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ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

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Page 1: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLAS

Beauty 2002June 17 - 21 Santiago de Compostela

ATLAS B-TRIGGER

John Baines Rutherford Appleton

Laboratory, UKRALOn behalf of the ATLAS Collaboration

Page 2: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

Outline

Introduction:

• LHC & ATLAS

• The ATLAS detector

• Trigger Architecture

• B-Physics Programme

• History & Recent Developments

ATLAS B-TRIGGER UPDATE

Page 3: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

• LHC: Switch on: 2007

• Peak Luminosity: 2x1033 cm-2s-1 1034cm-2s-1

• 4.6 23 interactions per bunch crossing

• Coast (fill) lasts ~10 hours

Factor ~2 drop in L during coast

• ~1 per 100 interactions produce bb

• B-physics programme includes: • CP violation measurements in B-decays• Flavour Oscillations in Bs

• Searches and measurements of very rare decays• Precision Measurements • Production Measurements

Requires a Highly Selective and Flexible Trigger

p p14 TeV

Introduction – LHC & ATLASLHCRing

Page 4: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

The ATLAS Detector

11m

23m

Page 5: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

CoM Energy 14 TeV

Design Luminosity 1034 cm-2 s-1

Interactions per x-ing 23

Bunch spacing 25 ns

• High rate (40 MHz)• High granularity large event

size (1-2 MBytes)

Trigger/DAQ at the LHC

Page 6: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

ATLAS Trigger Strategy

HLTHLT

Page 7: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

ATLAS Trigger/DAQ – Overview

> Latency: 2.5> Latency: 2.5s (max)s (max)

> Hardware based (FPGA, ASIC)> Hardware based (FPGA, ASIC)

> Calo/Muon (coarse granularity)> Calo/Muon (coarse granularity)

> Latency: ~10 ms (average) > Latency: ~10 ms (average)

> Software (specialised algs)> Software (specialised algs)

> Uses LVL1 > Uses LVL1 Regions of InterestRegions of Interest

>> All All sub-dets, sub-dets, fullfull granularity granularity

> Emphasis on early rejection> Emphasis on early rejection

> Latency: few sec (average)> Latency: few sec (average)

> Offline-type algorithms> Offline-type algorithms

> Full calibration/alignment info> Full calibration/alignment info

> Access to full event possible> Access to full event possible

LVL1

LVL1

LVL2

LVL2

EF

EF

Page 8: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

Event Selection relies on:– Processing in Steps

• Alternate steps of feature extraction / hypothesis testing

• Events can be rejected at any step if features do not fulfil certain criteria (signatures)

– Reconstruction in Regions of Interest (RoIs)• RoI size/position derived from previous step(s)

HLT Strategy

Emphasis on early event rejectionEmphasis on early event rejection

Emphasis on minimisingEmphasis on minimising

a. Processing timea. Processing time

b. Network traffic b. Network traffic

Page 9: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

Region of Interest (RoI) mechanismLVL1 finds an EM cluster in

the calorimeter or a muon track in the external muon

spectrometer

LVL2 uses LVL1 info to define a region

LVL2 accesses data for that region (a few percent of the total)

Page 10: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

HLT Strategy – Example

Iso–lation

pt>30GeV

Cluster shape

trackfinding

Iso–lation

pt>30GeV

Cluster shape

trackfinding

EM20i EM20i+

e30i e30i +

e30 e30+

e e +

ecand ecand+

t i m

e

Signature

Signature

Signature

Signature

Level1 seed

STEP 1

STEP 4

STEP 3

STEP 2

Strategy at HLT:Strategy at HLT:> Validate step-by-step> Validate step-by-step

> Check intermediate signatures> Check intermediate signatures

> Reject as early as possible> Reject as early as possible

Sequential/modular approachSequential/modular approach

facilitates tuning for early rejectionfacilitates tuning for early rejection

LVL1 claims two isolated LVL1 claims two isolated

e/m clusters with pT>20GeVe/m clusters with pT>20GeV

(possible signature: Z–>ee)(possible signature: Z–>ee)

Page 11: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

HLTSSW – Design

HLTSSW

Steering

ROBDataCollector

DataManager

HLTAlgorithms

Processing Application

EventDataModel

Processing Application

Event Filter

HLT Core Software

HLT Algorithms

Level2

HLT Selection Software

HLT DataFlow Software

Interface

Dependency

Package

HLTSSW runs on the L2/EF processorsHLTSSW runs on the L2/EF processors

Several external dependenciesSeveral external dependencies(Monitoring Svc, MetaData Svc, offline…)(Monitoring Svc, MetaData Svc, offline…)

Page 12: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

Core Components• Steering

– Controls the order in which HLT algorithms should run, given the result of the previous triggering step

• All possible signatures form the Trigger Menu

• All possible sequences form the Sequence Table

• RegionSelector – select detectors in RoI

• DataStore – stores data produced by each processing step

• Convertors – convert raw data to input objects on demand – “Lazy unpacking”

Page 13: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

HLT Select. Software: Components

HLTSSW

Steering

ROBDataCollector

DataManager

HLTAlgorithms

Processing Application

EventDataModel

Processing Application

Event Filter

HLT Core Software

HLT Algorithms

Level2

HLT Selection Software

HLT DataFlow Software

Interface

Dependency

Package

Page 14: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

Data access by an HLT algoAlgorithm Region

Selector

HLT Algorithm

RegionSelector

Trans.EventStore

Data Access

ByteStream

Converter

Data sourceorganized

by ROB

TransientEventStore

region

list DetElem IDs

ROB ID

raw event data

Data arrangedby DetElems

list DetElem IDslist DetElem IDs

Data arranged

by DetElems

DetElems: Detector Elements (e.g. Pixel wafers)DetElems: Detector Elements (e.g. Pixel wafers)

IDs: Identifiers – Allow access to Geometry and mapping to ROBsIDs: Identifiers – Allow access to Geometry and mapping to ROBs

For the Event Filter: data already in the TESFor the Event Filter: data already in the TES

Page 15: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

Event Data and Algs• Closely coupled to offline software

– Common class definitions (Track, Cluster etc) • Facilitate code migration between LVL2/EF/Offline

• Saves effort in development and maintenance

• Makes comparisons and performance studies easier

– Same arguments for data access mechanism

• However, special online requirements (esp. LVL2)– Timing

– Multi-threaded running

Page 16: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

Exercising the HLTSSW1. LVL1 seeding

• Get list of Read-out Buffers (ROBs) for RoI, initially identified by LVL1

2. Data access• Network retrieval of raw data from ROBs, on demand.

3. Data preparation• Unpacking of raw data into objects convenient for the

reconstruction algorithms, again done on demand.• Calibration of the data objects.

4. Algorithm• Perform feature extraction and then hypothesis validation. For

example, cluster finding and identification of the cluster.

5. Take Trigger Decision

Page 17: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

ByteStream converters• Bytestream conversion process:

– Raw data (as received from the detector electronics) Data objects (convenient for the HLT algorithms)

– Example of data objects: Calorimeter cells with energy, position, etc…

• Example of offline code used in online.– The interface to the converter is the ATLAS offline software

Transient Data Store.

• Creation on demand.– When the converter is called objects are only created from raw

data as needed.

• Caching of data.– The conversion will only happen if the data objects are not in

memory already.

Page 18: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

ATLAS Trigger Architecture

Implementation

Higher LevelTrigger

Hardware (ASIC/FPGA)

General Purpose Processors : offline

type algorithms

General Purpose Processors optimised algorithms

108 109 Hz2 x

< 2.5 s

~ 10 ms

~ few sec

Decision times

FPGA = Field Programmable Gate ArrayASIC = Application Specific Integrated Circuit

Page 19: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

ATLAS B-Physics ProgrammeCP Violation:

• Measurement of Asymmetry in:

Bd J/(ee) K0()

Bd J/() K0()

Control channels: B+ J/()K+

Bd J/()K0*(K+) & equiv. (ee)

• Measurement of Asymmetry in:

Bd

+ other hadron final states

• Analysis of Bs J/()(KK)

Bs,d J/()()

Rare decays of the type : Bd,s (X)

• Branching fraction for Bd,s

• Branching fractions for:

Bd 0 and Bd K*0

• F-B Asymmetry in d

Precision measurements, eg.

• Bc measurements :

Bc J/, Bc J/• b polarisation

b J/()o(p)

The following have been evaluated for possible inclusion in the ATLAS B-physics programme:

sin2

CP-viol. ampl. a,b (sin2

s s A// A 2-1

Measurement of Bs oscillations:

• Bs Ds and Bs Ds a1 with

Ds o KK ms

|Vtd| / |Vts|

Note: The B-physics programme will be discussed in detail in the ATLAS Physics Overview talk.

Searches for: B K+K--

Page 20: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

History & Recent Developments

l• Target for LHC startup luminosity is now 2 x 1033 cm-2 s-1, although:

• Actual start-up luminosity uncertain• Luminosity may vary fill to fill• During a coast luminosity is expected to fall by a factor ~2

Re-evaluate trigger thresholds (single muon pT threshold and ID reconstruction thresholds) Assess impact of removing triggers requiring the most resources (e.g. J/(ee)) Develop flexible trigger strategies - possibility to include more B-triggers as luminosity falls, e.g.

• di-muon trigger only at L = 2x1033 cm-2s-1

• add other triggers as L decreases (e.g. B(), Ds() based on ID full-scan or low ET RoI)• Financial constraints Investigate new possibilities for reducing resource requirements e.g.

• Low ET Level-1 calorimeter RoI used to guide reconstruction at Level-2• Level-2 RoI used to limit region for reconstruction at the Event Filter

• Possibility of reduced detector at start-up:• TRT only at || < 2 (c.f. full TRT || < 2.5)• Only 2 of the 3 Pixel layers (inner “B-layer” maintained)

Need flexibility to cope with evolution of detector

• ATLAS B-trigger strategy outlined in the DAQ and High Level Trigger Technical proposal in 2000 Since then,

• LHC delayed, start-up now expected in 2007 Main c.p.u purchase delayed to 2006 (cheaper/faster c.p.u – expect 180 SpecInt95 = 4.5 GHz PC)

~

~

RoI = Region of Interest

Page 21: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

Outline

Trigger Strategy : • Final states including two muons• Hadron Final States

• Muon Trigger• Rejection of from /K decays• Based on ID full-scan:

• Inner Detector (ID)• ID Full-Scan• Bd() trigger

• Ds((KK),) trigger• Alternative based on Calorimeter RoI

• Final states with electrons and muons• TRT Full-scan

• J/(ee) trigger• Alternative using calorimeter EM RoI

ATLAS B-TRIGGER UPDATE

RoI = Region of Interest

Page 22: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

Level-1 Level-2 & EF

Confirmation of Muons in:

• Precision Muon Chambers• Inner Detector

Trigger for Di-Muon Final States

At Least 2 Muons:

Minimum thresholds:• Muon Barrel: pT > 5 GeV• Muon End-Cap: pT > 3 GeV

Actual thresholds used will be determined by rate limitations

~~

Level-1 Di-Muon triggers mainly due to:• muons from heavy flavour decays• single muons giving double trigger in end-cap trigger chambersRate ~600 Hz (pT > 6 GeV threshold,

L= 2 x 1033cm-2s-1)

EF Selections:• Refit ID tracks in Level-2 RoI• Decay vertex reconstruction• Select J/() B() etc. using mass & decay length cuts• Search for hadrons from B K0*(h,h), etc. Select using mass cuts

Bd J/()(K/K*)Bs J/()B B K0*, etc.b 0 J/()Bc J/()

e.g.

Total Rate ~ 20 Hz (L= 2 x 1033cm-2s-1)

Page 23: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

Hadron Final StatesF

ull-S

can

RoI

-Gui

ded

• Refit ID tracks in Level-2 RoI • Decay vertex reconstruction

• Mass & Decay length cuts.

Level-1 Level-2 & EF

At Least 1 Muon:

pT > 6 - 8 GeV

Confirmation of Muon in:• Precision Muon Chambers• Inner DetectorFull-Scan of Inner DetectorMass cuts

• Refit ID tracks in Level-2 RoI • Decay vertex reconstruction• Mass & Decay length cuts

Confirmation of Muon in:• Precision Muon Chambers• Inner Detector• Confirmation of Jet in calorimeter• Scan of ID in Jet RoI• Mass Cuts

Opt

ion

s

Bd

Bs Ds Bs Ds a1

Ds o , o KK

>1 Muon: pT > 6 - 8 GeVPlus:>1 Jet cluster ET > 5 GeV

~

e.g.

Page 24: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

The Muon Trigger

• Level-1 trigger from Muon Trigger Chambers

• Muon confirmed at Level-2 using Precision Muon Chamber Data

• 20 points per , resolution ~ 80m

Better track measurement allows tighter threshold.

• Muon confirmed in Inner Detector:• Extrapolate Muon track to ID,• Search for ID track. • Combine parameters & apply

matching cuts.

Inner Detector

Muon Trigger Chambers (RPC)

Muon Precision Chambers (MDT)

RPC: Restive Plate ChambersTGC: Thin Gap ChambersMDT: Monitored Drift Tubes

Muon Trigger Chambers (TGC)

Page 25: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

Level-1 Single Muon Trigger: Rate: ~20kHz

pT > ~6 GeV @ L=1033 cm-2 s-1

–Most are from /K decay with true pT < 6 GeV

Level-2 Muon Confirmation:• Using Precision Muon Detector info.:

–Better track measurement allows tighter threshold.Rate: ~9 kHz35% b and c , 65% /K

• Using Combined Muon & ID info:Single Muon TriggerRate: ~5 kHz @ L=1033 cm-2 s-1

~50% /K

Rejection of /K decays

LVL2 muon standalone

LVL2 muon + ID

Eff

icie

ncy

(%

)E

ffic

ien

cy (

%)

100

80

60

40

20

0

100

80

60

40

20

00 2 4 6 8 10 12 14

0 2 4 6 8 10 12 14

muon pT (GeV)

muon pT (GeV)

Raising threshold by 2 GeV ~ factor 2.5 rate reduction e.g. pT > ~8 GeV (8)

Rate ~ 2 kHz @ L=1033 cm-2 s-1

Page 26: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

An HLT Algorithm: T2Calo

• LVL2 clustering algorithm for electromagnetic (EM) showers, seeded by LVL1 EM RoI positions.

• Main variables built:

(1) Energy of EM clusters

(2) Associated Hadronic Energy

Page 27: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

An HLT Algorithm: T2Calo (cont)

(3) E3x7/E7X7 in Layer 2

background

(4) (E1-E2)/(E1+E2) in Layer 1

signal

Page 28: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

System performance• Conditions of the

measurements:– RoI of (x = (0.3 x 0.3).– Dijet events at low luminosity

with pileup. – Machine: CPU 2.4 GHz Xeon

with 1 GByte of memory.

• Measure minimum time that the data converter function would take using no offline-inherited code.

• Remember: Average LVL2 processing budget is ~10 ms.

Largest contribution is from Data Preparation

Algorithm is the smallest contribution

New offline-compatible version incorporating these and other improvements approaches performance requirements (now 3-4 ms for data

preparation)

Page 29: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

SemiConductor Tracker (SCT) Si micro-strip detector:

6.4 cm x 12.8 cm. 80 m r/o pitch.

Barrel: 4 cylinders; End-cap: 9 Wheels each with2 stereo layers: + u or v (40 mRad) 8 hits along track i.e. 4 space-points.

ATLASInner DetectorSee Inner Detector Talk for more details

3.5m

=2.51.2m

Transition Radiation Tracker (TRT) : Straws 40 cm - 70 cm long filled with Xe/CO2/CH4.

Single sense wire per straw. ~36 measurements along track.Two readout thresholds - Electron ID via higher threshold Transition Radiation hits

Pixel Detector : Si wafer:2.1 cm x 6.5 cm with 50 m x 300/400 m pixel r/o. 2(3) measurements along track.Inner layer at R = 5.05 cm

Page 30: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

Start with the Pixels and SCT:• Less affected by material interactions• 3-D measurements • Full || coverage from start-up

IDscan - Inner Detector full-scan

SCT

Pixels

Hit Filter:• Forms groups of hits - group contains the hits from a track; may also contain some extra nearby hits

• Use muon track to define Z of vertex of primary i.p.• Form 2D histogram of SCT & Pixel hits• Select hits in bins with >3 layers hit• Group hits from neighbouring bins

Group Cleaner:•Select the hits from a group forming a track candidate

• Determine 0 and for hit triplets

• Fill 2D histogram in 0,1/pT

• Bin with hits from >4 layers => track candidate

Track Fit:•Determine track parameters

IDscan Algorithm

Page 31: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

No. Pixel Layers3 2

Efficiency for B events with

pile-up (L = 1033 cm-2s-1): B events, pT (,) > 4 GeV

B events selected offline

Background B X events

Level-2 rate ~20 Hz for 2 kHz 8

EF selection reduces rate to ~3 Hz

Event Filter Selection:

•Tighter mass cut

•Vertex fit cuts :

2 / Nd.o.f. < 8,

Lxy > 100 m,

xy< 5

B h+h- TriggerLevel-2 selection:

• Tracks separated from trigger

by R> 0.2

• pT > 3.9 GeV

o

Two opposite sign tracks with:

• pT + pT > 10 GeV

• z0 < 2 cm

• 4.3 < M() < 6.3 GeV

+ -

10 15 20 25 30 35 40 45 50

Bd pT spectrum both pT>4 GeV

100

80

60

40

20

0

Leve

l-2

Eff

icie

ncy

(%)

0 2 4 6 8M( (GeV)

Bd Events + min. bias

No.

Eve

nts

xyDecay Vertexy

x

Lxy

78% 80%

89% 93%

1.1% 1.1%

pT of Bd (GeV)

Page 32: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

No. Pixel Layers23

69% 68%

78% 79%

3.5% 3.8%

Ds Trigger

o

Level-2 Selection:

• Tracks: pT > 1.4 GeV

• R> 0.2 w.r.t. trigger Two opp. sign tracks satisfying:

• M(KK) - M() < 17 MeV

Third track with:

• M(KK) - M(Ds) < 74 MeV

K+

EF Event Selection:

• Tracks: pT > 1.5 GeV

• Mass cuts :

M(KK) - M() < 14 MeV

M(KK) - M(Ds) < 56 MeV

• vertex fit cuts:

2 prob. >0.5%, Lxy >200m

• Ds vertex fit :

2 prob>0.5%, Lxy > 200 m

Level-2 Efficiencies for Bs Ds((KK)) events with pile-up (L = 1033 cm-2s-1):

Signal events with pT (, and K) > 1.5 GeV

Signal events selected offline

Background B X events

Level-2 Trigger rate ~60 Hz for 2 kHz 8EF selection reduces rate to ~9 Hz

Signal Events + min. bias

Eve

nts

/ 2.

5 M

eV

Eve

nts

/ 20

MeV

0.95 1 1.1 1.2

M(KK) (GeV)

Signal Events + min. bias

1.25 1.5 1.75 2 2.25

M(KK) (GeV)

Page 33: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

Alternative Using Level-1 Jet RoI to guide B-physics Triggers

• LVL2 reconstruction inside RoI corresponding to ~10% of ID acceptance potential to save ~factor 10 execution time c.f. full-scan but with lower efficiency

Preliminary studies of an alternative to the full-scan using, instead, low ET Level-1 RoI to define regions to search ID at LVL2

• Studied using fast simulation + parameterisation of calorimeter

• Jet RoI (0.8 x 0.8 cluster) ET > 5 :

• Mean Multiplicity = 1.7 (B X events, pT > 6 GeV)

• Reconstruct tracks at Level2 inside regionse.g. for B() and Ds()

Jet RoI Multiplicity (ET > 5 GeV)

Jet RoI Multiplicity

0 1 2 3 4 5 6 7 8 9

No.

Eve

nts

~

Page 34: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

Using Level-1 Jet RoI to guide B-physics Triggers

B •pT 4 GeV

•RoI ET 5 GeV

B hadron pT (GeV)

1

0.8

0.6

0.4

0.2

0

Eff

icie

ncy

0 5 10 15 20 25 30

Actual efficiencies and c.p.u. savings depend on thresholds & multiplicities => to be studied using full simulation

Eff

icie

ncy

B Ds •pT Ds, 1

GeV

•RoI ET 5 GeVB hadron pT (GeV)

0 5 10 15 20 25 30

1

0.8

0.6

0.4

0.2

0

Efficiency for Jet RoI within || < 0.4, || < 0.4 of B hadron

Based on fast simulation + calorimeter parameterisation

Page 35: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

RoI Guided Reconstruction at the

Event FilterFollowing Level-2 B-trigger selection:

• Use Level-2 to guide reconstruction at the Event Filter

• Level-2 defines a region which contains all tracks forming Ds(), B() candidates

• Region corresponds to ~10% of the Inner Detector acceptance

Factor ~10 saving in resources compared to full reconstruction

Bd +-

0 0.5 1 1.5 2 2.5 3

2

1.5

1

0.5

0

Ds (K+K-)

2

1.5

1

0.5

00 0.5 1 1.5 2 2.5 3

Page 36: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

Electron & Muon-Electron Final States bb X

Bd(J/(ee)Ko)

bb eX Bd(J/()K0)

e.g.

Ful

l-Sca

nR

oI-G

uide

d

Opt

ion

s

•Refit ID tracks in Level-2 RoI •Decay vertex reconstruction•Mass & Decay length cuts

Level-1 Level-2 & EF

At Least 1 Muon:

pT > 6 - 8 GeV

Confirmation of Muon in:• Precision Muon Chambers• Inner DetectorFull-Scan of Inner Detector (SCT, Pixels & TRT)Mass cuts

•Refit ID tracks in Level-2 RoI •Decay vertex reconstruction•Mass & Decay length cuts

>1 Muon: pT > 6 - 8 GeV

Plus:

>1 EM cluster ET > 2 GeV

Confirmation of Muon in:• Precision Muon Chambers• Inner Detector

Confirmation of electron in EM RoI using:•Calorimeter•Inner DetectorPossible search for second electron

Page 37: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

TRT-SCAN

Histogram for a single muon

1/pT

• Each hit straw populates a set of bins forming a line in the histogram in transform space (0,1/pT) or (0,1/pL).

• Maxima in the histogram correspond to track candidates.

Set of trajectories through a

straw

• Track candidates are examined and can be split or merged if required.

• A track fit is performed to improve the track parameter resolution. Drift time information can be included at this stage.

• Track search using a Histogramming method based on a Hough Transform.

• Track trajectories are described by:

(0,pT) - barrel and (0,pL) - endcap.

• Sets of trajectories are defined with discrete steps in 0 and 1/pT or 1/pL.

• Each trajectory corresponds to a histogram bin.

No

. o

f h

its a

lon

g t

raje

cto

ry (

0,

1/p

T)

30

20

10

0

•Execution time scales linearly with:• inverse pT(pL) threshold• no. hits in event

Page 38: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

Event Filter Selection:

• Tighter mass cuts

• Vertex fit cuts :

2 / Nd.o.f. < 8,

Lxy > 220 m,

xy< 40

Two opposite-sign e tracks with:

• pT + pT > 4 GeV

• | | < 1.4, | z0 | < 2 cm

• cos(ee) > 0.2

• 2 < M(ee) < 3.5 GeV

+ -

J/eeTriggerLevel-2 Selection:

•Tracks: pT > 0.5 - 1.5 GeV

• Identified as electrons by TRT

Level-2 Efficiencies for Bd J/(ee)Ks events with pile-up (L = 1033 cm-2s-1)Recon. tracks pT > 0.8 GeV:

40% : Signal events with pT (e,e) > 1 GeV53% : Events selected offline 2% : Background B X events Level-2 Trigger rate ~40 Hz for 2 kHz 8

EF selection reduces rate to ~4 Hz

o

Signal Events + Min. Bias

0 1 2 3 4 5 M(ee) (GeV)

Page 39: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

RoI ET > 2 GeV

90%

Efficiency for e from B e

e+e- separation0 1 2 3

No.

Eve

nts

separationJ/ e+e-

e pT > 0.5 GeV

0 0.5 1 1.5 2e+e- separation

No.

Eve

nts

separationJ/ e+e-

e pT > 0.5 GeV

electron pT (GeV)

0 2 4 6 8 10 12 14

1

0.8

0.6

0.4

0.2

0

Eff

icie

ncy

RoI Multiplicity

EM RoI ET > 2 GeV

RoI Multiplicity

0 1 2 3 4 5 6 7 8 9

No.

Eve

nts

If only one e found at Level-1, could search larger region for 2nd e Level-2 Reconstruction in ~10% of ID acceptance

If both electrons found at Level-1:• confirmation at Level-2 inside small region about each electron

Alternative Using Level-1 EM RoIPreliminary study of the possibility of using calorimeter to provide RoI to search for low pT electrons at level-2 for J/(ee) and -eEM RoI ET>2 :

• Mean Multiplicity = 1.1 (B->X , pT > 6 GeV)

• Effic. to tag both e in J/(e,e) : 80% (e pT >3 GeV)

Fast Simulation + Calorimeter Parameterisation

Page 40: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

Execution Times• Execution times measured on a different platforms

• Determine scaling with occupancy

• Times scaled to a 4 GHz PC (assumed 160 SpecInt 95)

• Used to estimate resources needed for B-trigger

L=1033 cm-2 s-1 Time (ms)

muon 0.2

SCT in Muon RoI 0.3

IDscan 11

Event Filter 6

Execution Times Scaled to 4GHz PC

0 20 40Execution Time (ms)

No.

Eve

nts

Exe

cutio

n T

ime

(ms)

30

20

10

00 2000 4000 6000 8000 10000

No. space-points in Event

IDscan IDscan

Linear scaling with occupancy

Page 41: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

Resource EstimatesStudy several options for B-physics triggers:• Chosen to represent a broad range of possibilities• Do not necessarily reflect final choices

• di-muon trigger when L > 2x1033 cm-2s-1

• Add B(hh) and Ds() triggers for L < 2x1033 cm-2s-1

based on ID full-scan for events with muon pT > 8 GeV

• di-muon triggers only Minimal additional resources

Requires some additional resources

B-trigger based on level-1 RoI :• di-muon trigger• B(), Ds(), J/(ee) etc. based on Level-1 EM Jet &

EM RoI

Requires additional resources, but less than (2)

B-trigger based on level-1 RoI:• di-muon trigger when L > 2x1033 cm-2s-1

• Add B(hh), Ds(), J/(ee) etc. triggers for L < 2x1033 based on Level-1 EM Jet and EM RoI

Modest additional resources

Resources additional to those needed for full menu of high pT triggers

(1)

(2)

(3a)

(3b)

~

~

~

~

Page 42: ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford Appleton Laboratory, UK RAL On behalf of the ATLAS Collaboration

ATLASB-Trigger John Baines RAL

Summary•The ATLAS B-trigger strategy was outlined in the DAQ and High Level Trigger Technical proposal in 2000

•Since then, B-trigger strategy has been re-assessed in the light of:• LHC luminosity target for start-up doubled to 2 x 1033 cm-2s-1

• Detector changes, including possibility of reduced detector at start-up• Need to minimise trigger resources in the light of financial constraints

Develop flexible B-trigger strategies to:• Cope with evolution of detector • Provide possibility of adding more B-triggers as luminosity falls

Investigate new possibilities for reducing resource requirements e.g.• Low ET Level-1 calorimeter RoI used to guide reconstruction at Level-2• Level-2 RoI used to limit region for reconstruction at the Event Filter

• As a result ATLAS hopes to pursue a full programme of B-physics from LHC start-up

• Next review stage is the Technical Design Report (2003) – some architectural choices must be made based on physics simulation studies, prototyping and full system modelling.

Ready for first Physics in 2007