Revisiting the transition Xi cc(+ +)-> Xi((')+)(c) to understand the data from LHCb

The LHCb collaboration newly measured the decay rate of doubly charmed baryon Xi cc(+ + )-> Xi('+)pi(+), and a ratio of its branching fraction with respect to that of the decay Xi cc(+ + )-> Xi(+)pi(+) is reported as 1.41 +/- 0.17 +/- 0.10. This result conflicts with the theoretical predictions made by several groups. In our previous work, following the prescription given in early literature where the us diquark in Xi(+)(c) is assumed to be a scalar, whereas in Xi(')(+)(c) it is a vector, i.e., the spin-flavor structure of Xi(+)(c) is [us](0)c and that of Xi(')(+)(c) is [us](1)c, we studied the case of Xi(+)(+)(cc) -> Xi((')+) with the light-front quark model. Numerically we obtained Gamma(Xi(++)(cc) -> Xi('+)pi(+))/Gamma(Xi(+)(+)(cc) Xi(+)pi(+)) = 0.56 +/- 0.18, which is about half of the data. While abandoning the presupposition, we suppose the spin-flavor structure of [us]c in Xi(+)(c) may be a mixture of [us](0)c and [us](1)c, namely the spin-flavor function of Xi(+)(c) could be cos theta[us](0)[c] + sin theta[us](1)[c]. An alternative combination -sin theta[us](0)[c] + cos theta[us](1)[c] would correspond to Xi(')(+)(c). Introducing the mixing mechanism, the ratio Gamma(Xi(++)(cc) -> Xi('+)pi(+))/Gamma(Xi(+)(+)(cc) -> Xi(+)pi(+)) depends on the mixing angle theta. With the mixing scenario, the theoretical prediction on the ratio between the transition rate of Xi(+)(+)(cc) -> Xi('+)(c) and that of Xi(++)(cc) -> Xi(+)(c) can coincide with the data as long as theta = 16.27 degrees +/- 2.30 degrees or 85.54 degrees +/- 2.30 degrees is set. Definitely, more precise measurements on other decay portals of Xi(++)(cc) are badly needed for testing the mixing mechanism and further determining the mixing angle.