Fix dimuon mass hypo on DiMuonNoIPLine monitoring
This was supposed to be a change part of !1559 (merged) but then after rebasing the commit got lost.
It only changes the histogramming part of the code so no changes are expected in the references.
This was supposed to be a change part of !1559 (merged) but then after rebasing the commit got lost.
It only changes the histogramming part of the code so no changes are expected in the references.