Experimental approaches for determining in-medium properties of hadrons from photo-nuclear reactions

TL;DR

This paper reviews experimental methods to study how hadron properties change inside nuclear matter, focusing on meson production and decay in photo-nuclear reactions, with new high-statistics data on omega mesons.

Contribution

It introduces experimental approaches to probe in-medium hadron modifications, emphasizing the use of transparency ratios and meson line shapes, supported by new data on omega mesons from MAMI-C.

Findings

Transparency ratio relates to in-medium meson width.

Short-lived mesons decay inside the medium, revealing in-medium effects.

High-statistics data on omega meson photoproduction at MAMI-C.

Abstract

Properties of hadrons and their modification within strongly interacting matter provide a link between experimental observables and Quantum Chromodynamics (QCD) in the non-perturbative sector. The sensitivity of various observables to in-medium modifications of mesons is discussed. The transparency ratio, comparing the meson yield per nucleon within a nucleus relative to that on a free nucleon, is related to the in-medium width of the meson. While the transparency ratio can be determined for any meson lifetime the meson line shape only contains information on in-medium properties if the meson is so short-lived that it decays in the medium after production in a nuclear reaction. Light vector mesons are thus particularly suited for these investigations. The momentum distribution of mesons produced in a photo-nuclear reaction as well as the excitation function also show some sensitivity to different in-medium modification scenarios. As an example, high statistics data taken at MAMI-C on the photoproduction of \omega\ mesons are presented.