final results on tth h + -

Final results on ttH H+-Final results on ttH H+-

Akihiro, ITO, Reisaburo TANAKAOkayama University

Shoji ASAI, Junichi TANAKAICEPP, University of Tokyo

Junichi KANZAKIKEK

Many thanks to Lidija ZIVKOVIC (Weizmann)

ATLAS Higgs Working Group Meeting, September 22, 2003

2003/9/22 Final Results on ttH (H->tau+tau) 2

ContentsContents

1. ttH (H+-) analysis

2. tag algorithm

3. ATLFTAU

4. Summary


1. ttH (H+-) analysis1. ttH (H+-) analysis Physics Motivation: direct determination of top-Yukawa coupling

in the mass range MH=[100, 130]GeV/c2. Complementary to Hbb. Signal

Small cross section (Br 40fb @MH=120 GeV/c2) ttH WbWb … 9 different modes, followings are analyzed.

lb+jjb +l+h channel … same charge di-lepton ll Br=14%lb+jjb + h+h channel … single lepton Br=13%lb+jjb +l+l channel … tri-lepton Br= 4%lb+lb+l+h channel … tri-lepton Br= 2%lb+lb+h+h channel … di-lepton Br= 2%

BackgroundsHUGE tt ! (ttH)Br(H) / (tt) 10-4, ttW ttZ, ttWW, ttH(HWW) … irreducible backgrounds.

Key issue: -tag, fake-jet rejection

Israel 5 modesJapan 2 modes


0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

100 110 120 130 140 150 160 170 180

top-Yukawa coupling in ttH(Hbb,+-,W+W-)

2030%

L = 30 fb-1

Preliminary

Hbbpoor S/N

HW+W-

H+-

(Weizmann)

MH [GeV/c2]

gtt

H/g

ttH

Athens Physics Workshop (R.T.)


2 issues tag algorithm

ATLFTAU v.s. Weizmann- ATLFTAU: parametrized 50% fixed efficiency- Weizmann: inspired by TDR algorithm.

Is ttH(H-> ) lb+jjb + h+h possible?


2. tag algorithm 2. tag algorithm Issue: tag algorithm optimization for ttH ATLFTAU … 50% fixed efficiency for low Pt taus is not good. Leads to unreasonable low rejection factor.

Emulated Weizmann tau identification method Rj-track < 0.07 (distance between jet and nearest track) Ntrack = 1 or 3 (# of tracks with PT>5GeV/c in DR = 0.07) PT(track) > 5GeV/c (PT of track nearest to jet) I < 0.03 I = { ET(0.4) – ET(0.2) } / ET(0.2) PT(-jet) > 20GeV/c Ncell < 6 (# of cells in jet, COMMON/ATLFEVENT/ K(nj, 3) )

Observed good agreements on these variables. Though differences in PT(track) and I distributions.


0 50 100 150 200 2500.0

0.2

0.4

0.6

10

100

pT (GeV)

je

t re

ject

ion

efficien

cy tag efficiency and jet rejection

0 50 100 150 200 2500.0

0.2

0.4

0.6

10

100

pT (GeV)

jet

reje

ction

efficien

cy

algorithm

mH = 120 GeV50%

fake real pT--jet

E.Gross, June 25, 2003@Higgs WG


Weizmann cut on llb + jjb + hb + jjb + h + h + h High Level Trigger Lepton

PT > 20GeV/c, |η| < 2.5, Nlepto

n ≥ 1 Jet

PTj1 > 35GeV/c, PT

j2 > 25GeV/c

|η| < 4.5, Njet ≥ 2 b-jet ( efficiency = 70%)

PT > 20GeV/c, |η| < 2.5,

Nb-jet ≥ 2 -jet

PT > 20GeV/c, |η| < 2.0,

N-jet ≥ 2

Mass windows

60 < Mqq < 90 GeV

150 < Mbjj < 195 GeV

50 < M-jet,-jet < 120 GeV

Missing ET > 25GeVΦ( , missing ) < 1opposite charge of -jet

B-tag efficiency 70%


(GeV)

Labeled -jet

Other jetJapan

Israel

ATLFAST, ttH MH=120GeV, Low lumi.

Rj-track< 0.07 Ntrack= 1 or 3 PT> 5 GeV/c


(GeV)

Japan

Israel

ATLFAST, ttH MH=120GeV, Low lumi.

ConeR<0.3

N5I< 0.03 PT> 20 GeV/c

Very powerful cut !


Japan Israel

ttH 2.9 4.7

tt 8.9 5.9

Japan Israel

ttH(H)

efficiency 44% 44%

rejection 80 84

tt

Efficiency 38% 33%

rejection 72 100

Results with Weizmann tau ID

ttHlb+jjb + h+hMH=120GeV, Low lumi. 100fb-1

Remaining differenceYPAR(93) - fraction of tau-jet in a cone Rtau-jet

Japan: default 0.9Israel : 0.0 (optimistic?)

Ncell Ncell


(GeV)

Signal-jet

ETcell > 0.5GeV

(noise & pile-up) signal

tt

ttH tt

efficiency 4444% 3838%

rejection 8087 7278

Japan

ttH 3.0

tt 4.4

Think about ET cuts in cells ?

N4ET>0.5GeV

ttHlb+jjb + h+hMH=120GeV, Low lumi. 100fb-1


Japan

ttH tt

precuts 38.8 1555

Trigger 37.5 (97) 1405 (90)

Q1*Q2 < 0 28.3 (75) 658 (47)

18.6 (66) 399 (61)

MW wind. 11.2 (60) 155 (39)

Mtop wind 8.8 (79) 77.2 (50)

|W| 7.8 (89) 56.8 (74)

Missing ET6.0 (77) 39.0 (69)

Ptlep 5.5 (92) 34.6 (89)

PTj1 5.1 (93) 24.0 (69)

PTj1 3.5 (69) 10.7 (44)

M-jet,-jet wind 2.9 (80) 8.9 (83)

Japan

ttH tt

precuts 40.3 1256

Trigger 39.2 (97) 1131 (90)

Q1*Q2 < 0 30.4 (78) 516 (46)

20.3 (67) 248 (48)

MW wind. 12.2 (60) 86.1 (35)

Mtop wind 10.1 (83) 39.0 (45)

|W| 8.8 (87) 29.2 (75)

Missing ET6.6 (75) 16.0 (55)

Ptlep 5.9 (89) 15.1 (94)

PTj1 5.3 (90) 8.9 (59)

PTj1 3.4 (64) 4.4 (50)

M-jet,-jet wind 3.0 (88) 4.4 (100)

Without ETcell cut With ET

cell cut

Number of events for 100fb-1 (percentage wrt previous cut)


3. ATLFTAU3. ATLFTAUAtlftau Results

• Reasons• Fake -jet charge

Japan Israel

ttH 2.7 2.5

tt 126.7 22.1

6 times!

Japan Israel

Method

Random number [0,1]

< 0.5 Q=-1

> 0.5 Q=+1

Sum up charged track in

R = 0.07 from Jet


Generator

ATLFAST parameter

Japan Israel

Generator PYTHIA6.2 PYTHIA6.2

PDF CTEQ5L CTEQ5L

tt event number 500k 300k

cross section 492pb 490pb

Japan Israel

YPAR(90) 10.000 10.000

YPAR(91) 2.500 2.500

YPAR(92) 0.300 0.300

YPAR(93) 0.900 0.000

YPAR(93) : fraction in a cone R_tauj for tau-jet


ttH ttQ*Q2

ttH tt

Israel

Japan

Drops the ttH signal.But also artificial cut on tt.Unphysical effect.

Explains factor 3 difference


Japan Israel

ttH tt ttH tt

precuts 61.6 19532 75 20330

Trigger 59.0 (96) 18115 (93) 68.5 (91) 17671 (87)

Q1*Q2 < 0 20.1 (34) 1427 (7.9) 24 (35) 1426 (8.1)

12.5 (62) 685 (48) 15 (63) 704 (49)

MW wind. 8.1 (65) 308 (45) 8.4 (56) 301 (43)

Mtop wind 6.7 (83) 190 (62) 6.16 (73) 191.5 (64)

|W| 6.0 (90) 167 (88) 5.35 (87) 150 (78)

Missing ET4.8 (80) 133 (80) 4.5 (84) 117 (78)

Ptlep 4.5 (94) 108 (81) 4.3 (96) 96.5 (82)

PTj1 3.9 (87) 85.6 (79) 4.08 (95) 84.6 (88)

PTj1 2.8 (72) 48.7 (57) 3.08 (75) 44.5 (53)

M-jet,-jet wind 2.1 (75) 26.6 (55) 2.5 (81) 22.3 (50)

ATLFAST

Number of events for 100fb-1 (percentage wrt previous cut)Now identical condition YPAR(93)=0.0, Φcut good agreement.


4. Summary4. Summary Compared two analyses on ttH(H)

Tau hadronic mode: llb + jjb + hb + jjb + h + h + h -tag algorithm

ATLFTAU (50% eff. Fixed) - Unreasonable at low Pt. Problematic for ttH.

Weizmann algorithm - Ncell is a powerful parameter for tt rejection

but pile-up and noise should be taken into account. Full simulation with noise&pile-up under study.

ATLFAST (parametrized ATLFTAU)Good agreement between Japan and Israel results now.Discrepancies due to -jet charge assignment ,YPAR(93),Φ.

These are not critical for our final results …


ttH (H+-)

t( l b ) + t( l b ) + ( h ) + ( l )

t(l b ) + t(jjb) + ( h ) + ( l )

Sig. Bkg. tt ttZ ttW ttH

2-lepton 11.5 16.7 6.7 4.1 4.5 1.4

3 lepton 3.7 2.4 0.3 1.1 0.3 0.7

Our Results for AthensL=300 fb-1 MH=115GeV/c2

For 2 300 fb-1

S/B = 0.8S/B = 4.5 (Poisson)

t(lb) + t(jjb) + (h)+ (h)Similar sensitivity as di-lepton channel,but suffers from irreducible ttZ, ttWW …background.

final results on tth h + -

Documents