TAUJETETMISS

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TAU/JET/ETMISS TRIGGERS IN ATLAS
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OUTLINE

• Tau/Jet/ETMISS trigger description what is
  in the TDR and what is new.
• An example of an analysis optimization of
  tau and ETMISS triggers for W??? at L1031-32

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TAU/JET/ETMISS SOURCES AND INTEREST FOR PHYSICS

• Standard Model
• inclusive W?t? (Z?tt) production
• QCD.
• SM and MSSM Higgs
• 100-150 GeV SM Higgs qqH(tt)
• A/H ?tt
• H ?t? (mH lt mtop and mH gt mtop)
• SUSY
• Compositness

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The ATLAS trigger
Level 1 (hardware) Defines Regions of Interest
(RoI). Uses Calo cells and Muon chambers with
reduced granularity. e/g, m, t, jet candidates.
2ms
Execution time
lt75(100) kHz
High Level Trigger
10ms
Level 2 (software) Seeded by LVL1 RoI. Full
granularity of the detector Performs calo-track
matching
2 kHz
1s
200 Hz
Event Filter (software) Offline-like
algorithms. Refines LVL2 decision Full event
building
TIER 0 mass storage
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LVL1 Trigger Rates
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HIGH LEVEL TRIGGER RATES
The rates for the HLT taken considering the EF
performances equal to those one of the OFFLINE.
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LVL1 CALORIMETRIC SIGNAL PROCESSING
TAU/JET/ETMISS triggers are calorimetric but they
use two different processors
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TAU TRIGGER
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Hadronic Tau Trigger (I) (ATL-COM-DAQ-2003-030)
as in the TDR
For ?lt2.5
LVL1 trigger look at 4X4 matrix of calorimetric
towers (DhDf 0.1 x 0.1 each trigger tower). ET
threshold for the central core (EMHad) and
isolation thresholds between core and 12 external
towers for e.m. and had. calorimeters.
LVL2 trigger look at the shower shape in the
2nd layer of e.m. calorimeter and at the track
multiplicity inside the RoI defined at LVL1. Cut
on the ratio between ET contained in a 3x7 cell
cluster and ET in a 7x7 cell cluster and on track
multiplicity
second layer of EM calorimeter
h
track multiplicity in the RoI
f
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Hadronic Tau Trigger (II) (ATL-COM-DAQ-2003-030)
as in the TDR

• LVL3 (Event Filter)
• look at the complete event.
• The variables of the offline algorithms are used
  as an approximation of the LVL3 trigger five
  variables
• number of reconstructed tracks, within DR 0.3
  of the candidate calorimeter cluster, between 1
  and 3
• cut on isolation fraction, defined as the
  difference between the ET contained in a cone
  size of DR0.2 and 0.1 normalized to the total
  jet ET
• cut on EM jet radius, an energy weighted radius
  calculated only in the e.m. calorimeter
• cut on EM energy fraction, defined as the
  fraction of the total jet energy in the e.m.
  calorimeter
• threshold on the pT of the highest pT track.

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EFFECT OF TRIGGER SELECTIONS
HAD iso
ET core
EM iso
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TAU TRIGGER EVOLUTION
For the LVL1 different RoI sizes are under study
(timing, resolution and efficiency,)
LVL2 Calorimeter based approach
LVL2 Tracking based approach
Perform tracking and obtain (h,f)
(h,f) from EMSamp2 Calo variables (more variables
used than in the TDR)
Newstudied for Very Low Lumi 1031 cm-2 s-1
Current approach
Tracking ( of tracks, charge,)
Calorimeter variables
Final decision matching of cluster and tracks,
energy estimate with energy flow
Final decision matching of cluster and tracks,
energy estimate
Under developing an EF tracking based algorithm.
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JET AND ETMISS TRIGGER
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LVL1 JET TRIGGER
as in the TDR

• identify hadronic jets using calorimetric data
• classify them according to ET
• provide multiplicity of jets passing required
  threshold
• provide the coordinates of the candidates to the
  LVL2
• have an energy resolution as good as possible
  for high ET and low ET jets.

For ?lt3.2
JET ELEMENT DhDf 0.2 x 0.2 (now only one
sample in depth) Algorithm - 2x2 jet element
cluster (0.4x0.4) to identify a jet RoI, it is a
local ET maximum. - 4x4 jet element (or 3x3 or
2x2) trigger cluster to measure the jet
ET. Trigger cluster size -big enough to have
a good energy resolution for high ET jets
(containment) -not too big for low ET jets
(noise and pileup) RoI size and step size
-spatial resolution and jet separation.
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LVL2 JET RECONSTRUCTION

• LVL2 starts from LVL1 RoI information (?, f
  location)
• Iterative cone algorithm (R0.4) to calculate
  weighted ?, f energy center. Possible
  granularities cell-based, LVL1 trigger
  towers,.

Jet
Jet
Cone Size
several iterations needed timing is an important
key.
Jet calibration (energy scale and resolution) has
an important effect on trigger efficiency.
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JETS AT THE EVENT FILTER

• Study of jet reconstruction at the EF
• Size of Region of Interest (RoI)
• 16 (0.4x0.4), 32 (0.8x0.8), 64 (1.6x1.6)
• Different types of clusters
• topological clusters or calorimeter towers
• Algorithms
• Fast KT, Cone
• Dijets samples with 35 GeV lt PT lt 1120 GeV

• Results of the study
• Jet reconstruction is better with a higher size
  of RoI,
• Higher size of RoI requires more time,
• Topological clusters are faster than calorimeter
  towers but Towers reconstruct better pT of jets

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ETMISS TRIGGER
ETMISS is a global variable. LVL1 Calorimeter
energies summed into a map with a granularity
DhDf 0.2 x 0.2. Ex, Ey, ET, ETMISS are
computed. ETMISS trigger is not a standalone
trigger, but it will be used in association with
jet or tau trigger. Rapidity coverage critical
for ETMISS trigger performances.
as in the TDR
For ?lt5
For QCD events
trigger rate (KHz)
ETMISS (GeV)
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Possible Strategies for ETMISS Trigger at LVL2
and EF

• LVL2 possible strategy
• Based on LVL1 Missing ET ROI (with scalar ET,
  SEx, SEy)
• Based on LVL1 Jet ROIs
• - Use cell data for each RoI
• Based on Trigger Towers
• - Refine with better calibration and replace
  saturated towers
• For all the above, add muons

• EF possible strategy
• Using FEB header SEX, SEY from RODs
• Using full cell data.
• For both of these, add muons.

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Algorithms for Tau/Jet/ETMISS triggers are still
under development not a final decision
taken. ATLAS physics groups have started now to
include trigger information in the simulations to
perform analysis a trigger part to perform a
Trigger Aware Analysis has been added in the last
releases of the ATLAS software. The Tau Trigger
slice is going to be added now no analysis
available with the true simulation of the tau
trigger. Trigger effects can be emulated next
slides will show an analysis.
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Trigger aware analysis from user perspective
Trigger optimization and prospects for W ??n with
100 pb-1 (few weeks of data taking at very
low luminosity 1031-1032 cm-2s-1 )
Data samples 18 000 events W ? ?n 124000 dijet
events (J1-J2-J3) For topological studies 108
events from fast simulation
Daniel Froidevaux and Elzbieta Richter-Was

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Why W ??? ?

• Extract signal for most abundant source of
  t-leptons as early as possible. This requires a
  performant t and ETmiss trigger from the very
  start!
• For L 2 1033, baseline plan is to trigger
  on t25I XE30 at LVL1 (for a rate of about 2
  kHz) and to raise the thresholds to t35i xE45
  at the HLT (for an output rate of about 5 Hz) .
• Measurment of W ??n / W ?en to confirm good
  understanding of trigger/reco/identification
  efficiencies
• E/p measurement in single-prong ? decay for
  calorimeter calibration.

Assumed that trigger chain is fully operational
and that the detector operates more or less as
expected (especially in terms of ETmiss
performance).
Efficiencies of 80 for the t trigger and of
50 for the id/reco of t hadronic decays were
assumed.
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Algorithm to emulate LVL1 trigger

• seed RoI with topo-clusters, accept if ET gt 5
  GeV
• calculate energy in 2x2 and 4x4 towers of
  0.1x0.1 (hxf)
• noise subtraction not applied, cells with
  negative energy
• suppressed from enegy counting
• energy in HAD (originaly at EM scale) multiplied
  by 1.25
• remove overlapping RoI with iterative
  procedure,
• imposing separation by DR gt 0.3
• missing energy taken from uncalibrated calo
  off-line.

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More on LVL1-like RoIs
L1 tower multiplicity
signal
ET spectrum
multiplicity
DR between RoIs
ltgt 1.5
lt
Total QCD
DR between RoIs
ET spectrum
multiplicity
ltgt 0.78
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Energy resolution for signal RoI and threshold
efficiency
2x2 RoI
4x4 RoI
Threshold 0.75 20 GeV 90 efficient at
ETvisible 20 GeV
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Energy resolution for background RoI and
threshold efficiency
2x2 RoI
2x2 RoI
4x4 RoI
Threshold 0.75 20 GeV Factor 10 rejection at
ETvisible 20 GeV
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Isolation for EMTau RoI

• ETL1otherEM/ETL1core lt 1.0
• ETL1otherHAD/ETL1core lt 0.25
• ETL1core/ETL1tower gt 0.5
• ETL1otherEM/ETL1coreEM lt 1.0
• ETL1otherHad/ETL1coreHad lt 1.0

L1core 2x2 L1tower 4x4
Full cirles with threshold ETL1tower gt 0.75
20 GeV
signal
QCD
Isolation very loose .... Factor 5 rejection at
80 efficiency but almost no improvement if ET
threshold added.
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More on ETmiss we have only off-line available
ETmiss, ETMissFinal, ETTruthNonInt, ETMissAtlfast
truth
off-line
Atlfast
ETmiss is calculated at EM scale, from calo only.
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Concluding on LVL1-like selection
L1031
LVL1 trigger ETL1tower 20 GeV Isol ETmiss
20 GeV ( this means ETL1tower 0.75 20 GeV and
isol_1 isol_2 )
Isolation criteria rather weak. We use ETmiss
from uncalibrated calo at EM scale...
Rates 0.02 Hz signal ? 2 105 events for
100pb-1 60 Hz QCD bgd
S/B 0.0003

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The LVL2 like selectionexplore track-seeded
reconstruction

• Algorithm for tauL2
• start from track with pT gt 9 GeV accept
• if no more than 2 associated tracks
• in DR lt 0.2 and pT gt 2 GeV
• store info on track quality of leading
• track for futher discrimination
• build energy from simplified Eflow
• (energy overestimated by 10-20 mostly
  because noise not suppressed)
• calo identification variables from EM2
• or all EM calo
• Same definition for ETMISS as at LVL1

Signal response lt gt 1.16 s 0.17
Bgd response lt gt 0.86 s 0.18
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Concluding on LVL2-like selection
L1031
LVL2 trigger ETL2tower 20 GeV track quality
id EM2 id all Cal ETmissFinal 20 GeV
Loose triger selection, now we have to supress
bgd in off-line analysis
Rates 0.01 Hz signal ? 105 signal events on
tapefor 100pb-1 5 Hz QCD bgd
S/B 0.002
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Off-line analysis
We start offline analysis with S/B 0.002 and
predicted 105 signal events on tape Need
rejection 103 for effic 50 or increase
ETmiss threshold How fast bgd is supressed with
the off-line ETmiss threshold.
LVL2 thresh.
LVL2 thresh.
ETmiss gt 60 GeV gives bgd rejection 103,
signal accept 10 -gt still 104 evt for
100pb-1, S/B 0.2 without refined tau
indentification
Results with only fast-sim offline, ETmiss has no
instrumental tails !
108 QCD events in fine pTbins
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Now we can go back to plot from page 25
Off-line
60 GeV
Atlfast
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Now we can go back to full-sim samples
Verify what off-line tauid rejection is
possible.... since some discriminantion power
already explored when accepting LVL2
(calotracks) candidates. We take tauL2
candidate on tape (after LVL2 tauiD) and
check efficiency for matching tau1P, tau3P
identified with PDE-RS optimisation (one MVA
technique among many)
tau1P tau3P
tau1p (tau3p) track-based offline algorithm to
identify 1-prong (3-prong) tau decay.
signal bgd signal bgd
pT 20 40 GeV
discriPDERS gt 0.85 68 6.5
46 3.0 0.90
50 3.5 23 1.0
0.95 40 1.0
4 0.2
After L2 track-based trigger, discrimination
fairly flat as function of pT
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• Summary
• ? LVL1 and LVL2 selection (calotracks) emulated
• for W? tn analysis
• ? With rather soft selection ETmiss gt 20 GeV
  EMTauRoI gt 20 GeV
• estimated for 1031
• 60 Hz after LVL1
• 5 Hz after LVL2
• ? For off-line analysis start with
• S/B 0.002 105 signal events
  accepted for 100pb-1
• Increasing ETMISS threshold helps in the
  background rejection
• at 60 GeV threshold, supression 102-103 at
  10 efficiency.
• Offline tau selection has to do the final work
  to extract the signal.
• Low luminosity provides unique opportunity to
  study low energy ? hadronic signatures in ATLAS
  (in view of SUSY) important possibility to
  verify the understanding of tauID and ETMISS reco
  before attacking New Physcics.

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BACKUP SLIDES
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Sistema calorimetrico di ATLAS
EM LAr ? lt 3 Pb/LAr 24-26 X0 3 sezioni
longitudinali 1.2 ? ????? 0.025 ? 0.025 1
equal. Central Hadronic ? lt 1.7
Fe(82)/scintillatore(18) 3 sezioni
longitudinali 7.2 ? ????? 0.1 ? 0.1 End Cap
Hadronic 1.7 lt ? lt 3.2 Cu/LAr 4 sezioni
longitudinali ????? lt 0.2 ? 0.2 Forward
calorimeter 3 lt ? lt 4.9 EM Cu/LAr HAD W/LAr
3 sezioni longitudinali
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Tau Trigger Rate
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(No Transcript)
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More on ETmiss we have only off-line available
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S.Levy, HCP session, July 2005
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Signal and background at 14 TeV
cross-section (PYTHIA) signal 10 x higher
QCD bgd 102-103 x higher than in CDF.
( ERW, ATL-PHYS-2000-023)
signal
ltgt 22.6 GeV
spectrum rather soft for ETmiss, pTvis
signal
signal
ltgt 16.6 GeV
ltgt 18.4 GeV
(ATL-PHYS-2000-023)
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Results from past studies (ATLAS)
E/p measurements for calibration of hadronic
calorimeters
C. Biscarat COM-CAL-99-0003
280Hz rates predicted after HTL at 1033
Rejection 70 340 2
total id rejection 105
total id effic 25
.trigger-like ETmiss gt 35 GeV pTjet gt
20 GeV preselection veto iso lepton,
veto iso photon tau-jet selection track with
pTgt 30 GeV single-track veto if extra
tracks pTgt1 GeV in tau cone narrow-jet
calo isolation
Events for 100 pb-1 5270 W?tn?pn 3630
W?tn?rn 320 QCD jets (bb)
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Off-line analysis
108 QCD events in fine pTbins
We dont have enough events to continue with
full-sim samples. We have move to fast-sim
samples to study topological selection only and
to estimate how much bgd suppression is possible
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Off-line analysis
108 QCD events in fine pTbins
Vetoying any other jet a la CDF gives 30
accept for signal 25 acept for bgd
We have looked at few more distribributions....
nothing obvious to optimise on...
We started offline analysis with S/B 0.002
and predicted 105 signal events on
tape Need rejection 103 for effic 50 or
increase ETmiss threshold