Transcript Document

TAU/JET/ET
MISS
TRIGGERS IN ATLAS
Francesca Sarri, INFN
e Università di Pisa
MCWS, 25/10/2006 LNF
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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
L=1031-32
Francesca Sarri, INFN
e Università di Pisa
MCWS, 25/10/2006 LNF
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TAU/JET/ETMISS SOURCES AND
INTEREST FOR PHYSICS
• Standard Model:
– inclusive Wτν (Zττ) production
– QCD.
• SM and MSSM Higgs:
– 100-150 GeV SM Higgs: qqH(ττ)
– A/H ττ
– H+ τν (mH+ < mtop and mH+ > mtop)
• SUSY
• Compositness
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Level 1 (hardware):
Defines Regions of Interest (RoI).
Uses Calo cells and Muon
chambers with reduced granularity.
e/g, m, , jet candidates.
High Level Trigger
Execution time
The ATLAS trigger
2ms
<75(100) kHz
10ms
Level 2 (software):
Seeded by LVL1 RoI.
Full granularity of the detector
Performs calo-track matching
Event Filter (software):
Offline-like algorithms.
Refines LVL2 decision
Full event building
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e Università di Pisa
~2 kHz
1s
~200 Hz
TIER 0 mass storage
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LVL1 Trigger Rates
Selection at 2x1033 cm-2 s-1
Rates (KHz)
MU20
0.8
2MU6
0.2
EM25I
12.0
2EM15I
4.0
J200
0.2
3J90
0.2
4J65
0.2
J60+xE60
0.4
TAU25+xE30
2.0
MU10+EM15I
0.1
OTHERS (pre-Scales,calibration,…)
5.0
TOTAL
25
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HIGH LEVEL TRIGGER RATES
Selection
Physics coverage
2x1033 cm-2s-1
Rates (Hz)
Electron
Higgs, new gauge bosons,
extra dim., SUSY, W/Z,
top
e25i, 2e15i
~40
Photon
Higgs, SUSY, extra dim.
g60i, 2g20i
~40
Muon
Higgs, new gauge bosons,
extra dim., SUSY, W/Z,
top, B-Physics
m20i, 2m10
2m6 with mB /mJ/y
~50
Jets
SUSY, compositness,
resonances
j400, 3j165, 4j110
~25
Jet & ETmiss
SUSY, leptoquarks
j70 + xE70
~20
tau & ETmiss
Extended Higgs models
(e.g. MSSM), SUSY
35 + xE45
~5
Others
pre-scales, calibration, …
Total
~20
~200
The rates for the HLT taken considering the EF performances equal to those one of the OFFLINE.
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e Università di Pisa
LVL1 CALORIMETRIC SIGNAL PROCESSING
TAU/JET/ETMISS triggers are calorimetric but they use two
different processors
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e Università di Pisa
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TAU TRIGGER
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e Università di Pisa
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Hadronic Tau Trigger (I)
(ATL-COM-DAQ-2003-030)
as in the TDR
For | h|<2.5
LVL1 trigger:
look at 4X4 matrix of calorimetric towers
(DhDf = 0.1 x 0.1 each trigger tower).
ET threshold for the central core
(EM+Had) and isolation thresholds
between core and 12 external towers for
e.m. and had. calorimeters.
second layer of
EM calorimeter
h
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e Università di Pisa
+ track
multiplicity
in the RoI
f
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
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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 DR=0.2 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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e Università di Pisa
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EFFECT OF TRIGGER SELECTIONS
ET core EM iso
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HAD 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)
New:studied for
Very Low Lumi
1031 cm-2 s-1
Current approach
Tracking
(# of tracks, charge,…)
Final decision : matching of cluster
and tracks, energy estimate
Calorimeter variables
Final decision : matching of
cluster and tracks, energy
estimate with energy flow
Under developing an EF
tracking based algorithm.
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e Università di Pisa
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JET AND ETMISS
TRIGGER
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e Università di Pisa
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LVL1 JET TRIGGER
as in the TDR
• identify hadronic jets using calorimetric data;
For | h|<3.2
• 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.
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.
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e Università di Pisa
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 (h, φ location)
 Iterative cone algorithm (R=0.4) to calculate weighted h, φ energy
center. Possible granularities : cell-based, LVL1 trigger towers,….
Jet
L2
ROI
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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e Università di Pisa
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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 < PT < 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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e Università di Pisa
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ETMISS TRIGGER
ETMISS is a global variable.
as in the TDR
For |h|<5
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.
For QCD events :
Rapidity Mean value
coverage of ETMISS
All
0.9 GeV
|h| < 5
5.6 GeV
|h| < 4
8.8 GeV
|h| < 3
12.5 GeV
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e Università di Pisa
trigger rate (KHz)
Rapidity coverage : critical for ETMISS trigger performances.
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ETMISS (GeV)
Possible Strategies for ETMISS Trigger at
LVL2 and EF
LVL2 possible strategy:
• Based on LVL1 Missing ET “ROI” (with scalar ET, ΣEx, ΣEy)
• 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 ΣEX, ΣEY from RODs
• Using full cell data.
• For both of these, add muons.
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e Università di Pisa
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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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e Università di Pisa
MCWS, 25/10/2006 LNF
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“Trigger aware analysis” from user perspective
Trigger optimization and
prospects for W  with 100
pb-1
(few weeks of data taking at
very low luminosity 1031-1032 cm-2s-1 )
Data samples:
18 000 events W  
124000 dijet events (J1-J2-J3)
For topological studies ~10^8 events from fast simulation
Daniel Froidevaux and Elzbieta Richter-Was
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e Università di Pisa
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Why W  ?
 Extract signal for most abundant source of -leptons as early as
possible. This requires a performant  and ETmiss trigger from the
very start!
For L = 2 1033, baseline plan is to trigger on 25I + XE30 at LVL1
(for a rate of about 2 kHz) and to raise the thresholds to 35i +
xE45 at the HLT (for an output rate of about 5 Hz) .
 Measurment of W  / W e 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  trigger and of ~ 50%
for the id/reco of  hadronic
decays were assumed.
Francesca Sarri, INFN
e Università di Pisa
Expected
rates for
100 pb-1
W  ,
 hadron
W  e
Z  ,
1 hadron
s.B (pb)
11200
17300
1500
30i + xE35
~ 15000
~ 250000
~ 1300
20i + xE25
~ 60000
~ 560000
~ 3500
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Algorithm to “emulate” LVL1 trigger
 seed “RoI” with topo-clusters, accept if ET > 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 > 0.3
 missing energy taken from ”uncalibrated calo off-line”.
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L1 tower More
multiplicity
on LVL1-like RoI’s
signal
multiplicity
ET spectrum
<> = 1.5
<
DR
between RoI’s
Total QCD
multiplicity
ET spectrum
<> = 0.78
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e Università di Pisa
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DR
between RoI’s
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Energy resolution for signal RoI and
threshold efficiency
2x2 RoI
4x4 RoI
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e Università di Pisa
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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e Università di Pisa
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Isolation for EMTau RoI
1.
2.
3.
4.
5.
ETL1otherEM/ETL1core < 1.0
ETL1otherHAD/ETL1core < 0.25
ETL1core/ETL1tower > 0.5
ETL1otherEM/ETL1coreEM < 1.0
ETL1otherHad/ETL1coreHad < 1.0
signal
L1core = 2x2
L1tower = 4x4
Full cirles: with threshold
ETL1tower > 0.75 * 20 GeV
QCD
Isolation very loose .... Factor 5 rejection at 80% efficiency but almost no
improvement if ET threshold added.
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e Università di Pisa
MCWS, 25/10/2006 LNF
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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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e Università di Pisa
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Concluding on LVL1-like selection
L=10^31
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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e Università di Pisa
MCWS, 25/10/2006 LNF
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The LVL2 like selection:
explore track-seeded reconstruction
Algorithm for tauL2 :
Signal response
 start from track with pT > 9 GeV accept < > = 1.16
if no more than 2 associated tracks
s = 0.17
in DR < 0.2 and pT > 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
Bgd response
 Same definition for ETMISS as at LVL1
< > = 0.86
s = 0.18
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e Università di Pisa
MCWS, 25/10/2006 LNF
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Concluding on LVL2-like selection
L=10^31
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 tape”for 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 ~10^5
signal events “on tape”
Need rejection ~ 10^3 for effic ~ 50% or increase ETmiss threshold
How fast bgd is supressed with the off-line ETmiss threshold.
~ LVL2 thresh.
~ LVL2 thresh.
ETmiss > 60 GeV gives bgd: rejection 10^3, signal: accept 10%
-> still 10^4 evt for 100pb-1,
S/B ~ 0.2 without refined tau indentification
Results with only fast-sim offline, ETmiss has no instrumental tails !
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~ 10^8 QCD events in fine pTbins
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 (calo+tracks) 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) ; track-based offline algorithm to identify 1-prong
(3-prong) tau decay.
tau1P
pT = 20 – 40 GeV
discriPDERS > 0.85
0.90
0.95
signal
68%
50%
40%
tau3P
bgd
6.5%
3.5%
1.0%
signal
46%
23%
4%
bgd
3.0%
1.0%
0.2%
After L2 track-based trigger, discrimination fairly flat as function of pT
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e Università di Pisa
MCWS, 25/10/2006 LNF
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Summary:
 LVL1 and LVL2 selection (calo+tracks) emulated
for W  analysis
 With rather soft selection ETmiss > 20 GeV + EMTauRoI > 20 GeV
estimated for 10^31:
60 Hz after LVL1
5 Hz after LVL2
 For off-line analysis start with
S/B ~ 0.002 ~ 10^5 signal events accepted for 100pb-1
Increasing ETMISS threshold helps in the background rejection:
at 60 GeV threshold, supression 10^2-10^3 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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e Università di Pisa
MCWS, 25/10/2006 LNF
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BACKUP SLIDES
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e Università di Pisa
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Sistema calorimetrico di ATLAS
Electromagnetic
Liquid Argon
Calorimeters
Tile Calorimeters
EM LAr |h| < 3 :
Pb/LAr 24-26 X0
3 sezioni longitudinali 1.2 
DhD = 0.025  0.025 – 1% equal.
Central Hadronic |h| < 1.7 :
η=1.475
η=1.8
Fe(82%)/scintillatore(18%)
3 sezioni longitudinali 7.2 
η=3.2
DhD = 0.1  0.1
End Cap Hadronic 1.7 < h < 3.2 :
Cu/LAr – 4 sezioni longitudinali
Hadronic Liquid Argon
EndCap Calorimeters
s
Forward Liquid
Argon Calorimeters
Forward calorimeter 3 < h < 4.9 :
EM Cu/LAr – HAD W/LAr
 41.9%
 1.8

 1.8%  
E  E
 E
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e Università di Pisa
DhD < 0.2  0.2
3 sezioni longitudinali
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Tau Trigger Rate
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e Università di Pisa
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e Università di Pisa
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More on ETmiss : we have only off-line available
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e Università di Pisa
MCWS, 25/10/2006 LNF
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S.Levy, HCP session, July 2005
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e Università di Pisa
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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
<> = 22.6 GeV
spectrum rather soft
for ETmiss, pTvis
signal
signal
<> = 16.6 GeV
<> = 18.4 GeV
(ATL-PHYS-2000-023)
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e Università di Pisa
MCWS, 25/10/2006 LNF
41
Results from past studies (ATLAS)
E/p measurements for calibration of hadronic calorimeters
280Hz rates predicted after HTL at 10^33
C. Biscarat
COM-CAL-99-0003
Rejection
70
340
2
total id rejection: 10^5
total id effic: ~ 25%
.trigger-like:
ETmiss > 35 GeV + pTjet > 20 GeV
preselection:
veto iso lepton, veto iso photon
tau-jet selection: track with pT> 30 GeV
single-track:
veto if extra tracks pT>1 GeV in tau cone
narrow-jet:
calo isolation
-1
Events for 100 pb : | 5270 Wp | 3630 Wr | 320 QCD jets (bb)
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e Università di Pisa
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Off-line analysis
~ 10^8 QCD events in fine pTbins
We don’t 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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e Università di Pisa
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Off-line analysis
~ 10^8 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 ~10^5 signal events
“on tape”
Need rejection ~ 10^3 for effic ~ 50%
or increase ETmiss threshold
Francesca Sarri, INFN
e Università di Pisa
MCWS, 25/10/2006 LNF
44