Higgs Searches at Tevatron Stéphanie Beauceron LPNHE - Paris

DIS 04 Stephanie Beauceron - LPNHE Paris VI et VII 1

Higgs Searches atTevatronStéphanie Beauceron

LPNHE - Paris

on behalf of CDF and DØ Collaborations

CDF

Thanks to everybody for their contribution to this talk


• Standard Model Higgs• Higgs Beyond the

Standard Model• limits on Wbb/WH

production (Z+b)/(Z+j) ratio• limits on HWW(*)l+l-

production• limits on neutral Higgs at

high tanβ• limits on Non-SM h

production• limits on H++/H--

• Summary

Main Injector & Recycler

Tevatron

Chicago

p source

Booster

p

p

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1.96 TeV

CDFDØ

36×36 bunches396 ns bunch crossing

Outline


36×36 bunches396 ns bunch crossing

design: challengingbase: conservative

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Design

Base

FY’04 Integrated Luminosity

11/23/03 1/18/04 3/14/04

Measured luminosity

12 pb-1 / week is also above the design projection

Start of Fiscal Year

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Tevatron: current and projected performance


Standard Model Higgs

• Production cross sections are small 0.1 - 1 pb depending on MH

• MH 135 GeV

gg H bb dominated by QCD background

searches can be performed in W/Z associated production to handle backgrounds

• MH >135 GeV

gg H WW(*)l+l- final states can be explored at higher masses

H bb

H WW(*)

Dominant decay modes

Production Cross section


New EW constraintConstraint mH in the Standard Model

Direct searches at LEP2: mH>114.4 GeV @95%CL

Old Top mass combination

New Top mass combination using new DØ run I measurement

DIS 04 6

Higgs Beyond the Standard Model•MSSM

–5 physical Higgs:•Two CP-even scalars: h (lighter, SM-

like), H (heavier)•CP-odd scalar: A •Charged Higgs pair: H±

–At tree-level, two free parameters•Ratio of vacuum expectation

values:

•One higgs mass

•Other Possibilities–Left-Right Symmetric, Little Higgs,

Higgs Triplet models: Doubly Charged Higgs–SM extensions that suppress fermion

couplings •Fermiophobic Higgs•TopColor Higgs

d

u

v

vtan

222WAHmmm

Large enhancement of rates over HSMbb

MSSM Higgs Main Decay

h/H/Abb ~ 90%h/H/A ~ 10%H+ ~ 100%

(tan>1)

MSSM Higgs Production Cross section


DØ in Run II is able to b-tag up to |η| < 2.5

Performance being improved

b-jet tagging• Essential for Hbb searches

• Can make use of the track impact parameter (IP) measurements or secondary vertex reconstruction

• CDF: performance of sec. vtx. algorithm (after kinematics cuts)

– ~50% b-tag efficiency for ~0.6% light quark mis-tag rate in |η| < 1

Both experiments are demonstrating good b-tagging capabilities

DØ RunII Preliminary

b-tagging efficiency vs light quark mis-tag rate


DØ: W(e)bb production (1)• Motivation:

– Background to WH production• Event selection

– Central isolated e, pT > 20 GeV– Missing ET > 25 GeV– ≥ two jets: ET > 20 GeV, |η| < 2.5

• 2587 evts. in Lint=174 pb-1 of data

Good understanding of data

• Simulations with Alpgen plus Pythia through detailed detector response

• Cross sections normalized to MCFM NLO calculations


DØ: W(e)bb production (2)

• Observe 8, expect 8.3±2.2• Bkgd. dominated by top evts.

Require jets to be tagged, consistent result with different b-tagging algorithms

Good agreement between data and MC in

both cases

One b-tag

At least two b-tags



• W Transverse mass of 2 Tagged events, keep event with 25 GeV<MT(W)<125 GeV

We observed 5 events, expect 6.9 1.8 eventsSet limits on production of (Wbb) < 20.3 pb at 95% C.L.



• Optimize Wbb signal by suppressing the top production by requiring exactly two jets

Observe 2 evts., expect 2.5±0.5

Wbb Wc(c) Wjj tt+t Others

1.4±0.4

0.3±0.10.1±0.0

30.6±0.

20.1±0.0

3

• Sample composition

Probability(B)=0.04 ; Probability(S+B)=0.23

Standard Model without Wbb disfavored at 2 level

•Requiring all jets to be b-tag by the 3 b-tagging algorithms of DØ to reduce the background

Observe 2 evts., expect 0.3±0.1 (Bckd) + 0.6±0.2 Wbb (Signal)

DIS 04 12

Vertex view of 2nd candidate

3 views of high dijet mass (220 GeV) Wbb (WH) candidate

dijet mass (48 GeV)

ETmiss


DØ: W(e) H(bb) production

Observe 2 evts., expect 2.5±0.5

In Mass windows [85-135] we observe: 0 events0.54 ± 0.14 expect background0.03 ± 0.01 WH

Systematics studies:

Source Uncertainty(%)

Jet energy scale

14

Jet ID 7

b-tagging 11

Trigger & e ID 5

EM scale 5

MC simulations

15

Total 26Set limits on production of (WH)B(Hbb) < 12.4 pb for MH = 115 GeV at 95%

C.L.


CDF: W(e/)H(bb) production (1)

•Event selection

–Central isolated e/, pT > 20 GeV

–Missing ET > 20 GeV

–Two jets: ET > 15 GeV, || < 2

–Veto•Di-lepton, extra jet

Observe 2072 events in data in Lint=162 pb-1

•Simulations performed with Alpgen plus Herwig passed through detailed detector response

Good agreement betweendata and MC



•Enrich the b-content of events–Require at least one b-tagged jet

Observe 62 events in data Expect 61 ± 5 events

•Main contributions to the bkgd:

•Expect 0.3 evts from Higgs–Signal acceptance of ~ 1.8% for

MH = 110 – 130 GeV

good agreement betweendata and MC

Mistags

Wc(c) Wbb QCD top

14 13 12 10 9



Set limits on the Higgs production cross section times branching fraction at 95% C.L. :

×B < 5 pb

Systematics studies

Exceeds CDF’s Run I limit [PRL 79, 3819(1997)]

×B < 14 – 19 pb for MH = 70 – 120 GeV

Source Uncertainty (%)

ISR / FSR 19

Secondary vertex

8.6

Lepton ID 5

Jet energy scale

3

PDF 1

Trigger 0.7

Total 22


• Motivation– Background to ZH

production– Probes PDF of the b-quark

• LO diagrams for ZQ

• Measure cross section ratio (Z+b)/(Z+j) Many uncertainties cancel

DØ: Z(ee/)b production (1)• Data correspond to integrated

lumi. of 184 (ee), 152 () pb-1

• Event selection– Isolated e with pT > 15/20

GeV, || < 2.5/2.0– Z peak for signal, side bands

for bkgd. evaluations– Jet ET > 20 GeV, || < 2.5– At least one b-tagged jet

• Simulations performed with Pythia or Alpgen plus Pythia passed through detailed detector response

• Cross sections normalized to data

• Relative b- and c-quark content as given by MCFM NLO calculations


DØ: Z(ee/)b production (2)

• Transverse energy spectrum of b-tagged jets

– QCD and mistag bkgd. estimated from data

– MC: Pythia Zb normalized to data

• Measure cross section ratio Z+b/Z+j 0.024 ± 0.005 (stat)

(syst)

Theory: ~0.02 hep-ph/0312024

• Systematics studiesSource Uncertainty (%)

Jet tagging 16

Jet energy scale

11

Bkgd. estimation

6

(Z+c)/(Z+b)

3

Total 20

+ 0.005– 0.004


DØ: H WW(*) l+l- final states; l=e,

•Event selection–Isolated e/

•pT(e1) > 12 GeV, pT(e2) > 8 GeV•pT(e/1) > 12 GeV, pT(e/2) > 8 GeV

•pT(1) > 20 GeV, pT(2) > 10 GeV–Missing ET greater than

•20 GeV (ee, e); 30 GeV ()–Veto on

•Z resonance•Energetic jets

•Simulations done with Pythia passed through detailed detector response

–Rates normalized to NLO cross section values

•Data correspond to integrated lumi. of~ 180 (ee), 160 (e) and 150 () pb-1

Data vs MC afterevt. preselection


• Higgs mass reconstruction not possible due to two neutrinos

• Employ spin correlations to suppress the bkgd.

(ll) variable is particularly useful

• Leptons from Higgs tend to be collinear


W+ e+

W- e-

Azimuthal angle between e and (after event pre-selection)

Higgs of 160 GeV

Good agreement between data and MC in all

final states, and all variables examined so far


• Number of events after selections

• Dominant bkgd. in e sample


Signal acceptance is ~ 0.02 – 0.2 depending on the Higgs mass/final state

WW W+jets WZ tt

2.51±0.05

0.34±0.02

0.11±0.01

0.13±0.01

ee e

Observed 2 2 5

Expected 2.7±0.4

3.1±0.3 5.3±0.6 Excluded cross section times

Branching Ratio at 95% C.L.

DØ Run II Preliminary

Higgs of 160 GeV


bbbbbbqqgg , (=h,H,A)

•Event Selection:– Multi-jet data sample – At least 3 jets:

ET cuts on jets are optimized separately for different Higgs mass points, and for min. # jets required in the event

3 b-tagged jets– Look for signal in the invariant

mass spectrum from the two leading b-tagged jets

•Simulations performed with Pythia or Alpgen plus Pythia passed through detailed detector response

•Data correspond to integrated lumi. of 131pb-1

BR( ) ~ 90%bb

(Higgs signal at 95% C.L. exclusion limit)

DØ: Neutral Higgs Bosons at High Tan in Multi-jets Events

Dijet Mass


DØ: Neutral Higgs Bosons at High Tan in Multi-jets Events

Signal acceptance is ~ 0.2 – 1.5% depending on the Higgs mass/final state


•Some extensions of SM contain Higgs w/ large B(H)

–Fermiophobic Higgs : does not couple to fermions–Topcolor Higgs : couple to top (only non-zero fermion coupling)

•Data correspond to integrated lumi. of 191 pb-1

•Event selection– 2 Isolated with pT > 25 GeV, ||<1.05 (CC) or 1.5<||<2.4 (EC)

– pT > 35 GeV

•Dominant uncertainty in background estimation is in the measurement of mis-ID rate (~30%)

DØ: Search for Non-SM Light Higgs in H


•No clear evidence of excess

•Perform counting experiments on optimized sliding mass window to set limit on B(H) as function of M(H)

DØ: Search for Non-SM Light Higgs in H

DIS 04 26

•H++/H-- predicted in models that contain Higgs triplets

•Left-Right (LR) symmetric models•SUSY LR models : low mass (~100 GeV – 1 TeV)

•Event selection– 1 pair of same sign ee, or , or e in mass window of 10%*M(H++) (~3 detector resolution)

•same sign leptons decay contains low SM backgrounds, provide clean environment for new physics search

•Data correspond to integrated lumi. of 240 pb-1

CDF: Search for H++


Decay Channels

# predicted Evts

ee

e

8.06.08.1

6.05.08.0

4.04.09.0

•Background prediction for M(l+ l+) >80 GeV (>100 GeV for ee)

•Data : observe 0 event

Mass Limit

CDF 240 pb-1

D 106 pb-1

HL++ HR

++ HL++ HR

++

ee 135 ~102-113

135 113 116 95

e 115

CDF: Search for H++


Prospectives for Higgs• New study from CDF + DØ :

Improvement of the results with a detailed simulation.

5 discovery

3 evidence

95% CL exclusion

Statistical power onlySystematics not included

DIS 04 29

Summary• Hunting for Higgs at the Tevatron Run II has begun !• Understanding of the background processes to the Higgs production is

gradually improving• Result summary:

(Wbb)< 20 pb (WH) B(Hbb) < 12 pb (We) (WH) B(Hbb) < 5 pb (We and W) (Z+b)/ (Z+j) = 0.024 ± 0.005 (stat) (syst)– limits set on (H)B(HWW(*))– Search for Neutral Higgs in MSSM:

• excludes A and h/H for masses 90-150 GeV/c2 at high tan β (>~100)

– H++ Search: • Limits 115, 135, 135 GeV/c2 for exclusive HL

decays to e, ee, • Limits 110 GeV/c2 for exclusive HR

decays to – Search for H:

• Limits are set for the Branching Ratio vs Mass for both Fermiophobic and TopColor models

Already a lot of results and more are coming!

+ 0.005– 0.004


The upgraded CDF and DØ detectors

• Newsilicon detectordrift chamberTOF PID system

• Upgradedcalorimeter, muon systemDAQ/triggerdisplaced-vertex trigger

• New (tracking in B-field)silicon detectorfiber tracker

• Upgradedcalorimeter, muon systemDAQ/trigger(displaced-vertex trigger soon)


Run I CDF H+ Search


DØ H++ Search (1)•search assume the H±± decay branching ratio to like-sign muons to be 100%.

•Muon ID and analysis requirements•Make data quality requirements based on official good run lists •Select di-muon trigger events

•Have muon identification requirements based on:

– Track segments reconstructed in the muon system, isolation from signficant energy deposition in the calorimeter and an associated track from the central tracking system. The muon momentum is taken as the central track momentum

•Muons are required to have pT > 15 GeV and |eta| < 2

Dimuon mass spectra at various steps of the event selection procedure


DØ H++ Search (2)•Search assumes the H±± decay branching ratio to like-sign muons to be 100%. •Confidence level of the signal as a function of the H++ mass,for the left- and right-handed Higgs bosons

Documents

Higgs Searches at Tevatron Stéphanie Beauceron LPNHE - Paris