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Tau leptons as an exciting probe for New Physics in ATLAS

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Presentation on theme: "Tau leptons as an exciting probe for New Physics in ATLAS"— Presentation transcript:

1 Tau leptons as an exciting probe for New Physics in ATLAS
Anna Kaczmarska NZ14, Institute of Nuclear Physics PAN, Cracow ATLAS experiment Tau decays’ properties Tau signatures of New Physics Taus in Standard Model channels: Z→ττ, W→τν, ttbar Conclusions Results based on Monte-Carlo simulations at 14 TeV pp centre of mass energy

2 ATLAS (A Toroidal LHC ApparatuS)
Muon Detectors: fast response for trigger, good p resolution Energy-scale: e/γ ~0.1% muons ~0.1% Jets ~1% Inner Detector: high efficiency tracking, good impact parameter resolution 40MHz beam crossing Readout: 160M channels (3000 km cables) Raw data = 320Mbyte/sec (1TB/hour) Electromagnetic Calorimeters: excellent e/γ identification, E and angular resolution, response uniformity Hadron Calorimeters: Good jet and ET miss performance

3 Tau reconstruction in ATLAS
IFJ PAN: Anna Kaczmarska Elżbieta Richter-Wąs Tau reconstruction in ATLAS Decay modes Branching ratio leptonic 35.2% 1-prong (τ→nπ0π±ν) 49.5% 3-prong (τ→nπ0π±ππ±ν) 14.6% τ decay π0 π+ π- τ jet Tau hadronic decays in detector: ●Decay products very collimated Low track multiplicity Displaced secondary vertex Main sources of fake taus: QCD jets, electrons, muons 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%

4 Tau identification in ATLAS
IFJ PAN: Marcin Wolter Andrzej Zemła Tau identification in ATLAS Tau ID Algorithms: Cut analysis, Projected Likelihood Probability Density Estimator with Range Searches, Neural Network, Boosted Decision Tree Both reconstruction algorithms provide variables discriminating between taus and fakes from QCD background ~1000 Neural Network Rejection of fakes from QCD jets ~600 Radius of EM shower ATLAS 30% Dedicated algorithms for rejection of fake candidates from electrons Efficiency (reco τ) = 95% Rejection (e reco as τ) = 60 + Efficiency of tau identification

5 Higgs and New Physics signatures with tau leptons
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…

6 Standard Model signatures with tau leptons
Looking for New Physics is very exciting but first we have to … rediscover Standard Model 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 .. ) LHC will be a factory of W, Z and top 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

7 Z→τ(lepton)τ(had) events
IFJ PAN: Anna Kaczmarska Elżbieta Richter-Wąs Z→τ(lepton)τ(had) events 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%) 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 We Signal-to-background ratio 6:1 Expected events in 100 pb-1 Visible mass (GeV)

8 W→τν events Signal-to-background ratio 3:1
IFJ PAN: Paweł Malecki Elżbieta Richter-Wąs W→τν events 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 We 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 Expected events in 100 pb-1 ATLAS Track multiplicity of tau candidates

9 IFJ PAN: Tadeusz Szymocha Involvement starting now ttbar events 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: 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 t t τ

10 We hope to have early measurements with tau data this year!
Summary 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 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  ( ); E. Richter-Was convener of the ATLAS Tau WG in years External funding: EU Marie Curie reintegration grant ; Polish Government grant (supplement to EU MC grant); Polish Government grant N ; IN2P3 Collaboration IFJ PAN- LAPP Annecy We hope to have early measurements with tau data this year!

11 Backup Slides

12 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 Ideal signature to probe “New Physics” ! 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 Why are tau leptons so interesting? Tau leptons are massive particles with measurable lifetime undergoing electroweek interactions only. The production and the decay of the tau letons are well separated in time providing unbiased potential for measurements of the polarisation, spin correlations and the parity of resonances decaying into tau leptons. Also the excellent knowledge of tau decay modes from low energy experiments makes them an ideal signature to probe new physics. However tau leptons have possible several decay modes. ….. 1.0 min

13 The very first beam-splash event in ATLAS
10:19, 10th September 2008 Online display Offline display The LHC has been fully installed and it started operation with single beams on Now it is delayed until summer 2009 after an incident that happened on 13



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