ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford...
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Transcript of ATLAS Beauty 2002 June 17 - 21 Santiago de Compostela ATLAS B-TRIGGER John Baines Rutherford...
ATLAS
Beauty 2002June 17 - 21 Santiago de Compostela
ATLAS B-TRIGGER
John Baines Rutherford Appleton
Laboratory, UKRALOn 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
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
ATLASB-Trigger John Baines RAL
The ATLAS Detector
11m
23m
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
ATLASB-Trigger John Baines RAL
ATLAS Trigger Strategy
HLTHLT
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
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
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)
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)
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…)
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”
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
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
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
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
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.
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
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--
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
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
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)
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.
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)
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
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
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
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)
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
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
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)
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)
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
~
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
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
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
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
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)
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
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
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)
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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