ATLAS Tau Working Group Meeting CERN. Ryan D. Reece and Brig Williams. March 25, 2009

Transcript

1 Z ττ µτ ATLAS Tau Working Group Meeting CERN Ryan D. Reece and Brig Williams University of Pennsylvania Marc 25, 29 Ryan D. Reece (Penn) Z ττ µτ reece@cern.c / 25

2 Outline Introduction and Selection 2 Dijet Background b b Background 4 Cut Flow and Results Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 2 / 25

3 Introduction and Selection Ryan D. Reece (Penn) Z ττ µτ reece@cern.c / 25

4 Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 4 / 25

5 Preface Goal: to observe Z ττ µτ in early data (- pb ), to gain experience wit and evaluate tau reconstruction. We sow b b production is a dominant QCD background. We use a fake-rate scaling tecnique for getting sape and normalization of te b ackground. In tis Monte Carlo analysis, we use only fully simulated samples. We do not use b-tagging. We do not use te collinear approximation to reconstruce Z mass in order to accept more signal by avoiding te necessary cos(φ µ φ τ ) >.9 cut. Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 5 / 25

6 Preselection I produced my own ntuples directly from AODs using EventView. EventView does overlap removal based on selection precedence and R. All Muons η < 2.5 StacoMuonCollection bestmatc p T > GeV χ 2 fit /DOF < 4 R >. Electrons ElectronAODCollection isem & x7f7ff == (tigt) Tau-jets p T > GeV R >. only selected for overlap removal TauRecContainer E T > 5 GeV R >.4 Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 6 / 25

7 Post-selection ID Muons χ 2 fit /DOF < 4 χ 2 matc /DOF < 8 p T > 5 GeV Tau-jets Likeliood > 4 e/µ flags or prong carge(τ ) = In te case of multiple tau candidates in a single event, te candidates are sorted by Likeliood, and te candidate wit te largest Likeliood above 4 is cosen to do te mass combination wit a muon. Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 7 / 25

8 Dijet Background Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 8 / 25

9 p T of Muons pb / (2.5 GeV) 5 4 J, 7-5 GeV J2, 5-7 GeV J, 7-4 GeV p (µ) [GeV] T Muons from dijets are steeply falling in p T. Tis is te main reason for requiring p T (µ) > 5 GeV. Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 9 / 25

10 Two Muon Isolation Variables p (µ) > 5 GeV T J, 7-5 GeV p (µ) > 5 GeV T J, 7-5 GeV pb 4 J2, 5-7 GeV J, 7-4 GeV pb / (.5 GeV) 4 J2, 5-7 GeV J, 7-4 GeV N tracks (µ; R<.4, p > GeV) T N tracks (µ; R <.4, p T > GeV) = ET R<.4 (µ) < 2 GeV R<.4 E T (µ) [GeV] After tese cuts, tere are not enoug events lefo require tau ID. And to scale to pb requires large scale factors. Need a more exclusive sample. Were are tese muons coming from? Answer: Ryan D. Reece (Penn) Z ττ µτ reece@cern.c / 25

11 Sources of Muons in Dijets Nearest generator trut particle Parent of true generator muons Muon s trut associate in J2, 5-7 GeV Entries = 58 Muon s parent in J2, 5-7 GeV Entries = 498 µ + (8.7 %) - B (.7 %) B (.7 %) + B (4.7 %) B (.5 %) - µ (2.7 %) + K (7.6 %) π + - K (6.7 %) - π oter (2. %) (6.4 %) (5.9 %) D (7.4 %) D (6.4 %) - D + D (6.2 %) B s (5.4 %) B s (4.8 %) + D s oter (5.6 %) (2.2 %) Λ b (2.4 %) (4. %) Need to look at b-jets. b b µ + jets Using a b b sample leaves oue c c (D-mesons) contribution. We also miss contamination due to muons from π/k decay in fligt. How can tis be modeled? Ryan D. Reece (Penn) Z ττ µτ reece@cern.c / 25

12 b b Background Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 2 / 25

13 b b Background Dwarfs Oters Before tau ID pb / (5 GeV) 4 5 LLH > 4, e/µ flags pb / (5 GeV) m vis (µ, τ ) [GeV] m vis (µ, τ ) [GeV] Te b b sample was filtered for a muon wit p T > 5 GeV, but only as 44 k events. Still, no events survive te entire cut flow. Ryan D. Reece (Penn) Z ττ µτ reece@cern.c / 25

14 Tau ID Scaling In order to artificially inflate te sample size, we did not require tau ID cuts for te b b sample, and instead scaled its istogram entries by te fake-rate parametrized by E T and number of prongs. We do te scaling, tau candidate by tau candidate. If an event as multiple tau candidates, ten in istograms it contributes an entry for eac candidate scaled by te fake-rate for tat candidate. Case of tau candidates: w = ε ( ε 2 ) ( ε ) + ε ε 2 ( ε ) + ε ε 2 ε = ε + O(ε 2 ) w 2 = ( ε ) ε 2 ( ε ) + ( ε ) ε 2 ε = ε 2 + O(ε 2 ) Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 4 / 25

15 Jet Fake-rate J2 + J, cuts: LLH > 4, e/ µ flags all -prong -prong 2-prong -prong - 4-prong 5-prong 6-prong -2 ID fake rate ID fake rate - -2, cuts: LLH > 4, e/µ flags all -prong -prong 2-prong -prong 4-prong 5-prong 6-prong reconstructed E T (τ ) [GeV] reconstructed E T (τ ) [GeV] ε = n-prong candidates passing ID cuts n-prong candidates Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 5 / 25

16 Jet Fake-rate ID fake rate -prong J2+J -prong J2+J -prong bb -prong bb reconstructed E T (τ ) [GeV] Te b-jet fake-rate is witin statistical agreement wit te inclusive dijet fake-rate. Terefore, we use te more precisely measured dijet fake-rate. Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 6 / 25

17 Evaluating te Scaling pb / (5 GeV) 7 6 Passed tau ID cuts Scaled by fake rate m vis (µ, τ ) [GeV] Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 7 / 25

18 Cut Flow and Results Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 8 / 25

19 Tau ID pb / (2.) 4 2 pb pb LLH pb / (5 GeV) e flag µ flag m vis (µ, τ ) [GeV] Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 9 / 25

20 Muon Isolation pb 2 pb / (5 GeV) pb / (.5 GeV) N tracks (µ) pb / (5 GeV) m vis (µ, τ ) [GeV] R<.4 E T (µ) [GeV] m vis (µ, τ ) [GeV] Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 2 / 25

21 W vs Z Separation pb / (.5) pb / (5 GeV) pb / (2.5 GeV) cos(φ -φ ) + cos(φ -φ ) µ MET τ MET pb / (5 GeV) m vis (µ, τ ) [GeV] m T(µ, MET) [GeV] m vis (µ, τ ) [GeV] Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 2 / 25

22 Tracks and Carge pb pb N tracks (τ ) Accept: -prong and -prong carge(τ ) = Opposite Sign carge(µ) carge(τ ) Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 22 / 25

23 Final Visible Mass Plot Events / (5 GeV) pb Z τ τ W τ ν - pb "data" m vis (µ, τ ) [GeV] Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 2 / 25

24 Cut Flow Z ττ W µν W τν Z µµ t t b b generated N(µ) = p T (µ) > 5 GeV χ 2 fit (µ)/dof < χ 2 matc (µ)/dof < N(τ ) > N(e) = prong Likeliood > 4, e/µ flags N tracks (µ) = E P R<.4 T (µ) < 2 GeV cos φ > m T (µ, MET) < 5 GeV N(τ ) or prong carge(τ ) = OS m vis (µ, τ ) = 5 8 GeV 9.(2).46(4).6().29().5().5() cross sections in pb. S/B = 5. denotes te beginning of tau ID scaling Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 24 / 25

25 Summary We estimate a dominant part of te QCD background from b b using tau ID fake-rate scaling to artificially inflate te sample size. We introduce a novel way of separating Z from W + jets by noting angular correlations and cutting on cos(φ µ φ MET ) + cos(φ τ φ MET ) in addition to te transverse mass. Z ττ µτ can be selected wit S/B 5, neglecting te background from ligt-flavor dijets and π/k decay in fligt. Te lepton filtered JX samples sould take into consideration te ligt-flavor dijets, but we still need to figure oue background from π/k decay in fligt. Tis analysis expects 9 signal events in pb. Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 25 / 25

26 W + jets Background Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 26 / 25

27 Transverse Mass pb / (2.5 GeV) m T (µ, MET) [GeV] Transverse mass is small wen φ is small. m T (µ, MET) = 2 p T (µ) MET ( cos φ) Tere is a better separating variable... Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 27 / 25

28 Angular Correlations ) MET cos(φ τ -φ pb cos(φ µ -φ ) MET Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 28 / 25

29 Angular Correlations One could just cut along te diagonal, but since te cut is a straigt line, we can rotate tis space clockwise and project down. ) MET cos(φ τ -φ pb cos(φ µ -φ ) MET ( x ( x y y ) = ( cos(φµ φ MET ) cos(φ τ φ MET ) ) ( cos θ sin θ = sin θ cos θ θ = π/4 ) ) ( x y ) x = [cos(φ µ φ MET ) + cos(φ τ φ MET )] / 2 Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 29 / 25

30 Angular Correlations A variable tat is remarkably caracteristic for te signal! pb / (.5) cos(φ µ -φ ) + cos(φ τ -φ MET ) MET cut: cos(φ µ φ MET ) + cos(φ τ φ MET ) >.5 Ryan D. Reece (Penn) Z ττ µτ reece@cern.c / 25

31 Angular Correlations Before ) MET cos(φ τ -φ pb cos(φ µ -φ ) MET After ) MET cos(φ τ -φ pb cos(φ µ -φ ) MET Ryan D. Reece (Penn) Z ττ µτ reece@cern.c / 25

32 Angular Correlations Before pb / (2.5 GeV) 2.5 After pb / (2.5 GeV) m T (µ, MET) [GeV] m T (µ, MET) [GeV] Tis cut on te sum of cos φ accepts signal muc better tan a cut on transverse mass. Accepts kinematic pase space were neutrino from τ is ard and MET does not align wit te muon. Not dependent on MET scale or p T (µ). Only dependent on φ measurements of objects and MET. Smaller systematic error. Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 2 / 25

33 Back Up Slides Ryan D. Reece (Penn) Z ττ µτ reece@cern.c / 25

34 Raw Cut Flow Z ττ W µν W τν Z µµ t t b b generated N(µ) = p T (µ) > 5 GeV χ 2 fit (µ)/dof < χ 2 matc (µ)/dof < N(τ ) > N(e) = prong Likeliood > e flag µ flag N tracks (µ) = E P R<.4 T (µ) < 2 GeV cos φ > m T (µ, MET) < 5 GeV N(τ ) or prong carge(τ ) = OS m vis (µ, τ ) = 5 8 GeV unscaled number of events Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 4 / 25

35 OS vs SS W µν + jets and W τν µνν + jets are te dominant EW backgrounds, te jets faking tau ID. Opposite Sign pb / (5 GeV) OS 2.5 Same Sign pb / (5 GeV) SS m vis (µ, τ ) [GeV] m vis (µ, τ ) [GeV] W backgrounds are OS biased. Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 5 / 25

36 Datasets Dataset Events Cross Section [pb] R dt L [pb ] pb scale factor Z ττ 99 k W µν 2472 k W τν 47 k Z µµ 49 k t t 487 k b b 44 k J 86 k J2 64 k J 96 k Te W τν dataset was filtered ae generator for an electron or a muon. Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 6 / 25

37 Dataset File Names mc8.652.pytiaztautau.recon.aod.e47 s462 r54 mc8.62.pytiawmunu Lepton.recon.AOD.e52 s462 r54 mc8.622.pytiawtaunu Lepton.recon.AOD.e52 s462 r54 mc8.65.pytiazmumu Lepton.recon.AOD.e47 s462 r54 mc8.52.t McAtNlo Jimmy.recon.AOD.e57 s462 r54 mc8.845.pytiab bbmu5x.recon.aod.e47 s462 r54 mc8.5.j pytia jetjet.recon.aod.e44 s479 r54 mc8.5.j2 pytia jetjet.recon.aod.e44 s479 r54 mc8.52.j pytia jetjet.recon.aod.e44 s479 r54 Issues all reconstructed wit Atena r54: , OFLCOND--- HEC off:.5 < η <.5 and π/2 < φ < 2 Muon etcone variables mis-filled in AOD. etcone4 etcone. Tis means tat my muon calo isolation cut is actually on R <. and not R <.4. Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 7 / 25

38 Tau-jet Efficiency reconstruction efficiency all -prong -prong reconstruction + ID efficiency LLH > 4, e/ µ flags all -prong -prong true E T (τ ) [GeV] true E T (τ ) [GeV] ε = n-prong candidates (passing ID cuts), matced to a true n-prong τ true n-prong τ s tools to gerue τ : EVTrutTauDecayCompositeCreator, EVUDTrutTauVisible Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 8 / 25

39 Jet Fake-rate reconstruction fake rate J2 + J all -prong -prong 2-prong -prong 4-prong 5-prong 6-prong J2 + J, cuts: LLH > 4, e/ µ flags all -prong -prong 2-prong -prong - 4-prong 5-prong 6-prong -2 reconstruction + ID fake rate true E T (jet) [GeV] true E T (jet) [GeV] ε = n-prong candidates (passing ID cuts), matced to a true jet all true jets true jets = Cone4TrutJets Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 9 / 25

40 Jet Fake-rate J2 + J, cuts: LLH > 4, e/ µ flags all -prong -prong 2-prong -prong - 4-prong 5-prong 6-prong -2 ID fake rate ID fake rate - -2, cuts: LLH > 4, e/µ flags all -prong -prong 2-prong -prong 4-prong 5-prong 6-prong reconstructed E T (τ ) [GeV] reconstructed E T (τ ) [GeV] ε = n-prong candidates passing ID cuts n-prong candidates Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 4 / 25

41 Z ττ Track Spectrum.5 Entries 8775 Mean.88 RMS N tracks (τ ) LLH>4, e/µ µ flags true number of prongs true number of prongs reconstructed numtrack reconstructed numtrack Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 4 / 25

42 Anoter Angular Statistic ρ φ(φ b, φ MET ) φ(µ, τ )/2 pb / (.5) ρ Just anoter way of measuring tae MET is between te decay products, toug not as discriminatory as cos φ. Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 42 / 25

43 EventView Overlap Removal Note tat it is te deltarcut of te current inserter tat matters, noe deltarcut used for te overlapping particles previously inserted in te EventView. ttps://twiki.cern.c/twiki/bin/view/atlasprotected/removeoverlap Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 4 / 25

44 Tau Brancing Fractions τ 7.8% 9.% e ν e ν τ µ ν µ ν τ 7.4% π π ν τ 25.5% π ν τ.9% π 2π ν τ 9.% K Nπ NK ν τ.5% π π ν τ.% π π π + ν τ π π π + π ν τ 4.6% } leptonic 5% prong 5% } prong 5% Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 44 / 25

45 Entire Cut Flow Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 45 / 25

46 pb 5 4 pb / (2.5 GeV) pb / (.25) N(µ) pb / (.25) p (µ) [GeV] T χ 2 (µ)/dof fit χ 2 (µ)/dof matc Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 46 / 25

47 pb 4 2 pb / (5 GeV) pb N(τ ) N(e) pb / (5 GeV) m vis (µ, τ ) [GeV] m vis (µ, τ ) [GeV] Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 47 / 25

48 pb 4 pb / (5 GeV) pb / (2.) N tracks (τ ) pb / (5 GeV) m vis (µ, τ ) [GeV] LLH m vis (µ, τ ) [GeV] Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 48 / 25

49 pb 4 pb / (5 GeV) pb e flag µ flag pb / (5 GeV) m vis (µ, τ ) [GeV] m vis (µ, τ ) [GeV] Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 49 / 25

50 pb 2 pb / (5 GeV) pb / (.5 GeV) N tracks (µ) pb / (5 GeV) m vis (µ, τ ) [GeV] R<.4 E T (µ) [GeV] m vis (µ, τ ) [GeV] Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 5 / 25

51 pb / (.5) pb / (5 GeV) pb / (2.5 GeV) cos(φ -φ ) + cos(φ -φ ) µ MET τ MET pb / (5 GeV) m vis (µ, τ ) [GeV] m T(µ, MET) [GeV] m vis (µ, τ ) [GeV] Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 5 / 25

52 pb pb / (5 GeV) pb N(τ ) N tracks (τ ) pb / (5 GeV) m vis (µ, τ ) [GeV] m vis (µ, τ ) [GeV] Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 52 / 25

53 pb pb carge(τ ) carge(µ) carge(τ ) pb / (5 GeV) pb / (5 GeV) m vis (µ, τ ) [GeV] m vis (µ, τ ) [GeV] Ryan D. Reece (Penn) Z ττ µτ reece@cern.c 5 / 25