Apr 2007 - Sept 2008
Instability effects in top pair production at threshold
by
→
Europe/London
OC 218
OC 218
Description
By a line-shape scan of the e+ e- -> t t-bar threshold cross
section at the ILC a precise top mass measurement is possible. The
theoretical prediction via non-relativistic QCD (NRQCD) of the
line-shape is influenced by effects of the top instability, all of
which contribute to the imaginary parts of NRQCD Wilson
coefficients within an inclusive description.
Such effects are the decays t -> W b of the produced top
and antitop, but also
interferences of diagrams with the top decay products present in the final
states. Another contribution comes from the phase space matching, which
subtracts regions of the
top-antitop phase space, where the non-relativistic expansion is not valid.
In the talk it is discussed how these effects can be treated within
NRQCD and to what order they contribute to the cross section.