1 Top ID in tt → 6-Jet channel Erik Devetak Edinburgh Collaboration Meeting ( )‏

2 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

3 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

4 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)‏

5  All inclusive decays. Use only events where 6 jet reconstructed  Use kinematic fit to identify W.  Constrain MassW 1 =MassW 2  4-Jet combinatorics use less b like jets plot best result  Combine with b jets for top mass GeV W Mass W – kinematic fit Top Mass ( combine all b jets with W)‏ Top Mass Combine closest b E b-jet > 60GeV

6 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 Peak: Mean = 170 GeV Sigma = 11 GeV Mystery: Why substantial difference in performance wrt previous slide?

7 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