Standard model higgs searches at lhc
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Standard Model Higgs Searches at LHC. Suyong Choi Korea U. SM Higgs Production and Decay. SM Higgs Production Cross Sections at 7 TeV. SM Higgs Production Cross Sections at 14 TeV. Branching Fractions. SM Higgs . Sensitivity depends on Backgrounds Mass resolution.

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Standard Model Higgs Searches at LHC

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Standard model higgs searches at lhc

Standard Model Higgs Searches at LHC

Suyong Choi

Korea U


Sm higgs production and decay

SM Higgs Production and Decay


Sm higgs production cross sections at 7 tev

SM Higgs Production Cross Sections at 7 TeV


Sm higgs production cross sections at 14 tev

SM Higgs Production Cross Sections at 14 TeV


Branching fractions

Branching Fractions


Sm higgs

SM Higgs

  • Sensitivity depends on

    • Backgrounds

    • Mass resolution

More info in https://twiki.cern.ch/twiki/bin/view/LHCPhysics/CrossSections


Sm higgs search c hannels

SM Higgs Search Channels

  • – good mass resolution

  • - clean, good mass resolution

  • - not clean, worse mass resolution

  • – statistics

  • – statistics, clean

  • - clean, good mass resolution

  • Overall, they are very complicated analyses


  • Sm higgs searches at cms and atlas

    SM Higgs searches at CMS and ATLAS


    Cms sm higgs channels

    CMS SM Higgs Channels


    Atlas sm higgs channels

    ATLAS SM Higgs Channels


    Standard model higgs searches at lhc

    Boosted selection

    1 jet pT>150 GeV

    VBF selection


    Standard model higgs searches at lhc

    • W/Z+H


    Standard model higgs searches at lhc

    • Event categories divided into

      • 2 classes where the smallest of two photons is less or greater than 0.94

      • 2 classes where the largest is in endcap or barrel

      • Total of 2x2=4 classes

    Mass resolution for


    Standard model higgs searches at lhc

    Excess:

    SM signal x5


    Consistency

    Consistency

    • P-value - Probability that background to produce fluctuation as large as observed

    2.3

    @123.5 GeV


    Upper limit

    Upper Limit

    Data disfavors Higgs in 127 – 131 GeV @ 95% CL


    Atlas

    ATLAS

    Mass resolution

    1.7 GeV


    Atlas1

    ATLAS

    • 114 – 115, 135-136 GeVexcluded @ 95% CL


    Standard model higgs searches at lhc

    • ZZ selection

      • A second lepton pair:

      • for 4e, 4

      • Two sets of cuts for low-mass and high-mass Higgs

    • Signal efficiencies


    Standard model higgs searches at lhc

    • Higgs mass resolutions


    Standard model higgs searches at lhc

    • Backgrounds

      • Reducible - , ,

      • Irreducible -

      • All derived from data

    72 observed

    exepected

    Theory:


    Low mass region

    low mass region

    • 13 events observed

    • expected

    • No significant excess


    Limits from

    Limits from

    340~465 GeV

    180~305 GeV

    134~158 GeV

    expected exclusion: 130-160 GeV, 182-420 GeV


    Atlas2

    ATLAS

    71 events observed

    629 events expected

    Below 180 GeV,

    8 events observed

    9.31.5 events expected

    2e2μ events (m=123.6 GeV, m=124.3 GeV), one 4μ event(m=124.6 GeV)


    Atlas3

    ATLAS


    Atlas4

    ATLAS

    135 – 156 GeV

    excluded

    181-234 GeV

    excluded

    255-415 GeV

    excluded


    Further selections

    Further selections

    • mass-dependent selection

      • , , ,


    Yields after signal selection

    Yields after signal selection

    • Experimental uncertainties only

    • Signal efficiency uncertainty ~ 20%

    • Background uncertainty in signal region ~ 15%


    Limits

    Limits

    129-270 GeV Excluded @ 95%CL

    127-270 GeV expected exclusion


    Atlas5

    ATLAS


    Atlas6

    ATLAS


    Atlas7

    ATLAS

    • 2.05 fb-1

    110 events observed

    9110 expected

    If Higgs of certain mH existed


    Standard model higgs searches at lhc

    • 145 – 206 GeV excluded @ 95% CL

      • Excpected exclusion: 134 – 200


    Standard model higgs searches at lhc

    • Dilepton trigger

    • Veto events with 3rd lepton

    • Cuts to reject Fake Missing ET

    • Final selection

      • MET cut – mass dependent

      • MT


    Backgrounds

    Backgrounds

    • MET modelingusing events

      • reweighting according to n-jets, boson pT

      • Less reliance on MC simulation

    • Data driven methods to estimate non-resonant backgrounds

      • Top pair, single top, WW, W+jets,


    Limits1

    Limits

    270-440 GeV excluded at 95% CL


    Cms combination

    CMS Combination


    Standard model higgs searches at lhc

    Expected exclusion: 117 – 543 GeV


    Standard model higgs searches at lhc

    Global p-value 1.9 with LEE in 110~145 GeV

    0.6 with LEE in 110~600 GeV


    Cms combined higgs exclusion limits

    CMS Combined Higgs Exclusion Limits


    Atlas combination results

    Atlas Combination results


    Consistency with background only hypothesis

    Consistency with Background only hypothesis

    • 3.6 excess

      • : 2.8

      • ZZ*: 2.1

      • WW*: 1.4

    • With LEE

      • 3.6→2.3

      • 7% to observe excess in

      • ~30% to observe excess in ZZ

    • SM expectationis 2.4 for 126 GeV Higgs

    1.9x10-4


    Combined atlas sm higgs exclusion limits

    Combined ATLAS SM Higgs Exclusion Limits

    95% exclusion limits:

    112.7 - 115.5 GeV

    131 – 237 GeV

    251 – 453 GeV

    Expected 95%CL

    exclusion:

    124.6 – 520 GeV

    99% exclusion limits:

    131 – 230 GeV

    260 – 437 GeV


    Summary and outlook

    Summary and Outlook

    • Atlas and CMS data narrowed the allowed mass range for SM Higgs

      • ATLAS : 115.5 – 131 GeV

      • CMS : 114 – 127 GeV

    • 20 fb-1 more data per experiment in 2012 allows 5 observation per experiment at mH=125 GeV


    Backup

    backup


    Dataset

    Dataset

    Lumi

    Uncertainty

    4.5%

    Good data up to 4.7 fb-1 used in the updated analyses


    Backgrounds1

    Backgrounds


    Ww selection event yields

    WW Selection event yields


    Standard model higgs searches at lhc

    • Background modeling

      • MC simulation of background was not used for background estimation, but in agreement with data

      • 30% non-prompt photons

      • 5th order Bernstein polynomial fitted to the

        • Maximize sensitivity


    Standard model higgs searches at lhc

    • Signal

      • in 5 GeV steps (9 mass points)

      • POWHEG NLO + PYTHIA

      • Higgs reweighted to NNLL+NLO

        • Using HqT program

    • Fine corrections to photon energies

      • Intercalibration

      • Transparency corrections

      • Improves resolutions by 10%


    Standard model higgs searches at lhc

    • Diphoton trigger

      • Asymmetric ET thresholds

      • complementary photon quality selections

      • 100% trigger efficiency

    • Photon energy corrected for conversions upstream of Electromagnetic calorimeter

      • Boosted decision tree regression trained on MC samples


    Standard model higgs searches at lhc

    • Vertex location

      • Mean number of pp interactions ~ 9.5

      • RMS spread in beam direction ~ 6 cm

      • 10mm accuracy in vertex location ensures that energy resolution is not spoiled

    • Identifying the correct vertex

      • Kinematic properties of tracks emerging from the vertex and their correlation with diphoton kinematics

        • Sum of track , momentum balance

      • Converted tracks point to vertex

    • 3% gain in efficiency


    Standard model higgs searches at lhc

    • Photon kinematic selection

      • ,

      • , excl. barrel-endcap transition

    • Backgrounds

      • Irreducible

      • Fakes: , dijet


    Standard model higgs searches at lhc

    • Photon isolation

      • Energies in Ecal and Hcal – affected by pile up

        • Estimate effect of pileup in the event by average energy density away from jets

      • charged tracks around the photon candidate – fake vertex allows non-isolated photon to appear isolated

        • Calculate track isolation w.r.t. vertex that maximizes it

    • Photon quality

      • H/E

      • Transverse width of a photon shower

      • Electron track veto (E/p)


    Standard model higgs searches at lhc

    • Dividing photon candidates

      • Different S/B for photons of different criteria

      • Barrel vsEndcap

        • Barrel photon has less QCD background

        • Energy in a 3x3 crystals around highest energy / supercluster energy

        • Photons with large have less probability to have converted


    Standard model higgs searches at lhc

    • Photon ID efficiencies

      • Measured using , excluding track veto eff.


    Systematic uncertainties in

    Systematic Uncertainties in


    Standard model higgs searches at lhc

    • 3 channels – 4e, 4, 2e2

    • Covers 110 – 600 GeV

    • Used 4.7 fb-1

    • Triggers

      • Dilepton triggers with asymmetric thresholds of pT>8, 17 GeV


    Standard model higgs searches at lhc

    • Offline

      • Electrons pT>7 GeV, , (90% for

      • MuonspT>5 GeV, , 98% efficient

      • Small impact parameter significance<4

      • Z1: lepton pair with mass closest to mZand


    Standard model higgs searches at lhc

    • 2 leptons + MET

      • ee, e, 

      • 1 or 2 high pT leptons in the trigger

        • 97~99% efficiency for signal of mH=160 GeV

      • 0, 1, 2 jet categories considered


    Offline selection

    Offline Selection

    • Offline

      • Lepton pT 20 GeV, 10(15) GeV for e(ee,), Consistent with coming from Vertex

      • Jets ,

      • Projected missing ET>20(40) e(ee,)

      • Azimuthal opening angle dilepton-leading jet < 165 degrees (ee,)

      • Dilepton mass cut

        • Remove low mass resonances, Z

      • Reject events where jets tagged with soft leptons or large impact parameter tracks

        • Remove top events

      • Reject events with 3rd isolated lepton

        • Remove ZZ, WZ

      • Identify converted photons to reject


    Background estimation

    Background estimation

    • Mostly data driven

      • Apply antiselection, then extrapolate to signal region

      • W+jets, QCD multijets

      • ,

      • – select events

      • Statistics of control sample limits background estimate error


    Ww 0 jet baseline selection

    WW+0 jet baseline selection


    Ww 1 jet baseline selection

    WW+1-jet baseline selection


    Standard model higgs searches at lhc

    1 jet

    0 jet


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