1. American Physical Society Meeting St. Louis, MO April 12-15 th, 2008 Measuring the top mass at DØ using the Ideogram Method Amnon Harel aharel@fnal.gov aharel@fnal.gov University of Rochester

2. APS April Meeting 2008 Amnon Harel2 13/4/2008 Just like in the previous presentations:Introduction CDF D0 Tevatron Highest energy in the world ! Highest instantaneous luminosity in the world ! Lepton (isolated, p T >20 GeV, |η|<1.1/2.0) MET (>20GeV, triangle cut on ΔΦ(l,MET) ) This analysis uses 1fb -1 of data 4 Jets (p T >20 GeV, |η|<2,5) + maybe a couple of b-tags… Enjoying it while it lasts

3. APS April Meeting 2008 Amnon Harel3 13/4/2008 Data collected using lepton+jet triggers. Selected: 446 e+jets events and 409 μ+jets events Data Sample 50 100 150 0.20.40.60.81.0 P sig (D) Multijet background Estimated from data with a not-quite-as-isolated lepton W+jets background Fit likelihood discriminant: Aplanarity MET H’ T2 = H T2 / H || K’ T,min |Δη 12 | Number of b tags Signal and W+jets templates from MC. Discriminant, D, calibrated using MC: which is used in the fit for m t Work in progress

4. APS April Meeting 2008 Amnon Harel4 13/4/2008 Partons Chi 2 minimization to the measured objects Constraints: m t = m tbar ; m Wlv =m Wqq =80.4GeV jet Observed objects Constrained Kinematic Fit Fit output “ x ”: Parton-levelParticle-levelDetector-level Theory Experimental resolutions Do the fit for every combination of assigning a jet to a parton m t, σ=Δm t, χ 2 all * 12 Permutations * 2 solutions for neutrino p z

5. APS April Meeting 2008 Amnon Harel5 13/4/2008 Breit-Wigner Gauss Detector resolution  2,m i and  i from kinem. fit Depending on the assumed flavor of the jet and whether that jet is b tagged Ideogram Method Use b tagging: Maximal likelihood fit of:

6. APS April Meeting 2008 Amnon Harel6 13/4/2008 A Few Complications Only one jet-parton assignments is correct, we gain by adding a term: We also need the background term: Taken from the simulation Different for e+jets and for μ +jets. Work in progress BTW: DØ’s jet energy calibration is now accurate enough that we can also do the analysis without the in-situ JES calibration. Easier to get it right with more b tags Tuned for best performance

7. APS April Meeting 2008 Amnon Harel7 13/4/2008 The Sample Likelihood Combine events by multiplying event probabilities Probability Top Mass Probability Top Mass Probability Top Mass = Probability Top Mass P bkg But what’s the effect of the approximations in calculating P sample ? Do they bias the fitted mass? Work in progress & extract the most likely mass value:

8. APS April Meeting 2008 Amnon Harel8 13/4/2008 Ensemble Testing Uncalibrated Result: 175.57±1.88 pb Data Simulated Data sets (a.k.a. pseudo-experiments) Calibration Expected Results The Result: 175.71±1.89 pb Work in progress

9. APS April Meeting 2008 Amnon Harel9 13/4/2008 Systematic Uncertainties Source of systematic uncertainty Effect in GeV Jet energy scale+1.2 -2.2 Jet energy resolution+0.3 -0.4 Jet reconstruction and ID efficiency0.3 Trigger uncertainty+0 -0.8 MC calibration0.4 b tagging0.2 Multijet background0.2 Signal fraction0.1 Additional collisions0.1 Background modeling<0.1 Signal modeling<0.1 PDF uncertainty<0.1 TOTAL+1.2 -2.4

10. APS April Meeting 2008 Amnon Harel10 13/4/2008Conclusions Finalizing a measurement of m t using the ideogram method Double the data in the PRD –Data set well understood and modeled Improved description of partons ↔ reconstructed object correspondence in kinematic fit Improved treatment of misreconstructed signal

11. APS April Meeting 2008 Amnon Harel11 13/4/2008 Back up slides

12. APS April Meeting 2008 Amnon Harel12 13/4/2008 Aplanarity – from the momentum tensor of the jets & lepton MET From the two jets ( ij ) closest in (η,Φ) space: where is the transverse energy of jet i along the direction of jet j. Rapidity difference between the two leading (in p T ) jet: Number of b-tags Discriminating Variables

13. APS April Meeting 2008 Amnon Harel13 13/4/2008 Transfer Functions The correspondence between jets and partons is taken from the simulation as follows: Jet energies fitted as quadratic function of parton energy – separate b and light jets The fit is inverted yielding E parton (E jet ) Fit the widths of the jet resolutions around E parton (E jet ) – separate b and light jets

14. APS April Meeting 2008 Amnon Harel14 13/4/2008 Likelihood II Background term For e+jets

15. APS April Meeting 2008 Amnon Harel15 13/4/2008 Event Selection Lepton + jet trigger One isolated lepton with p T >20 GeV and –Muons: |η| < 2.0 or –Electrons: |η| < 1.1 MET>20 GeV A ΔΦ(l,MET) cut to reduce fake leptons ≥4 jets with p T >20 GeV & |η|<2.5 Data Sample

16. APS April Meeting 2008 Amnon Harel16 13/4/2008 Top Pair Production 85% 15% Top pairs produced by the strong interaction Top Pair

17. APS April Meeting 2008 Amnon Harel17 13/4/2008 All Hadronic Common decay mode High background Only jets Tau + Jets / Tau + l Uncommon decay mode High background Prelim. measurements BYSM: Still working to limit H + in t  H + b t t - W+W+ b q q b - W-W- q q’ t t - W+W+ b µ+µ+ νµνµ b - W-W- e-e- νeνe t t - W+W+ b µ+µ+ νµνµ b - W-W- q Classifying Top Pair Events SM: t  Wb ( ≈100%), then the W decays into lν or qq l = e/μ  clear experimental signatures Dilepton Uncommon decay mode Low background Top Pair Lepton + Jets Common decay mode Moderate background

18. APS April Meeting 2008 Amnon Harel18 13/4/2008Title Text