Optimal-Observable Analysis of Possible New Physics Using the b-quark in   gamma gamma -> tt -> bX
  We study possible anomalous top-quark couplings generated by SU(2) x U(1) gauge invariant dimension-6 effective operators, using the final b-quark momentum distribution in gamma gamma -> tt -> bX. Taking into account non-standard tt gamma, tbW and gamma gamma H couplings, we perform an optimal-observable analysis in order to estimate the precision for the determination of all relevant non-standard couplings. 
Bohdan Grzadkowski, Zenro Hioki, Kazumasa Ohkuma and Jose Wudka