ucl seminar, 16/2/07costas foudas, imperial college london 1 overview of the cms trigger and plans...

UCL Seminar, 16/2/07 Costas Foudas, Imperial College London

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Overview of the CMS Trigger andOverview of the CMS Trigger andPlans for LHC Start-upPlans for LHC Start-up

Overview of this talk:

• Trigger Challenges at LHC and Goals• The CMS Trigger System• Pilot run Triggers (2007)• Physics Triggers (2008)


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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


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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


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Challenge 2: PileupChallenge 2: Pileup

• In-time pile up: Same crossing different interactions• Out-of-time pile up: Tails from previous event• New events come every 25 nsec 7.5 m radial separation.• Out-of-time pile up: Due to events from different crossings.• Need a to identify the bunch crossing that a given event comes

from.

P.S

ph

icas


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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


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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.


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CMS Trigger and DAQCMS Trigger and DAQ

• 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


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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


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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.

• An example of this is CMS Global Calorimeter Trigger (GCT)


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CMS Level 1 Trigger Components CMS Level 1 Trigger Components

• Level-1 Decision is based on Calorimeter and Muon information (same actually in ATLAS)

128 CC

24 CC


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CMS L1 Latencey BudgetCMS L1 Latencey Budget

• Total Latency = 128 Bx or 3.2 sec


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The CMS GCT TaskThe CMS GCT 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


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The GCT DesignThe GCT Design

Concentrator Card (1/1)

Leaf Card (1/8)

Wheel Card (1/2)


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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

GTI


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CMS GCT CardsCMS GCT Cards


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The Leaf Card (eThe Leaf Card (e±±, Jets, E, Jets, ETT))

• Main processing devices: Xilinx Virtex II Pro P70• 32 x 5 Gbit/sec Links with Serializers/Deserializers • Each serves 1/6 of the detector in Jet finding mode.

Virtex-II Pro-P70

3x12 Channel 5 Gbit/s

Optical Links (eventually)


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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+


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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


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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


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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.


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Pilot Run in 2007 (900 GeV)Pilot Run in 2007 (900 GeV)


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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. Assuming 450GeV inelastic cross section 40 mb2. Assuming 450GeV cross section W → lν 1 nb3. Assuming 450GeV cross section Z → ll 100 pb


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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


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Trigger for Pilot Run 2007 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 Beam Bias Trigger just to ‘see’ beams.


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Beam Hallo Trigger (2007)Beam Hallo Trigger (2007)


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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


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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.


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Pilot Run 2007 HLTPilot Run 2007 HLT• 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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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 :


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Plans for 2008 Physics RunPlans for 2008 Physics Run

• At 1031 commissioning of the LHC 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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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 eGamma, jet, … triggers with low thresholds (above noise) and muons with no threshold (any muon segment found) -- & no isolation


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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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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 basedMinimal 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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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


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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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CMS Trigger OverviewCMS Trigger Overview

• CMS is 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.

ucl seminar, 16/2/07costas foudas, imperial college london 1 overview of the cms trigger and plans...

Documents

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trigger decision

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cms trigger andplans

level of selection

qcd events