1. 2008/12/10National Tsing Hus Univ.1 Measuring properties of top quark; Is it really top of SM? Yen-Chu Chen Institute of Physics Academia Sinica

2. 2008/12/10National Tsing Hus Univ.2 Content Introduction Production of top quark Properties of top quark: –Understanding the top quark –Or is it really the top of the Standard Model?

3. 2008/12/10National Tsing Hus Univ.3 Tevatron Ring ( ~4 miles)! Main injector Chicago CDF D0 pp collisions at √s = 1.96 TeV! Already 4 fb-1 recorded! Expect to collect 6 fb-1 by the end of 2009! ( 8 fb-1 by the end of 2010) The Tevatron

4. 2008/12/10National Tsing Hus Univ.4 Muon stations Calorimeter Silicon detector COT

5. 2008/12/10National Tsing Hus Univ.5 Top quark physics PP  t t  X b b  W  W  l  q l  q q' _ q' _ _ Production Cross section Top spin Rare decays, charged Higgs, etc. W helicity Top charge Top mass Charge asymmetry Life time, decay width Production mechanism FCNC Br(t → Wb)/Br(t → Wq)

6. 2008/12/10National Tsing Hus Univ.6 Sample separation Di-lepton (DIL) channel: –both W decay to leptons, –in practice uses only e, μ. Lepton+Jets (LJ) channel: –one W decays to leptons, –the other decays to quarks. Hadronic channel: –both W decay to quarks. t t W + W̅W̅ b b e +, μ +, u, c e –, μ –, u, c _ __ e, μ, d, s __ __ _

7. 2008/12/10National Tsing Hus Univ.7 Production of top quark Production mechanism Production cross section Forward backward asymmetry

8. 2008/12/10National Tsing Hus Univ.8 Production of top quark In the SM: 6.7 pb (m t = 175 GeV/c 2 ) Single top production: t-channel 1.98 ± 0.21 pb V tb b qq t s-channel 0.88 ± 0.07 pb V tb tq bq

9. 2008/12/10National Tsing Hus Univ.9 Production mechanism Di-lepton events; using data of 2 fb -1  =azimuthal correlation of the two leptons

10. 2008/12/10National Tsing Hus Univ.10 Fit result (DIL, 2 fb -1 ): F gg = 0.53 +0.36 -0.38 ( +0.35 -0.37 (stat) +0.07 -0.08 (sys)) Previous result (L+J, 1 fb -1 ): F gg = 0.07± 0.14(stat)± 0.07(syst)

11. 2008/12/10National Tsing Hus Univ.11 Production cross section DIL, 2.8 fb-1  = 6.67 ± 0.77(stat) ± 0.43(sys) ±0.39(lum) pb  = 7.81 ± 0.92(stat) ± 0.68(sys) ± 0.45(lum) pb

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14. 2008/12/10National Tsing Hus Univ.14 Single top production

15. 2008/12/10National Tsing Hus Univ.15 Forward backward asymmetry A fb = 0.17 ± (0.07)stat ± (0.04)syst To be compared with theory: A fb = 0.04 ± 0.01

16. 2008/12/10National Tsing Hus Univ.16 Properties of top quark Lift time –Expected: ~10 -25 sec Decay width Decay mode Mass and its implication –Expected: none, a free parameter in the SM W helicity in top decay –Expected: 70% LH, 30% Lo, ~0 RH Charge –Expected: +2/3

17. 2008/12/10National Tsing Hus Univ.17 Life time c  t < 52.5  m @ 95% CL

18. 2008/12/10National Tsing Hus Univ.18 Decay width  top < 12.7 GeV @ 95% CL

19. 2008/12/10National Tsing Hus Univ.19 Decay mode Br(t→Wb)/Br(t->Wq) = 1.12 +0.21 –0.19 (stat) +0.17 -0.13 (sys) (160 pb -1 ) Br(t→Zq) < 3.7% (1.9 fb -1 ) Br(t→Zc) < 13% (1.9 fb -1 ) Br(t→gc) < 12% (1.9 fb -1 ) Br(t→  c) < 18% (1.9 fb -1 )

20. 2008/12/10National Tsing Hus Univ.20 Mass of the top quark Tevatron Top mass, 2007 Mar. Reaching below 1% uncertainty! CDF and D0 are working together on the common systematic issues to reduce uncertainty.

21. 2008/12/10National Tsing Hus Univ.21 MTM method (CDF, 2.7 fb -1 ) log Lsig(mt, JES) = Σ i [log Li(mt, JES)] - n bg log Lavg(mt, JES | background)

22. 2008/12/10National Tsing Hus Univ.22 mt = 172.2 ± 1.0 (stat.) ± 0.9 (JES) GeV/c2

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24. 2008/12/10National Tsing Hus Univ.24 W helicity in top decay (1/Γ) (dΓ/dcosθ*) = f - (3/8) (1- cosθ*) 2 + f 0 (3/4) ( 1 - cosθ* 2 ) + f + (3/8) ( 1 + cosθ* ) 2, θ* is the decay angle of lepton in the W rest frame with respect to the W direction in the top rest frame f 0 = 0.703, f - =0.297, f + =3.4  10 -4

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26. 2008/12/10National Tsing Hus Univ.26 f 0 = 0.65 ± 0.19 ± 0.03 f + = -0.03 ± 0.07 ± 0.03

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28. 2008/12/10National Tsing Hus Univ.28 Combination in CDF for W helicity studies f 0 = 0.62 ± 0.11 assuming f_+ = 0.0 (the SM value) f + = -0.04 ± 0.05 assuming f_0 = 0.7 (the SM value) f 0 = 0.66 ± 0.16 and f + = -0.03 ± 0.07, correlation coeff = -0.82 with no assumption

29. 2008/12/10National Tsing Hus Univ.29 Charge of the top quark The particle we have been called “top” for more than ten years could be a top like quark from an exotic model. –D. Chang, and E. Ma, Phys. Rev. D58, 097301 (1998). –D. Chang, W.-F. Chang, and E. Ma, Phys. Rev. D59, 091503 (1999); The only way to tell is the charge of the top quark, all the other properties are the same: –SM : +2/3, XM : -4/3

30. 2008/12/10National Tsing Hus Univ.30 To get result of top charge in DIL samples Study top charge based on –jet charge calculation and –two kinds of pairing methods: MlbsMax and KIN Using single b tagged samples to reduce the background. Taking the part of not b tagged samples as control region. (Higher contamination, lower purity)

31. 2008/12/10National Tsing Hus Univ.31 Using jet charge to identify b flavor - common in both LJ and DIL - P jet pipi QiQi Additional tracks from the particles interacting with the detectors could cause bias, since they are mostly protons and   ! => pt > 1.5 GeV/c, |d0| < 0.15 cm, α = 0.5

32. 2008/12/10National Tsing Hus Univ.32 b quark charge from jet Assume jet charge symmetry: If > 0 → ; < 0 → Purity of identifying jet charge correctly: PYTHIA, Top mass 175 GeV/c 2 (ttop75) : – = 0.601 ± 0.007; = 0.614 ± 0.007 (DIL)

33. 2008/12/10National Tsing Hus Univ.33 Jet charge from di-jet (  trigger) data Calculate of the away jet: –Nos : number of opposite charge sign jets with respect to the lepton –Nss : number of same sign jets Found b fraction in jets. –There are also c decay, b mixing and background.

34. 2008/12/10National Tsing Hus Univ.34 Purity in di-jet data analysis is consistent with jet charge from Top MC. Take purity from MC study and apply the scale factor (SF) to take care of the difference between data and MC. SF = 1.01 ± 0.01 ± 0.03 No difference seen between jet charge from different muon charge sign samples!

35. 2008/12/10National Tsing Hus Univ.35 Pairing of lepton and b in DIL MlbsMax : –Calculate the invariant mass of lepton + jet paired –For wrong pairing this value tends to go larger than the correct pair. –Reject the pairing having the largest M lb 2 of the four possible pairs. –Make cut on the maximum M lb 2 to increase the purity. KIN : –Take the top mass as input and resolve the kinematic equation set.

36. 2008/12/10National Tsing Hus Univ.36 Pairing using MlbsMax Efficiency Purity Mlbs max cut correct pairing wrong pairing

37. 2008/12/10National Tsing Hus Univ.37 Efficiency and purity of MlbsMax Pythia MC Based on ttop75, top mass 175 GeV/c2 M lb 2 max cut at 21K Efficiency = 0.395 ± 0.004 Purity = 0.948 ± 0.002

38. 2008/12/10National Tsing Hus Univ.38 Pairing using KIN Assuming top mass to resolve the equation set of energy momentum conservation. Details described in: –CDF note 8638, page 51. –Presentation at top property meeting, 2008/08/22, Yen-Chu Chen

39. 2008/12/10National Tsing Hus Univ.39 Brief review of KIN pairing For given lepton and jet momenta, try to resolve the equation set via Newton’s method. Multiple solutions could be found –Pick the one having smaller m tt 2 Two possible way of pairing –Pick the one having higher reconstruction probability Probability of miss-reconstruction is higher in cases similar to RH W helicity than the cases similar to LH W helicity. The nature is mostly LH (30%) and LO (70%).

40. 2008/12/10National Tsing Hus Univ.40 Efficiency and purity of KIN SM (Pythia) SM (Herwig) LH (GGwig) LO (GGwig) RH (GGwig) t t rec. eff.0.97 ± 0.02 0.98 ± 0.020.95 ± 0.010.87 ± 0.01 Pairing purity0.72 ± 0.01 0.73 ± 0.01 0.67 ± 0.01

41. 2008/12/10National Tsing Hus Univ.41 MlbsMax vs. KIN EfficiencyPurityeD 2 KIN pairing0.97 ± 0.020.72 ± 0.010.19 ± 0.02 Mlb 2 pairing with cut at 21K 0.395 ± 0.004 0.948 ± 0.002 0.317 ± 0.004 Choose MlbsMax as nominal and KIN for cross check!

42. 2008/12/10National Tsing Hus Univ.42 Study of top charge, MC only Basic formula to get final top charge : Final form: P tq = fs * Ps + f nb * P nb + f LJ * P LJ + f bk * P bk The Four components: –Signal: true (l, b) pair from top decay –None b: the jet used in pair is not b –LJ faking DIL: L+J in HEP but identified as DIL –General DIL background, FAKE, DY, WW, WZ, ZZ

43. 2008/12/10National Tsing Hus Univ.43 DILLumi. Scaledb tgd. eff.b tgd eventsNot b tgd events. Total143.3 ± 13.1134.6 ± 12.3 t /t94.9 ± 7.188.1 ± 6.70.598 ± 0.003 52.8 ± 4.035.4 ± 2.7 WW6.8 ± 1.26.4 ± 1.10.034 ± 0.007 0.22 ± 0.066.18 ± 1.06 WZ1.6 ± 0.31.5 ± 0.20.022 ± 0.006 0.03 ± 0.011.46 ± 0.24 ZZ1.1 ± 0.91.0 ± 0.80.067 ± 0.013 0.07 ± 0.060.95 ± 0.74 Wr0.17 ± 0.180.16 ± 0.170.0 0.16 ± 0.17 DY->  5.3 ± 1.04.9 ± 1.00.028 ± 0.009 0.14 ± 0.054.8 ± 0.93 DY->ee,   12.8 ± 2.212.0 ± 2.0 ztopzb0.028 ± 0.006 0.14 ± 0.044.74 ± 0.80 ztopzt0.039 ± 0.005 0.19 ± 0.044.69 ± 0.80 xtoppb0.057 ± 0.011 0.13 ± 0.032.12 ± 0.36 FAKES21.8 ± 6.320.4 ± 5.90.34 ± 0.176.9 ± 3.913.51 ± 5.17 btop1w0.42 ± 0.06 btop2w0.35 ± 0.09 LJ0.37 ± 0.011.2 ± 0.12.1 ± 0.3 Event/pair estimation

44. 2008/12/10National Tsing Hus Univ.44 Efficiencies of jet charge cal. Jet charge calculation requires good tracks. The efficiencies of applying jet charge calculation are studied based on MC for top signal and various background samples respectively. The jets being b tagged or not do make difference in term of efficiency. ttop75b matchedNot b matched b tagged0.983 ± 0.0010.968 ± 0.014 Not b tagged0.706 ± 0.0040.647 ± 0.009

45. 2008/12/10National Tsing Hus Univ.45 Estimation of (l, b) pair of top (b tagged, jet q applied) b tgd evt.(l,b) pair estimateb tagged or notAfter jet q applied top signal52.7 ± 4.0b jets97.1 ± 7.4b tgd63.9 ± 4.9b tgd62.8 ± 4.8 Not b tgd33.2 ± 2.5Not b tgd23.4 ± 1.8 Non-b jets 8.4 ± 0.7b tgd0.41 ± 0.05b tgd0.40 ± 0.05 Not b tgd8.03 ±0.63Not b tgd5.2 ± 0.4 BKG (not LJ) 6.6 ± 3.9Non-b jets 13.2 ± 7.8b tgd6.59 ± 4.03b tgd6.6 ± 4.0 Not b tgd6.59 ± 4.03Not b tgd5.1 ± 3.1 LJ faking DIL 1.2 ± 0.1b jets1.5 ± 0.1b tgd1.27 ± 0.12b tgd1.2 ± 0.1 Not b tgd0.24 ± 0.03Not b tgd0.2 ± 0.03 Non-b jets 1.0 ± 0.1b tgd0.08 ± 0.02b tgd0.1 ± 0.02 Not b tgd0.89 ± 0.09Not b tgd0.7 ± 0.1 Tot. evt/pair60.6 ± 5.6121.1 ± 10.8105.6 ± 7.2 Data61122105

46. 2008/12/10National Tsing Hus Univ.46 MlbsMax + jet charge not b tagged samples SignalNon-bbkgLJ Fraction0.395 ± 0.0470.075 ± 0.0100.517 ± 0.0570.031 ± 0.005 P lb 0.920 ± 0.003N/A 0.74 ± 0.03 PbPb 0.589 ± 0.005N/A 0.61 ± 0.04 P tq (est)0.575 ± 0.0010.50 0.55 ± 0.02 P tq (MC)0.576 ± 0.0060.52 ± 0.020.50 ± 0.10.49 ± 0.02 P s (sig+LJ) = 0.570 ± 0.006 P bkg (non-b + bkg) = 0.502 ± 0.012 These samples are dominated by backgrounds. Using jets that are b matched. None b fraction = 0.61 Assumed values

47. 2008/12/10National Tsing Hus Univ.47 MlbsMax + jet charge b tagged samples SignalNon-bbkgLJ Fraction0.78 ± 0.050.062 ± 0.0060.14 ± 0.050.018 ± 0.002 P lb 0.932 ± 0.002N/A 0.67 ± 0.03 PbPb 0.608 ± 0.005N/A 0.61 ± 0.04 P tq (est)0.593 ± 0.0040.50 0.54 ± 0.01 P tq (MC)0.588 ± 0.0040.51 ± 0.020.57 ± 0.080.52 ± 0.03 P s (sig+LJ) = 0.586 ± 0.008 P bkg (non-b + bkg) = 0.55 ± 0.07 Using jets that are b matched. None b fraction = 0.38 Assumed values

48. 2008/12/10National Tsing Hus Univ.48 Systematic uncertainties of MlbsMax on b tagged samples moreless Uncertainty of jet charge calibration± 0.007 PDF (± 0.34% of pairing purity)0.0007-0.0007 ISR/FSR-0.006-0.002 JES ( ± 1 sigma)0.001-0.002 Top mass (175 on samples of 170)0.003--- MC generator (Herwig – Pythia)-0.002 W hel.-0.001 (LH/Lo) P tq (Comb) = 0.584 ± 0.004 (stat) +0.008 -0.010 (sys)

49. 2008/12/10National Tsing Hus Univ.49 KIN + jet charge not b tagged samples SignalNon-bbkgLJ Fraction0.388 ± 0.0470.073 ± 0.0100.526 ± 0.0560.033 ± 0.005 P lb 0.720 ± 0.003N/A 0.67 ± 0.02 PbPb 0.593 ± 0.003N/A 0.60 ± 0.02 P tq (est)0.541 ± 0.0010.50 0.54 ± 0.01 P tq (MC)0.543 ± 0.0040.51 ± 0.010.500.53 ± 0.02 P s (sig+LJ) = 0.546 ± 0.004 P bkg (non-b + bkg) = 0.501 ± 0.009 Using jets that are b matched. None b fraction = 0.59 Assumed values

50. 2008/12/10National Tsing Hus Univ.50 KIN + jet charge b tagged samples SignalNon-bbkgLJ Fraction0.81 ± 0.040.064 ± 0.0060.11 ± 0.040.021 ± 0.002 P lb 0.706 ± 0.002N/A 0.65 ± 0.02 PbPb 0.614 ± 0.003N/A 0.61 ± 0.02 P tq (est)0.547 ± 0.0010.50 0.53 ± 0.01 P tq (MC)0.544 ± 0.0030.513 ± 0. 010.56 ± 0.060.58 ± 0.02 P s (sig+LJ) = 0.545 ± 0.003 P bkg (non-b + bkg) = 0.543 ± 0.066 Using jets that are b matched. None b fraction = 0.37 Assumed values

51. 2008/12/10National Tsing Hus Univ.51 Systematic uncertainties of KIN b tagged samples moreless Uncertainty of jet charge calibration± 0.013 PDF (± 1.0% of pairing purity)0.002-0.002 ISR/FSR-0.010-0.003 JES ( ± 1 sigma)0.0030.001 Top mass (175/170 on samples of 170/175)0.0020.001 MC generator (Herwig – Pythia)0.002 W hel.0.002 (Lo)-0.001(LH) P tq (Comb) = 0.545 ± 0.003 (stat) +0.014 -0.020 (sys)

52. 2008/12/10National Tsing Hus Univ.52 Result from 1.5 fb -1 This combines both DIL and LJ. Result shows good agreement with SM! Exclude the XM at 87% CL. But with 2 fb -1, which we have investigated for more than a year, the result from DIL will come soon; final blessing next week!

53. 2008/12/10National Tsing Hus Univ.53 Is it really the truth/top of SM? Up to date most of the results are consistent with SM expectation. However unexpected result(s) might arise in near future! Experience learned at Tevatron is very important to LHC.

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55. 2008/12/10National Tsing Hus Univ.55 Back up slides

56. 2008/12/10National Tsing Hus Univ.56 The issue in LJ faking DIL There is correlation between pairing and jet charge calculation! The formula of top charge fails! Pairing correct Pairing wrong Jet q correct Jet q wrong Jet q purity Pairing correct0.73 ± 0.04 Pairing wrong0.48 ± 0.05

57. 2008/12/10National Tsing Hus Univ.57 Checking top signal Jet q purity Pairing correct0.611 ± 0.006 Pairing wrong0.602 ± 0.023 Such correlation is not seen in top signal MC!

58. 2008/12/10National Tsing Hus Univ.58 Top Q MlbsMax, not b tagged samples P tq (sig+bkg) = 0.527 ± 0.004 +0.008 -0.010 ; P tq (data) = 0.50 ± 0.08 -4/3 +4/3 -2/3 +2/3

59. 2008/12/10National Tsing Hus Univ.59 Top Q KIN, not b tagged samples P tq (sig+bkg) = 0.519 ± 0.002 ± 0.015 ; P tq (data) = 0.52 ± 0.05 -4/3 +4/3 -2/3 +2/3