Vector Meson in Nuclear Medium

Abstract

Vector mesons immersed in nuclear medium are expected to change their properties due to partial chiral symmetry restoration and/or many body nuclear effects. Expected changes range from the decrease in the mass,1),2) increase in the width,3)–7) and appearance of new structures,8),9) every aspect of which if measured will lead to a new understanding of strong interaction. Several experiments are reporting preliminary results,10)–12) which indeed hint to nontrivial changes and new structures appearing at nuclear matter. With further refined experiments and with exclusive measurements of final state particles, the background could be substantially reduced and vector meson kinematics controlled. Then detailed information on the changes of vector meson properties inside nuclear matter can be extracted, which will then serve as a basis for understanding symmetry restoration in QCD, generation of hadron masses, and QCD phase transition.13) While the prospects of looking directly into the nuclear matter through vector meson seem so exciting, a careful model independent theoretical analysis on the vector meson properties at nuclear matter has to be carried out simultaneously before any conclusion on medium effects can be made. Moreover, model calculations contain parameters determined at kinematical configurations different from that used in calculating vector meson properties in medium. Therefore, it is crucial to introduce QCD constraints that have to be satisfied by any model calculations. In particular, as the properties of vector mesons are revealed through their spectral densities, we will formulate the constrains on them.