Measurement of excitation spectra in the ${}^{12}$C$(p,d)$ reaction near the $\eta'$ emission threshold

TL;DR

This study measured excitation spectra in the $^{12}$C$(p,d)$ reaction near the $ ext{eta'}$ emission threshold to search for bound states, finding no evidence but constraining interaction models.

Contribution

The paper provides the first experimental excitation spectra near the $ ext{eta'}$ threshold in carbon, setting limits on bound state formation and $ ext{eta'}$-nucleus interactions.

Findings

No distinct bound state structures observed.

Constraints established on formation cross section.

Limits set on $ ext{eta'}$-nucleus interaction strength.

Abstract

Excitation spectra of $^{11}$C were measured in the $^{12}$C$(p,d)$ reaction near the $\eta'$ emission threshold. A proton beam extracted from the synchrotron SIS-18 at GSI with an incident energy of 2.5 GeV impinged on a carbon target. The momenta of deuterons emitted at 0 degrees were precisely measured with the fragment separator FRS operated as a spectrometer. In contrast to theoretical predictions on the possible existence of deeply bound $\eta'$ mesic states in carbon nuclei, no distinct structures were observed associated with the formation of bound states. The spectra were analyzed to set stringent constraints on the formation cross section and on the hitherto barely-known $\eta'$-nucleus interaction.