Studying the Medium Effects of the $\omega$ and $\phi$ Mesons at JLab

The E01-112 experiment at Jefferson Lab (JLab) in Newport News, VA, USA is an investigation of the properties of the $\rho$, $\omega$, and $\phi$ mesons in dense nuclear matter. The vector mesons are produced by a high-intensity photon beam, with energies up to 4~GeV, incident on targets ranging from $^{2}$H to Pb. Using the CEBAF Large Acceptance Spectrometer (CLAS) in Hall B at TJNAF, the mesons are reconstructed by means of their rare leptonic decay to $e^{+}e^{-}$, eliminating any hadronic final state interactions. These data make possible an analysis of the in-medium widths of the $\omega$ and $\phi$ mesons. The in-medium widths can be accessed by measuring the amount of absorption inside the nucleus. An increase in the in-medium $\omega$N and $\phi$N cross sections leads to an increase in the number of absorbed mesons. The signature of absorption is a decrease of the nuclear transparencies as a function of the number of target nucleons. The results indicate a substantial widening of the $\omega$ and $\phi$ mesons in the medium. The CBELSA/TAPS Collaboration has published transparency ratios for the channel $\omega \rightarrow \pi^{0}\gamma$, that also shows an increase in the in-medium width. The JLab results show a greater absorption than what was measured by CBELSA/TAPS.