We present a study of ttbar pairs produced in ppbar collisions at 
a center of mass energy of 1.96 TeV and decaying in tau+jets channel. 
We consider tau decaying into hadrons, thus tau+jets channel has  five 
 jets in the final state, one from a tau, two from b quarks and two from a W, 
plus a large amount of missing energy from two tau neutrinos. We search for 
this channel in 311 pb^-1 of data selected with TOP_MULTIJET trigger 
 up to August 2004. 

After SECVTX b-tagging and requiring at least one tau candidate, selection 
 is performed using two neural netorks in cascade, the first trained 
 mostly by global variables, the second by tau specific ones. 
This technique is preferred to a standard one with just one network
 because, for a fixed efficiency on signal, it allows to obtain 
a better S/N: for a top mass of 175 GeV/c^2 we obtain S/N = 1/1.3 
(18 signal events expected). 

Making a binned likelihood fit on the output of the second net, we then
 measure ttbar production cross section. For a top mass of 175 GeV/c^2
we obtain

   7.1 +/- 2.3 (stat) +/- 0.9(syst) pb


Posted to /cdf/pub/thesis/cdf8027_amerioPhDTh_tauJets.ps.gz
    http://www-cdf.fnal.gov/thesis/cdf8027_amerioPhDTh_tauJets.ps.gz

Posted by amerio