Lepton Photon Symposium LP01 Searches for New Particles Gail G. Hanson Indiana University

Lepton Photon Symposium LP July 2001Gail G. Hanson 2 OUTLINE Standard Model Higgs Search MSSM Higgs Search Non-SM Higgs Searches Searches for Supersymmetry Single Top Quark Production Searches for Leptoquarks Searches for Excited Fermions Technicolor Searches

Lepton Photon Symposium LP July 2001Gail G. Hanson 3 STANDARD MODEL HIGGS BOSON November 3, 2000, LEP Experiments Committee (LEPC) presentation: 2.9 s.d. incompatibility with background (1 - CL b ) =

Lepton Photon Symposium LP July 2001Gail G. Hanson 4 SM HIGGS SEARCH CHANNELS Production from Higgsstrahlung e + e   H 0 Z 0 : “Four-Jet Channel:” e + e   H 0 Z 0  bbqq “Missing Energy Channel:” e + e   H 0 Z 0  bb “Tau Channel:” e + e   H 0 Z 0     qq and qq     “Lepton Channel:” e + e   H 0 Z 0  bbe + e  and bb    

Lepton Photon Symposium LP July 2001Gail G. Hanson 5 HIGGS CANDIDATE?

Lepton Photon Symposium LP July 2001Gail G. Hanson 6 STATISTICAL PROCEDURE Likelihood ratio Q(m H ) = Each event is assigned a probability density s i of being a signal at Higgs mass m H and a probability b i of being background. Each event is then assigned a weight w i = (s i + b i )/ b i The likelihood of the sample L is the product of the weights. The logarithm is taken, and then the method is log-likelihood ratio. Two hypotheses: Background only (CL b ) Signal + background (CL s = CL s+b /CL b )

Lepton Photon Symposium LP July 2001Gail G. Hanson 7 EVENT WEIGHTS AT 115 GeV Exp.Channel Rec. m H (GeV) Nov. 3 s/bCurrent s/b 1ALEPH4-jet ALEPH4-jet ALEPH4-jet L3E-miss OPAL*4-jet DELPHI4-jet ALEPHLept ALEPHTau ALEPH4-jet OPAL4-jet

Lepton Photon Symposium LP July 2001Gail G. Hanson 8 CURRENT COMBINED RESULTS All four experiments published in L3 has also published final analysis. New combination: Maximum likelihood ratio at m H = GeV. Probability of background fluctuation 2.1 s.d.

Lepton Photon Symposium LP July 2001Gail G. Hanson CL b = 3.4% CL s+b = 44% m H > GeV, 95% C.L. (115.4 GeV expected)

Lepton Photon Symposium LP July 2001Gail G. Hanson 10 RECONSTRUCTED HIGGS MASS Purity of selection: LooseMediumTight

Lepton Photon Symposium LP July 2001Gail G. Hanson 11 MSSM HIGGS

Lepton Photon Symposium LP July 2001Gail G. Hanson 12 SUPERSYMMETRY PARAMETERS

Lepton Photon Symposium LP July 2001Gail G. Hanson 13 MSSM HIGGS SEARCHES Combined LEP Experiments: m h 0 > 91.0 GeV, m A 0 > 91.9 GeV, 95% C.L. 0.5 < tan  < 2.4 excluded m h -max, m t <174.3GeV

Lepton Photon Symposium LP July 2001Gail G. Hanson 14 2HDM(II):  = Higgs mixing angle 1  m h 0  58 GeV and 10  m A 0  65 GeV excluded at 95% C.L. for all , tan  m h > GeV ADLO comb. Flavour Independent h   m h > GeV ADLO comb. HIGGS SEARCHES IN EXTENDED MODELS

Lepton Photon Symposium LP July 2001Gail G. Hanson 15 SEARCHES FOR SUPERSYMMETRIC PARTICLES Gravity mediated supersymmetry breaking: R-parity: R-parity conservation: SUSY particles are produced in pairs The lightest SUSY particle (LSP) is stable R-parity violating supersymmetry decays Gauge mediated supersymmetry breaking:

Lepton Photon Symposium LP July 2001Gail G. Hanson 16 SUSY MAP no

Lepton Photon Symposium LP July 2001Gail G. Hanson 17 SEARCHES FOR SLEPTONS

Lepton Photon Symposium LP July 2001Gail G. Hanson 18 STOP AND SBOTTOM Limit for  M > 10 GeV  0o0o 97 GeV 56 o 95 GeV Limit for  M > 10 GeV  0o0o 100 GeV 68 o 92 GeV

Lepton Photon Symposium LP July 2001Gail G. Hanson 19 SQUARKS AND GLUINOS

Lepton Photon Symposium LP July 2001Gail G. Hanson 20 CHARGINOS   m   > GeV for m > 300 GeV

Lepton Photon Symposium LP July 2001Gail G. Hanson 21 LIMIT ON THE LSP MASS ~ M  0 > 45.6 GeV M  0 > 54 GeV M  0 > 60 GeV

Lepton Photon Symposium LP July 2001Gail G. Hanson 22 R-PARITY VIOLATION ±

Lepton Photon Symposium LP July 2001Gail G. Hanson 23 SINGLE TOP QUARK PRODUCTION H1 events with isolated leptons with large missing p T Flavor Changing Neutral Currents (FCNC) CDF searched for ISR and QCD corrections for LEP combination. FCNC suppressed at tree level in SM (GIM mechanism). Small contributions at one- loop level. In e + e   SM ~ 10  9 fb. Extended models, e.g. SUSY and multi-Higgs, can allow FCNC at tree level.

Lepton Photon Symposium LP July 2001Gail G. Hanson 24 EVENTS WITH ISOLATED LEPTONS AND LARGE MISSING p T Primary Standard Model process is single W production H1 electron muon obs. exp.obs. exp. P T X <25 GeV P T X >25 GeV ZEUS electron muon obs. exp.obs. exp. P T X >25 GeV

Lepton Photon Symposium LP July 2001Gail G. Hanson 25 LEPTOQUARKS Leptoquarks carry baryon and lepton number. Scalar or vector. F = L + 3B is preserved

Lepton Photon Symposium LP July 2001Gail G. Hanson 26 EXCITED FERMIONS

Lepton Photon Symposium LP July 2001Gail G. Hanson 27 TECHNICOLOR m  T > 89.1 (79.8) GeV for N D = 9 (2) m  T > 77 (62) GeV for N D = 9 (2)

Lepton Photon Symposium LP July 2001Gail G. Hanson 28 SUMMARY AND CONCLUSIONS Is there a light Higgs boson? Will have to wait until ~ 2007 to find out m H > GeV, 95% C.L., from direct search. “Hint” of 2 s.d. signal at m H = GeV Is there another mechanism for electroweak symmetry breaking? Will we find supersymmetry? Technicolor? Still only questions!…..