Moriond QCD 2001Enrico Piotto EP division CERN SM Higgs Search at LEP in Channels other than 4 Jets Enrico Piotto EP Division, CERN SM Higgs Search at LEP in Channels other than 4 Jets Enrico Piotto EP Division, CERN e + e - --> HZ-->bb, e + e - --> W - W + e e -->H v e v e -->bb e e e + e - --> HZ-->bb e + e - e + e - --> HZ-->bb µ + µ - e + e - --> HZ-->qq  +  -

Moriond QCD 2001Enrico Piotto EP division CERN SM Higgs branching ratios For m h =115 Gev/c 2 : BR(H  bb)  78 % BR(H  )  7.5 % BR(H  gg)  7% BR(H  WW)  5 %

Moriond QCD 2001Enrico Piotto EP division CERN LEP 4 jets : 56% 2 Jets & missing energy : 16% 2 jets & 2 leptons: 5% z  qq,  h ,bb qq  : 8% Search potential: the probability to confirm a signal if it is true.

Moriond QCD 2001Enrico Piotto EP division CERN Backgrounds For m h =115 Gev/c 2, assuming 100% efficiency, 3.3 events are expected in a LEP experiment from 2000 data taking and using the final states other than 4 jets. Several hundred thousands of background events are expected. The strategy: sequential cuts to remove the bulk of the background; likelihood ratio or neural network to further discriminate the signal from the background.

Moriond QCD 2001Enrico Piotto EP division CERN B-tag: the fundamental tool B hadrons produced at LEP will fly for few mm and their decays products will have large p T wrt jet and large impact parameters with respect to light quark hadrons. Combining different variables with Neural Network or Likelihood a probability that a jet comes from a b quark is derived. Z-->bb Z-->cc Z-->uds OPAL

Moriond QCD 2001Enrico Piotto EP division CERN Missing energy channel v v b b Main background near threshold: b quark pair 2 photons ISR 2 ISR escape undetected at low angle: the qq  events will have 2 nearly coplanar jets with low p T. DELPHI Higgs m=115 qqn(  ) 4 fermions

Moriond QCD 2001Enrico Piotto EP division CERN H kinamatic Higgs m h =115 Double symmetric radiative events are nearly collinear. Higgs events may be acollinear even at the kinematic limit. The Higgs boost may come from: widht of Z 0 WW fusion

Moriond QCD 2001Enrico Piotto EP division CERN Mass reconstruction DELPHI In the missing energy channel the energy flow and the jet reconstruction are critical aspects of the analysis. A mass resolution of  3 GeV/c 2 can be achieved assuming a Z boson recoiling mass. But: for an event at rest, the Z recoil constraint artificially peaks the visible mass at  s-m z

Moriond QCD 2001Enrico Piotto EP division CERN Most significant H candidates Selecting LEP candidates with (s/b) 115 >0.3: 3rd most significant LEP candidate Observed: 14 Expected (s+b): 14 Signal: 7 10th most significant LEP candidate 14th most significant LEP candidate

Moriond QCD 2001Enrico Piotto EP division CERN L3 H cme GeV Two b-tagged jets M h = GeV/c 2 missing mass = 94 GeV/c 2 M=5.5 GeV 7.3 mm from PV 1.4 mm from PV

Moriond QCD 2001Enrico Piotto EP division CERN Leptonic channel e -,  e -,  b b Low background channel. Neural Network are used to identified . Good mass resolution also without constrained fit. Danger: ISR photons, or photons from electron radiation, can artificially increase the di-jet mass if associated with one jet. OPAL

Moriond QCD 2001Enrico Piotto EP division CERN Example    If the  is associated to the muon -> a perfect ZZ If the  is included in the jet: a very high di-jet mass -> good high mass Higgs candidate !

Moriond QCD 2001Enrico Piotto EP division CERN Leptonic channel b b e -,  S/b Hee candidate: it is the 5th most significant LEP candidates (ALEPH). M h =118GeV/c 2, M rec =78.8GeV/c 2 b-tag=1.4 H  candidate: it is the 8th most significant LEP candidates (ALEPH). M h =115GeV/c 2

Moriond QCD 2001Enrico Piotto EP division CERN ALEPH Hee cme 205 GeV

Moriond QCD 2001Enrico Piotto EP division CERN ALEPH H  cme 208 GeV

Moriond QCD 2001Enrico Piotto EP division CERN S/b of candidates Selecting candidates with (s/b) 115 >0.3: observed: 14 expected (s+b):14 Hqq: 9 H : 3 Hl + l - : 1 H  : 1 (70%)(20%)(7%)(3%) Theoreticalbranchings H H He + e - H 

Moriond QCD 2001Enrico Piotto EP division CERN 1-CL b

Moriond QCD 2001Enrico Piotto EP division CERN Conclusions  bbvv, bb e + e -,bb µ + µ -, qq  +  - together have the same potential discovery as the four jets channel;  a coherent view compatible with the expected branching ratios emerges from LEP leptonic and hadronic candidates; BUT  letponic candidates are consistent with both the background and  signal+background hypotheses.  leptonic channels are affected by irreducible background;  all the data presented here are based on the papers published soon after the end of data-taking;  all LEP collaborations are reviewing their analysis taking into account final calibrations and data processing and more MC;  the final LEP word on higgs will be hopefully for summer 2001.

Moriond QCD 2001Enrico Piotto EP division CERN Backup

Moriond QCD 2001Enrico Piotto EP division CERN Backup: qq  cross section

Moriond QCD 2001Enrico Piotto EP division CERN Backup

Moriond QCD 2001Enrico Piotto EP division CERN Backup Higgsstrahlung WW-fusion Total M h =115 Gev E cm =206Gev