Higgs to tt at CDF

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 MA120 GeV/c2, tanb30
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)
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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, Z Yoshio
Ishizawas talk - with a 3rd, 4th b-quark.
Avto Kharchilavas
talk 2) Look for other higgs decays - tt
is promising (down by x10, but only
Weak bgs) - gg Sungwon Lees talk
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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
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The Trouble with t

• QCD jets! They can look like th
• Fight with energy, isolation.

Triggered th object - cluster-matched
track with pT gt 4.5 GeV. - no tracks w/ pT
gt 1.5 Gev in 10-300 iso. annulus.

• Electron th
• ? central electron (ET gt 8 GeV) th object
  (30nb at L3)
• Muon th
• ? central muon (pT gt 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.
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Reconstructing th
2 g clusters

• Tighten isolation.
• Reconstruct p0.
• - use EM calorimeter for g energy.
• - use ShowerMax for g position.
• Remove electron candidates.
• mtrksp0 lt 1.8
• Look for characteristic
• 1, 3 track enhancement.

1 g cluster p-
Signature of hadronic tau decay!
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Background Removal
Jets tend to be soft. Requiring scalar sum of
energy of objects in event gt 50 GeV further
reduces backgrounds.
PTt1 PTt2 ET gt 50 GeV
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W associated backgrounds

• Define zvector Bisector of visible t dirs
• Pvisz project VISIBLE ts onto z
• Pz Pvisz ET . z

Wjet events ? ET more back-to-back with jets.
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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.
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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
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Predicted vs. Observed Events
CDF Run 2 Preliminary (195 pb-1)
source teth tmth combined
Z/g ? tt 132.317.1 104.113.3 236.429.5
Z/g ? ee, mm 1.80.2 4.90.4 6.70.6
VV, tt 0.70.1 0.80.1 1.50.1
Jet ? t fakes 12.03.6 7.02.1 19.05.7
Total predicted BG 146.817.5 116.813.5 263.630.1
Observed 133 103 236
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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 tanb30
used as acceptance model.
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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
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Fit Results
From pseudoexperiments
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Fit Results
Very conservative treatment of energy scale
shift causes poor limit at low mass. ? will get
better.
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Limit Table
Need NLO calculation of higgs production to get
exclusion in M, tanb plane.
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Whats Next?

• Have gt 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.
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Conclusion

• Direct Search for A ? tt performed at CDF
• Didnt find evidence of higgs, but
• achieved excellent acceptance
• lower than expected jet ? t fake rates
• CDF expects 4 fb-1 of data by end of Run 2
• if MSSM higgs exists (at higher tanb)
• we will see it!