H. Jürgen Schreiber, ECFA/DESY Prague, Nov 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
H. Jürgen Schreiber, ECFA/DESY Prague, Nov 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
H. Jürgen Schreiber, ECFA/DESY Prague, Nov Typically, we expect ~ 100 H Z signal events and ~ 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
H. Jürgen Schreiber, ECFA/DESY Prague, Nov 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 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: 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
H. Jürgen Schreiber, ECFA/DESY Prague, Nov 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 ( 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 HH H 6
H. Jürgen Schreiber, ECFA/DESY Prague, Nov 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
H. Jürgen Schreiber, ECFA/DESY Prague, Nov 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
H. Jürgen Schreiber, ECFA/DESY Prague, Nov 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
H. Jürgen Schreiber, ECFA/DESY Prague, Nov 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
H. Jürgen Schreiber, ECFA/DESY Prague, Nov
H. Jürgen Schreiber, ECFA/DESY Prague, Nov
H. Jürgen Schreiber, ECFA/DESY Prague, Nov
H. Jürgen Schreiber, ECFA/DESY Prague, Nov