ATLAS HLT Steering
Andrey Belkin ([email protected])
Johannes Gutenberg – Universität Mainz
36. Herbstschule für Hochenergiephysik
Maria Laach, September 2004
Overview
ATLAS detector
Trigger system
Steering
Performance tests
Status and outlook
September 2004
Andrey Belkin ([email protected])
Johannes Gutenberg – Universität Mainz
The ATLAS Trigger System, p. 2
Physical peculiarities
High collision rate:
about 40MHz
Strong reduction of data
rate is needed
Background: one
physically interesting
Event in up to 108
Events
The Trigger System must
be very effective
September 2004
Andrey Belkin ([email protected])
Johannes Gutenberg – Universität Mainz
The ATLAS Trigger System, p. 3
LHC / ATLAS detector
Large Hadron Collider (LHC): p-p Storage Ring at CERN (Geneva), center of mass energy √s=14TeV,
length 26,6 km, design luminosity 1034 1/(cm2 s), collision rate 40 MHz
ATLAS detector: Angle acceptance ~4π, data channels O(108), length 40m, height 22m, weight 7000t
Muon detectors (|η|<2,7)
Toroid magnets
Main goals:
Solenoid magnets (2T)
• Higgs-Bosons
• New physics (e.g. SUSY)
Electromagnetic calorimeter (|η|<5)
Hadronic calorimeter (|η|<5)
Inner detector (Silicon-pixel, -strip Detektoren, Transition Radiation Tracker)
September 2004
Andrey Belkin ([email protected])
Johannes Gutenberg – Universität Mainz
The ATLAS Trigger System, p. 4
Calorimetry
hadronic
calorimeter
e.m.
calorimeter
e.m. (e, γ)
September 2004
hadron
Andrey Belkin ([email protected])
Johannes Gutenberg – Universität Mainz
The ATLAS Trigger System, p. 5
Space angles and
granularity
η = -ln tan(θ/2)
Data: isolated traces on e.m./had planes, calorimeter
values, tracks, etc.
Isolation: a tower upon two calorimeter levels (e.m.,
had), slides and seeks isolated elements
We need to reconstruct the event by given data
The main data reduction at the first step is in „Regions
of Interest“ concept
Areas selected by Trigger Regions of Interest (RoIs)
September 2004
Andrey Belkin ([email protected])
Johannes Gutenberg – Universität Mainz
The ATLAS Trigger System, p. 6
The idea of three-stage architecture: reject highrated background processes at the earliest possible
time leaving complex and slow algorithms for the
latest steps. For example, Lvl-1 reduces data of
Event to RoIs, Lvl-2 applies calorimeter data, EF
applies track and isolation data
Trigger system
High-rate process selection in three stages:
Level-1
- Data from Calorimeter trigger (analog energy sums from
calorimeter cells ∆η×∆ϕ = 0.1×0.1), Muon trigger, RoIs, etc.
- Trigger decisions within maximum 2 µs
→ Hardware/Firmware implementation
- Event rate must be reduced from 40 MHz to 75-100 kHz
T
HLT: Level-2, Event Filter (my part)
- Event rate must be reduced from 75 kHz to 1-2 kHz
and then to 100-200 Hz
L
- Trigger decisions within maximum 1 ms-1 sec
→ Software implementation on a computer farm
H
- Reconstruction and selection of Events
September 2004
Andrey Belkin ([email protected])
Johannes Gutenberg – Universität Mainz
The ATLAS Trigger System, p. 7
Steering
In order to reconstruct the Event we need to apply
algorithms that combine all gathered by LVL1
data (energy, RoI, track, etc.) and test if it is
physically interesting one
For this, the HLT implements Steering, which is a
mechanism to drive running of algorithms in
certain sequences for classifying and selecting
Events according to given schema
September 2004
Andrey Belkin ([email protected])
Johannes Gutenberg – Universität Mainz
The ATLAS Trigger System, p. 8
EMTAUROI
...
MUONROI
...
HLT workflow
tau_cand ?
g_cand ?
...
...
e_cand ?
L2Alg_ApprECand(...)
Example: electron reconstruction, at the end we are
interested in finding one isolated electron of energy at least
25 GeV
In the schema of interesting Events we specify e25i
From the LVL1 we receive different RoIs, like
EMTAUROI, MUONROI, JETROI, etc.
In principle, we need to define in reconstruction sequence
that EMTAUROI leads to creation of three hypotheses:
tau_cand, g_cand, e_cand
The hypotheses are created and passed by Steering to
corresponding algorithms that approve or decline them,
like L2Alg_ApprECand(…)
If the hypothesis is approved the Steering looks into the
reconstruction sequence for next hypotheses and
algorithms, like e25_calo, e60_calo to
EFAlg_ApplyCalo(…), then track and isolation processing
If all hypotheses were successful, at the end we will
approve the e25i hypothesis and then the Steering will
report the match to the schema element e25i and will save
the Event
September 2004
Andrey Belkin ([email protected])
Johannes Gutenberg – Universität Mainz
Steering
e25_calo ?
e_cand !
e60_calo ?
...
...
EFAlg_ApplyCalo(...)
Steering
e25_calo !
Schema:
e25i
...
...
Steering
e25i !
...
Success! Save Event
The ATLAS Trigger System, p. 9
Processing buffer
We operate with different objects, like energy, RoIs, etc.
This objects are linked to corresponding hypothesis that is
just a label, like e25_calo, e25i
When the hypothesis is passed to processing, the algorithm
retrieves the physical data from storage by hypothesis label
Hypotheses and objects are linked together with “uses”,
“excludes”, “seeded by” relationships
We can navigate through the tree of linked objects in order
to obtain all data of each hypothesis
September 2004
Andrey Belkin ([email protected])
Johannes Gutenberg – Universität Mainz
The ATLAS Trigger System, p. 10
Processing of trigger objects tree
uses
EMTAUROI
Object of
EMTauRoi class
tau_cand
seeded by
e_cand
excludes
g_cand
tau_cand
excludes
g_cand
excludes
e_cand
g_cand
e_cand
tau_cand
Algorithm
• Receive input hypothesis
• Navigate through the tree and process data, attach
new objects
• Approve input hypothesis to activate it and initiate
the creation of a new hypothesis
September 2004
Andrey Belkin ([email protected])
Johannes Gutenberg – Universität Mainz
The ATLAS Trigger System, p. 11
Sequences of algorithms
and the Menu
Sequences
<SEQUENCE
<SEQUENCE
<SEQUENCE
<SEQUENCE
level="L2" input="EMTAUROI" algorithm="L2Alg_RoI2Cand/roi2cand/roi2cand"
output="e_cand" />
level="EF" input="e_cand"
algorithm="EFAlg_Cand2Calo/cand2calo/cand2calo"
output="e25_calo" />
level="EF" input="e25_calo" algorithm="EFAlg_Calo2Track/calo2track/calo2track"
output="e25_track" />
level="EF" input="e25_track" algorithm="EFAlg_Track2Result/track2result/track2result" output="e25i" />
<SEQUENCE level="EF" input="e_cand"
algorithm="EFAlg_Cand2Calo/cand2calo/cand2calo"
output="e15_calo" />
<SEQUENCE level="EF" input="e15_calo" algorithm="EFAlg_Calo2Track/calo2track/calo2track"
output="e15_track" />
<SEQUENCE level="EF" input="e15_track" algorithm="EFAlg_Track2Result/track2result/track2result" output="e15i" />
Menu
<SIGNATURE signature_id="e25i" prescale="1" forced_accept="0">
<TRIGGERELEMENT te_name="e25i" />
</SIGNATURE>
<SIGNATURE signature_id="e15ix2" prescale="1" forced_accept="0">
<TRIGGERELEMENT te_name="e15i" />
<TRIGGERELEMENT te_name="e15i" />
</SIGNATURE>
September 2004
Andrey Belkin ([email protected])
Johannes Gutenberg – Universität Mainz
The ATLAS Trigger System, p. 12
jobOption
ApplicationMgr.DLLs += { "GaudiAud" };
AuditorSvc.Auditors += { "ChronoAuditor" };
AuditorSvc.Auditors += { "MemStatAuditor" };
// Set output level threshold (2=DEBUG,3=INFO,4=WARNING,5=ERROR,6=FATAL)
MemStatAuditor.OutputLevel = 4;
MessageSvc.OutputLevel = 2;
ApplicationMgr.EvtMax = 10000;
TriggerConfig.sequenceListFileLocation = "realseqlist.xml";
TriggerConfig.signatureListFileLocation = "realsiglist.xml";
//...
Lvl1Conversion_L2.useL1Simulation = "NO";
Lvl1Conversion_L2.useMuons = "NO";
// ...
September 2004
Andrey Belkin ([email protected])
Johannes Gutenberg – Universität Mainz
The ATLAS Trigger System, p. 13
Tests
Ongoing tests of stability and consistence, bugs finding
Performance tests
Combinatoric explosure checks
P4-2GHz standalone, simple menu and sequences: 3-5ms for 1
Event
September 2004
Andrey Belkin ([email protected])
Johannes Gutenberg – Universität Mainz
The ATLAS Trigger System, p. 14
Current status and outlook
Computer cluster with multiprocessor PCs, Steering,
Navigation, Processing buffer, some real algorithms
(electromagnetic, partially muon)
Performance tests
Completing the system
September 2004
Andrey Belkin ([email protected])
Johannes Gutenberg – Universität Mainz
The ATLAS Trigger System, p. 15