Track Reconstruction in Hadronic Tau Decays at the ATLAS Detector

Transcription

1 rack Reconstruction in Hadronic au Decays at the ALAS Detector Dirk Duschinger DPG Fruehjahrstagung Wuppertal March 9, 25 Dirk Duschinger rack Reconstruction in Hadronic au Decays / 2

2 Introduction au Leptons heaviest known lepton with m τ =.777 GeV decay length cτ = 87 μm leptonic and hadronic decay modes in general low multiplicity, i.e. predominantly or 3 charged pions physics analyses with tau final states often require reconstructed or 3 prong taus it is crucial to associate correct number of tracks to the tau others 3π ± π ν 7% 8% 3π ± ν 4% π ± 2π ν 4% 39% π ± π ν hadronic mode 65% leptonic mode 35% 7% π ± ν /8 Dirk Duschinger (dirk.duschinger@cern.ch) rack Reconstruction in Hadronic au Decays 2 / 2

3 Run tau track reconstruction started from a loose track selection working point collect tracks in cone ΔR < apply quality criteria to suppress pileup tracks, etc. p > GeV # pixel hits 2 # silicon hits 7 z sin(θ) <.5 mm d < mm JINS 3 (28) S83 Dirk Duschinger (dirk.duschinger@cern.ch) rack Reconstruction in Hadronic au Decays 3 / 2

4 Problems during run Fraction.9.7 ALAS work in progress Reco 2p Reco 3p Reco 4p Events ALAS work in progress s=8ev Simulation p [,] p [,4] p [4,7] p [7,] p [,3] p [3,e+2] hadronic tau transverse decay position [mm] p (τ h ) [GeV] poor efficiency to reconstruct 3 prong tau decays with 3 tracks at high p due to track merging non-negligible amount of taus decay inside the pixel detector large efficiency drop to reconstruct these tracks due to pixel hits requirement Dirk Duschinger (dirk.duschinger@cern.ch) rack Reconstruction in Hadronic au Decays 4 / 2

5 Performance of track selection in run 2 starting from loose working point apply cuts from run efficiency to reconstruct correct prongness.4 ALAS work in progress Loose + run Simulation, truth prong s = 3 ev.2 efficiency to reconstruct correct prongness.4 ALAS work in progress Loose + run Simulation, truth 3 prong s = 3 ev tau p reco [GeV] tau p reco [GeV] Dirk Duschinger (dirk.duschinger@cern.ch) rack Reconstruction in Hadronic au Decays 5 / 2

6 track p distribution for various tau p regions a.u. Signal 8 Signal 2 5 GeV Signal 5 8 GeV GeV Background 8 Background 2 5 GeV Background 5 8 GeV GeV ALAS work in progress Simulation track p [GeV] distribution already gives good separation power strong dependence on tau p partly similar effects for other distributions Dirk Duschinger (dirk.duschinger@cern.ch) rack Reconstruction in Hadronic au Decays 6 / 2

7 How to increase track selection performance optimizing quality cuts in bins of tau p can get quite challenging to find best thresholds hard to handle correlations not further considered use MVA techniques BD s are trained using MVA signal: tracks from tau decays background: pileup, conversions, underlying event, mis-reconstructed tracks added tau p and η to input variables of tracks to account for such dependencies Dirk Duschinger (dirk.duschinger@cern.ch) rack Reconstruction in Hadronic au Decays 7 / 2

8 Results using the BD approach better efficiency for prong worse performance for 3 prong prong 3 prong efficiency to reconstruct correct prongness.4 ALAS work in progress Loose + run Simulation, truth prong BD s = 3 ev.2 efficiency to reconstruct correct prongness.4 ALAS work in progress Loose + run Simulation, truth 3 prong BD s = 3 ev tau p reco [GeV] tau p reco [GeV] Dirk Duschinger (dirk.duschinger@cern.ch) rack Reconstruction in Hadronic au Decays 8 / 2

9 Results using the BD approach overall better efficiency for and 3 prong combined efficiency to reconstruct correct prongness.4 ALAS work in progress Loose + run Simulation, truth inc prong BD s = 3 ev tau p reco [GeV] Dirk Duschinger (dirk.duschinger@cern.ch) rack Reconstruction in Hadronic au Decays 9 / 2

10 High p track association efficiency extended training to very large p using high mass Z/γ * ττ samples loose + run selection BD based selection track association efficiency.2 Recop Recop Reco2p Reco3p Reco4p ALAS work in progress Simulation, truth prong track association efficiency.2 Recop Recop Reco2p Reco3p Reco4p ALAS work in progress Simulation, truth prong τ p reco [GeV] τ p reco [GeV] overall better performance than standard selection small p dependence for loose + run selection is reduced Dirk Duschinger (dirk.duschinger@cern.ch) rack Reconstruction in Hadronic au Decays / 2

11 High p track association efficiency track association efficiency extended training to very large p using high mass Z/γ * ττ samples loose + run selection Recop Recop Reco2p Reco3p Reco4p ALAS work in progress Simulation, truth 3 prong τ p reco [GeV] track association efficiency BD based selection Recop Recop Reco2p Reco3p Reco4p ALAS work in progress Simulation, truth 3 prong τ p reco [GeV] BD approach shows better performance than standard selection at high p reconstruction as prong is strongly reduced increase from 9% to 26% in the highest bin Dirk Duschinger (dirk.duschinger@cern.ch) rack Reconstruction in Hadronic au Decays / 2

12 Conclusions BD approach shows better performance compared to standard selection BD trained for high p taus reduces problem of track merging and decays within the pixel detector large room for improvements in optimizing training, especially input variables, options, thresholds on BD score Dirk Duschinger (dirk.duschinger@cern.ch) rack Reconstruction in Hadronic au Decays 2 / 2

13 BACKUP Dirk Duschinger rack Reconstruction in Hadronic au Decays 3 / 2

14 Run tau track reconstruction started from a loose track selection working point collect tracks in cone ΔR < apply quality criteria to suppress pileup tracks, etc. p > GeV # silicon hits 7 # pixel hits 2 z sin(θ) <.5 mm d < mm impact parameter were calculated wrt. tau vertexfound by au Jet Vertex Association (JVA) JVA: find vertex with largest fraction: f JVF (jet vtx) = Σptrk vtx Σp trk Dirk Duschinger (dirk.duschinger@cern.ch) rack Reconstruction in Hadronic au Decays 4 / 2

15 Problems during run prong 3 prong Number of selected τ -prong µ= µ=2 µ=2 with JVA ALAS Preliminary Simulation Number of selected τ 3-prong µ = µ=2.5 µ=2 with JVA ALAS Preliminary Simulation Number of tracks Number of tracks additional pileup and conversion tracks due to too loose cuts lost tau tracks due to too tight cuts or wrong vertex decision Dirk Duschinger (dirk.duschinger@cern.ch) rack Reconstruction in Hadronic au Decays 5 / 2

16 Results using the BD approach efficiency to reconstruct correct prongness.4 ALAS work in progress Loose + run Simulation, truth prong BD s = 3 ev.2 efficiency to reconstruct correct prongness.4 ALAS work in progress Loose + run Simulation, truth 3 prong BD s = 3 ev tau p reco [GeV] tau p reco [GeV] overall better performance for prong slighly worse performance for 3 prong Dirk Duschinger (dirk.duschinger@cern.ch) rack Reconstruction in Hadronic au Decays 6 / 2

17 variables used for training Dirk Duschinger rack Reconstruction in Hadronic au Decays 7 / 2

18 BD Score distribution MVA overtraining check for classifier: BD dx (/N) dn / Signal (test sample) Background (test sample) Signal (training sample) Background (training sample) Kolmogorov Smirnov test: signal (background) probability = 73 (.2) ALAS work in progress BD response U/O flow (S,B): (.,.)% / (.,.)% Dirk Duschinger (dirk.duschinger@cern.ch) rack Reconstruction in Hadronic au Decays 8 / 2

19 distribution of quality parameters run : z JV sin(θ) <.5 mm run : d < mm a.u. Signal 8 Signal 2 5 GeV Signal 5 8 GeV GeV Background 2 5 Background 5 8 Background 8 GeV GeV GeV ALAS work in progress Simulation a.u. Signal 8 Signal 2 5 GeV Signal 5 8 GeV GeV Background 2 5 Background 5 8 Background 8 GeV GeV GeV ALAS work in progress Simulation * sin(θ) wrt. JV [mm] track z [mm] track d Dirk Duschinger (dirk.duschinger@cern.ch) rack Reconstruction in Hadronic au Decays 9 / 2

20 distribution of quality parameters run : # pixel hits 2 run : # silicon hits 7 a.u. Signal 8 Signal 2 5 GeV Signal 5 8 GeV GeV Background 2 5 Background 5 8 Background 8 GeV GeV GeV ALAS work in progress Simulation a.u. Signal 8 Signal 2 5 GeV Signal 5 8 GeV GeV Background 2 5 Background 5 8 Background 8 GeV GeV GeV ALAS work in progress Simulation # pixel hits # silicon hits Dirk Duschinger (dirk.duschinger@cern.ch) rack Reconstruction in Hadronic au Decays 2 / 2

21 rack distribution comparison Loose + run BD approach ALAS work in progress Simulation prong 3 prong ALAS work in progress Simulation prong 3 prong prong 3 prong number of associated tracks number of associated tracks BD approach is able to reduce taus being reconstructed with 3 tracks but also 2 and prong is reduced more taus are reconstructed with 2 prong for the BD approach than for Loose + run Dirk Duschinger (dirk.duschinger@cern.ch) rack Reconstruction in Hadronic au Decays 2 / 2

22 track selection definitions ALAS work in progress RUN track selection: minpt minnsihits 7 minnpixelhits 2 maxzsinheta.5 maxd RUN2 Loose-primary track selection: minnsihitsifsisharedhits useetadependentmaxchisq true RUN2 Loose selection: minpt 4. maxabseta 2.5 minnsihits 7 maxnpixelsharedhits maxnscsharedhits 2 maxonesharedmodule true maxnsiholes 2 maxnpixelholes RUN2 ight-primary selection: minnsihits 9 minetaforstrictnsihitscut.65 minnsihitsaboveetacutoff minnblayerhits maxnpixelholes Dirk Duschinger (dirk.duschinger@cern.ch) rack Reconstruction in Hadronic au Decays 22 / 2