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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). Minimum Bias Events. 22. 70 mb deep inelastic component. - PowerPoint PPT Presentation
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LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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Overview of the LHC Triggers andOverview of the LHC Triggers andPlans for LHC Start-upPlans for LHC Start-up
Overview of the talk:
• Triggering Challenges at LHC• Trigger Systems at LHC• Pilot run Triggers (2007)• Physics Triggers (2008)
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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Minimum Bias EventsMinimum Bias Events
• 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.
22
70 mb deep inelastic component
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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Higgs -> 4
Trigger Challenge at LHCTrigger Challenge at LHC
• We want to select this type of event (for example Higgs to 4 muons) which are superimposed by this……
+30 MinBias
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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Challenge 2: PileupChallenge 2: Pileup
• 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.
P.S
ph
icas
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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Trigger Goals at LHCTrigger 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) Wl : 100 Hz t-tbar:10Hz (4) H(100 Gev): 0.1 Hz H(500 GeV): 0.01 Hz
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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The CMS Trigger SystemThe 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.
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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The CMS L1 Calorimeter TriggerThe CMS L1 Calorimeter Trigger
• FE: Front End • P: Pipeline• RCT: Regional Calorimeter Trigger• GCT: Global Calorimeter Trigger• GT: Global 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
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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Trigger and DAQ (CMS Example)Trigger and DAQ (CMS Example)
• 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
Detector Frontend
Computing Services
ReadoutSystems
FilterSystems
Event Manager Builder Networks
Level-1Trigger
RunControl
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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The ATLAS Trigger SystemThe ATLAS Trigger System
• 40 MHz input • 100 KHz Level 1 rate
(similar with CMS)• 1 KHz Level 2 rate• 1-2 102 Hz HLT output• Event Size ~1 Mbyte• Traditional 3 level
system.• Regions of interest.
2.5 s
~10 ms
~ sec
~2 kHz
~200 Hz
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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LHCb Trigger System ILHCb Trigger System I
• Architecture is similar to CMS….
Visible collisions
L = 2 1032 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
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
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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Level-1 StrategyLevel-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.
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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CMS L1 Latency BudgetCMS L1 Latency Budget
• Total Latency = 128 Bx or 3.2 sec
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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The Calorimeter Trigger TaskThe 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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Jet Finders: A summary Jet Finders: A summary
• 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.
jet=(-1)ln(tan(jet/2))
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Cone Jet FindersCone 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
R022 )()( R
i
iTT EE , i
iiTT
EE ,
1
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Example AlgorithmsExample Algorithms
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 towerspass Fine Grain & H/E
–One group of 5 EM ET < Thr.
Jet or ET
–12x12 trig. tower ET sliding in 4x4 steps w/central 4x4 ET > others
: isolated narrow energy deposits–Energy spread outside veto pattern sets veto
–Jet if all 9 4x4 region vetoes off
Electrons/photon finder Jet Finder
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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The GCT DesignThe GCT Design
Concentrator Card (1/1)
Leaf Card (1/8)
Wheel Card (1/2)
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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The GCT DesignThe GCT Design
• 63 Source cards• 8 Leaf cards• 2 Wheel cards• 1 Concentrator 31 Source Cards 32 Source Cards
3 Jets Leafs 3 Jets LeafsWheel WheelConcentrator e/ Leafs
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CMS GCT CardsCMS GCT Cards
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The Leaf Card (eThe Leaf Card (e±±, Jets, E, Jets, ETT, MET), MET)
• Main processing devices: Xilinx Virtex II Pro P70• 32 x 1.125 Gbit/sec Links with Serializers/Deserializers • Each serves 1/6 of the detector in Jet finding mode.
Virtex-II Pro-P70
3x12 Channel 1.125 Gbit/s
Optical Links
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Data Sharing SchemeData Sharing Scheme
• 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
η- η+
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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CMS GCT StatusCMS GCT Status
• 63 Source cards• 8 Leaf cards• 2 Wheel cards• 1 Concentrator
31 Source Cards 32 Source Cards
3 Jets Leafs
3 Jets Leafs
Wheel WheelConcentrator e/ LeafsBy March 07
By March 07
By March 06
GTI
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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Trigger Commissioning and Testing Trigger Commissioning and Testing without Beamwithout Beam : : Patterns TestsPatterns 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
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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Trigger Commissioning and Testing Trigger Commissioning and Testing without Beamwithout Beam : : Cosmic Ray TestsCosmic 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.
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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Pilot Run in 2007 (900 GeV)Pilot Run in 2007 (900 GeV)
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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900 GeV Beam Settings900 GeV Beam Settingskb 43 43 156 156
ib (1010) 2 4 4 10
* (m) 11 11 11 11
intensity per beam 8.6 1011 1.7 1012 6.2 1012 1.6 1013
beam energy (MJ) .06 .12 .45 1.1
Luminosity (cmLuminosity (cm-2-2ss-1-1)) 2 102 102828 7.2 107.2 102828 2.6 102.6 102929 1.6 101.6 103030
event rate (kHz) 0.4 2.8 10.3 64
W rate (per 24h) 0.5 3 11 70
Z rate (per 24h) 0.05 0.3 1.1 7
1. Inelastic cross section @ 900 GeV: 40 mb2. Cross section W → lν @ 900 GeV: 1 nb3. Cross section Z → ll @ 900 GeV: 100 pb
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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Particle Distributions:Particle Distributions:
• 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.
Will not be better at 900 GeV
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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CMS Trigger for Pilot Run 2007 CMS Trigger for Pilot Run 2007 CMS Trigger Mode of Operation:
• 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.
• 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.
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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Beam Hallo Trigger (2007)Beam Hallo Trigger (2007)
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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Scintillator Trigger 2007 Scintillator Trigger 2007
• To be installed at the front faces of HF• Useful for : (a) Commissioning (b) Calibration (may be) (c) Alignment
OPAL Scintillators
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Beam Pipe Rings Trigger 2007 Beam Pipe Rings Trigger 2007
• Simple Activity Triggers• Useful for: (a) Commissioning (b) Calibration (may be) (c) Alignment
OR OR
AND
GCT Ring-EnergyOver 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
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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Feature Bits Trigger 2007Feature 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.
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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Pilot Run 2007 HLT CMSPilot 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.
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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Physics Event rates in2007 Physics Event rates in2007
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Expectations for 2007 Pilot Run 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 :
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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Pilot Run HLT ATLAS/CMS 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)
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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LHCb Level-0 DecisionLHCb Level-0 Decision
• 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.
MuonDetectors
Calorimeters
Pile up Veto
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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LHCb plans: Pilot run 2007LHCb 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
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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Staged commissioning plan Staged commissioning plan for protons@7TeVfor protons@7TeV
III
No beam Beam
ShutdownMachine checkout
7TeV
Beam setup
25ns ops IInstall Phase II and MKB
Stage I II III
No beam Beam
Hardware commissioning
7TeV
Machine checkout
7TeV
Beam commissioning
7TeV
43 bunch operation
75ns ops 25ns ops I Shutdown
2008
2009
Widely varying conditions in 2008
Steady state operation in 2009
Mike Lamont
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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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 days @ 50% 1.2 nb-1
Multi-bunch at injection &through ramp - collimation
- - - - 2 days -
Physics 12 x 12 3 x 1010 17 m 1.1 x 1029 2 days @ 50% in physics 6 nb-1
Physics 43 x 43 3 x 1010 17 m 4.0 x 1029 2 days @ 50% in physics 30 nb-1
Commission squeeze – singlebeam then two beams, IR1, IR5
- - - - 2 days -
Measurements squeezed - - - - 1 day -
Physics 43 x 43 3 x 1010 10 m 7 x 1029 3 days - 6 hr t.a. - 70% eff. 75 nb-1
Commission squeeze to 2mcollimation etc.
- - - - 3 days -
Physics 43 x 43 3 x 1010 2 m 3.4 x 1030 3 days - 6 hr t.a. - 70% eff. 0.36 pb-1
Commission 156 x 156 - - - - 1 day
Physics 156 x 156 2 x 1010 2 m 5.5 x 1030 2 days - 6 hr t.a. - 70% eff. 0.39 pb-1
Physics 156 x 156 3 x 1010 2 m 1.2 x 1031 5 days - 5 hr t.a. - 70% eff. 2.3 pb-1
28 days total 3.1 pb-1
Pilot physics Month in 2008Pilot physics Month in 2008
Rapidly changing conditions, with collision rate below 50kHz till 156x156
From Mike Lamont talk at CMS week
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2008 Physics Run ATLAS/CMS2008 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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Rates at 10Rates at 1031-3331-33 cm cm–2–2ss–1–1
1033 1032
1031108 107
106
105 104
103
102 101
100
101 100
10-1
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
Assume in 2008:
L1T Out < 5x104 Hz
HLT Out < 1.5x102 Hz
LHC Forum, Coseners House, 13.4.07 Costas Foudas, Imperial College London
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Level-1 Trigger ArsenalLevel-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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Lowest Nominal L1 Trigger Lowest Nominal L1 Trigger ThresholdsThresholds
• 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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DAQ ConfigurationsDAQ ConfigurationsFrom Sergio Cittolin, Monday Plenary
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2008: Startup Trigger 2008: Startup Trigger
• Take all minimum bias identified at L1T to HLT There will be sufficient bandwidth 20-50 kHz
• Validate L1T and run simple HLT algorithms
(1) HLT algorithms could be calorimeter and muon based
Minimal use of trackingApply thresholds (none applied at L1)Stream data by trigger type
(2) Calibration triggers• ECAL: 0
• Jets: + Jet• Tracks: J/ → isolated
(3) Prescale minbias as neededOutput bandwidth limit 1 GB/sRate limit 500-1000 Hz full events, 1-2 MB/events
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2008 Operations @ 75ns, 25ns2008 Operations @ 75ns, 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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Electron Trigger Data vsElectron Trigger Data vsTrigger Emulator ITrigger Emulator I
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Electron Triggers vsElectron Triggers vsTrigger Emulator IITrigger Emulator II
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Electron Trigger DataElectron Trigger Datavs Trigger Emulator IIIvs Trigger Emulator III
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Plans for 2008 Physics Run IPlans 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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LHC Trigger OverviewLHC 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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