Studying the in-medium $φ$ meson spectrum through kaons in proton-nucleus reactions

Abstract: Exploring the mass modifications of $\phi$ mesons in nuclei provides insights into the nature of strongly interacting matter. Specifically, $\phi$ meson mass shifts can be related to the in-medium modification of the strange quark condensate. Therefore, the partial restoration of chiral symmetry can be studied by observing the mass shifts through the decay channels $\phi \rightarrow e^+e^-$, and $\phi \rightarrow K^+K^-$. In this paper, we examine the possibility of observing the $\phi$ meson mass modifications of the $\phi$ mesons in 30 GeV proton-nucleus (C, Cu, Pb) collisions, to be studied at the J-PARC E88 experiment, through the kaonic decay channel, with the off-shell Budapest Boltzmann-Uehling-Uhlenbeck (BuBUU) transport model. By applying different mean fields to the kaons, we examine their effects on the invariant mass spectra. Our simulations suggest that, although different mean fields for the kaons do affect the spectrum, there is a common observable effect primarily driven by the $\phi$ mass shift. However, due to the threshold associated with the two kaons, the signal we observe is quite different from the one expected in dilepton spectra. Therefore, to meaningfully constrain the mass shift, it will be useful to include both kaon and dilepton channels in the analysis of the experimental data.