  For a local field K with positive residue characteristic p, we introduce, in
the first part of this paper, a refinement bAr_K of the classical Artin
distribution Ar_K. It takes values in cyclotomic extensions of Q which are
unramified at p, and it bisects Ar_K in the sense that Ar_K is equal to the sum
of bAr_K and its conjugate distribution. Compared with 1/2 Ar_K, the bisection
bAr_K provides a higher resolution on the level of tame ramification. In the
second part of this article, we prove that the base change conductor c(T) of an
analytic K-torus T is equal to the value of bAr_{K} on the Q_p-rational Galois
representation X^*(T)_{Q_p} that is given by the character module X^*(T) of T.
We hereby generalize a formula for the base change conductor of an algebraic
K-torus, and we obtain a formula for the base change conductor of a semiabelian
K-variety with potentially ordinary reduction.
