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Future e+e- Collider Sensitivity to the HZ Coupling M. Dubinin, H.J. Schreiber and A. Vologdin Standard Model-like Higgs couplings to fermions studied W, Z boson and in detail trilinear Higgs self-coupling 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 H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 1 We explore the potential of linear e+e- collider HZ coupling through rare decay H Z Reaction (2-to-4 particle reaction): e e e e Z H signal events (H Z) are imbedded account for complete irreducible background Assuming MH = 120, 140, 160 GeV at s 500 GeV and Ldt = 1 ab -1 Event generation: CompHEP PYTHIA (for some reducible background reactions) Higgs boson width and H Z branching fractions imported from HDECAY H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 2 Typically, we expect ~ 100 H Z signal events and ~ 50.000 irreducible background events principal cuts (at generation level) E 10 GeV 5o 175o 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, Z qq signal event topology: 2 hadronic jets orginating from the Z boson together with an energetic photon and large missing energy H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 3 Possible reducible background ee WW ( ) eW ( ) WWZ ( ) millions of events; small part might mimic ZZZ ( ) the signal e e Z ( ) tt ( ) tt ( ), WWZ ( ), ZZZ ( ) could be effectively removed by selection procedures applied some surviving contributions from e e WW ( ) e W ( ) e e ( * / Z ) ( ) which are included in the final M(Z) and in BF(HZ) / BF (H Z) H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 4 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: - Evis < 240 GeV - ET < 210 GeV - # of charged particles > 3 - missing mass: 180 - 400 GeV ensures clean elimination of e e HZ ( Z ) ( ) jet (quality) cuts: • Ejet > 8 GeV • |cos jet| < 0.95 • (between 2 jets) > 20o • # of particles/jet > 3 ( M qq ~ M Z ) H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 5 Event selection using consecutive cuts e+ H Z H e- 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 ( e e e e H ) B( H Z ) 52 % (23 %, 41 %) B( H Z ) for MH = 120 (140, 160) GeV H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 6 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) Results very similar; DURHAM (ycut = 0.004) PUCLUS somewhat less reducible background Resulting M(Z)|PUCLUS • Higgs signal clearly visible • B( H Z ) 61 % (28 %, 52 %) B( H Z ) for MH = 120 (140, 160) GeV H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 7 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 • Higgs bosons clearly established • ‚Higgs-likeness‘ method best signal-to-background ratios (due to best reducible background rejection) • BF ( H Z ) 44 % (23 %, 39 %) BF ( H Z ) for MH = 120 (140, 160) GeV Significant improvement by longitudinally polarized beams: e.g. e- polarisation: - 80 % e+ polarisation: + 60 % (ambitious) BF ( H Z ) 26 % (15 %, 23 %) BF ( H Z ) ( H Z ) ( H Z ) g HZ g HZ 27 % (16 %, 24 %) if tot (H) has an error of 5 % 14 % (8 %, 12 %) H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 9 •Overlap of hadrons to H signal events after passing selection procedures - no loss or distortions • Inclusion of leptonic Z decays, Z ll , or Z Z fusion events, neglected so far only slight improvement on BF ( H Z ) BF ( H Z ) • Due to our present knowledge, Higgs-strahlung e e HZ ( Z ) Z including huge reducible and irreducible backgrounds at e.g. s 300 GeV less precision on BF (H Z ) • Completely open whether full luminosity of 1 ab-1 at s = 500 GeV with desired beam plarisation is delivered to this measurement lower bounds on g HZy g HZy H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 10 H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 11 H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 12 H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 13 H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 14