ATLAS Workshop on Refinement of Local Hadronic Calibration and its Application to Top Physics

SESSION 4: tt(bar) selection, top mass reconstruction, QCD background, analysis tools

Conveners : D. Pallin , F. Spano'

General links :

RingbergWorkshop08

Agenda

ATLAS Calorimetry Calibration Workshops

Top Working Group

Top Meetings

Outline

Topics Summary

Top Mass measurement summary
Cross section summary

Ttbar Semileptonic channel

1. Selection :
   1. Signal and BKG cross sections
   2. Triggers aspects ( D. Berge talk 10mn)
      1. Efficiency measurement, monitoring, redundancy
   3. Selection algorithms
      1. Basic Selection for xsec measurement
         1. X-sec Commissioning cuts
         2. b-tag impact
      2. Basic selection for mass measurement
         1. Mass Selection cuts; 2btag selection for mass measurement ; events after selection
         2. with loose b tag perf (2 b-tag+1-tag)
         3. No b-tag (at LHC start)
      3. Differences between cross section and mass selection
   4. Impact of Jet scale and pile-up on Jet Pt cut
      1. * Jet en scale impact for likelihood fit
   5. Impact of ETMiss
      1. ETMiss cut and QCD BKG for Xsec
         1. Cutting on ET miss vs electron fake rate
         2. Isolated lepton rate in multi jet events: latest and previous and critical points
            1. Communication on Isolated lepton rate in multi-jet events
            2. electron fake rate estimate and triangular cuts
            3. ETmiss calib
   6. Open issues
      1. 1. Bkg studies
            1. QCD multijets 2-5 light jets ; bb+0,1,2,3 light jets and lepton fake rate
            2. W+bb w+cc (negligeable contribution)
         2. Etmiss calibration and use at LHC start
         3. use of different jet algorithm (cone,Kt) and different constituents (tower, Topocluster) +Loc Had calib( YES/NOT)
         4. Use locally hadronic calibrated clusters (and jets) in cross section
         5. Pile-up effect
2. Reconstruction
   1. Reconstruction for cross section
   2. Association-Jet pairing: How to associate Jets to form the Hadronic Top
      1. Standard ; additional slide Methw1 ; Meth 1&2
      2. MVA
      3. Recons of the Leptonic Top
   3. Purification cuts/BKG substraction
      1. purification cuts for mass and for xsec
      2. MVA: Multivariate analysis
   4. Selection & Reconstruction of high pT Top (Elin Bergeas)
   5. Open issues
      1. Selection of a pure W sample to perform in-situ calibration (no b-tag)
      2. Kt/ cone ; Tower /Topcluster ; Local had calib( YES/NO) use for jets : differences for reconstruction
      3. comb BKG estimate with Evt mixing
3. Extraction of measurements (cross section/mass)
   1. Cross section - T6 link
      1. three methods (jet multiplicity, cut and count, likelihood fit to mass estimator)
      2. Cross section systematics and Jet/EtMiss scale
   2. Mass - T9 link; material
      1. with optimal b tag performances
      2. with loose b tag perf
      3. at LHC start
      4. Mass systematics

Top Quarks at 10 -14 TeV

1. Expectations on Cross sections and Kinematics material 1 material 2

Strategy for First Top measurements and feed back to the local Had calibration

1. Two goals
   1. Improve jet/Et miss energy scale ( see In-Situ Session)
      1. jet scale
         1. material for light jet calibration material1 ; material2, material3
         2. JES and jet angular resolution?
         3. b-jet calibration from light jet calibration material
         4. JES and Mtop in one go
         5. jet energy resolution effect , pile-up effect
      2. ETmiss calibration
      3. Is there any step of the analysis that can validate local hadron calibration as a whole or in part?
   2. Get a robust measurement
      1. Top mass with Local Hadronic Calibration (T Barillari)
      2. What are the weakest points of the analyses? At what level are measurements more sensitive to Hadron calibration. How do we minimize the sensitivity to get the best initial measurement?
      3. What aspect of the local hadron calibration has the largest impact on the measurement? Classification, weighting, out of cluster, dead material, out of jet/, other physics corrections? What is critical, fragile ?
2. Strategy at LHC start

• make the measurement robust against calibration problems
• and go towards a calibration scheme that will improve the measurement
• use top to refine the day0 calibration
  1. 1st pass :
     1. Simple selection with/without btag
     2. W selection and evaluation of light jet scale
     3. b-jet scale obtained from light jet scale+ MC modelling the difference Light-b jets
  2. 2nd pass :
     1. Selection redone using in-situ calibration from pass 1
     2. Check important variables, #jets(light and b-jets)) and leptons, E,phi,eta, DRjj DRjjb , ETmiss,..
     3. Check calib
     4. Check with other selections procedures
     5. Measurements ?
        1. Determine X-sec from various methods (croos check)
        2. Top mass from Mjjb ; Cross-check b jet scale vs Mtop PDG
        3. check BKG with Evt mixing
        4. W mass :use different jet algo & cluster (tower, Topo) +-Loc Had Cal to give inputs to Loc Had Calib

Tools

1. Top as a tool for performances studies
   1. Light jet scale
   2. B jet scale (not for Top mass measurement!)
   3. Trigger (use redundancy)
   4. Etmiss
2. Analysis tools and format
   1. Compare fast and full simu: can we do had calib with fast simu?
   2. Is the infrastructure ready for putting things back from in-situ?
   3. What format for the initial analysis?

-- DominiquePallin - 03 Jun 2008 -- FrancescoSpano - 03 Jun 2008 -- FrancescoSpano - 04 Jun 2008 -- DominiquePallin - 05 Jun 2008 -- FrancescoSpano - 06 Jun 2008 -- DominiquePallin - 08 Jun 2008 -- FrancescoSpano - 10 Jun 2008 -- DominiquePallin - 12 Jun 2008 -- FrancescoSpano - 13 Jun 2008

• JESpotpourridominique.pdf: JESpotpourridominique.pdf

• PresentationTop1.ppt: PresentationTop1.ppt