  The NA60 experiment measured dimuon production in In-In collisions at 158
AGeV. This paper presents a high statistics measurement of $\phi\to\mu\mu$ with
the specific objective to provide insight on the $\phi$ puzzle, i.e. the
difference in the inverse $T$ slopes and absolute yields measured by NA49 and
NA50 in the kaon and lepton channel, respectively. Transverse momentum
distributions were studied as a function of centrality. The slope parameter $T$
shows a rapid increase with centrality, followed by a saturation. Variations of
$T$ with the fit range of the order of 15 MeV were observed, possibly as a
consequence of radial flow. The $\phi$ meson yield normalized to the number of
participants increases with centrality and is consistently higher than the
yield measured by the NA49 experiment at any centrality.
