Itep winter school february 2012 moscow
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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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ITEP Winter School – February 2012 Moscow

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Itep winter school february 2012 moscow

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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;


Cms analysis on full 2011 data

CMS analysison full 2011 data


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 !


Itep winter school february 2012 moscow

Thankyou!

большое спасибо!


Backup

Backup


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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