How well can we reconstruct the tt̄ system near its threshold at future e⁺e^- linear colliders

We developed a new method for the full kinematical reconstruction of the tt̄ system near its threshold at future linear e⁺ e^- colliders. In the core of the method lies likelihood fitting which is designed to improve measurement accuracies of the kinematical variables that specify the final states resulting from tt̄ decays. The improvement is demonstrated by applying this method to a Monte Carlo tt̄ sample generated with various experimental effects including beamstrahlung, finite acceptance and resolution of the detector system, etc. In most cases the fit takes a broad non-Gaussian distribution of a given kinematical variable to a nearly Gaussian shape, thereby justifying phenomenological analyses based on simple Gaussian smearing of the parton-level momenta. The standard deviations of the resultant distributions of various kinematical variables are given in order to facilitate such phenomenological analyses. A possible application of the kinematical fitting method and its expected impact are also discussed.