Be a bit careful about the momentum definition in batchnorm layers, as they might differ from other definitions.
From the docs 11:

This momentum argument is different from one used in optimizer classes and the conventional notion of momentum. Mathematically, the update rule for running statistics here is x_hat_new = (1 - momentum) * x_hat + momentum * x_t, where x_hat is the estimated statistic and x_t is the new observed value.

Based on your posted formula (assuming alpha is the momentum) the definition differs as explained in the docs.