Hadrons in Dense Matter

Physical reason behind the mass-shift of vector mesons (ρ, ω, φ) in nuclear matter is discussed in the Walecka model and in QCD sum rules. Using analytic formulas for the mass-shift valid at low densities, it is shown that the energy dependent part of the self-energy in medium (wave function renormalization) is a main source for the negative massshift, while the energy independent part (the plasma frequency) has relatively a small effect. Future experiments in GSI (π−+A → X +ω ) and KEK-PS (p + A → X + φ ) to detect the twin peak structure of vector mesons in ee spectrum are reviewed. Also, it is proposed a new possible experiment using a S(strangeness) = 1 vector meson K∗(892) with its radiative decay K(892) → K + γ.