  Dimuon production is in many global parton distribution function analyses
calculated by assuming that it is proportional to inclusive charm production.
As this assumption breaks down at next-to-leading order in the perturbative
expansion, we present a direct calculation of dimuon production that does not
require an external acceptance correction. Our calculation utilizes
semi-inclusive deep inelastic scattering and a decay function fitted to
experimental data. We find our calculation to be in good agreement with
available experimental data. Here we also demonstrate that the acceptance
correction depends on the used parton distribution and perturbative order.
