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Higgs Searches at the Tevatron. Outline. Introduction Tevatron Standard Model (SM) Higgs Introduction Results Low & high mass Combination Non-SM Higgs Introduction Results Prospects & Conclusions. (See parallel sessions for full details). [ Thanks to all my Tevatron colleagues ].

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outline
Outline
  • Introduction
    • Tevatron
  • Standard Model (SM) Higgs
    • Introduction
    • Results
      • Low & high mass
      • Combination
  • Non-SM Higgs
    • Introduction
    • Results
  • Prospects & Conclusions

(See parallel sessions for full details)

[ Thanks to all my Tevatron colleagues ]

Gavin Davies – SUSY08

tevatron performance
Tevatron Performance
  • Over 4fb-1 delivered per experiment. Over 0.2fb-1 recorded last month.
  • Expect ~6fb-1 by Apr 2009, and 8fb-1 by Oct 2010.

Average data-taking efficiency > 85%

Results presented here use up to 2.4fb-1

(3fb-1 results at ICHEP)

Many thanks to Accelerator Division

05/02 05/04 05/06 05/08

Gavin Davies – SUSY08

standard model higgs
Standard Model Higgs
  • Higgs mechanism
    • Additional scalar field in SM Lagrangian

 mass to W,Z & fermions

    • Predicts neutral, spin 0 boson
      • But not its mass
  • Direct searches at LEP2
    • mH> 114.4 GeV
  • Improved mt & mw tighten indirect

constraints:

    • mH< 160 GeV (EW fit)
    • mH < 190 GeV if LEP2 limit included

 A light (SUSY?) Higgs is favoured

Gavin Davies – SUSY08

sm higgs production decay

Excluded

SM Higgs Production & Decay
  • Small production cross-sections
    • 0.1 -1 pb
  • Branching ratio dictates search
  • mH< 135 GeV
    • gg → H →bb overwhelmed by multijet (QCD) background
    • Associated WH & ZH production

with H →bb decay

    • Main backgrounds: W+bb, Z+bb,

W/Z jj, top, di-boson, QCD

  • mH> 135 GeV
    • gg →H → WW
    • Main background: WW

Gavin Davies – SUSY08

sm higgs topologies
SM Higgs Topologies
  • Low mass:
  • Intermediate mass:
  • High mass:

Leptonic decay of W / Z boson

provides ‘handle’ for event.

H  bb reduce SM background

High PTopposite sign leptons.

Missing ET

Gavin Davies – SUSY08

sm higgs snapshot
SM Higgs - snapshot
  • Higgs searches at a hadron machine challenging
  • Requires
    • Efficient triggering, lepton ID,

b-tagging, jet resolution..

    • Sizeable data-sets
  • Well established
    • Analyses use multivariate techniques
      • Neural net (NN), matrix element (ME)..
    • Regular Tevatron combinations
  • Approaching the SM expectation
    • Rapid improvement well beyond √L gain
  • Even better to come

Gavin Davies – SUSY08

slide8

Highest associated production cross-section

    • Use electron and muon channels
  • Selection
    • Isolated lepton, missing ET (MET), 2 jets
  • Backgrounds
    • W+jets, QCD, top, di-boson
  • Analyses
    • Separate channels: 1 &

2 b-tags, e or m, central

or forward

    • NN (and ME) based analyses

using kinematic variables

Gavin Davies – SUSY08

slide9

Exp/SM = 6.4

(14% improvement)

  • Cross section limits derived from NN distributions
    • Compare observed (obs) or

expected (exp) limit to SM prediction

  • Recent CDF analysis
    • Including isolated tracks
    • Increases acceptance by 25%

mH=115GeV

Gavin Davies – SUSY08

slide10
Large cross-section & acceptance but hard
  • Selection
    • Two jets, MET (not aligned in f with jets)
  • Backgrounds
    • Physics: W/Z + jets, di-boson, top – from Monte Carlo
    • Instrumental: Mis-measured MET with QCD jets – from data
  • Analyses
    • Optimised b-tagging, NN or decision tree (DT) discriminant

Exp/SM~8(both expts.)

Gavin Davies – SUSY08

slide11
And….
  • Not forgetting .. ZH → llbb
    • 1 and 2 b-tags, NN event selection
    • Exp/SM ~ 16-20 at 115GeV (1fb-1)
  • Sensitivity of existing channels rapidly improving
  • Add additional channels
        • Exp/SM ~ 45 at 120GeV
    • CDF
        • Exp/SM ~ 40 at 120GeV
        • Exp/SM ~ 25 at 115GeV
        • Adds 10% to CDF combination (≡ 20% more data)

Gavin Davies – SUSY08

slide12
Intermediate mass range
  • Selection
    • 2 like-sign high PT leptons (ee, em, mm)
  • Backgrounds
    • WW,WZ, charge flips (from data)
  • Analyses
    • DØ 1fb-1 and CDF 1.9fb-1
  • Exp /SM~25 at 140GeV
  • Exp /SM ~20 at 160GeV

Gavin Davies – SUSY08

slide13
Dominant for mH >135GeV
  • Selection
    • 2 isolated, opposite sign leptons,MET
  • Backgrounds
    • Drell-Yan, W+jets/QCD, tt, SM WW
  • Analyses:
    • WW from spin 0 Higgs
      • Leptons prefer to point in same direction
    • Use NN, using kinematic variables and ME as inputs

Gavin Davies – SUSY08

slide14



  • Matrix element
    • Use observed leptons & missing ET (xobs)
    • Integrate over LO theory predictions

for WW, ZZ, W+g, W+jet, Higgs

    • Construct LR discriminant from probabilities
  • Input ME information to NN
    • CDF – 4 ME’s and 6 kinematic variables
    • DØ – 1 ME and more kinematic variables
  • Cross section limit derived from NNoutput distribution

LR (H  WW)

Gavin Davies – SUSY08

slide15

Expected Limit / SM ~ 2.4

Observed Limit / SM ~ 2.1

Expected Limit / SM ~ 2.5

Observed Limit / SM ~ 1.6

Closing in on the SM

Gavin Davies – SUSY08

combination
Combination
  • Compare background and signal plus

background hypotheses using Poisson

likelihoods

  • Systematics included in likelihoods
  • Combine across channels within an

experiment

  • Combine across experiments
    • Since 2005 sensitivity improved

by a factor of 1.7 beyond √L gain

Gavin Davies – SUSY08

non sm higgs

f

f

f

f

b

f

b

f

Non-SM Higgs
  • MSSM
    • 2 Higgs doublets, ratio of vev’s = tanb
    • 2 charged (H)and 3 neutral Higgs particles: f =h, H, A
    • At large tan b
      • Coupling to d-type fermions enhanced by tanb → sαtan2b
      • sf  2 sA
    • For low & intermediate masses
      • Br(f → bb) ~90%, Br(f → tt) ~10%

f → ttand bf →bbborbf →btt topologies

Gavin Davies – SUSY08

neutral mssm higgs tt
Neutral MSSM Higgs tt
  • Smaller BR but cleaner
  • Signal: (eτhad) (μτhad) (eμ) pairs + MET
  • Background: Z→tt, jet fakes
  • Use visible mass:
    • No significant excess in visible mass, so proceed to set limits
      • Initially on sxBr then interpret in MSSM (FeynHiggs – arXiv:0705.0746v2)

arXiv:0805.2491

Gavin Davies – SUSY08

neutral mssm higgs tt1
Neutral MSSM Higgs tt
  • MSSM interpretation
    • Width included
    • Limits very similar for m<0
    • Expect to reach tanb~20 at low mA by end 2010
  • Most powerful constraints on tanb

Gavin Davies – SUSY08

neutral mssm higgs bb b b
Neutral MSSM Higgs  bb + b[b]
  • Signal
    • At least 3 b-tagged jets
    • Look for peak in dijet mass
  • Challenge - Large multijet background
    • Estimate from 2 b-tagged data and simulation
    • Composition: Sec. vertex mass (CDF) & fit to multiple b-tagging criteria (DØ)
    • No significant excess, so set limits, initially on sxBr then interpret in MSSM
  • arXiv:0805.3556

Gavin Davies – SUSY08

neutral mssm higgs bb b b1
Neutral MSSM Higgs  bb + b[b]
  • MSSM interpretation
    • Width included

Gavin Davies – SUSY08

going further
Going further…
  • Charged Higgs
    • Separate t  W+b & t  H+b

(H+ cs) via mass templates

  • And beyond MSSM
    • Fermiophobic Higgs
    • Doubly charged Higgs
  • arXiv:0803.1514
  • arXiv:0805.1534

HR > 127 GeV

HL > 150 GeV

CDF also looked for e/t final states

Gavin Davies – SUSY08

prospects sm higgs
Prospects – SM Higgs
  • Rapid evolution
    • Significantly better than √L
    • Increased trigger efficiency, lepton acceptance, improved b-tagging, NN discriminants
  • For 2010 expect, beyond √L gain
    • x 1.4 improvement at high mass and x 2.0 improvement at low mass

mH =160GeV

mH =115GeV

Gavin Davies – SUSY08

prospects sm higgs cont
Prospects – SM Higgs (cont)
  • End 2009
    • Very limited

allowed range

  • End 2010
    • Full exclusion
    • 3 evidence possible

over almost entire

range

Assumes two experiments

Gavin Davies – SUSY08

conclusions

ICHEP08?

Conclusions
  • Tevatron and CDF/ DØexperiments performing very well
    • Over 4fb-1 delivered, with 8fb-1 expected by end of 2010
  • New SM analyses keep coming in
    • Sensitivity almost improving linearly

with luminosity

    • Well established, common effort across

the Collaborations

  • Closing in on the SM
    • 2008 - go beyond at 160GeV ?
  • Have a clear roadmap to reach desired sensitivity
  • Wide range of BSM searches, ready for discovery
    • Expect to reach tanb ~20 at low mA

Exciting times ahead – will only get better!

Gavin Davies – SUSY08

slide26
And…

Thank you for your attention

Please see the parallel sessions for full details

Search for the SM Higgs Boson at DØ - Suyong Choi

Search for Charged Higgs Bosons at DØ - Yvonne Peters

Search for Charged Higgs in Top Quark Decays at CDF - Geumbong Yu

Search for BSM Higgs Bosons at DØ - Ingo Torchiani

Gavin Davies – SUSY08

slide27
Backup slides

Gavin Davies – SUSY08

cdf and d experiments
CDF and DØ experiments
  • Both detectors extensively upgraded for Run IIa
    • New silicon vertex detector
    • New tracking system
    • Upgraded muon chambers
  • CDF: New plug calorimeter & ToF
    • New solenoid & preshowers
    • Run IIb: New inner tracking layer & L1 trigger

Gavin Davies – SUSY08

d data taking
DØ data taking

Gavin Davies – SUSY08

slide30

Total

H →WW →lvlv

WH → lnbb

ZH →llbb

ZH → llbb

Gavin Davies – SUSY08

b tagging
B-tagging
  • Critical for low mass H bb
    • Improves S/B by > 10
  • Use lifetime information
    • Correct for MC / data differences
      • Measured at given operating points
  • Analyse separately (“tight”)

single & (“loose”) double tags

CDF: Secondary vertex reconstruction

  • Neural Net - improves purity
  • Inputs: track multiplicity, pT, vertex
  • decay length, mass, fit
  • Loose = 50% eff, 1.5 % mistag
  • Tight = 40% eff, 0.5 % mistag

DØ: Neural Net tagger

  • Secondary vertex & dca based inputs,

derived from basic taggers

  • High efficiency, purity
  • Loose = 70% eff, 4.5% mistag
  • Tight = 50% eff, 0.3% mistag

Gavin Davies – SUSY08

d b tagging
DØ B-tagging

Several mature algorithms used:

  • 3 main categories:

- Soft-lepton tagging

- Impact Parameter based

- Secondary Vertex reconstruction

Gavin Davies – SUSY08

b tagging d certification
B-tagging – (DØ) Certification
  • Have MC / data differences – particularly at a hadron machine
    • Measure performance on data
      • Tag Rate Function (TRF) Parameterized efficiency &

fake-rate as function of pT and η

    • Use to correct MC b-tagging rate
  • b and c-efficiencies
    • Measured using a b-enriched data sample
  • Fake-rate
    • Measured using QCD data

Gavin Davies – SUSY08

tau id
Tau ID
  • CDF: Isolation based
  • Require 1 or 3 tracks, pT > 1GeV in the isolation cone
    • For 3 tracks total charge must be ±1
    • pThad > 15 (20) GeV for 1 (3) prongs
    • Mhad < 1.8 (2.2) GeV
  • Reject electrons via E/p cut
  • Validated via W/Z measurements
  • Performance
    • Efficiency ~ 40-50%
    • Jet to tau fake rate ~0.001-0.005
  • DØ: 3 NN’s for each tau type
  • Validated via Z’s

Efficiency (NN>0.9):

t ~0.65, jets ~0.02

Gavin Davies – SUSY08

slide35
Cleanest channel, but low cross section
  • Selection:
    • Loose lepton ID, 2 jets
  • Backgrounds:
    • Z+jets, top, WZ, ZZ, QCD
  • Analyses
    • Constrain dijet mass
    • NN event selection
  • Exp/SM ~ 16

Gavin Davies – SUSY08

limit setting
Limit Setting

LEP: Low background, small systematics

Tevatron/LHC: High background, large systematics

  • Systematics, including correlations, taken into account
  • Main systematics (depending on channel):

- Luminosity and normalisation

- QCD background estimates

- Input background cross-sections

- Jet energy scale and b-tagging

- Lepton identification

- K-factors on W/Z + heavy flavour

  • Systematic uncertainties included in likelihood via gaussian smearing of expectation (‘profile likelihood’)
  • Background constrained by maximising profile likelihood (‘sideband fitting’)
  • Tevatron experiments use LEP CLs (modified frequentist) and Bayesian methods
  • Limit setting approaches agree to within 10%

Gavin Davies – SUSY08

spring 08 sm combination
Spring 08 SM Combination

Channel Lumi /Technique Final state

Total of 28CDF + DØ channels combined

Gavin Davies – SUSY08

spring 08 sm combination1
Spring 08 SM Combination

Gavin Davies – SUSY08

spring 08 sm combination2
Spring 08 SM Combination

Gavin Davies – SUSY08

mssm benchmarks
MSSM benchmarks
  • Five additional parameters due to radiative correction
    • MSUSY (parameterizes squark, gaugino masses)
    • Xt (related to the trilinear coupling At→ stop mixing)
    • M2 (gaugino mass term)
    •  (Higgs mass parameter)
    • Mgluino(comes in via loops)
  • Two common benchmarks
    • Max-mixing - Higgs boson mass

mh close to max possible value

for a given tan

    • No-mixing - vanishing mixing in

stop sector → small mass

for h

Gavin Davies – SUSY08

neutral mssm higgs tt2
Neutral MSSM Higgs tt

Limits: s x Br (ftt)

Evolution:

Full 2010 dataset (2 expts.)

Width:

Gavin Davies – SUSY08