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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


  • 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


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


  • 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


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


  • 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


  • 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




  • 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


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


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


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


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


  • 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


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