1. Higgs Searches at LEP2 E. Kneringer University of Innsbruck / Austria Collaboration LAKE LOUISE WINTER INSTITUTE Electroweak Physics 14 - 20 February 1999

2. E. KNERINGERLLWI - 19992 Motivation indirect searches results from direct searches with Outline  The Standard Model Higgs Boson  SUSY Higgses The Neutral Higgs Bosons of the MSSM Charged Higgses in General Two Doublet Models Invisible Higgs LEP EWWG summer ‘98

3. E. KNERINGERLLWI - 19993 The Standard Model Higgs Boson Situation at LEP2 Production and decay

4. E. KNERINGERLLWI - 19994 Search in Four Characteristic Event Topologies missing energy 4 jets general requirements:  compatibility with m Z  b-jets general requirements:  compatibility with m Z  b-jets Z 2 isolated high energetic leptons l = e,  Z  candidates

5. E. KNERINGERLLWI - 19995 Background Processes  tools to distinguish signal from background processes tagging of b-quark jets lepton identification ( e,  ) kinematic mass fits

6. E. KNERINGERLLWI - 19996 Analyses  extensively using Monte Carlo simulations for neural net training for setting cuts  optimizing the analyses for the individual channels to get the best combined analysis highest efficiency with lowest background best Higgs mass exclusion limit if there is no hint for a signal mHmH entries 38.0 42total 11.3  ZZ background subtraction at 189 GeV 189 GeV data

7. E. KNERINGERLLWI - 19997 Results for the SM Higgs  all data  observed limit: m H > 90.4 GeV/c 2 at 95 % C.L.* ) from gedanken experiments:  expected limit: m H > 93.4 GeV/c 2  bad luck  other LEP experiments have typically m H > 94 GeV/c 2 (expected and observed)  current best limit from L3: m H > 95.5 GeV/c 2 already above Z mass! *) C.L.: frequentist; P (  signal >  data ) > 95 % ALEPH preliminary

8. E. KNERINGERLLWI - 19998 Neutral Higgs Bosons of the MSSM  Reminder 2 parameters to parameterize model at tree-level: m h, tan  (m A,  ) Mass relations at tree-level m h < m Z |cos 2  |(+ radiative corrections !!!) m h < m A < m H m H > m Z (m H > max{m Z,m A }) m H± > m W (m H± 2 = m W 2 + m A 2 ) m A large  decoupling of heavy Higgses  2 complementary production processes: m h   s  m Z hZ Higgs strahlung  sin 2 (  ) m h,m A   s/2 hA associated pair-production  cos 2 (  ) 2 final states

9. E. KNERINGERLLWI - 19999 Analyses  candidate: 4 b-jet event m A + m h entries 189 GeV data

10. E. KNERINGERLLWI - 199910 Results for the MSSM Higgses  all ALEPH data combined  hA selection at large tan  ( eq. cos 2 (  ) ~ 1 ): m A > 82.2 GeV/c 2 m h > 82.2 GeV/c 2 at 95% C.L.  lucky  reinterpretation of hZ + hA searches at smaller values of cos 2 (  )... expected and observed C.L. for equal h and A masses and cos 2 (  ) =1 130 - 189 GeV data

11. E. KNERINGERLLWI - 199911 sin 2 (  ) - m h plane 130 - 183 GeV data hA hZ

12. E. KNERINGERLLWI - 199912 m h - tan  plane  results can also be expressed in the m h - tan  plane  for the benchmark sets of MSSM parameters (m top, M SUSY,...)  and for two extreme configurations of stop mixing (controlled by A t,  ) no mixing maximal mixing theoretically excluded theoretically excluded 130 - 183 GeV data

13. E. KNERINGERLLWI - 199913 Charged Higgs  search for pair-produced H + H   in the framework of general two-doublet models m W = m Z cos  W at tree level, i.e.  = 1 absence of flavor changing neutral currents  decays into heaviest energetically accessible fermion pairs  three analyses for the three channels leptonic   hadroniccs sc mixed  cs  cross section of the same size at LEP2 energies (for the mass limits reachable) m H+ = 59 GeV/c 2

14. E. KNERINGERLLWI - 199914       final state  final state topology: two acoplanar taus missing energy carried away by neutrinos (at least four neutrinos!) charged Higgs

15. E. KNERINGERLLWI - 199915 cs    final state  final state topology: two hadronic jets thin  -jet + missing energy  two complementary approaches: global analysis acoplanarity missing momentum thrust topological analysis  -jet reconstruction sensitivity well below m W charged Higgs reconstructed jet-jet mass

16. E. KNERINGERLLWI - 199916 Performance of analyses 183 GeV data Expected number of background events from SM processes as a function of m H±, compared to the number of events observed (mixed + four jet channel: sliding mass window): 60 events found by the three selections 57.9 events expected from SM processes consistency + no accumulation in the cssc mass distribution  combine analyses  put limits charged Higgs

17. E. KNERINGERLLWI - 199917 Results  only up to 183 GeV data  NO evidence for a signal  mass limits as a function of  (  )  Limit at 95% C.L. on the mass of charged Higgs bosons as a function of  (  ); the hatched region is excluded by the combination of all three channels.  m H± > 59 GeV/c 2 indep. of  (  ) [95% C.L.] charged Higgs

18. E. KNERINGERLLWI - 199918  (  ) for type II doublet models prediction 0.97 2 0.04 2

19. E. KNERINGERLLWI - 199919 Invisible Higgs decays Acoplanar leptons with mass ~ M Z Acoplanar jets with mass ~ M Z

20. E. KNERINGERLLWI - 199920 Summary  SM Higgs with 250 pb -1 collected with ALEPH at  s = 161, 172, 183 and 189 GeV 95% C.L. lower limit is m H > 90.4 GeV/c 2 very preliminary, very conservative  MSSM Higgs also lower energy data at 130 GeV included m h, m A > 82.2 GeV/c 2 for large tan   Charged Higgs data at 189 GeV not yet included m H+ > 59 GeV/c 2 independent of  (  )  Invisible Higgs h  neutralinos & GUT mass relation (M 1 ~ 0.5 M 2 ) relaxed  2 for  2 = 1: m h > 88 GeV/c 2 @ 95% C.L.

21. E. KNERINGERLLWI - 199921 Confidence Level  define estimator  as a measure for the experiment in question to contain signal events: n = # of observed events s = expected # of signal events P i n = prob. that i signal events are less signal like than observed  small  background like  large  signal like  define observed confidence level c where  data is the estimator of the actual experiment  s is the p.d.f. of the estimator for signal events  expected confidence level average of c where the # of observed events is distributed according to the expected background (i.e. in the absence of signal)  no event observed   = e  s,  data =  min, c = e  s

22. E. KNERINGERLLWI - 199922 interpretation of C.L.  m H > 90.4 GeV/c 2 at 95% C.L. means: given the hypothesis that the Higgs mass is and < 90.4 GeV/c 2 be  data the estimator as observed in the data and  signal the estimator for a gedanken experiment where the above hypothesis is true (i.e. distributed according to  s ) then P (  signal >  data ) > 95 % the quoted limit is the largest mass hypothesis for which this is true  it does NOT mean: P(m H > 90.4) > 95% or P(m H < 90.4) < 5%