DDØØ Higgs Physics Results Higgs Physics ResultsJyothsna RaniJyothsna Rani

Tata Institute of Fundamental ResearchTata Institute of Fundamental ResearchMumbai, IndiaMumbai, India

on behalf of the Don behalf of the DØ CollaborationØ Collaboration

Lake Louise Winter InstituteLake Louise Winter Institute2020thth – 26 – 26thth February 2005 February 2005

Alberta, CanadaAlberta, Canada

LLWI, 24th Feb 2005 Jyothsna Rani - Tata Institute 2

OutlineOutline• Standard Model Higgs searches

– Associated production of H with W– H W W* for mH > 135 GeV

• Non Standard Model Higgs searches– MSSM Neutral Higgs in (b)bh(b)bbb final state

Results presented here are based on 174 – 260 pb-1

NEWNEW

LLWI, 24th Feb 2005 Jyothsna Rani - Tata Institute 3

Missing Piece in Standard ModelMissing Piece in Standard Model• The mass of elementary particles in

the Standard Model is explained by the presence of Higgs boson.

• The mass of the Higgs boson is not predicted in SM.

• Precision measurements constrain: 114 GeV < mH < 260 GeV• Tevatron provides:

– Indirect search• Precision mt and mw measurements

– Direct searches• SM Higgs• non-SM Higgs

LEP

LLWI, 24th Feb 2005 Jyothsna Rani - Tata Institute 4

SM Higgs DecaysSM Higgs Decays• Search strategies are a

function of – Decay modes and – Production channels

• Two search strategies at Tevatron:– Low mass Higgs searches

mH < 135 GeV

H bb – High mass Higgs searches

mH > 135 GeV

H W W*

Excl

uded

at

LEP

Higgs Mass (GeV/c2)

LLWI, 24th Feb 2005 Jyothsna Rani - Tata Institute 5

SM Higgs Production at TevatronSM Higgs Production at TevatronGluon Fusion:

gg H ~ 1pbAt low mass (H bb ),

high QCD background.At High mass usable withH W W* decay mode.

Associated Production:WH or ZH ~ 0.1pbUsed at low mass withH bb decay mode.

Excl

uded

at

LEP

LLWI, 24th Feb 2005 Jyothsna Rani - Tata Institute 6

Identifying b-jetsIdentifying b-jets

do

PrimaryVertex

SecondaryVertexLxy

Secondary Vertex. Large Impact Parameter

of the tracks.

Tagging the b-jets is important for H bb decay modes.

Performance of Secondary Vertex Tagging algorithm

LLWI, 24th Feb 2005 Jyothsna Rani - Tata Institute 7

SM Higgs Search: WH SM Higgs Search: WH l lbbbb• Search Strategy:

– Use sample of W(e)+2 b-tagged jets.

– Require exactly 2 jets to suppress top background.

• 4.4 1.2 events expected and 6 events observed.

(WH)*BR(H bb ) < 9.0 pb @ 95% C.L. for mH =115 GeV

• Also (W bb ) < 6.6 pb @ 95% C.L. for pT(b) > 20 GeV

115 GeV

LLWI, 24th Feb 2005 Jyothsna Rani - Tata Institute 8

SM Higgs Search: H SM Higgs Search: H WW WW l lll

• Search strategy:• 2 high pT leptons and MET• WW comes from spin 0 Higgs:

leptons prefer to point in the same direction

W+ e+

W- e-

* BR(H→WW) < 5.7pb @ 95% C.L. for mH=160 GeV

LLWI, 24th Feb 2005 Jyothsna Rani - Tata Institute 9

Higgs in Minimal SupersymmetryHiggs in Minimal Supersymmetry• MSSM has pairs of Higgs

doublet fields– Hu couples to up-type quarks

and leptons and Hd to down-type– tan = <Hu>/<Hd>– 5 Higgs particles after EWSB:

h0, H0, A0, H+, H-

– h0 is predicted to be light: m h0 < ~ 130 GeV (MSSM)

h0, H0, A0 production @ Tevatron

Z+b Probe of b-quark PDF bh and single top production

(Z+b) / (Z+j) = 0.023 0.005 (DØ – hep-ex/0410078)

= 0.018 0.004 (CTEQ6 prediction)

~ tan

LLWI, 24th Feb 2005 Jyothsna Rani - Tata Institute 10

Higgs Production and Large tan Higgs Production and Large tan • Large tan → enhanced bbh/H/A

• At tree level , cross section rises like tan2 • A and h/H are produced simultaneously.

CP odd Higgs

CP even Higgs

h H

A

Total cross section

LLWI, 24th Feb 2005 Jyothsna Rani - Tata Institute 11

Analysis OverviewAnalysis Overview• Signal:

• at least 3 b-tagged jets • Invariant mass of two leading pT jets

• Backgrounds:• “QCD heavy flavor” : bbjj, ccjj, cccc, bbcc, bbbb• “QCD fakes” : jjjj• “Other” : Z(bb,cc), tt

• Kinematic cuts• Cut on pT of leading jets

(Optimized for each Higgs mass)

• Search for an excess of events in di-jet invariant mass distribution consistent with a Higgs signal shape.

Di-jet invariant mass in

3b-tagged events

260 pb-1

LLWI, 24th Feb 2005 Jyothsna Rani - Tata Institute 12

(b)bh Limits on (b)bh Limits on and tan and tan

Two benchmark scenarios Max Mixing: Xt = At - cot = 6; No Mixing: Xt = 0

For mA = 120 GeV

< 31 pb-1 @ 95% C.L. and tan < 55 @ 95% C.L. (Max Mixing)

260 pb-1 260 pb-1

NEWNEW

LLWI, 24th Feb 2005 Jyothsna Rani - Tata Institute 13

SummarySummary• Higgs hunting at Tevatron is ongoing.• SM Higgs searches:

– DØ placed limits on cross section on WH( bb). (Z+b) / (Z+j) ratio has been measured.– Understanding of backgrounds is improving.– H W W* searches placed limits on cross

section.• Non SM Higgs searches:

– Enhanced Higgs production at high tan is used to exclude (mA, tan) plane.

• Expect substantial improvements in Higgs hunting with ~0.6 fb-1 already on tapes.