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ITEP Winter School – February 2012 Moscow

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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  1. g ITEP Winter School – February 2012 Moscow

  2. Higgs searches before LHC LEP 95% CL MH < 114 GeV/c2 TEVATRON:  95% CL 158 GeV/c2 < MH < 175 GeV/c2;

  3. CMS analysison full 2011 data

  4. 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

  5. Conservative Cut and Count Analysis Observations: • Exclude Higgs masses from 132 GeV < mH < 238 GeV • Expected exclusion 129 GeV < mH < 236 GeV

  6. Full MVA Shape Analysis Observations: • Exclude Higgs masses from 129 GeV < mH < 270 GeV • Expected exclusion 127 GeV < mH < 270 GeV

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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.

  16. 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

  17. CMS SM Higgs Combination • Observations: • Exclude (95%): 127-600 GeV (exp. 117-583 GeV) • Exclude (99%): 129-525 GeV (exp. 128-500 GeV)

  18. CMS SM Higgs Combination • Some excess around ~124 GeV

  19. 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 !

  20. Thankyou! большое спасибо!

  21. Backup

  22. 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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