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g. ITEP Winter School – February 2012 Moscow. Higgs searches before LHC. LEP  95% CL M H < 114 GeV/c 2 TEVATRON:  95% CL 158 GeV/c 2 < M H < 175 GeV/c 2 ;. CMS analysis on full 2011 data. The Main Channel: H → WW → 2l 2 n. μ: 32 GeV. Signature:

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g

ITEP Winter School – February 2012 Moscow

higgs searches before lhc
Higgs searches before LHC

LEP 95% CL MH < 114 GeV/c2

TEVATRON:  95% CL 158 GeV/c2 < MH < 175 GeV/c2;

the main channel h ww 2l 2 n
The Main Channel: H → WW → 2l 2n

μ: 32 GeV

Signature:

  • 2 opposite charged leptons (leptons only e, μ)
  • 2 neutrinos missing transverse energy (MET)
  • No Higgs mass peak
  • Basically a counting analysis
  • Enhance sensitivity by subdividing into (0,1,2) jets

Analysis challenges:

  • Understand backgrounds
  • Normalize to control regions
  • Backgrounds: WW, W+jets, top, DY

e: 34 GeV

MET:

47 GeV

conservative cut and count analysis
Conservative Cut and Count Analysis

Observations:

  • Exclude Higgs masses from 132 GeV < mH < 238 GeV
  • Expected exclusion 129 GeV < mH < 236 GeV
full mva shape analysis
Full MVA Shape Analysis

Observations:

  • Exclude Higgs masses from 129 GeV < mH < 270 GeV
  • Expected exclusion 127 GeV < mH < 270 GeV
the golden mode h zz 4l
The Golden Mode: H → ZZ → 4l
  • Analysis overview:
    • 4 isolated high pT leptons
    • Consistent with Z decays
    • From same vertex
    • Fit mass peak with resolution: 2-4 GeV
    • Little background, main comes from non-resonant ZZ production, irreducible
    • Also Zbb and top (2l2n2b)

Background removal

  • Leptons from b-decays are non-isolated and displaced
  • Require isolation and small impact parameter
the golden mode h zz 4l1
The Golden Mode: H → ZZ → 4l

Observed events consistent with expectations:

  • Excluded regions: 134 < mH < 158 GeV/c2, 180 <mH < 305 GeV/c2 and 340 < mH <465 GeV/c2
high mass special h zz 2l 2
High Mass Special: H → ZZ → 2l2τ

Analysis overviews:

  • First time that there is a Higgs search with this final state.
  • Second Z going to tlth, thth and tetm other final states already accounted for H ZZ
  • Cross sections excluded between a factor 4 and 7 larger than that expected for the SM mH in the range 190 < mH < 500 GeV/c2
high mass special h zz 2l2 n
High Mass Special: H → ZZ →2l2n

Analysis overview:

  • Same final state as H→WW but with smaller production rate.
  • Starts to have sensitivity at about mH = 300 GeV
  • Limits based on cut based and shape of the MT distribution.
  • Excluding mass range between 270 -440 GeV/c2 @ 95% C. L
high mass h zz 2l 2jets or 2b jets
High Mass: H → ZZ → 2l 2jets (or 2b-jets)

Analysis overview:

  • Highest rate of H→ZZ analyses (20 times higher than H → ZZ→ 4l)
  • Analysis optimized separetely for two mass ranges
  • Intermediate mass range 2mW < mH < 2mZ has low sensitivity due to top background.
  • Signal discrimination: Great contribution of heavy flavour quarks and absence of gluons.
  • Angular Likelihood Discriminator.
  • Not yet excluding but getting there
low mass specialist h
Low Mass Specialist: H →γγ
  • Signature and background:
    • Two high momentum photons
    • Clean final-state topology with a mass peak that can be reconstructed with precision
    • Low mass Higgs
    • Background estimated from a fit to the data.
    • Large (irreducible) background from prompt two photons production.
    • Smaller fake photon background 
    • pp  jet + g , pp  jet + jet

86 GeV

Key analysis features:

  • Clean final-state topology
  • Energy resolution is almost everything: calibrate and optimize

56 GeV

low mass specialist h1
Low Mass Specialist: H →γγ
  • Limits evaluated using the two photon invariant mass distribution as observable.
  • The expected exclusion limit at 95% CL is between 1.5 and 2.0 times the Standard Model cross section in the mass range between 110 and 140 GeV/c2.
  • The observed limit disfavours at 95% CL a Standard Model Higgs boson decaying into two photons in the mass range 127 to 132 GeV/c2.

2.34 s

123.5 GeV/c2

low mass special h

Analysis overview:

    • DY  tt background in the mass region is huge for gluon-fusion.
    • 3 categories: incl. / VBF / boosted
    • VBF style most sensitive
    • Require 2 taus (at least one decaying leptonically)
      • e-μ, μ-τh and e-τh
Low Mass Special: H →ττ

Backgrounds

  • top, EWK, DY (irreducible)

VBF category

low mass special h1
Low Mass Special: H →ττ

Observations

  • Data exclude at 95% CL a Higgs boson with a production cross section between 2.9 and 6.3 times that in the standard model.
low mass special vh vbb
Low Mass Special: VH → Vbb

Analysis overview:

  • Enormous background in H → bb due to overwhelming QCD dijet production
  • UseVH with leptonicV decays
  • Also require high momentum: ‘boosted’ analysis
  • Limits based on M(jj) distribution or BDT output.
  • Backgrounds
    • V+jets,VV, top
  • Result
    • Upper limits calculated for 110 < mH < 135
    • Limit is around 3 at low mass
    • Further improvements possible
cms sm higgs combination
CMS SM Higgs Combination
  • Observations:
    • Exclude (95%): 127-600 GeV (exp. 117-583 GeV)
    • Exclude (99%): 129-525 GeV (exp. 128-500 GeV)
cms sm higgs combination1
CMS SM Higgs Combination
  • Some excess around ~124 GeV
conclusions
Conclusions
  • Higgs search in 2011 with CMS: ~5 fb-1 data
  • Excluded region : 127 GeV < mH < 600 GeV
  • Expected : 117 GeV < mH < 543 GeV
  • Small window left: 114.4 GeV < mH < 127 GeV
  • Looking beyond 95% CL → 99% CL:
    • Search will not stop at 95% CL exclusion
    • 99% CL exclusion: 129 GeV < mH < 525 GeV

Comments on low mass region:

  • Excluded less than expected
  • Small excess, but inconclusive at this point
  • Need more data to come to a conclusion
  • 2012 will be a decisive year !
slide20

Thankyou!

большое спасибо!

cms atlas combination
CMS + ATLAS COMBINATION

The region from 146 to 443 GeV/c2 is excluded at 99\% C.L., with the exception of three small regions between 220 and 320 GeV/c2.

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