1. H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 Future e + e - Collider Sensitivity to the HZ  Coupling M. Dubinin, H.J. Schreiber and A. Vologdin Standard Model-like Higgs couplings to studied in detail fermions W, Z boson and trilinear Higgs self-coupling - another important set of couplings induced by loops of heavy particles So far,Hgg in e + e - collisions and at LHC investigated H  either in e + e - interactions and at LHC investigated or  fusion process   H  X Hgg, H  and HZ  vertices 1

2. H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 We explore the potential of linear e + e - collider  HZ  coupling through rare decay H  Z  Reaction (2-to-4 particle reaction):  H signal events (H  Z  ) are imbedded  account for complete irreducible background Assuming M H = 120, 140, 160 GeV at 500 GeV and= 1 ab -1 Event generation: CompHEP PYTHIA (for some reducible background reactions) Higgs boson width and H  Z  branching fractions imported from HDECAY 2

3. H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 Typically, we expect ~ 100 H  Z  signal events and ~ 50.000 irreducible background events  principal cuts (at generation level) E   10 GeV 5 o     175 o 96 % Higgs events survive  ~ 50 % background discarded Even after these cuts small H event rate vs. huge irreducible background and background events have similar final state signatures as H  Z  events So far, 2 hadronic jets orginating from the Z boson together with an energetic photon and large missing energy  signal event topology: 3

4. H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 Possible reducible background millions of events; small part might mimic the signal could be effectively removed by selection procedures applied  some surviving contributions from which are included in the final M(Z  ) and in  BF(H  Z  ) / BF (H  Z  ) 4

5. H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 Large background and tiny signal event rates  different strateties for extracting signal events  consecutive cuts  jet finder(s)  „Higgs likeness“ Independent of the selection technique chosen  event (quality) cuts: - E vis < 240 GeV - E T < 210 GeV - # of charged particles > 3 - missing mass: 180 - 400 GeV ensures clean elimination of E jet > 8 GeV |cos  jet | < 0.95  (between 2 jets) > 20 o # of particles/jet > 3  jet (quality) cuts: 5

6. H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 Event selection using consecutive cuts Out of all photons E  > 20 GeV with E T > 15 GeV no further particle in a cone of half-angle 10 o if more than 1 photon, the one with largest energy is selected all remaining particles  2 jets M jj  M Z (84 - 105 GeV) Finally, M(Z  ) Higgs signals clearly established accounting for all Z decays and irreducible and reducible background (~ 17 % of the irreducible) and uncertainty of for M H = 120 (140, 160) GeV e+e+ e-e- Z HH H 6

7. H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 All particles reconstructed by SIMDET were passed through a jet cluster algorithm aim:isolate  from H  Z  ; one of the jets compatible with an isolated high-energy photon and all remaining jets should be compatible with Z Two jet finder: PUCLUS (PYTHIA) DURHAM (y cut = 0.004) Results very similar; PUCLUS somewhat less reducible background Resulting M(Z  ) |PUCLUS Higgs signal clearly visible for M H = 120 (140, 160) GeV Event selection using jet finders 7

8. H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 Probability P H is constructed giving a measure that an event is part of the signal P H : [0, 1 ] background events have preferably low P H signal events P H close to 1 Variables taken into account: E(  ), polar  cms (  ), polar  cms (Z)  -decay angels in H rest frame angles between ( , Z) |cms collinearity  (beam,  ) coplanarity  (beam, , Z) coplanarity  (beam, H,  ) transverse mass ( , missing system) transverse mass (H, missing system) FinallyP H > 0.98 Event selection by ‚Higgs-likeness‘ 8

9. H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 Higgs bosons clearly established ‚Higgs-likeness‘ method  best signal-to-background ratios (due to best reducible background rejection) for M H = 120 (140, 160) GeV Significant improvement by longitudinally polarized beams: e.g.e - polarisation:- 80 % e + polarisation:+ 60 % (ambitious) if  tot (H) has an error of 5 % 9

10. H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 Overlap of   hadrons to H signal events after passing selection procedures - no loss or distortions including huge reducible and irreducible backgrounds at e.g.  less precision on BF (H  Z  ) Due to our present knowledge, Higgs-strahlung Inclusion of leptonic Z decays, Z  or Z Z fusion events, neglected so far  only slight Completely open whether full luminosity of 1 ab -1 at = 500 GeV with desired beam plarisation is delivered to this measurement improvement on  lower bounds on 10

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