run ii standard model higgs searches at dØ

Run II Standard Model Higgs Searches Run II Standard Model Higgs Searches at DØat DØ

Gavin DaviesGavin Davies

Imperial College LondonImperial College London

On behalf of the DØ CollaborationOn behalf of the DØ Collaboration

SUSY2004Epochal Tsukuba, Tsukuba, Japan

SUSY04 Gavin Davies (Imperial) 2

Main Injector & Recycler

Tevatron

Chicago

p source

Booster

p

p

p p

1.96 TeV

CDF

DØ

OutlineOutline

36×36 bunches396 ns bunch crossing

Thanks to all my DØ colleagues

Introduction TevatronTevatron DØ detector Higgs production /

sensitivity Results

Wbb / WH production (Z+b) / (Z+j) ratio HWW l+l- searches(Non-SM results – see A. Turcot)

Conclusion


Tevatron Performance - ITevatron Performance - I

79% Average Efficiency

89% Current Efficiency


Tevatron Performance - IITevatron Performance - II

05/09/04

FY04 integrated luminosity

Measured Lumi


DDØØ detector detector

New (tracking in B field)New (tracking in B field) Silicon trackerSilicon tracker Fibre trackerFibre tracker PreshowersPreshowers SolenoidSolenoid

UpgradedUpgraded Muon systemMuon system Calorimeter Calorimeter DAQ/ triggerDAQ/ trigger

All needed for Higgs searches

“Build on existing strengths by improving the tracking and triggering”


SM Higgs productionSM Higgs production

Cross sections small: 0.1 - 1 pb Cross sections small: 0.1 - 1 pb

MMH H 135 GeV: decay to bb135 GeV: decay to bb gg gg H: QCD background too large H: QCD background too large HW & HZ associated production HW & HZ associated production

lower (but still large!) bkgd.lower (but still large!) bkgd. Best channels: Best channels:

WHWH→l→lννbb, ZH→bb, ZH→ννννbb, ZH→bb, ZH→llllbbbb

MMH H >135 GeV: decay to WW>135 GeV: decay to WW gg gg H H WW WW((**))ll++ll-- BR smallBR small

H bb

H WW(*)

Dominant decay modes


SM Higgs sensitivitySM Higgs sensitivity

Global fit – light HiggsGlobal fit – light Higgs

MMH H = 117 GeV= 117 GeV

MMHH < 251 GeV at 95% C.L < 251 GeV at 95% C.L..

New CDF+DØ in 2003 More detailed simulation

More refined analysis

Improved sensitivityImproved sensitivity

No systematics

LEP limit from direct LEP limit from direct searchessearches

MMHH > 114.4 GeV at 95% C.L. > 114.4 GeV at 95% C.L.

+67-45


The ChallengeThe Challenge

Higgs

Cross Sections (fb)

QCD & EWK cross sections much QCD & EWK cross sections much largerlarger

Needle in the haystackNeedle in the haystack……

Good understanding of detector, trigger..Good understanding of detector, trigger..

Good understanding of SM backgroundsGood understanding of SM backgrounds Use data & MC to estimate themUse data & MC to estimate them Useful: new enhanced LO MC’s Useful: new enhanced LO MC’s

(Alpgen)(Alpgen)

Study background processesStudy background processes Likelihood methods, NN’s require excellent Likelihood methods, NN’s require excellent

modeling of backgroundsmodeling of backgrounds

Look at channels beyond SM (SUSY) with Look at channels beyond SM (SUSY) with enhanced cross section (A. Turcot)enhanced cross section (A. Turcot)


b-jet taggingb-jet tagging Essential for HEssential for Hbb searchesbb searches

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

Several algorithms availableSeveral algorithms available

Performance being improvedPerformance being improved

IP

Can b-tag up to |η| < 2.5

DØ RunII Preliminary

b-tagging efficiency vs light quark mis-tag rate

(Also have on-line b-tagging)


W(W(ee)bb associated production - I)bb associated production - I Background to WH searchBackground to WH search Event selectionEvent selection

Central isolated eCentral isolated e p pT T > 20 GeV> 20 GeV Missing EMissing ETT > 25 GeV > 25 GeV ≥ ≥ two jets: Etwo jets: ETT > 20 GeV, | > 20 GeV, || < 2.5| < 2.5

2587 events (L2587 events (Lintint=174 pb=174 pb-1-1))

Good understanding of data

• MC: Alpgen & Pythia + detailed detector

response• Cross sections normalized to MCFM

NLO calculations


W(W(ee)bb associated production -II)bb associated production -II

Observe Observe 8 events8 events, expect , expect 8.3±2.28.3±2.2 Bkgd. dominated by top eventsBkgd. dominated by top events

Require jets to be b-taggedRequire jets to be b-tagged Use various b-tag algorithmsUse various b-tag algorithms

All yield consistentAll yield consistent resultsresults

Good agreement between data and MC

At least one b-tag

At least two b-tags


W(W(ee)bb associated production -III)bb associated production -III Exactly 2 jets: suppress top Exactly 2 jets: suppress top

production production Observe Observe 2 events2 events, expect , expect

2.5±0.52.5±0.5 Sample compositionSample compositionWbb 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

115 GeV

Set limit on production ofSet limit on production of

(Wbb) < 20.3 pb(Wbb) < 20.3 pb (95%c.l.)(95%c.l.)

(WH) x B(H(WH) x B(Hbb) < 12.4 pbbb) < 12.4 pb for Mfor MHH = 115 GeV = 115 GeV (95%c.l.)(95%c.l.)

SourceSource Uncertainty Uncertainty (%)(%)

Jet energy scale

14

Jet ID 7

b-tagging 11

Trigger & e ID 5

EM scale 5

MC simulations 15

Total 2626

•SystematicsSystematics


Z(Z(ee/ee/)b associated production - I)b associated production - I MotivationMotivation

Background to ZH searchBackground to ZH search Benchmark for SUSY Higgs Benchmark for SUSY Higgs

production via gbproduction via gbbhbh Probes PDF of the b-quarkProbes PDF of the b-quark

Examples of ZQ (Zj) LO diagramsExamples of ZQ (Zj) LO diagrams

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

Lumi of 184 (ee), 152 (Lumi of 184 (ee), 152 () pb) pb-1-1

Event selectionEvent selection Isolated eIsolated e with p with pT T > 15/20 > 15/20

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

for bkgd. evaluationfor bkgd. evaluation Jet EJet ETT > 20 GeV, | > 20 GeV, || < 2.5| < 2.5 At least one b-tagged jetAt least one b-tagged jet

• MC: Pythia or Alpgen + detailedMC: Pythia or Alpgen + detailed detector responsedetector response

• Cross sections normalized to Cross sections normalized to datadata

• Relative b- and c-quark content Relative b- and c-quark content from MCFM NLO calculationsfrom MCFM NLO calculations


Z+b/Z+j cross section ratio Z+b/Z+j cross section ratio

0.024 ± 0.005 (stat) (syst)0.024 ± 0.005 (stat) (syst)

Theory: ~0.02 Theory: ~0.02 (hep-ph/0312024)(hep-ph/0312024)

SystematicsSystematics

Z(Z(ee/ee/)b associated production - II)b associated production - II Transverse energy spectrum of b-Transverse energy spectrum of b-

tagged jetstagged jets QCD and mistag bkgd. estimated QCD and mistag bkgd. estimated

from datafrom data MC: Pythia Zb normalized toMC: Pythia Zb normalized to

datadata

+ 0.005– 0.004

SourceSource UncertaintyUncertainty

(%)(%)

Jet tagging 16

Jet energy scale 11

Bkgd. estimation 6

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

TotalTotal 2020


H H WW WW((**) ) l l++ll-- (l = e, (l = e, - I - I 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> 20 GeV (ee, e); 30 GeV ()

Veto on Z resonance Energetic jets

MC: Pythia + detailed detector response

Rates normalized to NLO cross section values

Lumi. of ~ 180 (ee), 160 (e) and 150 () pb-1

Data vs MC afterpreselection


H H WW WW((**) ) l l++ll-- (l = e, (l = e, Higgs mass reconstruction not Higgs mass reconstruction not

possible due to two neutrinospossible due to two neutrinos

Spin correlations suppress bkgd.Spin correlations suppress bkgd. (ll) variable is particularly (ll) variable is particularly usefuluseful

Charged leptons from Higgs collinearCharged leptons from Higgs collinear

W+ e+

W- e-

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

Good agreement between data and MC

Higgs of 160 GeV


H H WW WW((**) ) l l++ll-- (l = e, (l = e,

Excluded cross section timesBranching Ratio

Signal acceptance is ~ 0.02 – 0.2

(Higgs mass/final state) ee e

Observed 2 2 5

Expected 2.7 ± 0.4 3.1 ± 0.3 5.3 ± 0.6

Number of events after cutsNumber of events after cuts

WW W+jets WZ tt

2.51±0.05

0.34±0.02

0.11±0.01

0.13±0.01

Dominant bkgd. in e sample

DØ Run II Preliminary

Higgs of 160 GeV


ConclusionsConclusions

SM Higgs searches at DØ underway

Good understanding of backgrounds

First Tevatron Run II Results Limits set on Wbb, WH and HWW(*) production (Z+b) / (Z+j) measured

Many more results to come with improved statistics

run ii standard model higgs searches at dØ

Documents

gev mh

susy higgs production

datarelative b

improvedipcan b

production ibackground

production ofswbb

production iiobserve

production iiiexactly