Higgs Searches at the Tevatron (Run I )

Lorenzo Moneta Moriond QCD 17-23 March 2001 1

Higgs Searches at the Tevatron (Run I)

• Introduction• SM Higgs

– ZH & WH with H bb (CDF & D)

• MSSM Higgs – bb with =H0,h0,A0 (CDF)– H+ (CDF & D)

• Fermiophobic Higgs – H CDF & D)

• Conclusions

Lorenzo MonetaUniversity of Geneva

on behalf of CDF and D collaboration

¯

¯


Introduction

• Electroweak Symmetry breaking in the SM predicts existence of an Higgs boson but with unspecified mass– Higgs mass constraints scale where SM might break down

• if = MPlank then 130 < M(H) < 180

Current Status of Higgs searches • SM fit to Electroweak data indicates a light Higgs

– M(H) < ~ 200 GeV @ 95 % CL

• Direct searches from LEP2– 95 % CL limit is ~ 113 GeV– Indication of Higgs-like events in the last year data:

excess ~ 3 at M(H) 115 GeV


Tevatron (Run I)

Run I (Oct. 92 Feb. 96)

total integrated luminosity~ 120-1 pb / detector

Tevatron proton-antiproton collision @ s = 1.8 TeV

Expected ~ 2 fb-1 in Run IIa !

Silicon Vertex Detector

CDF DØ


tt

LEP

SM H0 production @ Tevatron

• Gluon Fusion

– too difficult (QCD background)• Higgsstrahlung

– SM cross section is very small • 1/20 (t-tbar) • 1/500 (Z/W + 2 jets)

– possible with Run II luminosity !– larger with new physics ??

for M(H) = 120 Gev/c2

with QCD NLO correction

• Vector Boson fusion• radiation off heavy quark

• very small in the SM

0Hgg

= 0.70 pb

ZH: = 0.10 pb

WH: = 0.16 pb

0VHqq

0Hqqqq 0Httqq


• M(H) < 130 GeV– dominant decay is

– final states are for W/ZH

– need lepton ID/MET + b-tags

• M(H) > 130 GeV– dominant decay is

–

final state with 2 leptons

– but smaller cross-section •

interesting at RunII !

SM Higgs decays

LEP

bbH

bbbbbbbbqq , , ,

WWH

jjZWWWWWVHWWHgg

**

*

/ For M(H) = 120 GeV/c2

%7 )(%70 )(

HBR

bbHBR


Tevatron Run I channels : (W/Z + H with M(H) < 130 GeV)

•

– BG: QCD multijets

•

– BG:

•

– BG: QCD,

•

– BG:

SM H signatures (W /Z + H)

bbqq

bb

bb

bb

tbqbtWZttbWb , , , ,

btZZttbZb , , ,

btZZttbZb , , ,Essential for these analyses:

• b tagging• good di-jet mass resolution

( 50% of W/Z H )

( 9% )

( 5.4%)

( 1.8%)


b tagging at the Tevatron

Techniques developed for top analyses. Two algorithms: – Soft Lepton Tagging (SLT) (CDF & DØ)

• semileptonic b decays:

• DØ: ( pT > 4 GeV) CDF: & e (pT > 2 GeV)

– Secondary Vertex Tagging (SVX) (CDF)• reconstruct a displaced vertex in the jet • b lifetime ~ 1.5 ps decay length ~ few mm• use capability of Silicon vertex detectors

secondary vertexprimary vertex

b jet(b-tag) ~ 20%/b-jet(mistag) ~ 0.2%/jet

(decay-length) ~ 100 m

b e,µ (in jets)

(b-tag) ~ 7%/b-jet(mistag) ~ 0.5%/jet

%20 ),(

%20 ),(

BReXcb

BReXb


bbWH 0 Search for

• Final states are lepton (e/) + MET + b’s• Event selection:

– high pTlepton: pT(lep) > 20 GeV & <1

– MET>20

– 2 jets with ET(j)>15, <2

– b-tags (single OR double jet tag)

• Backgrounds: –

Results (CDF & D) 106 pb-1

~ 0.2 – 0.3 %63 12 b-tagsCDF

~ 0.6 - 0.9 %2725 31 b-tagD

~ 0.6 – 0.8 %3630 51 b-tagCDF

Br x accept. (90<m(H)<130)

databackgchannelExp.

CDF

mbb

1 b-tag

2 b-tags

bbWH 0

tbqbtWZttbWb , , , ,

95% CL Limit on BR: 26-28 pb for 90<MH<130 (CDF)40-19 pb for 90<MH<120 (D)

from fit to di-jets mass:


bbWH 0 Search for

• Final states is MET + b’s• Event selection (CDF):

– MET>40 (trigger >35) + lepton veto

– 2 or 3 jets with ET(j)>15, <2

– (MET,j) > 60° for all jets (ET>8)

– (j1,j2) < 150°

– b-tags (single OR double)

• Backgrounds: – QCD and

Results (88 pb-1)

bbZH 0

btZZttbZb , , ,

95% CL Limit on BR: ~ 8 pb for 90<MH<130 ~ 0.4 – 0.5 %44 12 b-tagsCDF

~ 0.5 – 0.8 %4039 41 b-tagCDF

Br x accept.(90<m(H)<130)

databackgchannelExp.


bbWH 0 Search for

• Final states is di-leptons + b’s• Event selection (CDF):

– pT(lep)>20,10 GeV

– 76<M(l,l)<106 GeV

– 2 or 3 jets with ET(j)>15, <2

– MET < 50 GeV (against top di-lepton evts)

– 1 b-tag

• Backgrounds: –

Results (106 pb-1)

bbZH 0

btZZttqZqbZb , , , ,

~ 0.2 %53 11 b-tagCDF


databackgchannelExp.95% CL Limit on BR: 56-24 pb for 90<MH<130

mbb


bbWH 0 Search for

• Multi-jet final state with b’s• Event selection (CDF):

– Multi-jets trigger 4 jets with ET>125 GeV & ET>15

– double b-tag – pT(bb)>50 GeV

• Backgrounds: – mainly QCD (b’s + fakes) – also top and Z + jets

Results (91 pb-1)

bbqqHZW 0/

~ 1.5 – 2.9 %589~ 6002 b-tagCDF


databack.channelExp.

Need good Mbb resolution against background 95% CL Limit on BR: 30-16 pb for 90<MH<130

mbb

¯


Combined limit for SM Higgs

CDF combination of

95 % CL limit on

bbbbbbbbqq , , , )(),( 0 bbHBRZHWHpp

• x 30 SM cross-section (mH = 115)

• Limit is dominated by bb• Expected best limits from:

– bb and lbb• poor lbb limit due to a small

excess in observed events• Need more luminosity

– RUN II

limit = 7.4-8.2 pb for mH = 90-130 GeV/c2

LEP

SM

¯ ¯

¯

¯

115


MSSM Higgs Search

Two Higgs doublets in the MSSM – 5 Higgs particles

• two neutral CP-even: h0,H0

• One neutral CP odd: A0

• Two charged: H+,H-

– two free parameters: tan and mA

– Mass relations at tree level:• m(h0) < m(Z0) < m(H0); m (A0) < m(H0); m(H+) < m(W) • but after radiative corrections m(h0) < 130 GeV

– Couplings at large tan• enhanced to d-type quark and leptons • suppressed to u-type quark


In general dominant Higgs’s Branching Ratio are to bb (90%) and (10%)

MSSM Higgs production

• Small tan– SM-like cross-sections

• Large tan– enhanced hbb coupling– hbb/Hbb/Abb can have

large cross-sections ( tan

tan = 3 tan = 30

p

b

p

b

h H

¯

hH

¯¯¯¯


Search for

• Exploit enhanced Yukawa couplings looking for bb production ( = h,HA)

• large cross sections ( tan • 4-b’s jets final state • Event selection (CDF):

– Multi-jets trigger

• 4 jets with (ET)>125 GeV & ET>15

– ET(j) cuts depending on m() 3 b-tags – (bb) > 109° (against gbb)

• Backgrounds: – QCD (bb/cc), Z/Wjj, top

bbbbbbpp

0.28 % 23.5 1.10.28 %120

0.59 % 00.1 0.40.59 %300

0.16 %54.6 1.4 0.16 %70

Br x accept. databackgBR x acc. M() (GeV)

CDF results (91 pb-1)

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¯

¯


Limit for

• Limit (95%CL for M = 100 GeV):• convert BR limit in tan vs Higgs mass

exclusion – No mixing & Maximal Mixing for the stop

bbbbAHhbbpp )//(

Tevatron complements LEP !

BR < 25.7 pb

tan vs m(h) tan vs m(A)


Charged Higgs Searches

• Searches for t H+b when M(H+) < mt - mb

• decay t H+b can compete with SM decay t W+b• BR(t H+b) depends on tan

Direct Search (CDF): • look for H+ in t-tbar evts

– BR(H+ 1 for large tan– WHbb or HHbb channels in addition to WWbb – look for l + + MET + jj events (l = e,,)– use identifications via hadronic decays

(tracking + calorimeter) – backgrounds:

• Z + jj, W+3 jets, WW/WZ– acceptances for single and double H

production


Charged Higgs Searches

Indirect Search (CDF + D) • look for lepton disappearance in t-tbar events

• suppression of dileptons and lepton + jets events • rate of the two depends on BR(t H+b) • t-tbar cross-section independent of m(H), tan• given measured x-section (when BR(t H+b) = 0)

exclusion regions in the m(H+)-tanplane

New Exclusion regions at low and high tan

LEP2 (ADLO)

D0


Fermiophobic Higgs

• In some models Higgs couples only to vector bosons• BR(H ) dominant for light Higgs (m(H) < 100)

• Searches for W/Z + H jj– D search:

• di-photons + jets• Backgrounds from QCD

– fakes or real in jets

– CDF search • di-photons with e/ + MET or jj

• Limit For SM cross-section: M(H) > ~ 80 GeV (95% CL)

• LEP limit is ~ 105 GeV

D0


Conclusions

• SM Higgs searches are luminosity limited in Run I – no sensitivity to SM cross sections– no excess seen and set limits at ~30 SM cross-section – provided experience for Run II – developed techniques for low mass Higgs searches

• b tagging and di-jet mass resolution are crucial !

– good expectations for Run II see next talk on Run II prospects

• Nice exclusion results for MSSM Higgs: – bb search with sensitivity for high tan region– charged Higgs from t H+b

– probed regions inaccessible to LEP– very interesting in Run II

report of the Tevatron Higgs Working Group (hep-ph/0010338)

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Higgs Searches at the Tevatron (Run I )

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