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Anna Kaczmarska Przegląd IFJ PAN, 6.02.09 Kraków Tau leptons as an exciting probe for New Physics in ATLAS Anna Kaczmarska NZ14, Institute of Nuclear Physics.

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Presentation on theme: "Anna Kaczmarska Przegląd IFJ PAN, 6.02.09 Kraków Tau leptons as an exciting probe for New Physics in ATLAS Anna Kaczmarska NZ14, Institute of Nuclear Physics."— Presentation transcript:

1 Anna Kaczmarska Przegląd IFJ PAN, 6.02.09 Kraków Tau leptons as an exciting probe for New Physics in ATLAS Anna Kaczmarska NZ14, Institute of Nuclear Physics PAN, Cracow 1.ATLAS experiment 2.Tau decays properties 3.Tau signatures of New Physics 4.Taus in Standard Model channels: Z ττ, W τν, ttbar 5.Conclusions Results based on Monte-Carlo simulations at 14 TeV pp centre of mass energy

2 Anna Kaczmarska Przegląd IFJ PAN, 6.02.09 Kraków 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 E T 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)

3 Anna Kaczmarska Przegląd IFJ PAN, 6.02.09 Kraków τ decay π0π0 π+π+ π-π- π+π+ τ jet Decay modesBranching ratio leptonic35.2% 1-prong (τ nπ 0 π ± ν)49.5% 3-prong (τ nπ 0 π ± π π ± 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 ATLAS IFJ PAN: Anna Kaczmarska Elżbieta 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%

4 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 ATLAS IFJ PAN: Marcin Wolter Andrzej Zemła Neural Network Efficiency of tau identification Rejection of fakes from QCD 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 electrons Efficiency (reco τ ) = 95% Rejection (e reco as τ ) = 60 + ATLAS

5 Anna Kaczmarska Przegląd IFJ PAN, 6.02.09 Kraków 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 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 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: Zττ, Wτν, ttbar W( τ )W(l/jj)bb LHC will be a factory of W, Z and top

7 Anna Kaczmarska Przegląd IFJ PAN, 6.02.09 Kraków Z τ (lepton) τ (had) events IFJ PAN: Anna Kaczmarska Elżbieta 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: E T miss and τ -jet energy scale determination (precision ~3%) Expected events in 100 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 W e Signal-to-background ratio 6:1 Visible mass (GeV )

8 Anna Kaczmarska Przegląd IFJ PAN, 6.02.09 Kraków W τν events IFJ PAN: Paweł Malecki Elżbieta 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 e ν ) ratio of the τ and electron electroweak coupling to charged current: g τ /ge Triggered on single tau + E T miss 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 Track multiplicity of tau candidates ATLAS

9 Anna Kaczmarska Przegląd IFJ PAN, 6.02.09 Kraków Gives larger p T 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 Szymocha Involvement starting now ttbar events 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

10 Anna Kaczmarska Przegląd IFJ PAN, 6.02.09 Kraków Events with τs 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 τs in final states Summary 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

11 Anna Kaczmarska Przegląd IFJ PAN, 6.02.09 Kraków Backup Slides

12 Anna Kaczmarska Przegląd IFJ PAN, 6.02.09 Kraków 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 !

13 Anna Kaczmarska Przegląd IFJ PAN, 6.02.09 Kraków The very first beam-splash event in ATLAS 13 10:19, 10 th September 2008 Online display Offline 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

14 Anna Kaczmarska Przegląd IFJ PAN, 6.02.09 Kraków

15 Anna Kaczmarska Przegląd IFJ PAN, 6.02.09 Kraków


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