Responses of hadrons to chemical potential at finite temperature

A formulation to obtain the response of hadron masses to the chemical potential is developed on the lattice. As a first trial, screening masses of pseudoscalar and vector mesons and their responses are evaluated. We present results for two flavors of staggered fermions below and above $T_c$. The responses to both the isoscalar and isovector chemical potentials are sizable. They show different behaviours in the low and high temperature phases, which may be explained as a consequence of chiral symmetry breaking and restoration.