Higgs Results from D Ø

Higgs Results from DØpresented by

Per JonssonImperial College London

On behalf of the DØ Collaboration

Hadron Collider Physics 2004Michigan State University, East Lansing, June

14-18, 2004

HCP 04 Per Jonsson - Imperial College London 2

Outline• Introduction

– Tevatron– DØ detector– Higgs

production/sensitivity• Standard Model Higgs

– Limits on Wbb/WH– (Z+b)/(Z+j) ratio– HWW(*)l+l- searches

• Higgs Beyond the Standard Model– Limits on neutral SUSY

Higgs at high tan– 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

Thanks to all colleagues for their contribution to these studies


Tevatron Performance(1)


Tevatron Performance (2)

36×36 bunches396 ns bunch crossing

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The upgraded DØ detector

• New (tracking in B-field)– silicon detector– fiber tracker

• Upgraded– calorimeter, muon

system– DAQ/trigger

Needed for Higgs searches!


EW constraints on Higgs

MH constrained 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:


SM Higgs Production• Production cross sections are

small: 0.1-1 pb depending on MH

• MH< 135 GeV: decay to bb– gg H bb overwhelmed by

QCD background • searches can be

performed in W/Z associated production with lower background

• Best channels:– WHlbb, ZHbb

• MH > 135 GeV: decay to WW– gg H WW(*) l+l- final states

can be explored• clean, but small branching H bb

H WW(*)

Dominant decay modesWe may have Higgs in our data already!


SM Higgs Sensitivity

• New Higgs sensitivity study from CDF + DØ in 2003:

Statistical power onlySystematics not included

Improved sensitivity from refined analysis and detailed simulation

No systematics

The SM Higgs is a challenge, understanding of bkgs critical!


Higgs Beyond the Standard Model• Larger cross sections and/or cleaner

search topologies• MSSM

– 5 physical Higgses:• 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: tanud

• One Higgs mass: mA

• Other possibilities:– Left-Right Symmetric, Higgs

Triplet models: Doubly Charged Higgs

– SM extensions which suppress fermion couplings

• Fermio-phobic or TopColor Higgs

MSSM Higgs Main Decaysh/H/Abb ~ 90%h/H/A ~ 10%H+ ~ 100% (tan>1)

Enhanced over HSMbb(prop. to tan2


B-jet tagging• demonstrated good b-

tagging capability up to |<2.5

• Essential for Hbb searches

• New for DØ in Run II

DØ RunII Preliminary

b-tagging efficiency vs light quark mis-tag rate

Performance being improved

• Use track impact parameter (IP) measurements or secondary vertex reconstruction

• Several algorithms available


W(e)bb production (1)• Motivation:

– Background to WH production• Event selection includes:

– 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

• Simulations with Alpgen and Pythia through detailed detector response

• Cross sections normalized to MCFM NLO calculationsGood understanding of data


W(e)bb production(2)

• Require jets to be b-tagged:– use different b-tag

algorithms– consistent results with all

• Observe 8, expect 8.3±2.2• Background dominated by

top events

At least one b-tag

At least two b-tags

Good agreement between data and MC in both cases


W(e)bb production (3)• Exactly two jets: suppress top

production• Observe 2 events, expect

2.5±0.5• Sample composition:

Source Uncertainty(%)

Jet energy scale 14

Jet ID 7

b-tagging 11

Trigger & e ID 5

EM scale 5

MC simulations 15

Total 26

Systematics studies for Wbb:

Set limit on production of:

(Wbb) < 20.3 pb(Wbb) < 20.3 pb(WH)xBr(Hbb) < 12.4 pb for MH = 115 GeV at 95% C.L.

(Systematics smaller for WH)

Wbb Wc(c) Wjj tt+t Others

1.4±0.4

0.3±0.1

0.10±0.03

0.6±0.2

0.10±0.03


Z(eeb associated production (1)

• Motivation:– Background to ZH

production– Benchmark for SUSY

Higgs production via gbbh

– Probes PDF of the b-quark• Examples of ZQ (Zj) LO

diagrams:

• Data correspond to integrated luminosity of 184 (ee), 152 () pb-1

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

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

for background evaluation– 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

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


Z(eeb production (2)

• Transverse energy spectrum of b-tagged jets– QCD and mistag

background estimated from data

– MC: Pythia Zb normalized to data

• Measured cross section ratio Z+b/Z+j: – 0.024 ± 0.005 (stat)

(syst)– Theory: ~0.02

hep-ph/031202

• Systematics studies:Source Uncertainty (%)

Jet tagging 16

Jet energy scale

11

Bkgd. estimation

6

(Z+c)/(Z+b) 3

Total 20

+ 0.005– 0.004


HWW(*)l+l- (l=e,• Event selection includes:

– 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 afterpreselection


HWW(*)l+l- (l=e,• Higgs mass reconstruction

not possible due to two neutrinos

• Employ spin correlations to suppress the background– (ll) variable is

particularly usefulW+ e+

W- e-

• Charged leptons from Higgs are collinear

Good agreement between data and MC

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

Higgs of 160 GeV


HWW(*)l+l- (l=e, Signal acceptance is ~ 0.02 –

0.2 depending on the Higgs mass/final state

• Number of events after selectionee e

Observed 2 2 5

Expected2.7±0.4

3.1±0.3

5.3±0.6• Dominant Background in esample

WW W+jets WZ tt

2.51±0.05

0.34±0.02

0.11±0.01

0.13±0.01

DØ Run II Preliminary

Excluded cross section times

Branching Ratio at 95% C.L.

Higgs of 160 GeV


Neutral Higgs Bosons at High tan in Multi-jet

Events• 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

bbbbbbqqgg , (=h,H,A)BR( ) ~

90%bb

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

Dijet Mass


Neutral Higgs Bosons at High tan in Multi-jet

EventsSignal acceptance is ~ 0.2 – 1.5% depending on the Higgs mass/# of jets


Search for Non-SM Light Higgs in h• Small in the SM

• 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 the measurement of mis-ID rate (~30%)


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 Mh


H++/H-- Search(1)• H++/H-- appear in LR symmetric

and Higgs triplet models:– Leading order pair-production: qqZ/H++H—

Dominant decay mode: like-signed leptons

• Same sign muon decays contain low SM background:– clean environment for new

physics search• Select di-muon triggered

events • muon identification

requirements: – Isolated muons with 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 < 2

Di-muon mass spectra at various steps of the event selection procedure


H++/H-- Search (2)

• 2 candidates in L=107 pb-1, expected bkg of 0.34 from SM• Search assumes the H±± branching ratio to like-sign muons to be

100%• Confidence level of the signal as a function of the H±± mass, for

left- and right-handed Higgs bosons MH> 116 GeV MH> 95 GeV

DØ Run II prel. DØ Run II prel.


Summary• The hunt for Higgs in DØ Run II data is on!• The upgraded DØ detector is producing world class

results• Understanding of background processes progressing • Result summary:

(Wbb)< 20 pb (WH)xBr(Hbb) < 12 pb (We) (Z+b)/ (Z+j) = 0.024 ± 0.005 (stat) (syst)– limits set on (H)xBr(HWW(*))

– Search for Neutral Higgs in MSSM:• excludes A/h/H for masses 90-150 GeV at high tanβ

(>~100)– Search for h:

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

– H++ Search: • Lower mass limits of 116 and 95 GeV for HL

and HR

decays to • Limits set are unmatched or superior to Run I

Many results already and more with increased stats are coming soon!

+ 0.005– 0.004


• Extra slides…


W(e)bb production (3)

• W Transverse mass of 2 tagged events, keep events with 25GeV<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.


W(e)bb production (4)• Suppress top production

by requiring exactly two jets– Observe 2 events,

expect 2.5±0.5• Sample composition:Wbb Wc(c) Wjj tt+t Other

s

1.4±0.4 0.3±0.1 0.1±0.03

0.6±0.2

0.1±0.03• Requiring each jet to be tagged by all of

the 3 b-tagging algorithms reduces the background:

– Observe 2 events, expect 0.3±0.1 (Background) + 0.6±0.2 Wbb (Signal)

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

Standard Model without Wbb disfavored at 2 level


W(e)H(bb) production• Observe 2 events, expect

2.5±0.5• With 85 GeV< Dijet Mass<135

GeV : – 0 events– 0.54 ± 0.14 expect

background– 0.03 ± 0.01 WH

Source Uncertainty(%)

Jet energy scale 14

Jet ID 7

b-tagging 11

Trigger & e ID 5

EM scale 5

MC simulations 15

Total 26

Systematics studies for Wbb:

Set limit on production of (WH)xBr(Hbb) < 12.4 pb for MH = 115 GeV at 95% C.L.

(Systematics smaller for WH)


Views of high dijet mass (220 GeV) Wbb(WH)

candidate

ETmiss

Vertex view of the 2nd candidate (48 GeV)

Higgs Results from D Ø

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