Overview of the CMS Trigger and Plans for LHC Start-up

1
Overview of the CMS Trigger andPlans 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)

2
Minimum Bias Events
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.

3
Trigger Challenge at LHC

• We want to select this type of event (for example
  Higgs to 4 muons) which are superimposed by this

4
Challenge 2 Pileup
Challege 2
P.Sphicas

• 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.

5
Trigger Goals at LHC
Challeneg 3

• 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 11011 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-tbar10Hz (4) H(100 Gev) 0.1 Hz
• H(500 GeV) 0.01 Hz

Power, Rad. Hard. . . . . .
6
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.

7
CMS 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

8
The CMS L1 Calorimeter Trigger

• 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

128x25ns3.2 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
9
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.
• An example of this is CMS Global Calorimeter
  Trigger (GCT)

10
CMS Level 1 Trigger Components
128 CC
24 CC

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

11
CMS L1 Latencey Budget

• Total Latency 128 Bx or 3.2 ?sec

12
The 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.

13
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.

14
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

15
Example Algorithms
Electrons/photon finder
Jet Finder

• Electron (Hit Tower Max)
• 2-tower ?ET Hit tower H/E
• Hit tower 2x5-crystal strips gt90 ET in 5x5
  (Fine Grain)
• Isolated Electron (3x3 Tower)
• Quiet neighbors all towerspass Fine Grain H/E
• One group of 5 EM ET lt Thr.

• Jet or t ET
• 12x12 trig. tower ?ET sliding in 4x4 steps
  w/central 4x4 ET gt others
• t isolated narrow energy deposits
• Energy spread outside t veto pattern sets veto
• Jet ? t if all 9 4x4 region t vetoes off

16
The GCT Design
Concentrator Card (1/1)
Leaf Card (1/8)
Wheel Card (1/2)
17
The GCT Design
GTI
18
CMS GCT Cards
Concentrator
Source
Leaf
GT Interface
19
The Leaf Card (e, Jets, ET)
Virtex-II Pro-P70
3x12 Channel 5 Gbit/s Optical Links (eventually)

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

20
Data 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

21
CMS GCT Status
22
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

23
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.

24
Pilot Run in 2007 (900 GeV)
25
900 GeV Beam Settings
kb 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 (cm-2s-1) 2 1028 7.2 1028 2.6 1029 1.6 1030
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 mb
2. Assuming 450GeV cross section W ? l? 1 nb
3. Assuming 450GeV cross section Z ? ll 100 pb

26
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.

27
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 Beam 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.

28
Beam Hallo Trigger (2007)
29
Scintillator Trigger 2007
OPAL Scintillators

• To be installed at the front faces of HF
• Useful for
• (a) Commissioning
• (b) Calibration (may be)
• (c) Alignment

30
Beam Pipe Rings Trigger 2007

• 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

31
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 Ngt10 on
  both calorimeters.
• It is obvious from the second plot that Et will
  not do but we need energy.

32
Pilot 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.

33
Physics Event rates in2007
34
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

35
Staged commissioning plan for protons_at_7TeV
From Mike Lamont talk at CMS week
2008
Stage I
II
III
Hardware commissioning 7TeV Machine checkout 7TeV Beam commissioning 7TeV 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
Beam
No beam
Steady state operation in 2009
36
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 days _at_ 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 _at_ 50 in physics 6 nb-1
Physics 43 x 43 3 x 1010 17 m 4.0 x 1029 2 days _at_ 50 in physics 30  nb-1
Commission squeeze single beam 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 2m collimation 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
Rapidly changing conditions, with collision rate
below 50kHz till 156x156
37
Plans 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.

38
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 eGamma, jet, triggers with low
  thresholds (above noise) and muons with no
  threshold (any muon segment found) -- no
  isolation

39
Electron Trigger Data vsTrigger Emulator I
40
Electron Triggers vsTrigger Emulator II
41
Electron Trigger Datavs Trigger Emulator III
42
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

43
DAQ Configurations
From Sergio Cittolin, Monday Plenary
44
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 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 500-1000 Hz full events, 1-2 MB/events

45
Rates at 1031-33 cm2s1
1033 1032 1031
108 107 106
105 104 103
Assume in 2008 L1T Out lt 5x104 Hz HLT Out lt
1.5x102 Hz
102 101 100
101 100 10-1
We cannot trigger on all minbias Jet and soft
lepton triggers need to be operational at 1031
cm2s1 Isolated electron triggers also need to
be operational at 1032 cm2s1 All triggers need
to be operational at 1033 cm2s1
46
2008 Operations _at_ 75ns, 25ns

• For luminosities above 1031 cm2s1 we need to
  set thresholds at L1 and refine object ID at HLT
• 75ns operation possible till we see a luminosity
• of 1033 cm2s1
• 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

47
CMS 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.