# Theory on Hadrons in Nuclear Medium

## TL;DR

This paper reviews the theoretical framework for studying hadrons in nuclear matter, emphasizing the importance of analyzing small-width hadrons and chiral partners like $K^*$ and $K_1$ to understand mass shifts and chiral symmetry breaking.

## Contribution

It highlights the significance of studying $K^*$ and $K_1$ mesons in nuclear matter to probe hadron mass origins and chiral symmetry effects, proposing experimental measurements at JPARC.

## Key findings

- Mass shifts of $K^*$ and $K_1$ can be observed in nuclear targets.
- Measuring their masses and differences advances understanding of hadron mass origins.
- Chiral symmetry breaking effects are linked to these meson properties.

## Abstract

After decades-long attempts to measure the mass shift and understand the origin of hadron mass, it became clear that one has to analyze hadrons with small vacuum width. Also, to identify the effect of chiral symmetry breaking, one has to start by looking at chiral partners. In this talk, I will review why such consideration inevitably led us to consider $K^*$ and $K_1$ in nuclear matter [T. Song, T. Hatsuda, S H Lee, PLB792 (2019) 160-169]. With the kaon beam at JPARC, one could observe the mass shift of both particles in a nuclear target experiment. Once the masses and mass difference of $K^*$ and $K_1$ mesons are measured, we will be closer to understanding the origin of the hadron masses and the effects of chiral symmetry breaking in them.