A comparative measurement of $\phi\rightarrow K^+K^-$ and   $\phi\rightarrow \mu^+\mu^-$ in In-In collisions at the CERN SPS
  The NA60 experiment at the CERN SPS has studied $\phi$ meson production in In-In collisions at 158A GeV via both the $K^+K^-$ and the $\mu^+\mu^-$ decay channels. The yields and inverse slope parameters of the $m_T$ spectra observed in the two channels are compatible within errors, different from the large discrepancies seen in Pb-Pb collisions between the hadronic (NA49) and dimuon (NA50) decay channels. Possible physics implications are discussed. 
NA60 Collaboration: R. Arnaldi, K. Banicz, J. Castor, B. Chaurand, W.   Chen, C. Cical\`o, A. Colla, P. Cortese, S. Damjanov...
nucl-ex