Higgs to tt at CDF
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Transcript of Higgs to tt at CDF
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Higgs to Higgs to at CDF at CDF
Amit Lath
Rutgers University
Tev4LHC Workshop, Sep 17 2004
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MSSM Higgs Production MSSM Higgs Production
•MSSM Higgs is produced copiously! (at reasonably large tan)
•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, tan=30: (bbA) = (8.9e-3)(30)2 = 8.0 pb (ggA) = 5.2 pb
= 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
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 Ishizawa’s talk
- with a 3rd, 4th b-quark. Avto Kharchilava’s talk
2) Look for other higgs decays: - is promising (down by x10, but only Weak bgs) - Sungwon Lee’s talk
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How to get How to get • Trigger on isolated “pencil jets”
hadronic decays (h) • Ask for an e, , [or 2nd (h) ] in
event.
1 or
3 tr
acks
e or
decays ee, : leptonic decays (~36%).
, , , … : hadronic decays (~ 64%).
1st time at hadron collider!
(to be added to higgs search)
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The Trouble withThe Trouble with• QCD jets! They can look like h • Fight with: energy, isolation.
Triggered h object:
- cluster-matched track with pT > 4.5 GeV. - no tracks w/ pT > 1.5 Gev in 10-300 iso. annulus.
-Electron + h
central electron (ET > 8 GeV) + h object (~30nb at L3)
-Muon + h
central muon (pT > 8 GeV) + h object (~30nb at L3)
-h + h
two h objects, with extra L2 isolation (~13nb at L3)
LH
C ta
ke n
ote!
con
stan
t trig
ger
rate
bat
tles!
Not yet included in MSSM higgs search.
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Reconstructing Reconstructing hh
• Tighten isolation.
• Reconstruct 0. - use EM calorimeter for energy.
- use ShowerMax for position.
• Remove electron candidates.
• mtrks+ < 1.8
• Look for characteristic
1, 3 track enhancement.
Signature of
hadronic tau decay!
2 clusters
1 cluster + +-
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Background RemovalBackground Removal
|PT1| + |PT
2| + |ET| > 50 GeV
Jets tend to be soft. Requiring scalar sum of energy of objectsin event > 50 GeV further reducesbackgrounds.
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W associated backgroundsW associated backgrounds
• Define: –vector: Bisector of visible dirs
• Pvisproject VISIBLE ’s onto
• PPvis
W+je
t eve
nts
E T m
ore
back-
to-b
ack
with je
ts.
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Hadronic Hadronic signature signature
Nice 1, 3 track enhancement.
Only 1,3 track events.Only events with h , e/ opp. Charge.
Jet fakes
under good control!
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Hadronic Hadronic distributions distributions
Low levels of jett fakes
(~0.1% at higher pT)
Good agreement in ET
HT above cut of 50 GeV
Fakes well understood.Long-standing discrepancies between jet samples resolved.(Run 1 fakes ~ 1%)
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Predicted vs. Observed EventsPredicted vs. Observed Events
source eh h combined
Z/* → 132.3±17.1 104.1±13.3 236.4±29.5
Z/* → ee, 1.8±0.2 4.9±0.4 6.7±0.6
VV, tt 0.7±0.1 0.8±0.1 1.5±0.1
Jet → fakes 12.0±3.6 7.0±2.1 19.0±5.7
Total predicted BG 146.8±17.5 116.8±13.5 263.6±30.1
Observed 133 103 236
CDF Run 2 Preliminary (195 pb-1)
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MSSM Higgs SignalMSSM Higgs Signal
Pseudo scalar MSSM Higgs generated
with tan=30 used as acceptance model.
Define mvis =
m(p(1) + p(2) + p(ET))
Where p(ET) = (EX,EY,0,ET)
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Z/Higgs SeparationZ/Higgs Separation
Binned likelihood fit shown with
mA = 130 GeV component in yellow
Normalized to 195 pb-1
No Higgs component
Lum, Z-xscn, bg, all fixed w/in errors.
Linear
Semilog
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Fit ResultsFit Results
From pseudoexperiments
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Fit ResultsFit ResultsVe
ry c
onse
rvat
ive
trea
tmen
t of
ener
gy s
cale
shi
ft
cau
ses
poor
lim
it
at lo
w m
ass.
will
get
bet
ter.
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Limit TableLimit Table
Nee
d NLO
cal
cula
tion
of h
iggs
pro
duct
ion
to
get
exc
lusion
in
M, t
anb
plan
e.
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What’s Next?What’s Next?
• Have > x2 luminosity on tape already.• Understand energy scale better, limits (esp. at lower
mass) will get better.• Will add h h (ditau), e channels
– Ditau adds stats similar to e h channel.– e m small, but very clean.
• Also looking at: – Additional jet with b-tag.– Extending acceptance into plug region.– Neural nets for reconstruction.
First
tim
e at
had
roni
c
col
lider
.
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ConclusionConclusion
• Direct Search for A performed at CDF
• Didn’t find evidence of higgs, but…– achieved excellent acceptance – lower than expected jet fake rates
• CDF expects ~ 4 fb-1 of data by end of Run 2– if MSSM higgs exists (at higher tan)
we will see it!