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Top ID in tt → 6-Jet channel

Erik Devetak Edinburgh Collaboration Meeting(18-03-08)

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Talk outline

• Identifying the top in tt →6 jet channels

• 6-Jet Ycut optimization (Jet finder)

• True angular jet flavour and b tagging

• Looking at phase space at parton level (understand kinematics)

• B tag of tt

• W - Kinematic fit (using capability of MarlinReco)

• Top – Kinematic fitting

• Conclusion

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Flavour tagging with 6 Jets

First look if jets well separated at reconstruction level

Then look at b tag given only b jets at MC level

Performance not degraded in any noticeable way.

Still need to check degradation of parton (vertex) charge…

Caveat: Used SID fast MC – expecting worst performance with full MC but not dramatic decrease.

Closest jet to the MC b quark

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B - tagging identifying tt All inclusive decays. Use only events where 6 jets reconstructed Clear peak at 2 reconstructed b quarks. Good discriminator for top

Corruption from missing acceptance cuts and failure of b reconstruction reason of peak at 1

Useful to take care of such events! (not yet done)

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All inclusive decays. Use only events where 6 jet reconstructed

Use kinematic fit to identify W.

Constrain MassW1 =MassW2

4-Jet combinatorics use less b like jets plot best result

Combine with b jets for top mass

GeV

GeV

GeV

W MassW – kinematic fit

Top Mass ( combine all b jets with W) Top Mass

Combine closest b

E b-jet > 60GeV

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Top Mass - identifying the top All inclusive decays. Use only events where 6 jet reconstructed

If plot all 6 jets combinatorics top peak barely visible

Setting energy and momentum constrains peak is much sharper

Still present wrong w – b combinatorics.

Corruption from events with one top decaying leptonicaly.

Use previous slides to improve!GeV

GeV

Peak: 155-185

Mean = 170 GeV

Sigma = 11 GeV

Mystery: Why substantial difference in performance wrt previous slide?

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Conclusion Showed all components of reconstruction can deal with 6-jets events (vertex charge to come)

Optimized Y-cut

Showed b-tag response for the tt events

Found W mass Peak

Found top mass peak

Outlined method to ID the tt bar events!

Need acceptance cuts

Need better study of lepton events in 6 jet sample

Move to full MC