1. W+jets/Wbb+jets background in ttbar measurement (muon+jets) Brad Abbott, Guangshun Huang, Pat Skubic OU ATLAS Group We are measuring ttbar cross section using the mixing sample and the MC08 samples, following the CSC event selection. We have a couple of questions on W+jets/Wbb+jets backgrounds, and hope some experts could clarify the situation. Specifically, can we have larger statistics for these background MC, and is it practical to generate W(bb) with more jets? Thanks. Questions!

2. 2/10/2009 G.S.HuangW+jets/Wbb+jets background2 Question on ratio PS/ME From Wouter’s talk: Are they also PS only? If yes, what is the ratio PS/ME? Ratio PS/ME = 4% above PT=20 & DR=0.7  separate Wbb+jets samples were generated. Seems the current MC08 samples have PS+ME for Wbb+jets, but only PS for W+jets (is this true?). For absolute normalization, do we lose anything (e.g. ME) for W+jets?

3. 2/10/2009 G.S.HuangW+jets/Wbb+jets background3 W+jets/Wbb+jets: jet p T spectra Shown only leading jets, More jets, higher jet p T ; Is this expected?

4. 2/10/2009 G.S.HuangW+jets/Wbb+jets background4 w/o b-tagging 3-jet mass: background shape Normalized to 146 1/pb with b-tagging Wbb+jets W+jets

5. 2/10/2009 G.S.HuangW+jets/Wbb+jets background5 W+jets/Wbb+jets efficiencies Efficiency keeps going higher with more jets for existing MC samples; Interesting to know when it begins falling! This is without b-tagging.

6. 2/10/2009 G.S.HuangW+jets/Wbb+jets background6 W+jets/Wbb+jets event rates W+5jets roughly same amount with W+4jets; Wbb+3jets more than Wbb+2jets; Do we worry about W+  6jets and Wbb+  4jets? Has it been justified that we don’t need them? This is without b-tagging.