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Progress with Higgs self-coupling

Progress with Higgs self-coupling. Tomáš Laštovička WG6 Meeting 2 /11/2011. Why Higgs self-coupling ?.  represents trilinear coupling and quartic coupling (which is extremely difficult to measure at LHC/ILC/CLIC) h ard for LHC if the Higgs is light

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Progress with Higgs self-coupling

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  1. Progress with Higgs self-coupling Tomáš Laštovička WG6 Meeting 2/11/2011

  2. Why Higgs self-coupling ? •  represents trilinear coupling • and quartic coupling (which is extremely difficult to measure at LHC/ILC/CLIC) • hard for LHC if the Higgs is light • hard for ILC 500GeV if the Higgs is not so light (130-140GeV) • direct determination of the Higgs potential • Previous studies for ILC 500GeV • Ranging from 20% to 160% Sometimes FSR forgotten or not full sim/rec H0 H0

  3. Samples with 60BX Overlay – Full Sim/Rec i.e. qqqq, qqqqνee, qqqqee are not included, nor is the HHee channel (ZZ fusion)

  4. Analysis chain • FastJetkT algorithm, R = 0.7 in exclusive mode requesting 4 jets • MarlinKinFit • The combinations of 2+2 jets with highest probability of having the same invariant mass selected. • Analysis chain essentially follows the chain for H→bB analysis • Neural net selection input variables added • pTmax, pTmin, MarlinKinFit probability, ymin, ymax • Uncertainty on HH cross section for 2ab–1: • 4Q background only: 13% (11% for HHH) • 2Q backgrounds added: 19% (16% for HHH) Does not look bad! We should do better though…

  5. Control Plots I • Where is the problem? • Higgs invariant mass reconstruction is poor, so is the jet flavour tag it’s the jets, they are poorly reconstructed

  6. Control Plots II • ymin and ymax should be the most useful quantities in order to separate 4Q events from 2Q events

  7. Control Plots III • Invariant mass plot after neural net selection • Working point = lowest statistical uncertainty Signal: ~200 of 1240 Background: ~1440 (2Q contribution is around 400)

  8. How do the jets look like (MC level) • Red and green are particles from different Hs, blue squares are secondary vertices and black points are directions of Hs (no RPs and jets overlaid) φ η

  9. mH with and without overlay Cheated (according to jet angle) According to MarlinKinFit without overlay with overlay

  10. Future Steps • Aid jet finding using secondary vertex information • done: i add (and then remove) particles corresponding to sec. vertices • Change jet treatment • Complete 4Q backgrounds • Increase statistics for some high weight 2Q backgrounds • Lower CLIC energies: 1.4TeV • Various SM Higgs masses: add 130GeV, 140GeV • In longer run: investigate ZZ fusion The HHHanalysis looks rather promising

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