The associated production ttH is a key channel in the search for a Higgs 
boson in the mass range 115-130GeV. This low mass region is one of the 
most interesting ones, given the experimental indications and theoretical 
prejudice, but at the same time it is the hardest and least well covered 
Higgs mass region at the LHC. The topology of the ttH final state is quite 
complex, involving six jets (four of them b-jets), an energetic, isolated 
lepton and missing transverse energy. 

One of the main handles for eliminating most backgrounds in this channel 
is the full reconstruction of the two top quarks. This relies heavily on 
achieving the best possible jet energy resolution and energy scale, 
particularly for b-jets, because this allows for (a) narrower mass windows 
for the reconstructed objects and (b) higher probability to pick the 
correct pair of b-jets for reconstructing the Higgs invariant mass. Hence 
this channel will benefit greatly from the network.s existing expertise 
and the proposed work on optimizing the jet energy resolution as described 
above. Moreover, we will construct specific tools for this channel, for 
the optimal reconstruction of the full event topology, and we will develop 
techniques for determining the invariant mass spectrum of the background 
using real ATLAS data, rather than relying on simulations. 

The other important handle for suppressing the background in this channel 
is b-jet identification (b-tagging). Within the RTN, there is considerable 
expertise in this area from Higgs searches in previous experiments and we 
will profit from it to develop tools for systematically evaluating and 
improving the b-tagging performance in ATLAS.