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Higgs to tt at CDF

Higgs to tt at CDF. Amit Lath Rutgers University Tev4LHC Workshop, Sep 17 2004. MSSM Higgs Production. MSSM Higgs is produced copiously! (at reasonably large tan b ) Two main channels: bb  A NLO from Maltoni, Sullivan, Willenbrock NNLO from Harlander, Kilgore - gg  A

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Higgs to tt at CDF

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  1. Higgs to tt at CDF Amit Lath Rutgers University Tev4LHC Workshop, Sep 17 2004

  2. MSSM Higgs Production • MSSM Higgs • is produced copiously! • (at reasonably large tanb) • Two main channels: • bb  A • NLO from Maltoni, Sullivan, Willenbrock • NNLO from Harlander, Kilgore • -gg  A • HIGLU (NLO) program from M. Spira Do the math: For MA=120 GeV/c2, tanb=30: s(bbA) = (8.9e-3)(30)2 = 8.0 pb s(ggA) = 5.2 pb s = 13.2 pb ~2500 A produced with 200 pb-1 ! (x2 more if you consider h as well)

  3. Higgs Decays Higgs decays primarily to bb (~ 90%) - HUGE background from strongly produced bb. So what can we do? 1) Look for associated production - associated with W, ZYoshio Ishizawa’stalk - with a 3rd, 4th b-quark. Avto Kharchilava’s talk 2) Look for other higgs decays: - tt is promising (down by x10, but only Weak bgs) - gg Sungwon Lee’s talk

  4. How to get tt 1 or 3 tracks • Trigger on isolated “pencil jets” hadronic t decays (th) • Ask for an e, m, [or 2nd (th) ] in event. 1st time at hadron collider! (to be added to higgs search) t decays t enent, t mnμnt : leptonic decays(~36%). t  pnt, t  pp0nt, t  pppnt, … : hadronic decays(~ 64%). e or m

  5. The Trouble with t • QCD jets! They can look liketh • Fight with: energy, isolation. Triggered th object: -cluster-matched track with pT > 4.5 GeV. -no tracks w/ pT > 1.5 Gev in 10-300 iso. annulus. • Electron + th •  central electron (ET > 8 GeV) + th object (~30nb at L3) • Muon + th •  central muon (pT > 8 GeV) + th object (~30nb at L3) • -th +th •  two th objects, with extra L2 isolation (~13nb at L3) LHC take note! constant trigger rate battles! Not yet included in MSSM higgs search.

  6. Reconstructing th 2 g clusters • Tighten isolation. • Reconstruct p0. -use EM calorimeter for g energy. - use ShowerMax for g position. • Remove electron candidates. • mtrks+p0 < 1.8 • Look for characteristic 1, 3 track enhancement. 1 g cluster + p+- Signature of hadronic tau decay!

  7. Background Removal Jets tend to be soft. Requiring scalar sum of energyof objects in event > 50 GeV further reduces backgrounds. |PTt1| + |PTt2| + |ET| > 50 GeV

  8. W associated backgrounds • Define:z–vector: Bisector of visiblet dirs • Pvisz = project VISIBLE t’s onto z • Pz=Pvisz + ET.z W+jet events  ET more back-to-back with jets.

  9. Hadronic t signature Nice 1, 3 track enhancement. Jet  t fakes under good control! Only 1,3 track events. Only events with th , e/m opp. Charge.

  10. Hadronic t distributions Good agreement in ET Low levels of jett fakes (~0.1% at higher pT) Fakes well understood. Long-standing discrepancies between jet samples resolved. (Run 1  fakes ~ 1%) HT above cut of 50 GeV

  11. Predicted vs. Observed Events CDF Run 2 Preliminary (195 pb-1)

  12. MSSM Higgs Signal Define mvis = m(p(t1) + p(t2) + p(ET)) Where p(ET) = (EX,EY,0,ET) Pseudo scalar MSSM Higgs generated with tanb=30 used as acceptance model.

  13. Z/Higgs Separation Linear Semilog Normalized to 195 pb-1 No Higgs component Lum, Z-xscn, bg, all fixed w/in errors. Binned likelihood fit shown with mA = 130 GeV component in yellow

  14. Fit Results From pseudoexperiments

  15. Fit Results Very conservative treatment of energy scale shift causes poor limit at low mass.  will get better.

  16. Limit Table Need NLO calculation of higgs production to get exclusion in M, tanb plane.

  17. What’s Next? • Have > x2 luminosity on tape already. • Understand energy scale better, limits (esp. at lower mass) will get better. • Will add th th (ditau),te tm channels • Ditau adds stats similar to te th channel. • te tm small, but very clean. • Also looking at: • Additional jet with b-tag. • Extending acceptance into plug region. • Neural nets for reconstruction. First time at hadronic collider.

  18. Conclusion • Direct Search for A ttperformed at CDF • Didn’t find evidence of higgs, but… • achieved excellent acceptance • lower than expected jet tfake rates • CDF expects ~ 4 fb-1 of data by end of Run 2 • if MSSM higgs exists (at higher tanb) we will see it!

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