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Visible and Invisible Higgs at 350 GeV

Visible and Invisible Higgs at 350 GeV. Mark Thomson University of Cambridge. =. +. Recoil Mass. So far - only performed (possible?) for Z → mm and Z → ee Statistical precision limited by BRs of 3.5 % and 3.5 % Extend to Z → qq ~ 60 % of Z decays

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Visible and Invisible Higgs at 350 GeV

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  1. Visible and Invisible Higgs at 350 GeV Mark Thomson University of Cambridge = +

  2. Recoil Mass • So far - only performed (possible?) for Z→mm andZ→ee • Statistical precision limited by BRs of 3.5 % and 3.5 % • Extend to Z→qq~ 60 % of Z decays • Strategy – identify Z→qqdecays and look at recoil mass • Can never be truly model independent: • unlike for Z→mm can’t cleanly separate H and Z decays Muons “always” obvious Z Z Here jet finding blurs separation between H and Z Z Different efficiencies for different Higgs decays Z Tokyo, November 12, 2013

  3. Analysis Strategy • Higgs can either decay invisibly orvisibly • ForZ→qqdecays either • two jets or two jets + at least two other particles • Analysis strategy: • Force events into 2-, 3-, 4-, 5- and 6- “jet” topologies (R=1.5) • For each topology: • find two jets (> 3 tracks) most consistent with Z mass • determine mass of system recoiling against the • candidate Z First divide into candidate invisible and visible Higgs decays Tokyo, November 12, 2013

  4. Number of Jets Invisible decays • Require event to have • two “jets” or > two “jets” • cut on y23: the kT value at which the event transitions from 2 jets to 3 jets H→qq • Also use y34, the kT value at • which the event transitions • from 3 jets to 4 jets

  5. Invisible Decays Z Tokyo, November 12, 2013

  6. Invisible Higgs Decays • Start from 2-jet sample: cuts remove ~all Higgs background • (except H→ZZ*→vvvvand a little H→tt) • Cut on di-jet mass (Z) and recoil mass (H) to select events Tokyo, November 12, 2013

  7. That’s about it ! Both jets well measured (hopefully) Looks like Z Z produced centrally Mostly ZZ → qqvv 100 % invis. H decay Z Tokyo, November 12, 2013

  8. Relative Likelihood • Use relative likelihood selection • Input variables • [..more to come] Calculate absolute likelihood for given event type • NOTE: 2D mass distribution includes main correlations • Absolute likelihoods calculated for two main event types: • Combined into relative likelihood

  9. Results • Preliminary results Backgrounds • Assuming no invisible decays (1 sigma error): • Fixed for LCWS – updates for paper (Kelvin)

  10. Visible Decays Tokyo, November 12, 2013

  11. Visible Higgs Decays • Have two jets from Z + Higgs decay products: • H→qq: 4 quarks = 4 “jets” • H→gg : 2 quarks + 2 photons = 4 “jets” • H→tt: 2 quarks + 2 taus = 4 “jets” • H→WW*→lvlv: 2 quarks + 2 leptons = 4 “jets” • H→WW*→qqlv: 4 quarks + 1 lepton = 5 “jets” • H→WW*→qqqq: 6 “jets” • H→ZZ*→vvvv: 2 “jets” (invisible analysis) • H→ZZ*→vvqq: 2 quarks = 4 “jets” • H→ZZ*→qqll: 4 quarks + 2 leptons = 6 “jets” • H→ZZ*→qqqq: 6 quarks = 6 “jets” 4, 5 or 6 ? Tokyo, November 12, 2013

  12. e.g. H→qq • Force event into 4-, 5-, 6- jet topologies • For each, choose Z di-jet combination closest to Z mass as 4-jets as 5-jets as 6-jets • Clear Z and H signature in 4-jet reconstruction… Tokyo, November 12, 2013

  13. e.g. H→tt • Force event into 4, 5, 6 jets • For each, choose Z di-jet combination closet to Z mass as 4-jets as 5-jets as 6-jets • In 4-jet reconstruction – similar “peaks” to H→qq Tokyo, November 12, 2013

  14. e.g. H→WW*→qqlv • Force event into 4, 5, 6 jets • For each, choose Z di-jet combination closet to Z mass As 5-jets as 4-jets as 6-jets • In 5-jet reconstruction – similar “peaks” to H→qq Tokyo, November 12, 2013

  15. A number of challenges • How many jets ? • Background suppression ? • Cuts/MVA ? • Nothing particularly hard here… Tokyo, November 12, 2013

  16. A number of challenges • How many jets ? • Background suppression ? • Cuts/MVA ? • Nothing particularly hard here… BUT HARD ? • Don’t want to bias RELATIVE • efficiencies for different Higgs decays • Otherwise – not truly MI Tokyo, November 12, 2013

  17. A simple plan First…. Kill the background with targeted cuts (as much as possible) • Main backgrounds are large cross section processes: • ZZ • WW • qq In each case reconstruct event assuming it is the background – then use invariant mass… Tokyo, November 12, 2013

  18. e.g. ZZ → qqqq • Assume event is ZZ → qqqq • Therefore: force into 4 jets • Choose jet pairing (12)(34), (13)(24) or (14)(23) • with single jet-pair mass closest to Z mass ZZ HZ Z KILL BOX Tokyo, November 12, 2013

  19. e.g. WW → qqqq • Assume event is WW → qqqq • Therefore: force into 4 jets • Choose jet pairing (12)(34), (13)(24) or (14)(23) • with single jet-pair mass closest to W mass WW HZ W KILL BOX Tokyo, November 12, 2013

  20. e.g. WW → qqlv • Assume event is WW → qqlv • Therefore: force into 3 jets • Choose jet pairing (12) (13) (23) closest to W mass, • only consider jets with >2 track WW HZ W KILL BOX Tokyo, November 12, 2013

  21. Now treat as ZH→qq X 4, 5, or 6 jets? • Rarely helps going from 5 → 6: • even if a 6-jet final state, provided reconstruct • two “hard” jets from Z decay OK 4or 5 jets? • Default is to treat as 4-jets • Reconstruct as 5-jets if: • -log10(y45) < 3.5 AND • 5-jet reconstruction gives “better” Z mass and “better” Higgs recoil mass • “better” = closer to true masses Tokyo, November 12, 2013

  22. Signal mqqvsmrec H→qq H→tt H→WW* H→ZZ* Tokyo, November 12, 2013

  23. Signal mqqvsmrec H→qq H→tt Very similar distributions for all decays H→WW* H→ZZ* Tokyo, November 12, 2013

  24. Signal vs Background BACKGROUNDS H→qq H→tt qq ZZ WW H→WW* H→ZZ* Tokyo, November 12, 2013

  25. That’s about it ! Both jets well measured (hopefully) Looks like Z Z produced centrally ZZ, WW and qq Z HZ Clear Higgs “peak” + this is just a projection, clearer in 2D Tokyo, November 12, 2013

  26. Relative Likelihood • Use relative likelihood selection • Input variables • [..more to come] Calculate absolute likelihood for given event type • NOTE: 2D mass distribution includes main correlations • Absolute likelihoods calculated for two main event types: • Combined into relative likelihood

  27. Indicative Results • For optimal likelihood cut • signal ~12000 events • background ~ 50000 events Efficiencies same to ~10 % !!! Tokyo, November 12, 2013

  28. Combined Sensitivity + • c.f. recoil mass analysis: • Combined • almost model • independent Tokyo, November 12, 2013

  29. Summary = + • Results essentially unchanged… • Will make nicer plots for LCWS: • note: qq weights large ~14 • improvements still possible (likely) Tokyo, November 12, 2013

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