1 / 12

Flavour independent neutral Higgs boson searches at LEP

Flavour independent neutral Higgs boson searches at LEP. EPS conference 2005. Ivo van Vulpen NIKHEF. On behalf of the LEP collaborations. LEP and the LEP data-set.

terri
Download Presentation

Flavour independent neutral Higgs boson searches at LEP

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. Flavour independent neutral Higgs boson searches at LEP EPS conference 2005 Ivo van Vulpen NIKHEF On behalf of the LEP collaborations

  2. LEP and the LEP data-set The LEP collider: e+e- collider at CERN operated 1989-2000 (4 experiments: ALEPH, DELPHI, L3, OPAL)s  mZ (LEP1)ands = 130-209 GeV (LEP2) Most results (95% CL limits) based on LEP2: Int. Lum.  2.6 fb-1 LEP combined results on Higgs searches: http://lephiggs.web.cern.ch/LEPHIGGS/www/Welcome.html

  3. SM Higgs boson Production: shz(mh,√s) Decay: Gh(mh) In the SM we know everything about the Higgs boson Higgs-strahlung bb (>80%) h (except its mass) qq (70%) nn (20%)  l+l- (10%) Weak boson fusion B-tagging udsc-jets b-jets 2 b-jets + a “Z”. Excluded SM mh: mh > 115.3 GeV (expected) mh > 114.4 GeV (observed)

  4. hbb decays suppressed (light quarks and gluons)No sensitivity in standard analyses Models:2HDM(I): One doubletfor all fermions 2HDM(II): One up-type doublet One down-type doublet Neutral Higgs boson production at LEP Simplest SM extension: 2 complex Higgs Doublets  5 Higgs bosons (3 neutral) Neutral Higgs boson production Higgs boson decay Depends on model parameters mainly hbb Higgs strahlung Associated production MSSM

  5. What ifa neutral Higgs boson is produced, but … does not couple (strongly) to b-quarks … decays into light quarks or gluon pairs … has a cross section X times smaller or larger than SM prediction In general:Test predictions of any (new) model against LEP data Experimentalist:Exclude neutral Higgs boson production, with (H  hadrons) over mH range YES NO Cancel

  6. Neutral Higgs boson production at LEP e+e-  hZ e+e-  hA SU(2) x U(1) Details Higgs sector Assumption:Gh small (w.r.t detector resolution) Flavour independent (hadronic) Higgs boson search: Topology based (no b-tag information) Consider Higgs boson decays into all quark pairs and gluons Worst case scenario  Exclude and

  7. hZ production Higgs-strahlung qq/gg (100%) h 3 final states qq (70%) nn (20%)  l+l- (10%) Weak boson fusion SM Backgrounds: qq(g), W+W- , ZZ Experimental issues:  qqnn/qql+l-: Z-like object + recoil mass • 4-jets: topology+ masses (3 pairings)  Gluon pairs versus light-quark pairs: higher selection efficiency worse di-jet mass resolution

  8. hZ production: single experiment Single channel (qqm+m-) only 3% of all decays,but very clean DELPHI (all channels)Topologies:qqqq, qqnn, qql+l-Mh range: 4 < Mh <115 GeV SM hZ cross section C2Z(hhadrons) Mqq (GeV) Mh (GeV)

  9. hZ production: LEP combined Flavour Independent LEP results on hZ production: Expected Observed(GeV/c2) (GeV/c2) Flav.Ind. 113.0 112.9 C2Z(hhadrons) SM 115.3 114.4 Even without b-tag information, still a strong limit Mh (GeV)

  10. h A hA production 4-jet event at LEP Associated production qq/gg (100%) qq/gg (100%) 4-jet final state Experimental issues:  Analyses depend on h and A masses Topology (small mh or mA: 4 jets  3 jets) SM Backgrounds: qq(g) ~ 8 pb W+W- ~ 8 pb ZZ ~ 0.5 pb OPAL: also consider hAA  Pairing ambiguities: 4 jets (3 pairings)  Gluon pairs versus light-quark pairs: higher selection efficiency worse di-jet mass resolution

  11. LEP Flavour Independent results on hA production Exclude hA(hadronic) cross-sections relative to SM: hAA taken into account(6 parton final state) DELPHIhAhadrons MA (GeV) MA (GeV) Mh (GeV) Mh (GeV) For C2 =1: mh+mA < 140 GeV Interpretation in 2HDM models (parameter scan): see talk by P. Akesson

  12. Conclusions Limits on hZ and hA production (h,Agluons/quarks)LEP combined results on hZ (No signal observed) Cross section exclusion as function of mh (mA) Important experimental LEP legacy: More model independent summary of LEP data Important test for (future) model builders … SUSY, 2-3-4-5HDM, CP (non-)conserving, etc. LHC cannot easily cover low mass regions (allows check for any LHC prediction)

More Related