American Physical Society Meeting St. Louis, MO April th, 2008 Measuring the top mass at DØ using the Ideogram Method Amnon Harel University of Rochester

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

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 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

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

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:

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

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:

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

APS April Meeting 2008 Amnon Harel9 13/4/2008 Systematic Uncertainties Source of systematic uncertainty Effect in GeV Jet energy scale Jet energy resolution Jet reconstruction and ID efficiency0.3 Trigger uncertainty 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

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

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

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

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

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

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

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

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

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