1 / 22

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:

aliza
Download Presentation

ITEP Winter School – February 2012 Moscow

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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.

More Related