Latest Measurements Latest Measurements of Top Mass at CDF of Top - PowerPoint PPT Presentation

Latest Measurements Latest Measurements of Top Mass at CDF of Top Mass at CDF Un-ki Yang The University of Manchester CDF HEP Seminar at Manchester, Oct. 25, 2006 Healthy food to make 1 Manchester Physics program strong!

Top Quark  Discovery of the top quark in 1995  Massive new Fermion (about Au nucleus) • Decays before hadronization • Opportunity to study a “free” quark  Heaviest object in theory • Most sensitive to “loops” • Insight into generation of mass in Standard Model  Very statistics limited  D0 and CDF collected approximately 100 pb -1 in Run I (1992-1996) 2

Top Production and Decay  At the Tevatron, mainly primarily produced in pairs via strong interaction ( � ~7pb: 1 for every 10 10 collisions) LHC (90%) ~100 � 85% 15%  Top decays as free quark due to large mass ( � top ~ 4 x 10 -25 s )  Dilepton (5%, small bkgds) 2 leptons(e/ µ ), 2 b jets, missing E T (2 � s)  Lepton+Jet (30%, manageable bkgds) 1 lepton(e/ µ ), 4 jets (2 b jets), missing E T (1 � )  All-hadronic (44%, large bkgds) 6 jets (2 b jets) 3 Un-ki Yang, Manchester Seminar 2006

Why Top Mass?  Top mass is a fundamental SM parameter Run I  Important in loop corrections  Precise Top & W masses  Constraint on SM Higgs  Look for a deviation from the other EWK results  Constrain new physics (SUSY) with precise Higgs masses  Is it a SM top? consistency checks among three different channels (sensitive to new physics) 4

Summary of Run I Measurements  M top in Run I (~100pb -1 ) M top = 178.0 ± 4.3 GeV/c 2  Higgs mass fit + 73 GeV/c 2 M H = 126 � 48 M H < 280 GeV/c 2 @95% C . L  Run II goals (based on Run I) � M top � 3 GeV/c 2 @2fb � 1  .  Consistency among diff. channels (same top? non-SM decays like t->bH + )  Consistency with Xsection (non-SM X 0 , t’ contributions) 5 Un-ki Yang, Manchester Seminar 2006

CDF at Tevatron Multi-purpose detector: precision meas. & search for new physics  Silicon detector (SVX): top event b-tag: ~ 55%  COT: drift chamber Coverage: | � |<1 � Pt / Pt ~ 0.15% P T  Calorimeters: Central, wall, plug Coverage: | � |<3.6 EM: � E / E ~ 14% / �� HAD: � E / E ~ 80% / �� SVX EM cal Muon  Muon: scintillator+chamber muon ID up-to | � |=1.5 COT:tracking Had cal 6 Un-ki Yang, Manchester Seminar 2006

Great Performance Summer 2006 Delivered ~2.0 fb -1 � M top ~ 2.1 GeV Peak Inst. Lum ~2.3E32 cm -2 s -1 Spring 2006 � M top ~2.3 GeV Summer 2005 � M top ~ 2.9 GeV Run I � M top ~ 4.3 GeV 74% weight by CDF (D0: only 350pb-1) 7 Un-ki Yang, Manchester Seminar 2006

M top Measurement : Challenge 1  Not a just calculation of the invariant mass of W(jj) and b!!! N(jets) For Mtop =175 GeV Why M(bjj) � 175 GeV?  Require excellent jet energy  Measured jet energy correction and good modeling � quark energy from top decay of extra gluon radiations (40%)  Quarks: showering, hadronization, jet clustering  Extra radiated jets 8 Un-ki Yang, Manchester Seminar 2006

Jet Energy Scale(JES) Uncertainties Standard calib. (dijet, � -jets etc) In-situ calibration: W->jj resonance l W + b-jet � t t W - jet M jj (W) jet b-jet JES uncertainty: About 3 GeV of M top mostly statistical, scaled with lum 9 Un-ki Yang, Manchester Seminar 2006

Challenge 2  There are two top quarks & not all final states available  Good to have more than one:but too many possibilities to find a correct combination (all jets: 90), missing information in dilepton channel 3 constraints: two M(w)=80.4, one M(t)=M(tb) Ncomb(btag) 2(2) 12 (6) 360(90) 2 missing � 1 missing � No missing Unconstrained: Overconstrained: Overconstrained: Small BR Golden Channel Large bkgds 10 Un-ki Yang, Manchester Seminar 2006

B-tagging  B-tag: SecVtx tagger  B-tagging helps!: reduces wrong comb. and improves resolution 11 Un-ki Yang, Manchester Seminar 2006

Top Mass Measurements Template Matrix Element  Reconstruct m t event-by-event  Calculate probability as top mass - the best value per each event for all combinations in each event by Matrix Element calculation - maximize dynamic information  Create “templates” using fully simulated events for different top mass values, and bkgds  Build Likelihood directly from the probabilities  Maximum Likelihood fit using signal+backgrounds templates  Calibrate measured mass and it’s error using simulated events 12 Un-ki Yang, Manchester Seminar 2006

Strategy  Precision  Consistency (different channels, methods)  New Physics (bias) Method Njets B-tag JES Rec. variables Exact +extra Yes No Wjj+std Wjj No TMP 4 mt, m jj , Lxy LJ ME P(Mt,JES) TMP 2 mt DIL ME P(Mt) All-J TMP+ME 6 mt Only D0 Only CDF both 13 Un-ki Yang, Manchester Seminar 2006

Template Method in lepton+jets  Event selection • High-pt central leptons (e,mu): Pt>20 GeV • 4 jets: Et>15 GeV, | � |<2.0 l W + • Large missing Et > 20 GeV b-jet �  � 2 kinematic fitter: fully reco. ttbar system t t i � p T UE � p T i ) W - 2 UE ) 2 ( ˆ ( ˆ 2 = p T p T jet � � � + � i � j 2 2 i = l ,4 jets j = x , y jet b-jet ( m jj � m W ) ( m bjj � m t ) 2 + ( m l � � m W ) 2 + ( m bl � � m t ) 2 2 + + � W � W � t � t 2 2 2 2  Find m t that fits event best over all combinations (m W =80.4 GeV, m t =m tb )  Reject badly reconstructed event

Signal Templates (m t , JES) JES Reconstructed top mass (m t ) dist. For Mtop = 178 GeV

Backgrounds Templates Backgrounds:with btag control signal

Template Results in lepton+jets M top = 173.4 ± 2.5(stat. + JES) ± 1.3 (syst.) GeV / c 2  World best measurement (Sping06) 40% improvement on JES using Wjj  PRD/PRL with 320pb-1  Toward 2nd publication with 1fb-1 17 Un-ki Yang, Manchester Seminar 2006

Matrix Element Method in lepton+jets  Maximize kinematic and dynamic information  Calculate a probability for a signal and background as a function of the top mass  Integrate over all the unmeasured quantities convoluting the differential cross-section with the experimental resolutions P(x;M top ,JES) = 1 � dq 1 dq 2 f(q 1 )f(q 2 ) d � (y;M top ) W(x,y,JES) � Differential cross section: Transfer function: probability LO ME (qq->tt) only to measure jet x for parton y  JES is a free parameter, constrained in situ by the W(->jj) mass  Likelihood used to fit simultaneously M top and JES ( ) Nevents L ( f top , M top , JES ) � � f top P top , i ( M top , JES ) + (1 � f top ) P bkgd , i ( JES ) i 18 Un-ki Yang, Manchester Seminar 2006

M.E. results in lepton+jets  Event Selection: b-tag but with exact 4jets (166 events) M top = 170 . 9 ± 1 . 6 (stat.) ± 1 . 4 (JES) ± 1 . 4 (syst.)GeV/ c 2  Most precise world measurement (Summer 06): 1fb-1  Toward publication with few improvements using 1fb-1 19 Un-ki Yang, Manchester Seminar 2006

Template using Decay Length (Lxy)  Uses the average transverse decay length, Lxy of the b-hadrons  B hadron decay length � b-jet boost � M top (>=3jets) PRD 71, 054029 by C. Hill et al. 375 evts (B:111) + 15.7 (stat) ± 0.3( JES ) ± 5.6 (syst) GeV/ c M top = 183.9 � 13.9 2 Insensitive to JES, Statistics limited, but can make but need Lxy simulation big contributions at Run IIb, LHC 20 Un-ki Yang, Manchester Seminar 2006

Methods in dilepton  Unconstrained system; 2 neutrinos, but 1 missing E T observable  Template: • Assume η ( � ) ( or � ( � ), P Z (tt)) • Sum over all kinematic solutions, and (l,b) pairs, select the most probable value as a reco. M t  Matrix Element:  Integrated over unknown variables using the LO Matrix Element assuming jet angles, lepton are perfect, and all jets are b’s  Obtain P(Mtop) for signal and backgrounds  Calibrate off-set in pull and pull width using fully simulated MC 21 Un-ki Yang, Manchester Seminar 2006

Results in dilepton Template Matrix Element 78 evts (B:28) M top = 168.1 ± 5.6 ( stat ) ± 4.0(syst) GeV/ c M top = 164.5 ± 3.9 (stat) ± 3.9(syst) GeV/ c 2 2  Event selections: 2 leptons (Pt>20), 2jets (Et>15), MET> 25 GeV  Syst. error is comparable to the stat. error  Toward 2nd publications with 1fb -1 22 Un-ki Yang, Manchester Seminar 2006

Template in all-jets  Template method with fitted M top as observable  Choose among all possible comb ination of 6 jets using a kinematic fitter  Extract fitted M top  Event seletion: E T / � ( � E T ) < 3 (GeV) 1/2 • � E T � 280 GeV • n b-tag � 1 (b-tag) • 6 ≤ N jet ≤ 8 • Neural Network selection •  And data-driven to improve S/B = 1/2 (vs 1/8) background template 23 Un-ki Yang, Manchester Seminar 2006

Results in all-jets  Dominated by the JES uncertainty, plan to implement JES fit using Wjj  Toward 1st publication, along with other ME method M top = 174 . 0 ± 2 . 2 (stat.) ± 4 . 5 (JES) ± 1 . 7 (syst.)GeV/ c 2 24 Un-ki Yang, Manchester Seminar 2006

Comparisons of all channels Measurement Letpton+Jets All-jets Dileptons Mtop 170.9 174.0 164.5 JES 1.6 4.5 3.4 Signal 1.1 0.7 0.7 Backgrounds 0.2 0.9 0.9 Others 0.5 1.0 1.3 Total Syst. 1.9 4.7 3.9 Statistical ( GeV/c 2 ) 1.6 2.2 3.9 Total 2.5 5.2 5.5 25 Un-ki Yang, Manchester Seminar 2006