Offline tau reconstruction overview

1
Offline tau reconstruction overview
M. Pilar Casado (IFAE UAB)

• Introduction
• tauRec
• tau1P3P
• AOD and ESD
• Conclusion

2
t Decays
35, but they belong to another story

• t decay modes
• Leptonic decay modes
• t ?nt ne e (17.4)
• t ? nt nm m (17.8)
• Hadronic decay modes
• 1 prong
• t ? nt p
  (11.0)
• t ? nt p p0
  (25.4)
• t ? nt p p0 p0
  (10.8)
• t ? nt p p0 p0 p0
  (1.4)
• t ? nt K np0
  (1.6)
• 3 prong
• t ? nt 3 p np0
  (15.2)

How to identify them?
77
23
3
Introduction
4
Practical info

• tauRec
• Authors D. Cavalli, S. Resconi, F. Paige, S.
  Rajagopalan, M. Heldmann.
• Documentation
• Code http//atlassw1.phy.bnl.gov/lxr/source/atlas
  /
• Reconstruction/tauRec/
• Wiki page https//uimon.cern.ch/twiki/bin/view/At
  las/
• TopologicalClustering?topicTauRec
• Status in the offline releases Part of the
  offline reconstruction.
• tau1P3P
• Authors E. Richter-Was, T. Szymocha, L. Janyst.
• Documentation
• Code http//atlas-sw.cern.ch/cgi-bin/viewcvs-atla
  s.cgi/users/erichter/
• Web page http//project-tau1p3p.web.cern.ch/proje
  ct-tau1p3p/ESDtau1P3P/index.html
• Status in the offline releases Still not
  included.

5
tauRec

• Reconstruct t-candidate
• Start from different objects CaloClusters
  (default), Isolated tracks,
• Associate tracks from the TrackParticle container
  to the candidate
• Build the set of variables for t-identification,
  and then calculates Likelihood(s)
• Calibrate candidates
• Apply set of the basic cuts for t-identification

6
Some tau variables

• Some variables calculated in offline (and in the
  trigger!)

7
Variables used in tauRec

• Builds set of variables for t-identification
  they are pT dependant
• Calculate Likelihood from REM, FISO, Ntrack,
  Strip Width, Nstrip, Charge, Impact
• parameter, ET/pT(1sttrack)

REM
FISO
Charge
Ntrack
Nstrip
Impact parameter
Strip Width
ET/pT(1sttrack)
Signal A?tt?background QCD, 0ltpTlt44 full line and
134ltpTlt 334 dashed line
8
Tau1P3P (I)

• Motivation
• Tau1P3P dedicated to the tau identification in
  searches for the light Higgs or soft SUSY t's
  with ETvis 20-70 GeV.
• Explores exclusive features of the t lepton
• hadronic t IS NOT a jet but 1 track ??0 or 3
  tracks ??0
• Decay products well collimated in space, track
  direction can provide precise estimate for
  direction, if track sufficiently dominant.
• energy scale defined from energy-flow and not
  calorimetric.
• Publications
• 1. E. Richter-Was, H. Przysiezniak and F.
  Tarrade, ATL-PHYS-2004-030
• 2. E. Richter-Was, T Szymocha, ATL-PHYS-PUB-2005-0
  05.
• 3. D. Froidevaux et al., ATL-COM-PHYS-2005-024
• 4. E. Richter-Was, L. Janyst ATL-COM-PHYS-2005-008

9
tau1P3P (II)
in real life we will probably start from
regions indicated by calorimetric clusters above
ETcut
identify good quality hadronic track, pT
gt 9 GeV, find nearby good quality tracks
with pT gt 2 GeV in DR lt 0.2
t3P
t1P
2 nearby tracks (h,f) from bary centre of
tracks S charge -1
no nearby-track (h,f) from track at vertex
build ETeflow, use DR lt 0.2
build ETeflow, use DR lt 0.2
build discrimination variables use DR lt 0.2
as a core, 0.2 lt DR lt 0.4 for isolation only
build discrimination variables use DR lt 0.2
as a core, 0.2 lt DR lt 0.4 for isolation only

• t1P - single-prong candidates

• t3P - three-prong candidates

10
tau1P3P (III)
with D. Froidevaux, for more details see talk at
Nov. 2004 Physics Week
ETeflow ETemcl ETneuEM S pTtrack ...
used only EM cells within DR lt 0.2 around tau1P
direction
ETeflow/ETtruth
ETeflow/ETtruth
1 prong
3 prong
good resolution ETeflow/ETtruth t1P 65.2
in 0.9-1.1 88.3 in 0.8-1.2 t3P
73.4 in 0.9-1.1 93.8 in
0.8-1.2 good stability for ETtruth 20 70 GeV
ltgt1.011 s 0.0303
ltgt1.014 s 0.0663
ETeflow/ETtruth
ETeflow/ETtruth
1.2
1.2
0.8
0.8
11
Comparison of performance
12
Present AOD class for taus TauJet.h

• inherits from P4EEtaPhiM class,
  
• access to asociated tracks,
  
• access to associated CaloCluster,
  
• access to associated Vertex
  
• numTracks (use also for tau1p, tau3P)
  
• pEM 4-momenta of EM component
  
• other attributes set by the author
• authortau1P3P already implemented

13
Present ESD class for taus TauObject.h

• trying to integrate different basic principles
  of both algorithms
• access to associated cluster, tracks, vertex can
  be easily made
• common
• several variables are very specific for tauRec,
• and other for tau1P3P
• possible approaches
• ? create author like for AOD ?
• ? inherit from a basic class, different
  concrete classes ?
• ? add more variables/methods ?
• Details being discussed at the moment in the
  Tau group.

14
Conclusion

• There are two algorithms for tau reconstruction
  in the offline tauRec (cluster and track seeded
  algorithm) and tau1P3P (track seeded algorithm).
• There are many common variables EM radius, Strip
  width and fracETR12.
• Key differences
• H1 calibration vs energy flow.
• Likelihood vs PDE-RS.
• Energy resolution is similar for both packages.
  Efficiency is better for tau1P3P for ET lt 25 GeV.
• Whilst AOD is quite defined in the offline tau
  reconstruction, the ESD class is under
  discussion.