return ::sqrt(::pow(DecayVertexV0X() - tParentVertexPosition[0],2) +
::pow(DecayVertexV0Y() - tParentVertexPosition[1],2) +
::pow(DecayVertexV0Z() - tParentVertexPosition[2],2));
return ::sqrt(::pow(DecayVertexV0X() - tParentVertexPosition[0],2) +
::pow(DecayVertexV0Y() - tParentVertexPosition[1],2) +
::pow(DecayVertexV0Z() - tParentVertexPosition[2],2));