A reference would be Pandharipande's ICM address [*Cohomological field theory calculations*][1], section 1.3. The $R$-matrix is
$$
R(z)=\exp\bigg(-\sum_{k=1}^\infty \frac{B_{2k}}{2k(2k-1)}z^{2k-1}\bigg).
$$


  [1]: https://arxiv.org/abs/1712.02528