The Top Quark We Observe Gustaaf Brooijmans Indirect Searches for - PowerPoint PPT Presentation

The Top Quark We Observe Gustaaf Brooijmans Indirect Searches for New Physics at the Time of the LHC The Galileo Galilei Institute, March 23 rd , 2010 1 Gustaaf Brooijmans The Top Quark We Observe

• Top Quark Properties from Decays • Mass • Branching Ratios & V tb • V tb from Single Top • W Helicity • Top Quark Charge and Width • Top Quark Production • Cross-Section • Spin Correlations • Forward-backward asymmetry Gustaaf Brooijmans The Top Quark We Observe 2

Top History Date Milestone Statistics Luminosity √ s 1995 Observation 10’s 50 pb -1 1.8 TeV 1997 Properties ~100 120 pb -1 1.8 TeV Precision 2009 100’s - 1k few fb -1 1.96 TeV Properties Single Top 2009 10’s (?) 2 fb -1 1.96 TeV Observation 2011 Observation 5 k? ~1 fb -1 7 TeV Precision 2014 100 k? 10 (?) fb -1 14 (?) TeV Differential Gustaaf Brooijmans The Top Quark We Observe 3

Tevatron Gustaaf Brooijmans The Top Quark We Observe 4

Decays Gustaaf Brooijmans The Top Quark We Observe 5

Top Mass • Top quark’s existence 14 Mass of the Top Quark (*Preliminary) CDF-I di-l 167.4 10.3 4.9 ! ! established 18 years after D0-I di-l 168.4 12.3 3.6 ! ! bottom quark * CDF-II di-l 171.2 2.7 2.9 ! ! * • Long road to discovery due to D0-II di-l 174.7 2.9 2.4 ! ! CDF-I l+j 176.1 5.1 5.3 ! ! surprisingly large mass D0-I l+j 180.1 3.9 3.6 ! ! • Now known to better than 1% * CDF-II l+j 172.1 0.9 1.3 ! ! * D0-II l+j 173.7 0.8 1.6 ! ! • Interestingly, y top (m top ) ≅ 1 CDF-I all-j 186.0 10.0 5.7 ! ! • Precise measurement with * CDF-II all-j 174.8 1.7 1.9 ! ! * CDF-II trk 175.3 6.2 3.0 ! ! low Tevatron statistics driven * Tevatron March’09 173.1 0.6 1.1 ! ! hep-ex/0903.2503 (stat.) (syst.) ! by experimenters’ CDF March’07 2 /dof = 6.3/10.0 (79%) ! 12.4 1.5 2.2 ! ! 0 resourcefulness 150 160 170 180 190 200 2 m (GeV/c ) top Gustaaf Brooijmans The Top Quark We Observe 6

Matrix Element Analyses • Currently yield the most precise measurement of the top quark mass, also • Major contribution to the observation of single top • Big contribution in Higgs searches • Basically unbinned maximum likelihood fits • Event-by-event measured uncertainties • More weight for more signal-like event Transfer functions: • Determine event’s “signal probability”: generated → measured momenta b-tag prob matrix element Gustaaf Brooijmans The Top Quark We Observe 7

• Caveats: • LO matrix elements (typically madevent): • (Initially) require exact number of jets • Evaluation of NLO systematic not so easy • Recent development: add NN to discriminate further against background • Calibration, i.e. determination of transfer functions done by full simulation with pythia • What’s really measured is basically PMAS(6,1) • Group trying to figure out what that really means • Because with current precision, that is an important question! Gustaaf Brooijmans The Top Quark We Observe 8

Top Mass @ LHC • Use statistics to beat down the systematics • Will be very challenging to do better than Tevatron • ... but ultimately expect to get there • Intrinsic limit from measurement in final state • Can’t beat Λ QCD ! • Can we hope for ~500 MeV precision? • Only way to do better is probably threshold scan at lepton collider Gustaaf Brooijmans The Top Quark We Observe 9

Mass: CPT Test • Mass difference top - antitop: 3.8 ± 3.7 GeV DØ: Phys.Rev.Lett.103:132001,2009 Gustaaf Brooijmans The Top Quark We Observe 10

Is It Top? • Top ≡ weak isospin partner of bottom • “Partner” in the sense of having the largest EWK/CKM coupling to b • Measure • ...from fraction of b-tagged jets in pair production If unitary CKM matrix with 3 generations: |V tb | > 0.89 @ 95% CL DØ: Phys. Rev. Lett. 100 , 192003 (2008 ) Gustaaf Brooijmans The Top Quark We Observe 11

• Rare decays • t → Zc: < 3.7% @ 95% CL (CDF: PRL 101 192002 ) ATLAS CSC Book: arXiv:0901.512 • t → H + b: < 10-30% @ 95% CL (CDF: PRL 103 101803 , DØ: Phys.Lett.B682:278-286,2009, Phys.Rev.D80:051107(R),2009 ) • LHC prospects (ATLAS): • t → H + b: < ~3%, then systematics limited? • t → Zq, γ q: sensitive to ~10 -4 with 100 fb -1 • t → gq: sensitive to ~7 10 -3 • Radiative t → WbZ (predicted at ~5 10 -7 in SM) out of LHC reach Gustaaf Brooijmans The Top Quark We Observe 12

Single Top • Probe the top’s EWK coupling through production • Process now well-established at the Tevatron: Single Top Quark Cross Section August 2009 +0.56 CDF Lepton+jets 3.2 fb 2.17 pb 1 0.55 CDF: PRL 103 092002 +2.6 CDF MET+jets 2.1 fb 5.0 pb 1 2.3 +0.88 D Lepton+jets 2.3 fb 3.94 pb 1 DØ: Phys. Rev. Lett. 103 , 092001 (2009 ) 0.88 +0.58 Tevatron Combination 2.76 pb 0.47 Preliminary B.W. Harris et al., PRD 66, 054024 (2002) m top = 170 GeV N. Kidonakis, PRD 74, 114012 (2006) 8 0 2 4 6 Gustaaf Brooijmans The Top Quark We Observe 13

• Extracted measurements: • |V tb | > 0.71/0.78 @ 95% CL (CDF/DØ) Gustaaf Brooijmans The Top Quark We Observe 14

Single Top @ LHC • t-channel and Wt measurable with a few fb -1 , more needed for s-channel ATLAS CSC Book: arXiv:0901.512 Gustaaf Brooijmans The Top Quark We Observe 15

W Boson Helicity • But is the tWb coupling EWK? • Study angular distribution of the decays Longitudinal LH Contribution RH Contribution Contribution ≈ 0.3 in SM ≈ 0.0 in SM ≈ 0.7 in SM Gustaaf Brooijmans The Top Quark We Observe 16

• Two approaches: • Reconstruct cos θ * directly in l+jets and/or dilepton events, then use template or unfolding Best Fit SM Dileptons Leptonic W in Hadronic W in l+jets l+jets 2-D likelihood fit to templates Phys. Rev. Lett. 100 , 062004 (2008 ) Gustaaf Brooijmans The Top Quark We Observe 17

1.9 fb -1 CDF Templates CDF Unfolding Conference Note 9114 Conf. Note 9215 Gustaaf Brooijmans The Top Quark We Observe 18

• Or, use matrix-element technique 8 Graph -1 CDF Run II Preliminary (2.7 fb ) CDF Preliminary ( ∫ L dt = 1.9 fb -1 ) Assumes mt = 175 GeV/c2 + f 1 Matrix Element: (fix f + = 0.0) f =0.64 ± 0.08 ± 0.07 68.27% CL 0 Cos θ * Unfolding: 90% CL f =0.15 ± 0.10 ± 0.04 f =0.38 ± 0.21 ± 0.07 + 0 0.5 (fix f 0 = 0.7) f =0.01 ± 0.05 ± 0.03 + (fix f + = 0.0) f =0.66 ± 0.10 ± 0.06 0 Cos θ * Template: 0 f =-0.03 ± 0.07 ± 0.03 f =0.65 ± 0.19 ± 0.03 0 0.5 1 + 0 f 0 (fix f 0 = 0.7) f =-0.04 ± 0.04 ± 0.03 + (fix f + = 0.0) f =0.59 ± 0.11 ± 0.04 0 0 0 0.2 0.4 0.6 0.8 1 Conf. Note 10004 W-Helicity Fraction from Top Decay ➡ All measurements statistics-limited.... Gustaaf Brooijmans The Top Quark We Observe 19

Top Charge • Does it have charge +2/3? Look at the charge of the b associated with the W • Jet charge (CDF & DØ) • CDF Conf. Note 8967 : exclude 4/3 @ 87% CL • DØ: exclude complete sample is made of charge 4/3 quarks @ 92% CL Phys. Rev. Lett. 98 , 041801 (2007) • Soft lepton tag (CDF) • 45 events, 29 events best fit 2/3, 16 events 4/3 → 4/3 excluded @ 95% CL Conf. Note 9939 Gustaaf Brooijmans The Top Quark We Observe 20

Top Width • SM: Γ t ~1.4 GeV • Combine Γ (t → Wb) (from single top) and B(t → Wb) and assume B(t → Wq) = 1: • Γ t = 2.1 ± 0.6 GeV DØ: Conference Note D0 Note 6034-CONF • i.e. τ t = (3 ± 1) 10 -25 s • Using only Γ (t → Wb): • Γ t > 1.2 GeV @ 95% CL • τ t < 5 10 -25 s @ 95% CL • CDF direct measurement from m t , m jj : • Γ t < 7.5 GeV @ 95% CL ( Conf. Note 10035 ) Gustaaf Brooijmans The Top Quark We Observe 21

Production Gustaaf Brooijmans The Top Quark We Observe 22

Top Pair Production Dilepton CDF Conf. Note 9913 Conference Note D0 Note 6038-CONF l+jets Phys.Rev.D80:071102,2009 ➡ Not much room for anomalous production... Gustaaf Brooijmans The Top Quark We Observe 23

Spin Correlations • Top decays before hadronization → initial polarization information is reflected in top decay products _ • Tops have opposite/same helicity in qq/gg production • Measure angles of down-type fermions from W/top decay in _ top rest-frame wrt quantization axis (top in tt rest frame or beam axis) Gustaaf Brooijmans The Top Quark We Observe 24

• It’s a difficult measurement: Helicity Angle Bilinear Cos( )*Cos( ) , Fit Result ! ! l d 240 240 -1 CDF Run II preliminary L=4.3 fb 220 220 Opposite Helicity (OH) 200 200 Same Helicity (SH) 180 180 Backgrounds 160 160 Data 140 140 Events Events f : 0.80 +/- 0.25 +/- 0.08 OH 120 120 100 100 80 80 60 60 40 40 20 20 0 0 -1 -1 -0.8 -0.8 -0.6 -0.6 -0.4 -0.4 -0.2 -0.2 0 0 0.2 0.2 0.4 0.4 0.6 0.6 0.8 0.8 1 1 cos( cos( )*cos( )*cos( ) ) ! ! ! ! l l d d Conf. Note 10048 Conference Note 5950-CONF CDF: C = 0.60 ± 0.50 (stat) ± 0.16 (syst) (l+jets) CDF: C = 0.32 +0.55-0.78 (stat + syst) (dilepton) DØ: C = -0.17 +0.65-0.53 (stat + syst) (dilepton) SM: 0.78 (NLO) Gustaaf Brooijmans The Top Quark We Observe 25

Polarization in Single Top Conf. Note 9920 • Something for the LHC! Gustaaf Brooijmans The Top Quark We Observe 26