Top Jets & Boosted QCD the LHC

Transcription

1 Top Jets & Boosted QCD the LHC Seung J. Lee YITP, Stony Brook University with L. Almeida, G. Perez, G. Sterman, I. Sung, J. Virzi with L. Almeida, G. Perez, I. Sung, J. Virzi arxiv: , work in preparation Cornell University, September 3, 2008

2 Outline Introduction Emergence of high pt top (W,Z,h) jets at the LHC Jet mass: Signal & QCD BG (theory+mc) Jet substructure, massive jet event shapes Top polarization Summary

3 Introduction In the SM (& beyond) top is unique: only ultra heavy quark, m t H induce most severe fine tuning; controls flavor & custodial violation; linked to EW breaking in natural models.

4 Introduction In the SM (& beyond) top is unique: only ultra heavy quark, m t H induce most severe fine tuning; controls flavor & custodial violation; linked to EW breaking in natural models. Direct info is limited (Tevatron) At the LHC: 10 7 top/yr SM: more than 10 4 top/yr with γ t 5.

5 The challenge of highly boosted tops - First, let s consider NP particle, whose dominant decay channel is ttbar: X might be heavy

6 The challenge of highly boosted tops - First, let s consider NP particle, whose dominant decay channel is ttbar: X might be heavy

7 The challenge of highly boosted tops - First, let s consider NP particle, whose dominant decay channel is ttbar: X might be heavy Alas, above a TeV, top becomes similar to a light jet, signal is lost! b + µ + ν µ (missin

8 The challenge of highly boosted tops - First, let s consider NP particle, whose dominant decay channel is ttbar: X might be heavy Alas, New above object a TeV, top becomes emerges, similar to a light jet, signal is lost! top jet! b + µ + ν µ (missin

9 Resolution problem \w boosted tops The hadronic calorimeters cannot go below R~0.4

10 Resolution problem \w boosted tops The hadronic calorimeters cannot go below R~0.4 Why: Hadronic granularity is R~ 0.1 x 0.1 m 2 = (p 1 + p 2 ) 2 2p 2 [1 (1 R 2 /2)] = p 2 R 2 m R p (say with R, p = 0.2, 500, m 100GeV) pure geometrical mass:

11 Resolution problem \w boosted tops The hadronic calorimeters cannot go below R~0.4 Why: Hadronic granularity is R~ 0.1 x 0.1 m 2 = (p 1 + p 2 ) 2 2p 2 [1 (1 R 2 /2)] = p 2 R 2 m R p (say with R, p = 0.2, 500, m 100GeV) pure geometrical mass: If R between decay products of top is smaller than 0.4, you cannot resolve the top into daughter jets. (top jet = single jet)

12 Boosted top (w/z/h) jets & collimation Partonic Level

13 Boosted top (w/z/h) jets & collimation At final state jets level: Final state Jets Level - Define collimation rate as the fraction of top quark which reconstruct to a jet having 140 GeV < mj < 210 GeV

14 Top jets at the LHC

15 Top jets at the LHC b + µ + ν µ (missin (i) Jet mass. (ii) Jet substructure.

16 the LHC Are they different from high pt light jets? S/B~1/140, for pt(j) >1000 GeV, R=0.4 (~20 pb for jj+x, ~140 fb for ttbar+x) top-jet: call for theory, analysis & techniques Most (naive) direct attempt - mass tagging Skiba &Tucker-Smith, PRD(07); Holdom, JHEP (07); Frederix & Maltoni ( ); Ellis, Huston, Hatakeyama, Loch & Tonnesmann, PPNP (08); Agashe et. al. PRD(07).

17 Rejection based on jet mass Jet cone mass-sum of massless momenta in h-cal inside the cone: m 2 J =( i R P i) 2, Pi 2 =0 Jet cone mass is non-trivial both for S & B Understand S&B distributions from 1st principles & compare to MC data Add detector effects

18 Cone top-jet mass distribution Naively the signal is J δ(m J m t ) In practice: + detector smearing.

19 Cone top-jet mass distribution Naively the signal is J δ(m J m t ) In practice: Can understood perturbatively fast & small~10gev + detector smearing.

20 Cone top-jet mass distribution Naively the signal is J δ(m J m t ) In practice: Can understood perturbatively fast & small~10gev + detector smearing. Pure kinematical bw(qq) dist in/out cone much longer

21 Cone top-jet mass distribution Naively the signal is J δ(m J m t ) In practice: Can understood perturbatively fast & small~10gev + detector smearing. Pure kinematical bw(qq) dist in/out cone much longer

22 QCD cone jet mass distribution We are interested in the following processes:

23 QCD cone jet mass distribution We are interested in the following processes: Factorized hadronic cross section: PDF

24 QCD cone jet mass distribution We are interested in the following processes: Factorized hadronic cross section: PDF Hard perturbative (Born) cross-section At the leading order Jet function

25 QCD cone jet mass distribution Boosted QCD Jet via factorization:

26 QCD cone jet mass distribution Boosted QCD Jet via factorization: Contact with Data (MC):

27 QCD cone jet mass distribution Boosted QCD Jet via factorization: For large jet mass & small R, J i no large logs => can be calculated via Contact perturbative with Data QCD! (MC):

28 QCD Jet mass distribution, Q+G R 2 Main idea: calculating mass due to J 1 two-body QCD bremsstrahlung: p a p b J 2

29 QCD Jet mass distribution, Q+G R 2 Main idea: calculating mass due to J 1 two-body QCD bremsstrahlung: p a p b J 2 C quark jets: gluon jets: C (q) = C F = 4 3 C (g) = C A =3

30 QCD Jet mass distribution, Q+G R 2 Main idea: calculating mass due to J 1 two-body QCD bremsstrahlung: p a p b J 2 C quark jets: gluon jets: C (q) = C F = 4 3 C (g) = C A =3

31 QCD Jet mass distribution, Q+G R 2 Main idea: calculating mass due to J 1 two-body QCD bremsstrahlung: p a p b J 2

32 QCD Jet mass distribution, Q+G R 2 Main idea: calculating mass due to J 1 two-body QCD bremsstrahlung: p a p b J 2

33 Jet mass distribution theory vs. MC Revisiting our prediction:

34 Jet mass distribution theory vs. MC Revisiting our prediction: But, in practice, cannot distinguish partonic origin of a jet: can only give bounds:

35 Jet mass distribution theory vs. MC Revisiting our prediction: But, in practice, cannot distinguish partonic origin of a jet: can only give bounds:

36 Jet mass distribution theory vs. MC Sherpa, jet function convolved

37 Jet mass distribution theory vs. MC Sherpa, jet function convolved

38 QCD jet mass dist under control! Sherpa (CKKW) With Full Detector Simulation d# (P >1000 GeV) dm T J R = 0.4 Gluon Prediction R = 0.4 Lead Jet Mass (FullSim) R = 0.4 Lead Jet Mass (Truth) R = 0.4 Quark Prediction -1 Number of Events / 5 GeV / 10 fb Can Calculate Rejection Rate (for jet mass) " M JET (GeV)!

39 QCD jet mass dist under control! Rejection Ratio: (#of events for mt-δ < mj < mt+δ) / (total # of events) Can use our jet function to calculate it: Matches well with MC simulation (within 10%) For QCD dijet background, double mass tagging will reduce the background (typically, ɛ r 15% )

40 QCD jet mass dist under control! LEAD R = 0.4 Fractional Fake Rate vs P T fraction (GeV) P T Gluon Hypothesis Quark Hypothesis Data

41 Cross Section Uncertainty

42 Ex. SM ttbar vs. di-jet background! With transfer-functions ( full simulation )

43 Ex. SM ttbar vs. di-jet background! With transfer-functions ( full without simulation ) high efficiency! S/B~0.11 Double mass tagging at 25 fb -1 with detector resolution and Jet Energy Scale (JES) look hopeless b-tagging

44 Ex. SM ttbar vs. di-jet background! With transfer-functions ( full without simulation ) high efficiency! S/B~0.11 Double mass tagging at 25 fb -1 with detector resolution and Jet Energy Scale (JES) look hopeless b-tagging

45 Ex. SM ttbar vs. di-jet background! Jet Mass Peak Resolution Background Fit Background + Signal Fit

46 Ex. SM ttbar vs. di-jet background! Jet Jet Mass Peak Resolution Background + Signal Background Fit +detector Background + Signal Fit (GeV) M J

47 Ex. SM ttbar vs. di-jet background! Jet Mass jet_mass Entries Mean x Mean y RMS x RMS y

48 Ex. SM ttbar vs. di-jet background! Jet Mass jet_mass Entries Mean x Mean y RMS x RMS y

49 Ex. SM ttbar vs. di-jet background! jet_mass Entries Mean x Mean y Need Extra Handles RMS x RMS y Jet Mass to distinguish Signal from Background!

50 Pseudo-rapidity independence

51 Average Jet Mass (IR Mass cut needed) <MJ> PT, R <M J > QCD Jets R = 0.4 QCD Jets R = 0.5 QCD Jets R = 0.6 QCD Jets R = <M J > (GeV) P T

52 Jet sub-structure

53 Why jets? What else? QCD amplitudes have soft-collinear singularity Observable: IR safe, smooth function of E flow Sterman & Weinberg, PRL (77) Jet is a very inclusive object, defined via direction + pt ( + mass) Even R=0.4 contains O(100) had-cells => huge amount of info is lost

54 Jet-shapes Jet-shapes = inclusive observables dependent on energy flow within individual jets Once jet mass is fixed at a high scale Large class of jet-shapes become perturbatively calculable IR safe jet-shapes combined with IR safe jet algorithm provide a bridge between Direct theory prediction Data/MC output

55 Jet-shapes Jet-shapes = inclusive observables dependent on energy flow within individual jets Once Can jet mass analyze is fixed a single at a event high scale by a Large class variety of jet-shapes of jet shapes become perturbatively => the resolution calculable associated with each one need not be dramatic! IR safe jet-shapes combined with IR safe jet algorithm provide a bridge between Direct theory prediction Data/MC output

56 IR-safe jet-shapes which know top from QCD jets? Successes in high jet mass => jet function is well described by single gluon radiation QCD, top: linear, planar E-deposition in the cone Almeida, SJL, Perez, Sterman, Sung, & Virzi, arxiv: c.f. Wang, Thale: similar event shape, sphericity tensor arxiv: IR-safe E-flow tensor: Planar flow:

57 Planar flow (Pf), QCD vs top jets LO: Pf ~ 0 for QCD (2-body decay) O(1) for top: smooth (for istropic 3-body decay, Pf~1) α s NLO (due to large m): O( ) for QCD nominal for top

58 Planar flow (Pf), QCD vs top jets LO: Pf ~ 0 for QCD (2-body decay) O(1) for top: smooth (for istropic 3-body decay, Pf~1) α s NLO (due to large m): O( ) for QCD nominal for top

59 Planar flow (Pf) Planar flow (Pf), QCD vs top jets Planar flow, Pf (P 0.07 = 1 TeV, R = 0.4, "no mass cuts") LO: Pf ~ 0 for QCD (2-body decay) T O(1) for top: smooth 0.04 (for istropic 3-body decay, Pf~1) α s NLO (due to large m): O( ) for QCD 0.01 QCD jets nominal for top Top jets

60 What about 2 body jet, Z/W/h Berger, K ucs and Sterman (03): introduced for e+e- annihilation Angularities on a cone: Almeida, SJL, Perez, Sterman, Sung, & Virzi, arxiv: =>

61 Theory: angularity, QCD vs Z 1.5 R Τ 2 vs. Τ 2 for z 0.05 Long. h ±1 MG/ME R Τ Τ 2

62 Madgraph: angularity, QCD vs Z Angularity,! a (a = -2, z = 0.05, R = 0.4) 0.3 Z Long. jets QCD jets MG/ME Angularity (! -2 )

63 Top Polarization Daughter particles remember top polarization For Urel top: helicity=chirality Can do polarization analysis like it was done for the tau Want to use PT to probe top polarization: PT is a directly measured quantity (c.f. For polarization method, need to use derived quantities with biases, like center of mass boost etc.) - Different from spin-spin correlation where you expand in s wave (for non-relativistic top)

64 Top Polarization ~30% ~70% b W + t t W + b Left!Handed W Longitudinal W

65 Top Polarization ~30% ~70% b W + tr t t W + b Left!Handed W Longitudinal W

66 Top Polarization ~30% ~70% b quark: - back-warded (soft PT) b W + for tr - forwarded (hard PT) tr t t for tl For SM, parity even (PT distribution will be flat) look for new Physics where parity is violated W + Left!Handed W b Longitudinal W

67 Top Polarization ~30% ~70% lepton:forwarded for tr back-warded for tl W direction of flight l + l + tr W + W + W direction of flight!! Left!Handed W Longitudinal W

68 Top Polarization ~30% ~70% lepton:forwarded for tr back-warded for tl W direction of flight l + l + tr W + W + W direction of flight!! Left!Handed W Longitudinal W For Boosted Longitudinal W: letpon is forwarded

69 pt(top) > 1TeV P T (b) distribution 0.06 MG/ME P T (b) from t pt_b_1 P T (b) from t Entries Mean RMS L R PT(b) is limited by W boson mass P T (b) (GeV) Hadronic Top b quark as a spin analyzer

70 pt(top) > 1TeV P (lepton) distribution T 0.14 MG/ME P T (l) from t pt_e_1 P T (l) from t Entries Mean RMS L R P T (l) (GeV) for example with the KK gluon, you'll see suddenly only leptons/bs that follows the RH curves Leptonic Top charged lepton as a spin analyzer

71 Sherpa (CKKW) Without Detector Simulation KK gluon bump Example: KK gluon lepton PT is harder near the KK gluon plateau

72 Sherpa (CKKW) Without Detector Simulation KK gluon bump Also relevant for SUSY: heavy stop decaying into top and wino, etc... Example: KK gluon lepton PT is harder near the KK gluon plateau

73 MG/ME Without Detector Simulation 400 M tt vs. p T b for M KKG 3TeV KK PT b gluon bump M tt Example: KK gluon b-quark PT is harder near the KK gluon bump

74 MG/ME Without Detector Simulation 400 M tt vs. p T b for M KKG 3TeV KK PT b gluon bump Also relevant for SUSY: heavy stop decaying into top and wino, etc... M tt Example: KK gluon b-quark PT is harder near the KK gluon bump

75 Summary LHC => new era, precision top physics Theory+technique to tag t/w/z/h jets Understand jet mass, but it s not enough Introduce Jet-shapes: very useful, but more to do (exp +analyses+theory)

76 Backup: Top Polarization 30% 70% ~0% Polarization: daughter particles of top still remembers the information tl t b t W + W + t W + b b b is forwarded for tl Left!Handed W Longitudinal W Right!Handed W lepton is back-warded for tl W direction of flight lepton is in general better spin analyzer compared to b-quark, but b can be used for the hadronic top tl l + l + W + W + W +!!! l + W direction of flight

77 Backup: 30% B-tagging efficiency & 1% light jet Jet Mass Peak Resolution Background Fit Background + Signal Fit