1. Overview of the LHC Triggers and Plans for LHC Start-up
Overview of the talk:
Triggering Challenges at LHC
Trigger Systems at LHC
Pilot run Triggers (2007)
Physics Triggers (2008)
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2. Costas Foudas, Imperial College London
Minimum Bias Events 22
70 mb deep inelastic component
Challenge 1
At full LHC Luminosity we have 22 events superimposed on any discovery signal.
First Level Event Selection requires considerable sophistication to limit the enormous data rate.
Typical event size: 1-2 Mbytes.
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3. Trigger Challenge at LHC
Higgs -> 4m
+30 MinBias
We want to select this type of event (for example Higgs to 4 muons) which are superimposed by this……
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4. Costas Foudas, Imperial College London
Challenge 2: Pileup
Challege 2
P.Sphicas
In-time pile up: Same crossing different interactions
New events come every 25 nsec  7.5 m radial reparation.
Out-of-time pile up: Due to events from different crossings.
Need to identify the bunch crossing that a given event comes from.
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5. Costas Foudas, Imperial College London
Trigger Goals at LHC
At LHC we want to select events that
have:
(1) Isolated leptons and photons,
(2) -, central- and forward-jets
(3) Events with high ET
(4) Events with missing ET.
The QCD- are orders of magnitude
larger than any exotic channel .
QCD events must be rejected early
in the DAQ chain and selecting them
using high ET cuts in the trigger will
simply not work.  Need to select events at
the 1:1011 level with almost no dead-time.
HLT must then be able to run full blown
reconstruction software and selection filters
Indicative event rates:
Inelastic: 109 Hz; (2) Wl : 100 Hz
t-tbar:10Hz (4) H(100 Gev): 0.1 Hz
H(500 GeV): 0.01 Hz
Challege 3
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6. Costas Foudas, Imperial College London
The CMS Trigger System
40 MHz input
100 KHz FLT rate
3.2 sec Latency
100 Hz written at the output
Event Size 1-2 Mbytes
The requirements on the Level-1 Trigger are demanding.
Level-1 Trigger: Custom made hardware processor.
High Level Trigger: PC Farm using reconstruction software and event filters similar to the offline analysis.
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7. The CMS L1 Calorimeter Trigger
Y/N
TPG
RCT GT
GCT P FE
Detector data stored in
Front End Pipelines.
Trigger decision derived
from Trigger Primitives
generated on the detector.
Regional Triggers search
for Isolated e/ and  and
compute the transverse,
missing energy of the event.
Event Selection Algorithms
run on the Global Triggers
128x25ns=3.2 µsec
later i.e. 128 bunch-
crossings latency
FE: Front End
P: Pipeline
RCT: Regional Calorimeter Trigger
GCT: Global Calorimeter Trigger
GT: Global Trigger
Synchronization
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8. Trigger and DAQ (CMS Example)
Detector Frontend
Computing Services
Readout
Systems
Filter
Event
Manager
Builder Networks
Level-1
Trigger
Run
Control
The First Level decision is distributed to the Front-end as well as the readout units.
Front-end and readout buffers take care of Poisson fluctuations in the trigger rate.
Hand-shaking using back-pressure guarantees synchronization
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9. The ATLAS Trigger System
40 MHz input
100 KHz Level 1 rate
(similar with CMS)
1 KHz Level 2 rate
Hz HLT output
Event Size ~1 Mbyte
Traditional 3 level system.
Regions of interest.
2.5 ms
~10 ms
~2 kHz
~ sec
~200 Hz
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10. Costas Foudas, Imperial College London
LHCb Trigger System I
LHCb trigger:
Two trigger levels:
L0: hardware
HLT: software
Trigger Strategy:
Enhance the b content in sample
High Pt particles (e,, ,hadrons)
Displaced tracks
Increase b content: 1%  ~50-60%
Follow seed particles of the decays
Trigger divided in alleys
Favor inclusive channels
Visible collisions
L = cm-2 s-1
L0: [hardware]
high Pt particles
calorimeter + muons
4 μs latency
HLT [software]
1 MHz readout
~1800 nodes farm
On tape:
Exclusive selections
Inclusive streams
~2 kHz
1 MHz
10 MHz
Architecture is similar to CMS….
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11. Costas Foudas, Imperial College London
Level-1 Strategy
Selecting events using physics filters at the High Level Trigger level (HLT CPU farms) will not do. The rate must be cut earlier before the HLT is overwhelmed by MHz of background QCD jet events.
It follows that the first level of selection, the First Level Trigger, should include algorithms of considerable sophistication which can find Isolated Electrons, Jets and detect specific event topologies.
This is a challenging task because we only have 15x25 ns = 375 ns to accomplish it for all sub-triggers. Jets take longer: 24x25 nsec = 600 nsec; which is many orders of magnitude faster than offline.
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12. Costas Foudas, Imperial College London
CMS L1 Latency Budget
Total Latency = 128 Bx or 3.2 sec
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13. The Calorimeter Trigger Task
Jet Triggers: Central, Tau and Forward jet finding and sorting.
Jet Counters: Count Jets in 12 different regions of the detector or 12 different thresholds within the detector.
Electron/ triggers: Select and Sort the e/ candidates from Regional Calorimeter Trigger.
Total Transverse, Total Missing Transverse and
Total Jet Transverse Energy calculation.
Receive the Muon data and send them to the Global Muon Trigger.
Luminosity Monitoring and readout all the RCT and GCT data for every L1A.
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14. Costas Foudas, Imperial College London
Jet Finders: A summary
jet=(-1)ln(tan(jet/2)) 
Particles strike the detectors and deposit their energy in the calorimeters.
Energy deposits in the calorimeters need to be recombined to reconstruct the transverse energy and direction of the original parton.
This is done using tools that are called Jet finders.
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15. Costas Foudas, Imperial College London
Cone Jet Finders
Searches for high transverse energy seeds and a cone in the - space is drawn around each seed.
Energy depositions within a cone are combined and the Et weighted  is calculated:
The new cone is drawn and the process is repeated until the cone transverse energy does not change R0
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16. Costas Foudas, Imperial College London
Example Algorithms
Electrons/photon finder
Jet Finder
Electron (Hit Tower + Max)
2-tower ET + Hit tower H/E
Hit tower 2x5-crystal strips >90% ET in 5x5 (Fine Grain)
Isolated Electron (3x3 Tower)
Quiet neighbors: all towers pass Fine Grain & H/E
One group of 5 EM ET < Thr.
Jet or t ET
12x12 trig. tower ET sliding in 4x4 steps w/central 4x4 ET > others
t: isolated narrow energy deposits
Energy spread outside t veto pattern sets veto
Jet  t if all 9 4x4 region t vetoes off
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17. Costas Foudas, Imperial College London
The GCT Design
Concentrator Card (1/1)
Leaf Card (1/8)
Wheel Card (1/2)
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18. Costas Foudas, Imperial College London
The GCT Design
63 Source cards
8 Leaf cards
2 Wheel cards
1 Concentrator
31 Source Cards
32 Source Cards
3 Jets Leafs
Wheel
Concentrator
e/ Leafs
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19. Costas Foudas, Imperial College London
CMS GCT Cards
Source
Leaf
Concentrator
GT Interface
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20. The Leaf Card (e±, Jets, ET, MET)
Virtex-II Pro-P70
3x12 Channel Gbit/s Optical Links
Main processing devices: Xilinx Virtex II Pro P70
32 x Gbit/sec Links with Serializers/Deserializers
Each serves 1/6 of the detector in Jet finding mode.
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21. Costas Foudas, Imperial College London
Data Sharing Scheme η- η+
Each Jet Leaf Card Serves 3 Regional calorimeter crates or 1/3 of half Barrel calorimeter (forward calorimeters have been included as edges of the barrel).
Each Leaf Searches for Jets using a 3x3 region sliding window.
Each Leaf has access to boundary data from neighbours via data duplication at the input of each Leaf
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22. Costas Foudas, Imperial College London
CMS GCT Status
63 Source cards
8 Leaf cards
2 Wheel cards
1 Concentrator
31 Source Cards
32 Source Cards
3 Jets Leafs
Wheel
Concentrator
e/ Leafs
By March 07
By March 06
Source Card
Concentrator Card
Leaf Card
GTI
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23. Trigger Commissioning and Testing without Beam : Patterns Tests
Install, integrate trigger chain and connect TTC system.
Propagate patters from the Trigger front end all the way to HLT and DAQ.
GCT is given here as an example but other systems will perform similar tests,
GCT: Electron Patterns Tests (March 07)
(1) The Source Cards will be loaded with events containing 4 electrons in
various parts of the detector.
(2) Empty crossings will be loaded in between the electron events. Each
Source Card can store half and orbit worth of data (~1500 thousand
crossings) which can be either empty or test events.
(3) The data will be propagated from the Source Cards via the optical
links, to the two electron Leaf Cards and from there to the concentrator
all the way to the Global Trigger and also to the DAQ.
(4) The data will also be processed by the GCT emulator and the results
of the emulator and the hardware will be compared.
Goals: (a) Exercise and validate a given trigger path.
(b) Establish synchronization: 4 electrons should arrive at GT at
the correct crossings with the correct energy, rapidity and phi.
(c) Establish agreement between software and firmware
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24. Trigger Commissioning and Testing without Beam : Cosmic Ray Tests
Take Cosmic Ray (CR) runs. Trigger using the muon detectors (RPC,DT,CSC). However be aware that CR do not come synchronously with the clock and do not necessarily go through the interaction point where the muon systems are optimized to trigger.
Raw rate estimated ~ 1.8 KHz for muon momentum
above 10 GeV. This should decrease a lot after cuts on timing and muon direction are folded in.
Goals: (a) Exercise and validate the data taking system.
(b) Establish coarse synchronization.
(c) Start aligning the detectors.
Almost no Level-1 cuts; HLT runs Level-1 simulation to validate the Level-1 trigger; Muon reconstruction at HLT but no momentum cuts.
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25. Costas Foudas, Imperial College London
Pilot Run in 2007 (900 GeV)
Does it make sense now ??
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26. Costas Foudas, Imperial College London
900 GeV Beam Settings kb 43
156
ib (1010) 2 4 10
* (m) 11
intensity per beam
beam energy (MJ)
.06
.12
.45
1.1
Luminosity (cm-2s-1)
2 1028
event rate (kHz)
0.4
2.8
10.3 64
W rate (per 24h)
0.5 3 70
Z rate (per 24h)
0.05
0.3 7
Inelastic cross section @ 900 GeV: mb
Cross section W → lν @ 900 GeV: nb
Cross section Z → ll @ 900 GeV: pb
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27. Particle Distributions:
Will not be better at 900 GeV
Particles go forward and have energy below 1 GeV.
Need to be able to Trigger forward at low energy.
Obviously you do not want
a transverse energy trigger.
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28. CMS Trigger for Pilot Run 2007
CMS Trigger Mode of Operation:
L1T identifies collisions and accepts all events
HLT verifies L1T bits, and stream events to calibration, e, , jets..
In other words we need a Minimum Bias Trigger just to ‘see’ beams.
Ideas on how to do this:
(1) Random Level-1 triggers at 1% level.
(2) CMS will be using the OPAL scintillators mounted at the
front face of the Hadron Forward Calorimeter (HF).
(3) Energy/Et over threshold from the first 2 rings around
the beams pipe (both sides) in coincidence.
(4) Feature Bits from the forward regions will be used to
count trigger towers over threshold.
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29. Costas Foudas, Imperial College London
Beam Hallo Trigger (2007)
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30. Costas Foudas, Imperial College London
Scintillator Trigger 2007
OPAL Scintillators
To be installed at the front faces of HF
Useful for :
(a) Commissioning
(b) Calibration (may be)
(c) Alignment
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31. Beam Pipe Rings Trigger 2007OR
AND
GCT Ring-Energy
Over Threshold
GT Logic and
Trigger Decision
GCT can compute the energy or
transverse energy in rings around
the beam pipe form both sides
of the calorimeter; energy is better.
Global Trigger can set threshold
on energy or transverse energy.
Forward and Rear in Coincidence
Simple Activity Triggers
Useful for:
(a) Commissioning
(b) Calibration (may be)
(c) Alignment
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32. Costas Foudas, Imperial College London
Feature Bits Trigger 2007
Feature bits are derived from the energy of a trigger tower after applying programmable thresholds.
These bits end up also on GCT along with the jet data.
GCT can count number of towers over threshold around the beam and place cuts such as N>10 on both calorimeters.
It is obvious from the second plot that Et will not do but we need energy.
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33. Costas Foudas, Imperial College London
Pilot Run 2007 HLT CMS
Minimum selection at Level-1.
Validate Level-1 Triggers using the Level-1 emulators running in HLT. Migrate algorithms to Level-1 as soon as they are understood.
Main rate reduction at HLT.
CMS (CSC): Halo Muons for alignment.
We should be able to time the detectors.
Validate detector and data taking concepts
A course alignment will be possible.
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34. Costas Foudas, Imperial College London
Physics Event rates in2007
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35. Expectations for 2007 Pilot Run
To gain the first experience with LHC beams validate as much as possible the detectors and prepare for the 2008 Physics run.
Some calibration studies may be possible from phi-symmetry
However, we should also see :
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36. Pilot Run HLT ATLAS/CMS
CMS: Minimum selection at Level-1.
CMS:Validate Level-1 Triggers using the Level-1 emulators running in HLT. Migrate algorithms to Level-1 as soon as they are understood.
CMS:Main rate reduction at HLT.
CMS (CSC) +ATLAS: Halo Muons for alignment.
ATLAS: Activity HLT trigger based on tracking, calorimeter and scintillators.
ATLAS: Muon (5 GeV) OR Calorimeter (10 Gev e/gamma) OR Jet (25 GeV)
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37. Costas Foudas, Imperial College London
LHCb Level-0 Decision
Muon
Detectors
Calorimeters
Pile up Veto
Selects high Pt particles.
Level-0 decision derived from calorimeter, muon and pileup veto information: 10 MHz 1 MHz 1032)
Pile-up Veto removes crossings with multiple vertices.
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38. Costas Foudas, Imperial College London
LHCb plans: Pilot run 2007
Goal: Select single High-Pt particles.
Start selection using the hadronic calorimeter to select clusters with High-Pt.
Trigger rate = 50 – 100 Hz
The data will be used for:
(a) Timing alignment
(b) Detector main alignment with B-field= off
(c) Turn on Magnetic Field and test E/p (RICH)
(d) Test Velo with Magnetic Field off and validate
impact parameter algorithms
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39. Staged commissioning plan for protons@7TeV
Mike Lamont
2008
Stage I II
III
Hardware commissioning
7TeV
Machine checkout
Beam commissioning
43 bunch operation
75ns ops
25ns ops I
Shutdown
No beam
Beam
Widely varying conditions in 2008
2009
III
Shutdown
Machine checkout
7TeV
Beam setup
25ns ops I
Install Phase II and MKB
No beam
Beam
Steady state operation in 2009
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40. Costas Foudas, Imperial College London
Pilot physics Month in 2008
From Mike Lamont talk at CMS week
Sub-phase
Bunches
Bun. Int.
beta*
Luminosity
Time
Int lumi
First Collisions
1 x 1
4 x 1010
17 m
1.6 x 1028
12 hours
0.6 nb-1
Repeat ramp - same conditions -
2 50%
1.2  nb-1
Multi-bunch at injection &
through ramp - collimation
2 days
Physics
12 x 12
3 x 1010
1.1 x 1029
2 50% in physics
6 nb-1
43 x 43
4.0 x 1029
30  nb-1
Commission squeeze – single
beam then two beams, IR1, IR5
Measurements squeezed
1 day
10 m
7 x 1029
3 days - 6 hr t.a. - 70% eff.
75 nb-1
Commission squeeze to 2m
collimation etc.
3 days
2 m
3.4 x 1030
0.36 pb-1
Commission 156 x 156
156 x 156
2 x 1010
5.5 x 1030
2 days - 6 hr t.a. - 70% eff.
0.39 pb-1
1.2 x 1031
5 days - 5 hr t.a. - 70% eff.
2.3 pb-1
28 days total
 3.1 pb-1
Rapidly changing conditions, with collision rate below 50kHz till 156x156
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41. Costas Foudas, Imperial College London
2008 Physics Run ATLAS/CMS
At 1031 commissioning of the LHC Trigger algorithms can be tried.
Algorithm cuts will be relaxed.
Level-1 Rate will be up to 50 KHz.
Redundancy between triggers will be used to compute the trigger efficiency using data.
200 Hz ‘on tape’
Emphasis: To understand the Trigger and the detector at LHC running conditions.
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42. Costas Foudas, Imperial College London
Rates at cm–2s–1
Assume in 2008:
L1T Out < 5x104 Hz
HLT Out < 1.5x102 Hz
We cannot trigger on all minbias
Jet and soft lepton triggers need to be operational at 1031 cm–2s–1
Isolated electron triggers also need to be operational at 1032 cm–2s–1
All triggers need to be operational at 1033 cm–2s–1
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43. Level-1 Trigger Arsenal
Minimum Bias
Hadron Calorimeter Feature bits
Program HB, HE & HF feature bits to ID towers with energy greater than noise
HF ET rings
Implemented on GCT - but to get minbias efficiently one needs to use HF E rather than ET
Beam Scintillation counters
Any TOTEM elements available (doubt it..)
Normal L1 triggers
Can operate e-gamma, jet, … triggers with low thresholds (above noise) and muons with no threshold (any muon segment found) -- & no isolation
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44. Lowest Nominal L1 Trigger Thresholds
Electron/ trigger
A trigger tower pair (50 crystals) over threshold - so 5 above noise (40 MeV) implies about 2 GeV minimum
We will use non-isolated e/ path
Jet trigger
A jet is composed of 288 trigger towers with nominal noise floor of ~250 MeV per tower which implies a minimum threshold of 10 GeV if we stay above 3
Muon trigger
Muon will not make it until it gets to 3 GeV
Accept poor quality and possibly when any segment is seen in the DTTF or CSCTF or RPC
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45. Costas Foudas, Imperial College London
DAQ Configurations
From Sergio Cittolin, Monday Plenary
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46. Costas Foudas, Imperial College London
2008: Startup Trigger
Take all minimum bias identified at L1T to HLT
There will be sufficient bandwidth kHz
Validate L1T and run simple HLT algorithms
(1) HLT algorithms could be calorimeter and muon
based
Minimal use of tracking
Apply thresholds (none applied at L1)
Stream data by trigger type
(2) Calibration triggers
ECAL: 0
Jets:  + Jet
Tracks: J/y → mmisolated 
(3) Prescale minbias as needed
Output bandwidth limit 1 GB/s
Rate limit Hz full events, 1-2 MB/events
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47. Costas Foudas, Imperial College London
ns, 25ns
For luminosities above 1031 cm–2s–1 we need to set thresholds at L1 and refine object ID at HLT
75ns operation possible till we see a luminosity
of 1033 cm–2s–1
Average of 5 interactions per crossing at the peak. Only in-time pileup relevant
Going to 25ns - 1 operation, i.e. at 33% bunch intensity, keeps the luminosity about the same but pileup goes down:
Now about 1-2 interactions per crossing
Pileup plays a less significant role
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48. Electron Trigger Data vs Trigger Emulator I
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49. Electron Triggers vs Trigger Emulator II
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50. Electron Trigger Data vs Trigger Emulator III
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51. Costas Foudas, Imperial College London
Plans for 2008 Physics Run I
LHCb: At 1031 LHCb is almost an order of magnitude away from the target Luminosity (2x1032).
15% of all Level-0 triggers are overlapping  excellent for computing trigger efficiencies and understanding the algorithms.
With 35 Kbytes/event LHCb will be writing 2 KHz on disc.
BS  + need 0.5 fb-1
J/  + can write 300 Hz which are 50% pure and are excellent for momentum and impact parameter calibration
Out of 1 MHz Level-0 rate there should be 600 Hz D* good for calibrating the RICH.
Exclusive triggers (B  hh, B  DS+h, B  + ) can be activated.
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52. Costas Foudas, Imperial College London
LHC Trigger Overview
The LHC experiments are gearing up for the first data. Preparations of almost two decades come to a conclusion and I am sure it will be a very exciting time.
However, the trigger and DAQ systems at LHC are orders of magnitude more complicated than before but also more sophisticated producing samples of purity not seen before .
Understanding the first samples will not be easy, it will take time and requires a methodical and systematic approach.
But you can be sure that he who understands his detector first will be closer to discovery using the data after 2008.
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