atlas tau trigger

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


Contents

• LHC start-up

• ATLAS experiment

• Motivation of tau trigger

• ATLAS Trigger and Tau Trigger

• Tau Trigger Efficiency from data

• Timing measurements

• Conclusions


ATLAS first eventATLAS first event (10 Sep)

Triggered by L1TAU, L1 Min. Bias and L1JET


LHC projectLHC cooldown status (24 Sep):


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.


ATLAS experiment


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


Barrel toroids


Barrel: 3 independent readouts:

I (inner) - M (middle) - O(outer)

Muon spectrometer (barrel)

O

M

I

Chambers alternate with barrel toroids


Tile barrel Tile extended barrel

LAr forward calorimeter (FCAL)

LAr hadronic endcap (HEC)

LAr EM endcap (EMEC)

LAr EM barrel

Calorimetry


Tracking detectors

~ 6m long, 1.1 m radius

Si Strips Tracker : SCT Transition Radiation Tracker : TRT Pixels

Beam pipe


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)


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”


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


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


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.


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


• 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)


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


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


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


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.


L2 variables (high energy taus)C

alor

imet

erT

rack

ing

ATLAS preliminary

ATLAS preliminary


Event Filter variables (high energy taus)

ATLAS

Cal

orim

eter

ATLAS preliminary


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.


Efficiency curves

Efficiencies normalized with respect to offline.

tau20i

ATLAS preliminary

ATLAS preliminary


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.


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.


Tau Trigger Menu at 1031cm-2s-1


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


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


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.


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!


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…


Backup slides


Level 1 Trigger

Schematic view ofthe level 1 trigger

Hardware based


Resolution at each level

ATLAS Preliminary


Single Tau Trigger Rates

Min. bias with =70mb, lumi 1031cm-2s-1

Only statistical errors

atlas tau trigger

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