Future e + e - Collider Sensitivity to the HZ  Coupling

1. Future e+e- Collider Sensitivity to the HZ Coupling M. Dubinin, H.J. Schreiber and A. Vologdin Standard Model-like Higgs couplings to fermions W, Z boson and trilinear Higgs self-coupling studied in detail Hgg, H and HZ vertices - 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 1 H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002

2. 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 MH = 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 H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002

3. Typically, we expect ~ 100 H  Z signal events and ~ 50.000 irreducible background events  principal cuts (at generation level) 96 % Higgs events survive E  10 GeV 5o   175o  ~ 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 H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002

4. 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 H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002

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

6. e+ H Z H e- Event selection using consecutive cuts • Out of all photons • E > 20 GeV with ET > 15 GeV • no further particle in a cone of half-angle 10o • if more than 1 photon, the one with largest energy is selected • all remaining particles •  2 jets • Mjj  MZ (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 MH = 120 (140, 160) GeV H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 6

7. Event selection using jet finders 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 (ycut = 0.004) Results very similar; PUCLUS somewhat less reducible background • Resulting M(Z)|PUCLUS • Higgs signal clearly visible for MH = 120 (140, 160) GeV H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 7

8. Event selection by ‚Higgs-likeness‘ Probability PH is constructed giving a measure that an event is part of the signal PH : [0, 1 ] background events have preferably low PH signal events PH 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) Finally PH > 0.98 H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 8

9. Higgs bosons clearly established • ‚Higgs-likeness‘ method •  best signal-to-background ratios • (due to best reducible background rejection) for MH = 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 % H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 9

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

11. H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 11

12. H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 12

13. H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 13

14. H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 14