TAU08, NovosibirskM. Pilar Casado (IFAE & UAB) 1
ATLAS Tau Trigger
Belanger-Champagne, C; Benslama, K; Bosman, M; Brenner, R; Casado, MP; Czyczula, Z; Dam, M; Demers, S; Farrington, S; Igonkina, O; Kalinowski, A; Kanaya, N; Osuna, C; Pérez, E; Ptacek, E; Reinsch; A; Saavedra, A; Sopczak, A; Strom, D; Torrence, E; Tsuno, S; Vorwerk, V; Watson, A; Xella, S
X-th International workshop on Tau Lepton PhysicsNovosibirsk, 22 – 25 Sep, 2008
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Contents
• LHC start-up
• ATLAS experiment
• Motivation of tau trigger
• ATLAS Trigger and Tau Trigger
• Tau Trigger Efficiency from data
• Timing measurements
• Conclusions
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ATLAS first eventATLAS first event (10 Sep)
Triggered by L1TAU, L1 Min. Bias and L1JET
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LHC projectLHC cooldown status (24 Sep):
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Expected LHC Performance
Year/Parameter 2008 2009
Beam energy 5 TeV 7 TeV
Peak luminosity 1031cm-2s-1 1033cm-2s-1
Integrated luminosity
~10 pb-1 ~few fb-1
Latest news: Start-up in spring 2009.
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ATLAS experiment
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Length= 55 m Width = 32 m Height = 35 m
Depth =100 m
Underground cavern in Point 1 for the ATLAS detector
The Underground Cavern at Point-1 for the ATLAS Detector
TAU08, NovosibirskM. Pilar Casado (IFAE & UAB) 815-April-2008 ATLAS RRB8
37 Countries 169 Institutions 2500 Scientific Authors total(1800 with a PhD, for M&O share)
Albany, Alberta, NIKHEF Amsterdam, Ankara, LAPP Annecy, Argonne NL, Arizona, UT Arlington, Athens, NTU Athens, Baku, IFAE Barcelona, Belgrade, Bergen, Berkeley LBL and UC, HU Berlin, Bern, Birmingham, UAN Bogota, Bologna, Bonn, Boston, Brandeis,
Bratislava/SAS Kosice, Brookhaven NL, Buenos Aires, Bucharest, Cambridge, Carleton, Casablanca/Rabat, CERN, Chinese Cluster, Chicago, Chile, Clermont-Ferrand, Columbia, NBI Copenhagen, Cosenza, AGH UST Cracow, IFJ PAN Cracow,
UT Dallas, DESY, Dortmund, TU Dresden, JINR Dubna, Duke, Frascati, Freiburg, Geneva, Genoa, Giessen, Glasgow, Göttingen, LPSC Grenoble, Technion Haifa, Hampton, Harvard, Heidelberg, Hiroshima, Hiroshima IT, Indiana, Innsbruck, Iowa SU, Irvine UC, Istanbul Bogazici,
KEK, Kobe, Kyoto, Kyoto UE, Lancaster, UN La Plata, Lecce, Lisbon LIP, Liverpool, Ljubljana, QMW London, RHBNC London, UC London, Lund, UA Madrid, Mainz, Manchester, CPPM Marseille, Massachusetts, MIT, Melbourne, Michigan, Michigan SU, Milano, Minsk NAS, Minsk NCPHEP,
Montreal, McGill Montreal, FIAN Moscow, ITEP Moscow, MEPhI Moscow, MSU Moscow, Munich LMU, MPI Munich, Nagasaki IAS, Nagoya, Naples, New Mexico, New York, Nijmegen, BINP Novosibirsk, Ohio SU, Okayama, Oklahoma, Oklahoma SU, Olomouc, Oregon, LAL Orsay, Osaka, Oslo, Oxford, Paris VI and VII, Pavia, Pennsylvania, Pisa, Pittsburgh, CAS Prague,
CU Prague, TU Prague, IHEP Protvino, Regina, Ritsumeikan, UFRJ Rio de Janeiro, Rome I, Rome II, Rome III, Rutherford Appleton Laboratory, DAPNIA Saclay, Santa Cruz UC, Sheffield, Shinshu, Siegen, Simon Fraser Burnaby, SLAC, Southern Methodist Dallas, NPI Petersburg, Stockholm,
KTH Stockholm, Stony Brook, Sydney, AS Taipei, Tbilisi, Tel Aviv, Thessaloniki, Tokyo ICEPP, Tokyo MU, Toronto, TRIUMF, Tsukuba, Tufts, Udine/ICTP, Uppsala, Urbana UI, Valencia, UBC Vancouver, Victoria, Washington, Weizmann Rehovot, FH Wiener Neustadt, Wisconsin, Wuppertal,
Würzburg, Yale, Yerevan
ATLAS Collaboration
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Barrel toroids
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Barrel: 3 independent readouts:
I (inner) - M (middle) - O(outer)
Muon spectrometer (barrel)
O
M
I
Chambers alternate with barrel toroids
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Tile barrel Tile extended barrel
LAr forward calorimeter (FCAL)
LAr hadronic endcap (HEC)
LAr EM endcap (EMEC)
LAr EM barrel
Calorimetry
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Tracking detectors
~ 6m long, 1.1 m radius
Si Strips Tracker : SCT Transition Radiation Tracker : TRT Pixels
Beam pipe
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ATLAS Trigger
H
L
T
DATAFLOW
40 MHz
75 kHz
~2 kHz
~ 200 Hz
120 GB/s
~ 300 MB/s
~2+4 GB/s
Event Building N/workDataflow Manager
Sub-Farm InputEvent Builder
EB
SFI
EBNDFMLvl2 acc = ~2 kHz
Event Filter N/work
Sub-Farm Output
Event FilterProcessors EFN
SFO
Event FilterEFP
EFPEFP
EFP
~ sec
~4
GB
/sEFacc = ~0.2 kHz
Trigger DAQ
RoI BuilderL2 Supervisor
L2 N/workL2 Proc Unit
Read-Out Drivers
FE Pipelines
Read-Out Sub-systems
Read-Out Buffers
Read-Out Links
ROS
120 GB/s
ROB ROB ROB
LVL1
DE
T R/O
2.5
s
Calo MuTrChOther detectors
Lvl1 acc = 75 kHz
40 MHz
RODRODROD
LVL2 ~ 10 ms
ROIB
L2P
L2SV
L2N
RoI
RoI data = 1-2%
RoI requests
underground (USA15)
surface (SDX1)
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ATLAS contributions
• Poster by Z.Czyczula (Copenhagen), “Tau Physics with First Data at ATLAS”
• Talks:– M.P.Casado (Barcelona), “ATLAS tau trigger” – F.Sarri (Pisa), “Search of the Higgs boson decaying
into tau-leptons at ATLAS” – A.Kalinowski (Univ. of Regina), “Tau Lepton
Reconstruction and ID with the ATLAS Detector at LHC”
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Tau Trigger Motivation
• ATLAS tau trigger aims at selecting hadronic decays of tau leptons, mainly one or three charged pions plus neutrals and one neutrino.
• It is difficult due to the high rate and occupancy but increases tremendously the physics potential. More information about tau
triger in CERN-OPEN-2008-020
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Motivation at 1031cm-2s-1
• Fundamental for W→ (first source of taus, 200000 with tau15i in 100 pb-1 at 1031cm-2s-1).
• Measure:– Cross section (pp→W)xBR(W→).– Leptonic branching
fractions of W.– Lepton universality.
• Relevant only for very first data at low instantaneous luminosity due to trigger rates.
See CERN-OPEN-2008-020
ATLAS preliminary
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Motivation at 1033cm-2s-1
• Essential in the following studies:– Charged Higgs of Minimal Supersymmetric Standard
Model (MSSM) H± →.– In states with more than one lepton, like SM Higgs
boson, MSSM neutral Higgs boson, Z’ boson decays, or decay chains in SUSY particles.
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Z’→ → hh at 800 GeVTrigger: tau35i(*) + met40
Collinear mass distribution for a hadron-hadron final states for a Z’ signal of 800 GeV. (Collinear aproximation: visible products and neutrino travel together.)
Reconstructed visible mass distribution for hadron-hadron final states for a Z’ signal of 800 GeV.
(*) tauXXi: First part is type of particle, “XX” is the ET threshold, and “i” indicates an isolation requirement in addition.
ATLAS preliminary ATLAS preliminary
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• The first level trigger (L1) finds regions of activity in the detector, and passes this information to the second level trigger (L2).
• The second level accesses the data in the region of activity determined by L1 (a few percent of the total).
• The third level trigger (or Event Filter) can also operate in the region determined by L2.
ATLAS Trigger: Regions of Interest (RoI)
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Level 1 Tau Trigger
– Tau Cluster: Energy in the two most energetic neighboring EM towers + the central 2x2 hadronic towers.
- EM Isolation: Energy in the isolating ring between 2x2 and 4x4 in the EM calorimeter.
- Hadronic Isolation: Energy in the isolating ring between 2x2 and 4x4 in the hadronic calorimeter.
x = 0.1 x 0.1
|| < 2.5
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Performance of L1 Tau Trigger
Efficiencies normalized with respect to offline (optimized to select those tau events which are likely to be reconstructed with the offline tau algorithms).
Dijet sample 8<pT<140 GeV
ATLAS preliminary
ATLAS preliminary
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HLT (L2 + EF) Selection
Basic concepts: Guided and simultaneous
reconstruction (for the different regions of activity)
• Each level uses the information of the preceeding level
• The reconstruction is done simultaneously for the different regions of activity.
• The rejection is applied as soon as possible.
• The second level trigger access only a few % of the total amount of data.
• In the third level the whole even is also accessible.
Isolation
pt>15GeV
Cluster shape
trackfinding
Isolation
pt>15GeV
Cluster shape
trackfinding
TAU15i TAU15i+
tau15i +
tau15 tau15+
tau tau +
cand cand+
Signature
Signature
Signature
Signature
L1 seed
STEP1
STEP4
STEP3
STEP2
tim
e
Example: Z +-
tau15i
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Tau HLT Selection
Refine (,) with thecalorimeter and calculate
shape variables
Determine tracking variables
including recalculation of (,)
Matching of calorimeter cluster and track collection
L2 selection EF selection
Similar to L2, but using
sophisticated offline algorithms.
The whole event and detailed
calibrations are available.
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L2 variables (high energy taus)C
alor
imet
erT
rack
ing
ATLAS preliminary
ATLAS preliminary
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Event Filter variables (high energy taus)
ATLAS
Cal
orim
eter
ATLAS preliminary
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Efficiencies per level
0
20
40
60
80
100
120
tau10i tau15i tau20i tau25i tau35i tau45i tau60
Eff
icie
ncy
(%
)
L1
L2 calo
L2 tracking
EF
Efficiencies calculated with respect to the preceeding level.
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Efficiency curves
Efficiencies normalized with respect to offline.
tau20i
ATLAS preliminary
ATLAS preliminary
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Rates per level
1
10
100
1000
10000
100000
tau1
0i
tau1
5i
tau2
0i
tau2
5i
tau3
5i
tau4
5i
tau6
0
Rat
e (H
z)
L1
L2 calo
L2 tracking
EF
Rates calculated on QCD background for L= 1031cm-2s-1.
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Tau Trigger MenusMenu Motivation
Single tau To be used in combination with other triggers (as MissET, leptons or jets), except for very high ET.
Single track Select RoIs with a single track to align the tracker & for E/p measurements.
tau + missing ET Wide spectrum of physics. At 1031 priority is W→
tau + l (+jets) Double tau decays (Z,H/A,…)
tau + tau (+jets) As tau + l (+jets) with both taus decaying hadronically
tau + jets, tau + bjets
ttbar studies
Commiss. items HLT decision is neglected, record only a fraction.
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Tau Trigger Menu at 1031cm-2s-1
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Z→: important at 1031 cm-2s-1
• 14000 events with tau15i in 100pb-1 at 1031cm-2s-1.
• Measure:– trigger efficiency in
Z→(h) lepton– ID efficiency.– Detector calibration: ET
miss & -jet energy scale determination.
– Cross section (SM measurement)
See CERN-OPEN-2008-020
ATLAS preliminary
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Efficiency measurement on data
• Z→→lep hadron– Tag the lepton (electron or
muon) and probe the other side.
– Background: top and QCD.– Expect 1200 signal events
in 100pb-1 with 30% background.
– Do first single tau trigger turn-on curves.
30pb-1
30pb-1
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Efficiency measurement on data
• tau + MissET trigger with ttbar– Tag 4jet25, study tau decay
offline.– Background: hadronic ttbar,
single top and QCD.– Expect ~130 signal events
in 100pb-1 with ~85 background events.
– Strategy to determine combined tau trigger efficiency with first data.
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Timing results
Time in ms,per RoI
Time in ms,per event
Mean algorithm execution time for each signature of the tau slice.
The average execution time of each algorithm remains roughly equal between signatures, while the average total time per event decreases as a
result of the lower number of RoIs per event for high energy signatures.
Timing is important in HLT because it gives latency. If it takes too long, we can not process data!
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Conclusions
• The tau trigger has recorded the first single beam events from the LHC.
• The detector and trigger will be commissioned as soon as we have the first collisions.
• The tau trigger will be used standalone for high thresholds and in combined mode for low energies.
• Hope to have early measurements with tau data and maybe some discoveries next year…
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Backup slides
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Level 1 Trigger
Schematic view ofthe level 1 trigger
Hardware based
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Resolution at each level
ATLAS Preliminary
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Single Tau Trigger Rates
Min. bias with =70mb, lumi 1031cm-2s-1
Only statistical errors