO
fwd
brl
Sort
4 SCSI connectors on Logic Board
3x4 on input board

28. L1 Global Trigger
Logic combinations of trigger objects sent by the Global Calorimeter Trigger and the Global Muon Trigger
Best 4 isolated electrons/photons ET, h, f
Best 4 non-isolated electrons/photons ET, h, f
Best 4 jets in forward regions ET, h, f
Best 4 jets in central region ET, h, f
Best 4 t-Jets ET, h, f
Total ET SET
Total ET of all jets above threshold HT
Missing ET ETmissing, f(ETmissing)
12 jet multiplicities Njets (different ET thresholds and h-regions)
Best 4 muons pT, charge, f, h, quality, MIP, isolation
Thresholds (pT, ET, NJets)
Optional topological and other conditions (geometry, isolation, charge, quality)
128 algorithms running in parallel

29. Level-1 Trigger table (2x1033)
Threshold
(GeV)
Rate (kHz)
Cumulative Rate (kHz)
Isolated e/g 29
3.3
Di-e/g 17
1.3
4.3
Isolated muon 14
2.7
7.0
Di-muon 3
0.9
7.9
Single tau-jet 86
2.2
10.1
Di-tau-jet 59
1.0
10.9
1-jet, 3-jet, 4-jet
177, 86, 70
3.0
12.5
Jet*ETmiss
88*46
2.3
14.3
Electron*jet
21*45
0.8
15.1
Min-bias
16.0
TOTAL

30. Level-1 Trigger table (1034)
Threshold
(GeV)
Rate (kHz)
Cumulative Rate (kHz)
Isolated e/g 34
6.5
Di-e/g 19
3.3
9.4
Isolated muon 20
6.2
15.6
Di-muon 5
1.7
17.3
Single tau-jet
101
5.3
22.6
Di-tau-jet 67
3.6
25.0
1-jet, 3-jet, 4-jet
250, 110, 95
3.0
26.7
Jet*ETmiss
113*70
4.5
30.4
Electron*jet
25*52
1.3
31.7
Muon*jet
15*40
0.8
32.5
Min-bias
1.0
33.5
TOTAL

31. VME
interface
PSB
GTL6U
GTL_CONV
Global Trigger Crate

32. Trigger Control System Board

33. High-Level Trigger Runs on large CPU farm
Code as close as possible to offline reconstruction
Selection must meet CMS physics goals
Output rate to permanent storage limited to O(102)Hz
Reconstruction on demand
Reject as soon as possible
Trigger “Levels”:
Level-2: use calorimeter and muon detectors
Level-2.5: also use tracker pixel detectors
Level-3: includes use of full information, including tracker
“Regional reconstruction”: e.g. tracks in a given road or region

34. HLT selection: , , jets and ETmiss
Muons
Successive refinement of momentum measurement; + isolation
Level-2: reconstructed in muon system; must have valid extrapolation to collision vertex; + calorimeter isolation
Level-3: reconstructed in inner tracker; + tracker isolation
-leptons
Level-2: calorimetric reconstruction and isolation
Level-3: tracker isolation
Jets and Etmiss
Jet reconstruction with iterative cone algorithm
ETmiss reconstruction (vector sum of towers above threshold)

35. HLT selection: electrons and photons
Issue is electron reconstruction and rejection
Higher ET threshold on photons
Level-2
Level-3
Level-1
Level-2.5
Photons
Threshold cut
Isolation
Electrons
Track reconstruction
E/p, matching (Dh) cut
ECAL reconstruction
Pixel matching
Electron reconstruction
key is recovery of radiated energy
Electron rejection
key tool is pixel detector

36. HLT Summary: 2x1033 cm-2s-1 TOTAL Trigger Threshold (GeV) Rate (Hz)
Cuml. rate (Hz)
Inclusive electron 29 33
Di-electron 17 1 34
Inclusive photon 80 4 38
Di-photon
40, 25 5 43
Inclusive muon 19 25 68
Di-muon 7 72
Inclusive tau-jet 86 3 75
Di-tau-jet 59 76
1-jet * ETmiss
180 * 123 81
1-jet OR 3-jet OR 4-jet
657, 247, 113 9 89
Electron * jet
19 * 45 2 90
Inclusive b-jet
237 95
Calibration etc 10
105
TOTAL

37. HLT performance — signal efficiency
With previous selection cuts
Channel
Efficiency
(for fiducial objects)
H(115 GeV)gg
77%
H(160 GeV)WW* 2m
92%
H(150 GeV)ZZ4m
98%
A/H(200 GeV)2t
45%
SUSY (~0.5 TeV sparticles)
~60%
With RP-violation
~20%
Wen
67% (fid: 60%)
Wmn
69% (fid: 50%)
Topm X
72%

38. DAQ and Filter Farm Preserie

39. Summary
The CMS Trigger System is close to become reality after a long period of simulation studies, hardware prototyping and system construction
The CMS trigger design meets the challenging LHC requirements:
Large rate reduction
High efficiency for signal events
Wide inclusive selection (open to the unexpected)
Huge flexibility allowing future adaptation to the unknown

40. Reserve

41. Drift Tube local-trigger
trigger boards TRB
server board SB
to Sector Collector
8 cm
Synchronous pipelined system (40 MHz)
16 cm
2 metres

42. Global Muon Trigger Efficiencies
Optimal combination high efficiency, small rate
2.0
87.4
AND
2.9
97.3
SMART
5.4
98.1 OR
Rate
kHz
for 14 GeV
e % |h|<2.1
GMT Option
Rates for L=2x1033 cm-2s-1 DT
CSC
RPC
GMT smart
Muon Trigger Efficiency
GMT OR
GMT AND
GMT smart
GMT Efficiency

43. RPC Trigger Algorithm Pattern of hit strips is compared
to predefined patterns
corresponding to various pT
Implemented in FPGAs

44. Global Trigger Algorithms
An algorithm is a logical combination of trigger objects satisfying defined threshold, topology and quality criteria
There are 128 algorithms running in parallel.
Example:
Two leptons back-to-back in , opposite charge, with missing Et above threshold + -
.AND. E T to t Th re sh
e/
.OR.
>
Particle condition
for muons
for Et miss
for e/ 