Anna Kaczmarska Przegląd IFJ PAN, 6.02.09 Kraków Tau leptons as an exciting probe for New Physics...
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Transcript of Anna Kaczmarska Przegląd IFJ PAN, 6.02.09 Kraków Tau leptons as an exciting probe for New Physics...
Anna Kaczmarska
Przegląd IFJ PAN, 6.02.09 Kraków
Tau leptons as an exciting Tau leptons as an exciting probe for New Physics in probe for New Physics in
ATLASATLAS Anna Kaczmarska NZ14, Institute of Nuclear Physics PAN, Cracow
1. ATLAS experiment2. Tau decays’ properties3. Tau signatures of New Physics4. Taus in Standard Model channels:
Z→ττ, W→τν, ttbar5. Conclusions
Results based on Monte-Carlo simulations at 14 TeV pp centre of mass energy
Anna Kaczmarska
Przegląd IFJ PAN, 6.02.09 Kraków
ATLAS (A Toroidal LHC ApparatuS)ATLAS (A Toroidal LHC ApparatuS)
Energy-scale:e/γ ~0.1%muons ~0.1%Jets ~1%
Muon Detectors: fast response for trigger, good p resolution
Electromagnetic Calorimeters: excellent e/γ identification, E and angular resolution, response uniformity
Hadron Calorimeters: Good jet and ET miss performance
Inner Detector: high efficiency tracking, good impact parameter resolution
•40MHz beam crossing•Readout: 160M channels (3000 km cables)•Raw data = 320Mbyte/sec (1TB/hour)
Anna Kaczmarska
Przegląd IFJ PAN, 6.02.09 Kraków
τ decay
π0
π+
π-
π+
τ jet
Decay modes Branching ratio
leptonic 35.2%
1-prong (τ→nπ0π±ν) 49.5%
3-prong (τ→nπ0π±ππ±ν) 14.6%
Tau hadronic decays in detector:●Decay products very collimated • Low track multiplicity • Displaced secondary vertex
Main sources of fake taus: QCD jets, electrons, muons
Tau reconstruction in ATLASTau reconstruction in ATLASIFJ PAN: Anna KaczmarskaElżbieta Richter-Wąs
Two ways for reconstruction of taus in ATLAS
Using tracks as seeds and energy from Energy Flow method (using Tracker + EM Calorimeter)
Using calorimeter clusters as seeds and energy only from calorimeters
Two ways for reconstruction of taus in ATLAS
Using tracks as seeds and energy from Energy Flow method (using Tracker + EM Calorimeter)
Using calorimeter clusters as seeds and energy only from calorimeters
Reconstruction efficiency for candidates reconstructed with both seeds (1P/3P):• τ’s in signal events ~60%• fake τ’s from QCD jets ~4-8%
Anna Kaczmarska
Przegląd IFJ PAN, 6.02.09 Kraków
Tau ID Algorithms:
Cut analysis, Projected Likelihood Probability Density Estimator with Range Searches, Neural Network, Boosted Decision Tree
Tau identification in ATLASTau identification in ATLASIFJ PAN: Marcin WolterAndrzej Zemła
Neural Network
Efficiency of tau identification
Reje
cti
on
of
fakes f
rom
QC
D jets
30%
~600
~1000
Both reconstruction algorithms provide variables discriminating between taus and fakes from QCD background
Radius of EM shower
Dedicated algorithms for rejection of fake candidates from electronsEfficiency (reco τ) = 95%Rejection (e reco as τ) = 60
+
ATLAS
Anna Kaczmarska
Przegląd IFJ PAN, 6.02.09 Kraków
Higgs and New Physics signatures with tau Higgs and New Physics signatures with tau leptonsleptons
Higgs Processes
Standard Model
VBF production, H→ττ
MSSM Higgs
bbH/A , H/A→ττ H+ in tt→H+b Wb,
gb→bH+, H+→τν
SUSY signatures with τ’s in final states
discovery
tau polarization measurement to constrain the underlying SUSY model
Extra dimensions… exotic physics…
Anna Kaczmarska
Przegląd IFJ PAN, 6.02.09 Kraków
To understand performance of complex detector
calibration, particle reconstruction algorithms, triggers… etc
To measure basic SM processes (cross-sections…) and compare them to theory and various Monte-Carlo tools
SM processes are background for New Physics
Direct sensitivity new physics (e.g. rare top decays .. )
Standard Model signatures with tau leptonsStandard Model signatures with tau leptons
Looking for New Physics is very exciting but first we have to … rediscover Standard Model
• Large statistics even with low luminosity
- analysis possible already with 100 pb-1 of integrated luminosity
• All of those channels have tau signatures: Z→ττ, W→τν, ttbar→W(τ)W(l/jj)bb
LHC will be a factory of W, Z and top
Anna Kaczmarska
Przegląd IFJ PAN, 6.02.09 Kraków
ZZ→τ→τ(lepton)(lepton)ττ(had)(had) events eventsIFJ PAN: Anna KaczmarskaElżbieta Richter-Wąs
Z→τ(e/μ)τ(had) will provide a statistically significant sample of τ leptons for 100 pb-1
measurement of the cross-section and the τ-ID efficiency
selected by lepton trigger -> unbiased sample of τ(had) decays
measurement of the τ trigger efficiencies
detector calibration: ETmiss and τ-jet energy scale determination (precision ~3%)
Expect
ed e
vents
in 1
00
pb
-
1
• Cross check between τ(e)τ(had) and τ(μ)τ(had) final states• Use of opposite-sign and same-sign e/μ-τ(had) events to control background •Dominant backgrounds
• QCD jets • We
Signal-to-background ratio 6:1 Visible mass (GeV)
Anna Kaczmarska
Przegląd IFJ PAN, 6.02.09 Kraków
WW→τν →τν eventseventsIFJ PAN: Paweł MaleckiElżbieta Richter-Wąs
The most abundant source of τ‘s in SM processes
measurement of the cross-section
branching ratios for leptonic W decays: BR(W→τν)/BR(W→eν)
ratio of the τ and electron electroweak coupling to charged current: gτ/ge
• Triggered on single tau + ETmiss
• Dominant backgrounds• QCD jets • We
•Signal purity and cross-section estimated on the basis of characteristic double peak structure in the track multiplicity distribution.
Signal-to-background ratio 3:1
Expect
ed e
vents
in 1
00
pb
-
1
Track multiplicity of tau candidates
ATLAS
Anna Kaczmarska
Przegląd IFJ PAN, 6.02.09 Kraków
Gives larger pT range of τ’s complementary to that from the W and Z processes
studies of τ trigger and tau ID efficiency
to complete the scan of the ttbar channels for cross-section measurements
to search for the effects beyond the SM in the top quark decay:
IFJ PAN: Tadeusz SzymochaInvolvement starting now
ttbar eventsttbar events
bHtRebt
btR 1),(
• ttbar→W(τν )W( qq‘ )bb channel• about 300 signal events with S:B
of 20:1 are expected for 100 pb-1
• ttbar →W(τν )W(lν)bb channel• dominated by W→lν+3jets events. • about 67 events can be observed
with S:B of 1:1 for 100 pb-1
τ t t
Anna Kaczmarska
Przegląd IFJ PAN, 6.02.09 Kraków
Events with τ’s from Standard Model will be observed with the first data of LHC
excellent possibility of understanding detector performance
Tau leptons will be the key to the Higgs and New Physics discovery:
SM Higgs, MSSM Higgs, SUSY, extra dimensions, new theories…
ATLAS group in IFJ PAN strongly involved in:
τ leptons reconstruction and identification algorithms
Standard Model physics with τ’s in final states
SummarySummary
We hope to have early measurements with tau data this year!
Important for our success are strong links with expertise of IFJ PAN Theory group (NO4), MC package Tauola for tau decays
Leading role of IFJ PAN group in preparation of 9 Internal Notes documenting expected tau performance (2007-2008); E. Richter-Was convener of the ATLAS Tau WG in years 2007-2008
External funding:
EU Marie Curie reintegration grant 2006-2007; Polish Government grant 2007-2008 (supplement to EU MC grant); Polish Government grant N202 006434 2008-2010; IN2P3 Collaboration 08-129 IFJ PAN- LAPP Annecy
Anna Kaczmarska
Przegląd IFJ PAN, 6.02.09 Kraków
Backup Slides
Anna Kaczmarska
Przegląd IFJ PAN, 6.02.09 Kraków
Why are tau leptons so interesting?Why are tau leptons so interesting?
massive particles measurable lifetime undergo electroweak interaction only production and decay well separated in time
potential for measurement of the polarisation, spin correlations, parity
excellent knowledge about tau decay modes from low-energy experiments
however ..... several decay modes possible jet-like signature huge background from QCD multi-jet production
Make it quite difficult for being observed in the experimental environment of pp collisions at ATLAS
Ideal signature to probe “New Physics” !
Anna Kaczmarska
Przegląd IFJ PAN, 6.02.09 Kraków
The very first beam-splash event in ATLAS
13
10:19, 10th September 2008
Online displayOffline display
The LHC has been fully installed and it started operation with single beams on 10.09.08. Now it is delayed until summer 2009 after an incident that happened on 19.10.08
Anna Kaczmarska
Przegląd IFJ PAN, 6.02.09 Kraków
Anna Kaczmarska
Przegląd IFJ PAN, 6.02.09 Kraków