1. Top quark search update
By Henry Brown

2. 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%

3. 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

4. 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

5. 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

6. 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

7. Invariant Mass

8. Delta Phi

9. 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

10. 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