The authors present the first analytical two-loop NRQCD amplitude for e+e- to J/psi+eta_c as an expansion in m_c^2/s, with cross-section predictions consistent (within uncertainties) with B-factory data.
BOKASUN: a fast and precise numerical program to calculate the Master Integrals of the two-loop sunrise diagrams
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abstract
We present the program BOKASUN for fast and precise evaluation of the Master Integrals of the two-loop self-mass sunrise diagram for arbitrary values of the internal masses and the external four-momentum. We use a combination of two methods: a Bernoulli accelerated series expansion and a Runge-Kutta numerical solution of a system of linear differential equations.
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Analytical two-loop amplitudes of $e^{+} e^{-} \longrightarrow \boldsymbol{J} / \boldsymbol{\psi}+\boldsymbol{\eta}_c$ at $B$ factories
The authors present the first analytical two-loop NRQCD amplitude for e+e- to J/psi+eta_c as an expansion in m_c^2/s, with cross-section predictions consistent (within uncertainties) with B-factory data.