The ATLAS High Level Trigger

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The ATLAS High Level Trigger

Véronique Boisvert CERN

On behalf of the ATLAS Trigger/DAQ High Level Trigger Group

Université de Montréal-McGill Seminar

August 18^th 2003 Rockefeller Center NY, USA

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Outline



Physics Motivation



Selection Strategies



ATLAS detector



LHC environment



Trigger Architectures



High Level Trigger (HLT) Selection Software



Measurements



Conclusions

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The Big Questions

Is there unification of all forces?

What breaks it?

What breaks EW Symmetry?

What is the origin of mass?

What is the physics beyond The SM? New particles?

New interactions?

Flavor Puzzles:

Can we understand the masses And mixing of fermions.

Where does CP come from?

Are there more forces?

Particles? Symmetries?

Explain the masses of The p and e, and the

Relative strengths of The fundamental forces

Do we understand the Structure and fate of

The universe?

Are there extra Dimensions? What is the

structure of spacetime?

What is the right description Of gravity and where does it Become relevant for particle

Physics?

VLHC 100TeV

pp

0.5-1.0 TeV e+e- Collider

Mu Collider

Nu Factory

High Luminosity

Z Factory

B,K,tau/charm Factory

Tevatron 2TeV

pp

Particle Astrophysics 14 TeV

Pp

LHC

Can we explain the universe?

Why is it matter dominated?

Cosmological Constant?

Dark Matter Problem?

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Some Answers from the LHC



Electroweak symmetry breaking



Precise Standard Model measurements



B physics



Physics beyond the Standard Model:

 SUSY

 Exotics



The unknown!

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Electroweak Symmetry Breaking

 SM Higgs:

 114.4GeV < m_H< 1TeV

 LHC Higgs production and cross-sections

 Higgs decays:

 Fully hadronic:

 Large QCD background

 Gold plated modes:

 H 

 Signature:  pT >= 50GeV/c

 ~6 for mH=120GeV, 30 fb^-1

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Electroweak Symmetry Breaking

 Gold plated modes:

 H ZZ(*) 4l

• Signature: 4 high pT l

• =3-25 (dep. mH), 30fb^-1

•

Other typical signatures:

• tt,bb,ll,ll,lljj

•

MSSM Higgs

• Typical signatures for H⁰, h⁰, A, H^:

• ,,,tb

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Precision Measurements of SM

 High Luminosity and High E

 LHC is the ultimate factory:

 B, top, W, Z, H, …

 1:10¹³ for Higgs

 Deviations from SM

 Hints of new physics

 Precise W mass

 W jj 

• Large QCD background

• W e()

•  reco. in transverse plane!

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Precision Measurements of SM

 Precise W mass

 Very dependent on E scale (0.02%)

 Built-in calibration system

 e,, ATLAS, CMS: mW~15MeV (today ~34MeV)

 Precise Top mass: tt

 t Wb Signatures:

• Jets (including b-jets), l, Etmiss

• All channels, ATLAS, CMS:

mt~1-2GeV (today ~ 5.1GeV)

• Indirect m_H~25%! (today

LHC

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B physics



Copious production of B’s:

 CP-violation, B_s oscillations, Rare decays, etc.



B

_d

 J/ K

_S

• Max performance: (sin2)=0.010

• Min performance: (sin2)=0.016

• Rare decays

• Forward-Backward A: B_0d  K*⁰ ⁺^-

• Lowest mass region: enough accuracy to detect New Physics

• Signatures: di-leptons (), semi- exclusive reconstruction

q²/M_B² A_FB

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SuperSymmetry

 SM is an effective theory:

 Gauge coupling unification (families, gravity, etc.)

 Fine-tuning

 Hierarchy problem

 SUSY: supersymmetric partners s-1/2

 Pros:

 Elimination of fine-tuning by exact cancellations between partners

 Quark masses: radiative corrections in SUSY

 Consistent with string theories (incl. gravity)

 Cons:

 No observation!  broken, many free parameters and extensions

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SUSY

 MSSM particle spectrum, current limits:

 m_l,_ > 90-100 GeV (LEP)

 m_q,_g > 250 GeV (Run 1)

 Lightest SUSY Particle (LSP) is ₁₀

 Cold dark matter candidate

 Do neutralino reconstruction!

 Signature: E_Tmiss

 Decay chains

 No SM background, 2-body kinematics

 Need jets, l, E_Tmiss



l

m

q^~_L

^_

~

q

l



l

^

^_

~

R

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Beyond the SM

 SUSY, Technicolor, Little Higgs, New fermions and gauge bosons, compositeness,…

 Large Extra Dimensions

 Solves hierarchy problem:

 1 fundamental scale: EW scale (TeV)

 Gravity is weak because propagate in 3+n dimensions

 Cosmological implications

 Constraints from astrophysics

 Possible explanation for dark matter

 Etc.

 Tests Gravity and String Theory in the lab!

3-brane bulk

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Beyond the SM

 n2: ADD

 Graviton emission

 Signature: jet() + ETmiss

 Randall-Sundrum:

 n=1

 Warped

 2 branes (Planck and TeV)

 Radion: represents

fluctuations of the distance between the 2 branes

 Signature: Higgs like

 Mini black holes!

Gr

r

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So far…

 With a little bit of luck the LHC could completely revolutionize our field!

 Highlighted possible signatures

 Other constraints on the trigger architecture?

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The LHC at CERN

From: P. Sphicas 2003

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The LHC environment



Interaction rate: L x (pp) = 10

³⁴

cm

^-2

s

^-1

x 70mb = 10

⁷

mb

^-1

Hz x 70mb = 7x10

⁸

Hz!



~3600 bunches in LHC

 Length of tunnel is 27Km

 Time between bunches: 25ns! (40MHz bunch x rate)

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The LHC environment



Interactions per crossing: ~23!

 Minimum bias events overlap each event of interest

 We have “pile-up”

 “In-time”: particles from same crossing but different pp interaction

 “Out-of-time”: left-over signals from previous crossings

 Need bunch crossing identification

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Time of flight…

22 m

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pp collisions at high luminosity

HZZ  4

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T/DAQ challenges



efficient signal selection and excellent background rejection



Interaction rate: 7x10

⁸

Hz

 Store data at 100 Hz



Bunch crossing rate: 40MHz

 Out of time Pile-up

 Synchronization over detectors



High number of channels at high occupancy



It’s online!!

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Selection Strategies



2 main guiding principles:

 Inclusive selection

 Mostly 1 or 2 objects (electron, muon, photon, jet, b- tagged jet, tau, ETmiss, ET)

 High p_T: > O(10GeV/c)



Worry about:

 Low mass objects (eg B physics)

 Exclusive selection, topology, etc.

 Biases in selection

 Use complementary selections

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Selection Strategies

Object

Object Examples of physics coverageExamples of physics coverage NomenclatureNomenclature Electrons Higgs (SM, MSSM), new gauge

bosons,

extra dimensions, SUSY, W, top e25i, 2e15ie25i, 2e15i Photons Higgs (SM, MSSM), extra

dimensions, SUSY 60i, 260i, 220i20i Muons Higgs (SM, MSSM), new gauge

bosons,

extra dimensions, SUSY, W, top 20, 220, 21010 Jets SUSY, compositeness, resonances j360, 3j150, 4j100j360, 3j150, 4j100 Jet+missing E_T SUSY, leptoquarks j60 + xE60j60 + xE60

Extended Higgs models (e.g. MSSM),

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So far…

 The LHC environment is brutal to a Trigger DAQ system

 How to get the job done:

 Trigger Architecture

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The ATLAS Trigger Architecture

40 MHz

75 kHz

~1 kHz

~100 Hz

~1 sec

~10 ms

2.5 s

Level 1 Level 1 trigger trigger

High Level TriggerHigh Level Trigger Level 2Level 2 trigger trigger

Event Event Filter Filter

Region of Interest RoI

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Introduction: Regions of Interest

 Typically a few ROI / event

 Ex: Pixel 0.2x0.2

~ 92 Modules ~ 332 channels

 Only few % of event data

required!

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ATLAS, CMS vs Other detectors

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ATLAS vs CMS

 ATLAS:

 Smaller bandwidth

 But more complex

 CMS:

 Simpler system

 But very high bandwidth

 dependent on technology

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So far…



Introduced ATLAS Trigger Architecture



Let’s look at the HLT Selection Software

 Handle to making the Trigger decision

 Measurements

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HLT Selection principles



Fast

 Early rejection

 Seeding

 Data on demand (RoI or whole event)



Modify easily signatures



Precise knowledge of detectors and algorithms:

offline community

 Use offline code in the HLT software

 Develop Trigger Alg in offline framework

 Study boundary between Level 2 and EF

 Performance studies for physics analysis

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HLT Selection principles

 Offline into online: not an easy task!

 Requirements of speed and multi-threading on core infrastructure

 different steering philosophy:

 Offline: typically process entire events in a sequential fashion (post data on a whiteboard)

 Online: seeded and early rejection

 Appointment of a Reconstruction Task Force

 Look at issues regarding offline-online unification

 High Level Design (data flow, EDM)

 Subdetectors reconstruction

 Combined reconstruction

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HLT Design Overview

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HLT Selection Software

HLTSSW

Steering

ROBData Collector

Data Manager

HLT Algorithms Processing

Application

Event DataModel Processing

Application

Interface Dependency Package

Event Filter

HLT Core Software

HLT Algorithms

Level2

HLT Selection Software

HLT DataFlow Software

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The Steering

 Requirement:

 Early rejection

 Chosen strategy:

 Seeding mechanism

 Step wise process

Iso lation

p_T>

30GeV

Cluster shape

track finding

Iso lation

p_T>

30GeV

Cluster shape

track finding

EM20i + EM20i e30i + e30i

e30 + e30

e + e

ecand + ecand Signature 

Signature 

Level1 seed 

STEP 1 STEP 4

STEP 3

STEP 2

Steering

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HLT algorithms: e, selection

 Level1: selects calorimeter info over coarse granularity

 Level2:

 1)cluster E, position, shower- shape variables

 Refine L1 position: max E (1, 1)

 Refine (1, 1) with Energy

weigthed average in window 3x7:

(c, c)

 Parameters to select clusters:

 Sam. 2: R_^shape = E37/E77

 Sam. 1: R_^shape = E1-E2/E1+E2

EM LAr calorimeter

~190,000 channels

For 25GeV: _E/E~7%, _~8mrad, _r~1.6mm

HLT Algorithms

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HLT algorithms: e, selection



Level 2:

 2) need Track in InDet for el: Pixel, SCT

algorithm

 Z-finder

 Hit Filter

 Group Cleaner

 Track Fitter

z





Momentum res.: p_T/p_T ~ 0.1 p_T (TeV) Impact parameters: _r< 20m _z < 100m

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HLT algorithms : e, selection



Event Filter:For electrons passing Level 2, reexamined at EF

 Use offline reconstruction algorithms

 Calibrated data for the InnerDetector

 More tools for reconstruction since full event



Measurements: single el, p

_T

=25GeV/c

 Fully simulated events, latest software

 Pile-up for low and high lum

 Up to date geometry, amount of material, B field

Trigger Step Rate (Hz) Efficiency (%) Level2 Calo 2114±48 95.9.3

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The Data Access

Algorithm Region Selector

HLT

Algorithm Region

Selector

Trans.

Event Store

Data Access

Byte Stream Converter

Data source organized

by ROB

Transient EventStore

region list DetElem IDs

ROB ID raw event DetElems data

list DetElem IDs list DetElem IDs

DetElems Data Manager

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Collection Number Number of ROBs

Pixel module 1744 81

SCT side of module 8176 256

TRT straw layer 19008 256

LAr Trigger Tower 7168 768

Tile module 256 32

Muon MDT chamber 1168 192

Muon CSC chamber 32 32

Muon RPC chamber 574 32

Muon TGC chamber 1584 32

Data access granularity

Preliminary

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The Event Data Model

 Raw Data in byte stream format

 Level1, Level2, EF results, ROB data

 Different formats of Raw Data for particular subdetector

 RawDataObjects are object representation of Raw Data

 For InnerDetector the RDOs are skipped for Level2 (data preparation in converters)

 Features

 Clusters, Tracks, electrons, jets, etc.

 MCTruth info

 For debugging and performance evaluation

 Trigger Related data

 ROI objects, Trigger Type, Trigger Element, Signatures

Offline dependencies!

Event DataModel

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HLT Selection Software

HLTSSW

Steering

ROBData Collector

Data Manager

HLT Algorithms Processing

Application

Event DataModel Processing

Application

Interface Dependency Package

Event Filter

HLT Core Software

HLT Algorithms

Level2

HLT Selection Software

HLT DataFlow Software

<<import>>

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Timing Measurements

Timing on 2GHz machine Level2 Calo ~2ms Level2 Tracking ~3ms

~EF ~0.5s

Steering

Algorithms

Region Selector Data Access

1GHz, 3 seeds: 1.2ms

Infrastructure: ~23μ

aaae: Muo <8(GHz) Lar/Tile <(GHz)

Iereeor iproveeuerwa

1GHz, Tile: 0.03ms, Pixel:0.2ms, TRT:1.1ms

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Measurements



Putting it all together in the most realistic

environment: the Level 2 Test bed

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Conclusions



The LHC: quite a challenge!



The LHC detectors Trigger DAQ systems

 Interesting comparisons coming!



The ATLAS architecture

 RoI mechanism 

 Use of offline code in online environment 

 HLT selection software is adequate and performant

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