Aug 21, 2006 The Next Steps ---- DOE Visit 2006

1

The Next Step

João Guimarães da CostaHarvard University

DOE Site VisitAug 21, 2006

Aug 21, 2006 The Next Steps ---- DOE Visit 2006 2

TopCross Section

HiggsSearch

Little Higgs

SUSY: Stop

Top samplekinematics

Top Rare Decays(FCNC)

tt+ET Search

(see Ingyin’s talk)

tt+X Search

Aug 21, 2006 The Next Steps ---- DOE Visit 2006 3

Improvements in Top Cross Section

• Reduce major systematic uncertainties– B-tagging efficiency (see Daniel’s talk)

– Background: W + heavy flavor

– Smaller improvements• Better treatment of mistags• Improvements in Non-W background

estimation

• Complementary B-tagging technique– Soft Electron Tagger (see John Paul’s talk)

Systematic limited

1012141618202224262830

100 1000 10000

Rel. Uncertainty

Luminosity (pb-1)R

elat

ive

Unc

erta

inty

(%

)

Projections

Aug 21, 2006 The Next Steps ---- DOE Visit 2006 4

B-tagging Efficiency Systematic(see Daniel’s talk)

Similar technique will be used at LHC

Aug 21, 2006 The Next Steps ---- DOE Visit 2006 5

Background: W + Heavy Flavor

W+bbX W+ccX W+cX

~35% of top background is W+HF

Current uncertainty: ~30%

Aug 21, 2006 The Next Steps ---- DOE Visit 2006 6

Cross Section using Jet Spectrum FitChecking the W + heavy flavor prediction in W+jets data

Fit Results

W + HF underestimated by 26%

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Background: W + Heavy Flavor

• Difficult to model– W+heavy flavor cross section has large uncertainties

• Depend on PDF, hadronization and fragmentations scales and mass of b,c quarks

– Heavy flavor fractions cancel most uncertainties

W+bbX W+ccX W+cX

Get these from Monte Carlo

Aug 21, 2006 The Next Steps ---- DOE Visit 2006 8

Background: W + Heavy Flavor

• Calibrate using generic jet data– In Run I, the MC underestimated the gluon splitting component

– Measure gluon splitting in data

Distance between dijets in , space

DoubleTagged

Gluon splittingFlavor excitation

Direct production

Aug 21, 2006 The Next Steps ---- DOE Visit 2006 9

W+HF Fractions Measurement• Run 2: Measurement was

done with low Et sample

Distance between dijets in , space

~ 27% uncertainty

Run II:

Gluon splitting

Work in Progress

Aug 21, 2006 The Next Steps ---- DOE Visit 2006 10

Top Cross Section with Soft Electron TagsPro

babili

ty t

o r

em

ain

()

c470 940 m

Most decays happen quickly

primary vertexsecondary vertex

impact parameter

~ 1 mm

Lifetime b-tagger

P.V.

e,μ

b

Soft Lepton Tagger

Advantages:• Recover b-tagging efficiency

• SecVtx: 48% efficient per b-jet• SLT: Extra ~10% per b-jet in top events

• Sensitive to different new physics

• Discrepancy on cross section would be indication of new physics• Interesting events seen in run I (superjets)

• Excess of SecVtx + SLT tagged events

(see John Paul’s talk)

~ 60% of top events

Aug 21, 2006 The Next Steps ---- DOE Visit 2006 11

tt + X: Is there new physics in the top sample?

Event Kinematics Analysis: Double Tag Sample

“The most likely place to find new physics is in the tt + X sample……”

Nima Arkani-Hamed

Top Sample: 408 single tag events 119 double tag events

Heavy objects decaying into tt+Xwould distort the kinematics distributions

Aug 21, 2006 The Next Steps ---- DOE Visit 2006 12

New Physics in the Large Top Sample?

Event Kinematics Analysis

Variables Single Tag

Double Tag

Event HT 0.95 0.78

Missing ET 1.0 0.80

Tagged Jet ET 0.59 0.26

Tagged Jet 0.79 0.16

Tagged Jet Mass 0.79 0.72

W transverse mass 0.71 0.89

Primary Vertex Z 0.90 0.69

KS Probabilities

Aug 21, 2006 The Next Steps ---- DOE Visit 2006 13

Heavy Tops: Generic Analysis

• Heavy Top “T”:– Little Higgs theories

– Fermionic particle

– Cross Section: ~1pb at 300 GeV

• Stop:– Small cross section

Heavy pair-produced particles decaying into tt + ET

Collaborating: • With our colleagues in the theory group• With Kevin and Verena on ATLAS

Massive particle: T• More central events SM top• Larger acceptance

Same final state as tt but different kinematics

Aug 21, 2006 The Next Steps ---- DOE Visit 2006 14

Heavy Top Search: Kinematics

• No killer variable– Large correlations

Advance analysis technique

Missing Energy (GeV) HT (GeV)

W Transverse Mass (GeV)

Aug 21, 2006 The Next Steps ---- DOE Visit 2006 15

Heavy Top Search: Neural Net Technique

Expected Limit

Work in progress:• Cover full range of possible masses• Investigate MC sample with TT production• Look at data

Takes care of correlations automatically

Aug 21, 2006 The Next Steps ---- DOE Visit 2006 16

Search for the SM Higgs

Measurement done in the W+Jets sample

Aug 21, 2006 The Next Steps ---- DOE Visit 2006 17

W+jets Background (W+HF)

• W + heavy flavor is major background for Higgs

W+HF

Aug 21, 2006 The Next Steps ---- DOE Visit 2006 18

Search for the SM Higgs

Aug 21, 2006 The Next Steps ---- DOE Visit 2006 19

Conclusions

• Top Physics– Transition from statistics limited analysis to systematic limited analysis

– Explore new large top sample searching for new physics• Soft electron tagger

• Kinematics studies

• Search for heavy particles decaying into tt

• Higgs Physics– Too early to see SM Higgs at CDF

– However, we can establish the ground work for a possible discovery

Lots of exciting things to do at CDF