Top quark search update By Henry Brown

Reminder Looking for , e final states from W decays Top always goes to W & b Primary background is Z ->   Signal cross section ~ 170 pb-1 Branching ratio for our final states is 2.4%

Recent developments Have run QCD samesign search – no candidates pass cuts in either ++ or – events (Great!) No w+jet contribution (would expect to see events in ++ or --, no a priori charge conjugation) Revised some estimates & have now included WW production in our signal yields Cuts have been made harsher to remove nearly all Z contribution

Cuts Invariant Mass < 95 GeV Pt (μ) < 15 GeV - inherent to stripping line Pt (e) < 15 GeV IP (μ) > 35 μm - Leptons from PV for W decays IP (e) > 35 μm

Data 10 Events MC Expectation (before efficiency) : 5.08 sig 0.09 Z 8.45 WW Currently using working point efficiency ~70% (to be confirmed with full detector simulation this week) Gives MC expectation of 9.52

WW Production Cross section approximately 44.5 pb Branching Ratio ~ 2.5% (same as ttbar) Acceptance is O(3%) Same as top, looking for leptonic decays of the W

Invariant Mass

Delta Phi

To do: Kurt and I are working on the errors of these (does a random distribution work?) Full detector MC simulation (having some Gauss issues) – Karol Errors on W+jet need work Isolation studies on WW production to see if we can separate it from ttbar any further

Conclusion May have first signs of ttbar & WW production at LHCb Hoping to get internal note out as soon as possible after detector simulation Looking good for ‘first observations’, might not have statistics to claim 3 sigma affects