Medium Modifications of the Rho Meson in Nuclear Photoproduction

Abstract

We extend our recent study of dilepton invariant-mass spectra from the decays of ρ mesons produced by photon reactions off nuclei. We specifically focus on experimental spectra as recently measured by the CLAS Collaboration at the Thomas Jefferson National Accelerator Facility using carbon and iron nuclei. Building on our earlier work, we broaden our description to a larger set of observables to identify sensitivities to the medium effects predicted by microscopic calculations of the ρ spectral function. We compute mass spectra for several target nuclei and study the spectral shape as a function of the 3-momentum of the outgoing lepton pair. We also compute the so-called nuclear transparency ratio which provides an alternative means (and thus consistency check) of estimating the ρ width in the cold nuclear medium.

In-medium hadronic spectral functions through the soft-wall holographic model of QCD

“…Hadronic spectral functions at finite quark chemical potential have been investigated by the Nambu-Jona Lasinio model [2,3], QCD sum rules [4,5] and effective models [6][7][8][9]. On the other hand, this is a hard problem to deal with using lattice simulations, because of the sign problem occurring at nonzero chemical potential.…”

K+ and K- potentials in hadronic matter are observable quantities

“…Experimentally measured phase shifts allow via the tρ approximation to predict the optical potential in matter at low densities. When higher densities are of interest more complicated approaches have to be employed and many efforts have been made to investigate the properties of ρ, ω, K + and K − mesons in matter [1][2][3][4]. Especially the production of strange mesons has created a lot of interest because it has been proposed to use them to test the properties of the nuclear environment, in particular of the nuclear equation of state [5].…”

How to determine experimentally the K+ nucleus potential and the K+ N rescattering cross section in a hadronic environment?

“…The tρ approximation allows predicting the optical potential of the mesons in low-densities matter by experimentally measured phase shifts. At higher densities more sophisticated approaches have to be employed and in the last two decades many efforts have been made to investigate the properties of ρ, ω, K + and K − mesons in matter [1][2][3][4]. These calculations are complex because most of the mesons can form baryonic resonances which have other decay branches.…”