top quark mass measurements

Transcription

1 top quark mass measurements Ulrich Heintz 11/8/006 DESY seminar - Ulrich Heintz 1

2 outline the top quark the top quark factory top quark production and decay top quark mass in the lepton+jets channel top quark mass in the dilepton channel putting it all together beyond the Tevatron conclusion 11/8/006 DESY seminar - Ulrich Heintz

3 outline the top quark the top quark factory top quark production and decay top quark mass in the lepton+jets channel top quark mass in the dilepton channel putting it all together beyond the Tevatron conclusion 11/8/006 DESY seminar - Ulrich Heintz 3

4 11/8/006 DESY seminar - Ulrich Heintz 4 the standard model particle zoo standard model describes the fundamental particles and their interactions fermions six quarks six leptons electroweak doublets constituents of matter bosons force mediators R R L R R L R R L R L R L R L e b t b t s c s c d u d u e e τ υ τ µ υ µ υ τ µ quarks leptons () ( ) ( ) g SU W Z W SU U L 3 1 strong electroweak 0 + γ

5 the top quark is the most massive quark leptons quarks e 0.5 MeV ν e d 7 MeV u 3 MeV µ MeV ν µ s 110 MeV c τ MeV ν τ volume of spheres mass no measurable extend (<10-18 m) b 4300 MeV 1300 MeV t 171,000 MeV 11/8/006 DESY seminar - Ulrich Heintz 5

6 it is there why study the top quark? properties are fundamental parameters it is the dominant contributor to sm corrections m t >>m b largest contributor to radiative corrections, e.g. to W mass it couples strongly to the Higgs sector maybe we can learn about EWSB it is as close as we can get to a ``bare quark short lifetime τ 10-4 s < Λ -1 QCD 10-3 s top decays before hadronizing 11/8/006 DESY seminar - Ulrich Heintz 6 no confinement effects can perform

7 top quark mass measurements importance of m t (radiative corrections) t H 0 W W W W b m W = m tree W (1 + O(m t ) + O(logm H )) measuring α, G F, θ w, m Z, m W, and m t checks consistency of model and constrains m H 11/8/006 DESY seminar - Ulrich Heintz 7

8 how do we measure quark masses? quarks are confined quarks cannot be observed in isolation measure mass of color-singlet bound states (hadrons) use lattice QCD to relate to quark mass top is short-lived τ 10-4 s decays to Wb before it can form hadrons reconstruct mass from its decay products 11/8/006 DESY seminar - Ulrich Heintz 8

9 outline the top quark the top quark factory top quark production and decay top quark mass in the lepton+jets channel top quark mass in the dilepton channel putting it all together beyond the Tevatron conclusion 11/8/006 DESY seminar - Ulrich Heintz 9

10 Tevatron Run I ( ) s = 1.8 TeV Ldt = 10 pb -1 We are here Design 8. fb fb -1 Run II (001-present) Base 4.1 fb -1 s = 1.96 TeV peak luminosity /cm /s Ldt today at DØ delivered.0 fb -1 recorded 1.7 fb -1 analyzed 900 pb -1 Ldt plan 4-8 fb -1 by /8/006 DESY seminar - Ulrich Heintz 10

11 Tevatron CDF DØ km 11/8/006 DESY seminar - Ulrich Heintz 11

12 muon toroid DØ detector calorimeter beam pipe 11/8/006 DESY seminar - Ulrich Heintz 1

13 DØ detector 11/8/006 DESY seminar - Ulrich Heintz 13

14 CDF detector muon detector calorimeter tracker vertex detector 11/8/006 DESY seminar - Ulrich Heintz 14

15 outline the top quark the top quark factory top quark production and decay top quark mass in the lepton+jets channel top quark mass in the dilepton channel putting it all together beyond the Tevatron conclusion 11/8/006 DESY seminar - Ulrich Heintz 15

16 top-antitop pair production top-antitop pair production p p q q g t p g t 85% 15% t p g t strong interaction ( flavorblind ) at s=1.96 TeV σ(tt) = 6.7±0.4 pb expect 1 event every crossings! Cacciari et al. JHEP 0404:068 (004) Kidonaki & Vogt, Phys. Rev. D (003) the proverbial needle in a hay stack 11/8/006 DESY seminar - Ulrich Heintz 16

17 top-antitop pair production top decay t Wb B 100% W decay W lν B 11% W qq B 67 % final state signatures b-jet e,µ e,µ ν ν MET b-jet Dilepton (BR~5%, low background) e+jets 15% b-jet µ+jets 15% e,µ jet all jets 44% ν MET jet b-jet Lepton+jets (BR~30%, moderate background) ee 1.% b-jet eµ µµ.4% 1.% jet jet jet jet b-jet All-hadronic (BR~46%, huge background) τ+jets 1% 11/8/006 DESY seminar - Ulrich Heintz 17

18 b-jet tagging b µ + anything (11%) jets with muons b lifetime 1.6 ps b-jet tagging travels a few mm before decaying large impact parameter secondary vertex primary vertex 11/8/006 DESY seminar - Ulrich Heintz 18

19 jet energy scale calibration transverse momentum balance γ + jet events calibrate jets against electromagnetic response calibrate electromagnetic response with Z e + e - systematically limited W jets tt Wb Wb lνb qqb events fit for m t and jet energy scale α jes simultaneously statistically limited 11/8/006 DESY seminar - Ulrich Heintz 19

20 outline the top quark the top quark factory top quark production and decay top quark mass in the lepton+jets channel top quark mass in the dilepton channel putting it all together beyond the Tevatron conclusion 11/8/006 DESY seminar - Ulrich Heintz 0

21 lepton+jets event kinematics tt Wb Wb eν qq displaced vertex hadrons jet 1 (b) hadrons jet (b) t ν e,µ hadrons jet 3 jet 4 11/8/006 DESY seminar - Ulrich Heintz 1

22 unknowns p zν and m t 4 constraints lepton+jets event kinematics m(e,ν) = m W quadratic equation for p z (ν) choose smaller value m(j 3,j 4 )=m W m(j,j 3,j 4 )=m t m(e,ν,j 1 )=m t perform -C kinematic fit for m t 11/8/006 DESY seminar - Ulrich Heintz

23 lepton+jets event kinematics complications combinatorics j 1,j,j 3,j 4 b,b,w (1 permutations) b,j,j 3,j 4 b,b,w (8 permutations) b,b,j 3,j 4 b,b,w ( permutations) gluon radiation initial state radiation momentum from initial quark/antiquark or spectators overestimate m t final state radiation momentum from t or b quarks underestimate m t many techniques 11/8/006 DESY seminar - Ulrich Heintz 3

24 template method first technique used to measure top quark mass used by DØ and CDF pick an estimator (e.g. mass from kinematic fit) compute probability density using events simulated with a range of values of m t (templates) maximum likelihood fit to extract measured m t 11/8/006 DESY seminar - Ulrich Heintz 4

25 CDF lepton+jets channel (680 pb -1 ) require one electron or muon 4 jets missing p T tags 1 tag 1 tag 0 tags tight loose b-tags p T jets 1-3 >15 >15 >15 >1 GeV p T jet 4 >8 >15 >8 >1 GeV background 4.0±1.3.± ± top events /8/006 DESY seminar - Ulrich Heintz 5

26 template method perform kinematic fit m fit keep jet assignment with lowest χ if χ <9 CDF Run II Preliminary Events/5 GeV/c Events/5 GeV/c m reco (GeV/c ) t -tag 1-tag(L) All Events RMS = 7 GeV/c Corr. Comb (47%) RMS = 13 GeV/c m reco (GeV/c ) t All Events RMS = 31 GeV/c Corr. Comb (18%) RMS = 13 GeV/c m reco (GeV/c ) 11/8/006 DESY seminar - Ulrich Heintz 6 Events/5 GeV/c Events/5 GeV/c tag(T) t 0-tag All Events RMS = 3 GeV/c Corr. Comb (8%) RMS = 13 GeV/c m reco (GeV/c ) t All Events RMS = 37 GeV/c Corr. Comb (0%) RMS = 1 GeV/c

27 template method parametrize histograms of m fit as a function of m t and α jes 11/8/006 DESY seminar - Ulrich Heintz 7

28 template method reconstruct hadronic W decay mass of all pairs of untagged jets parametrize as function of m t and α jes CDF Run II Preliminary Entries/5 GeV/c Entries/5 GeV/c tag All Events RMS = 36 GeV/c Corr. Comb (50%) RMS = 14 GeV/c m (GeV/c ) jj 1-tag(L) All Events RMS = 41 GeV/c Corr. Comb (17%) RMS = 17 GeV/c m (GeV/c ) jj m (GeV/c ) jj 11/8/006 DESY seminar - Ulrich Heintz 8 Entries/5 GeV/c Entries/5 GeV/c tag(T) 0-tag All Events RMS = 47 GeV/c Corr. Comb (1%) RMS = 15 GeV/c All Events RMS = 53 GeV/c Corr. Comb (1%) RMS = 17 GeV/c m (GeV/c ) jj

29 template method simultaneously fit m fit and m jj templates gaussian constraint on α jes = 0 ± δ α α δα (σ c ) JES CDF Run II Preliminary (680 pb ln L=8.0 ln L=4.5 ln L=.0 ln L= (GeV/c ) M top m t = ±.5(stat jes) ± 1.3(syst) GeV total /8/006 DESY seminar - Ulrich Heintz 9-1 ) pdf CDF Conf. Note 815 source b-jet scale res jet scale bkg jet scale ISR FSR generators background b-tagging MC stats error (GeV)

30 DØ lepton+jets channel (370 pb -1 ) kinematic event selection charged lepton exactly 4 jets missing p T >0 GeV p T >0 GeV p T >0 GeV η <1.1 (e) η <.0 (µ) η <.5 e+jets µ+jets l+jets events top 41 ± 9 6 ± 8 66 ± 1 W+jets 30 ± 9 59 ± 8 89 ± 13 QCD 15 ± 5 ± 1 0 ± 11/8/006 DESY seminar - Ulrich Heintz 30

31 developed by DØ matrix element method Nature 49, 638 (004) compute probability to observe each event build event-by-event likelihood use all kinematic information from the events LO ttbar matrix element relative probability to be signal/background no kinematic fit dσ ( y, m ) = t M dlips 11/8/006 DESY seminar - Ulrich Heintz 31

32 matrix element method probability density for an event o if the mass of the top quark is m t L evt ( o m, α, f ) = f p ( o m, α ) + ( 1 f ) p ( o α ) t jes top top combine all events in a joint likelihood sig top fraction t jes jet scale parameter top bkg jes ln L n 1 n t α jes top = i 1 i α t jes ( o Ko m,, f ) = lnl( o m,, f ) top and maximize wrt m t, α jes, f top 11/8/006 DESY seminar - Ulrich Heintz 3

33 calculate signal probability p sig ( o m, α ) normalization t matrix element method jes 1 ( x) f ( x) dσ ( q, m ) W ( o q, α ) = ( ) dxdxf tt t jes σ m tt t use only events with exactly 4 jets to minimize ISR/FSR assume p T (tt) = 0 all angles and electron momentum are well measured use MC integration techniques for remaining 5(6) integrations consider all possible jet-parton assignments all possible solutions for the z-component of the neutrino momenta 11/8/006 DESY seminar - Ulrich Heintz 33 pdf transfer function parametrize detector response M dlips

34 matrix element method divide sample into subsamples with 0,1, b-tags take advantage of small backgrounds in b-tagged samples use b-tags to assign relative weights to jet permutations no tags 1 tag tags + = GeV = 173 ± 5 GeV = GeV mt 1 mt m t /8/006 DESY seminar - Ulrich Heintz 34

35 matrix element method -d fit in m t, α jes source sig/bkg model pdf b frag/decay α(p T ) b response error (GeV) b tagging f top 0.15 QCD bkg 0.9 MC calibration 0.48 total /8/006 DESY seminar - Ulrich Heintz 35

36 matrix element method fit lepton+jets data accepted by PRD, hep-ex/ m t = GeV α jes = m t = ( stat jes) ± 1.4( syst) 4.7 GeV 11/8/006 DESY seminar - Ulrich Heintz 36

37 developed by DØ ideogram technique use ideas by DELPHI for W mass measurement use power of kinematic fit use all kinematic information 11/8/006 DESY seminar - Ulrich Heintz 37

38 ideogram technique probability density for an event o if the mass of the top quark is m t L evt ( o m, α, f ) = f p ( o m, α ) + ( 1 f ) p ( o α ) t jes top top dσ ( y, mt ) = M combine all events in a joint likelihood sig top fraction t jes jet scale parameter top bkg jes dlips ln L n 1 n t α jes top = i 1 i α t jes ( o Ko m,, f ) = lnl( o m,, f ) top and maximize wrt m t, α jes, f top 11/8/006 DESY seminar - Ulrich Heintz 38

39 compute signal probability p sig ideogram technique convolution of Gaussian and Breit-Wigner at every solution of kinematic fit probability for D if signal [ ] 4 χi ( o m, α ) = p ( D) e f G( m, m', σ ) BW ( m', m ) dm' + ( 1 f ) S( m, m ) t jes sig i= 1 fit χ i fit mass i fit error t i t correct permutation wrong permutation 0 tags tags 1 tag 11/8/006 DESY seminar - Ulrich Heintz 39

40 ideogram technique maximize likelihood wrt m t, f top, α jes m t = 173.7±4.4(stat jes) GeV 11/8/006 DESY seminar - Ulrich Heintz 40

41 ideogram technique source error signal model 0.73 GeV background model 0.0 GeV pdf 0.0 GeV b fragmentation 1.30 GeV p T dependence of jes b response b tagging trigger jet efficiency/resolution f top QCD background 0.45 GeV 1.15 GeV 0.9 GeV +0.6/-0.3 GeV 0. GeV 0.1 GeV 0.8 GeV MC calibration 0.5 GeV total.1 GeV m t = ± 4.4( stat jes) ±.1( syst) GeV D0 note 5099-CONF 11/8/006 DESY seminar - Ulrich Heintz 41

42 outline the top quark the top quark factory top quark production and decay top quark mass in the lepton+jets channel top quark mass in the dilepton channel putting it all together beyond the Tevatron conclusion 11/8/006 DESY seminar - Ulrich Heintz 4

43 dilepton event kinematics tt Wb Wb eν µν jet 1 (b) jet (b) ν e ν p T = - p T µ 11/8/006 DESY seminar - Ulrich Heintz 43

44 dilepton event kinematics neutrinos 4 unknowns 3 constraints ( ) ( ) W l m( νb) m( νb ) + l = l + m ν = m l ν = M and kinematically underconstrained 0,,4 kinematic solutions for each value of m t -fold combinatoric ambiguity dynamical likelihood methods neutrino weighting (νwt) developed by DØ in Run I matrix element weighting (MWT) following idea by Dalitz&Goldstein, Kondo, first published by DØ 11/8/006 DESY seminar - Ulrich Heintz 44

45 dilepton channel at DØ selection jets with p T >0 GeV charged opposite sign leptons (e,µ) with p T >15 GeV further channel specific selections expected/observed event yield in 370 pb -1 ll notag ll b-tag ll l+track top bkg all ± ± ±0.3 data events 30 events 11/8/006 DESY seminar - Ulrich Heintz 45

46 matrix element weighting assumem t calculate p ν, p ν, p ν, p ν x x y y using assumptions and kinematic observables assign each hypothesis a likelihood ( m ) = f ( x) f ( x) p( E * m) p( E * m) w t ( ) sum w m t over up to 4 solutions and jet permutations average over detector resolution l R. H. Dalitz and G.R. Goldstein, Phys. Rev. D 45, 1531 (199) l 11/8/006 DESY seminar - Ulrich Heintz 46

47 matrix element weighting use value of m t at which w(m t ) is maximal as mass estimator full simulation + background (for b-tagged sample) fraction of events/bin Mean RMS fraction of events/bin Mean RMS fraction of events/bin Mean RMS m peak (GeV) m peak (GeV) m peak (GeV) m t =155 GeV m t =175 GeV m t =195 GeV 11/8/006 DESY seminar - Ulrich Heintz 47

48 matrix element weighting maximize likelihood wrt m t L 6 events (ll notag,ll btag) ( m ) t = n bins = i 1 n s s i ( m ) n s + n t + n b b b i n i 11/8/006 DESY seminar - Ulrich Heintz 48

49 matrix element weighting check performance using MC ensembles offset slope = 1.9 ± 0.1GeV = ± m t δ jes 11/8/006 DESY seminar - Ulrich Heintz 49

50 neutrino weighting assumem,η, t calculate p ν, p ν, p ν, p ν x x y y using assumptions and kinematic observables (except missing p T ) assign each hypothesis a likelihood ν ν ν ν ( p p p ) ( p/ y p y p y ) w( m ) t ( ) ν η ν = e / x σ σ sum w m over all values of η ν, η ν t, up to 4 solutions and jet permutations average over detector resolution x x e 11/8/006 DESY seminar - Ulrich Heintz 50

51 ( ) neutrino weighting divide into 10 bins and normalize w m t each event is characterized by 9 component vector 11/8/006 DESY seminar - Ulrich Heintz 51

52 11/8/006 DESY seminar - Ulrich Heintz 5 neutrino weighting compute likelihood by comparing to MC results for different values of m t ( ) ( ) [ ] ( ) [ ] = = = N j i ij ij j t s dw h w w h w w N m w f ~ exp ~ exp 1 r ( ) ( ) ( ) ( ) ( ) = = n i b s i b b t i s s b s b b b s b t b n n w f n m w f n n n n p n n g n n m n n w L 1,,,,,,, r r r σ 30 events (ll,l+track)

53 DØ dilepton results MWT: νwt: m t = 176. ± 9.(stat) ± 3.9(syst) GeV m t = ± 7.4(stat) ± 5.6(syst) GeV m t = ± 6.7(stat) ± 4.8(syst) GeV source jet scale resolutions gluon radiation pdf background MC statistics total uncertainty submitted to PRL hep-ex/ /8/006 DESY seminar - Ulrich Heintz 53

54 CDF matrix element analysis CDF Conf. Note 8369 source jet scale generator method sample composition background ISR/FSR pdf total error 3.5 GeV 0.9 GeV 0.6 GeV 0.7 GeV 0.7 GeV 0.4 GeV 0.8 GeV 3.9 GeV m t =164.5 ± 3.9(stat) ± 3.9(syst) GeV 11/8/006 DESY seminar - Ulrich Heintz 54

55 outline the top quark the top quark factory top quark production and decay top quark mass in the lepton+jets channel top quark mass in the dilepton channel putting it all together beyond the Tevatron conclusion 11/8/006 DESY seminar - Ulrich Heintz 55

56 all hadronic top decays DØ (Run I 110 pb -1 ) b-tagging neural network discriminant kinematic fit m t = 178.5±13.7(stat)±7.7(syst) GeV CDF (Run II 1 fb -1 ) template technique m t = 174.0±.(stat)±4.8(syst) GeV CDF Conf. Note /8/006 DESY seminar - Ulrich Heintz 56

57 m top =171.4±.1 GeV δ stat = 1. GeV δ syst = 1.8 GeV top mass combination χ = 10.6 (10 d.o.f.) see also hep-ex/ /8/006 DESY seminar - Ulrich Heintz 57

58 what does top say about the Higgs? m H 89 ± 36 GeV m < % CL = H 11/8/006 DESY seminar - Ulrich Heintz 58

59 outline the top quark the top quark factory top quark production and decay top quark mass in the lepton+jets channel top quark mass in the dilepton channel putting it all together beyond the Tevatron conclusion 11/8/006 DESY seminar - Ulrich Heintz 59

60 Run I Measured 110 pb -1 Run II (fb -1 ) the future CDF Top Mass Uncertainties Run II Measured 318 pb pb -1 Projections in 1996 Run II (8fb -1 ) Projections In 005 δm top = δm top Run I / Lum Run II / Lum Run Int. Lum [pb -1 ] 11/8/006 DESY seminar - Ulrich Heintz 60

61 the future Large Hadron Collider CERN, Geneva, Switzerland start of operation 007 proton-proton collisions s = 14 TeV σ tt 800 pb δm t 1 GeV 8.5 km 11/8/006 DESY seminar - Ulrich Heintz 61

62 the future linear e + e - collider relative cross section 1S LO NNLO NLO Yakovlev & Groote, PRD (001) center of mass energy (GeV) e e γ,z determine m t to MeV from 1S peak t t 11/8/006 DESY seminar - Ulrich Heintz 6

63 the future 11/8/006 DESY seminar - Ulrich Heintz 63

64 outline what do we know about the top quark? why study the top quark? top quark production top quark decay top quark properties beyond the Tevatron conclusion 11/8/006 DESY seminar - Ulrich Heintz 64

65 we have come a long way 1995: template fit in lepton+jets channel m t = 176±13 GeV 006: many techniques: template, ideogram, dynamical likelihoods, lifetime many channels: lepton+jets, dileptons, all jets the trend is to use maximal information keep all events use all kinematic information in the events use discriminants to determine their signal/background world average m t = ±.1 GeV 11/8/006 DESY seminar - Ulrich Heintz 65

66 thank you 11/8/006 DESY seminar - Ulrich Heintz 66