In-medium properties of light vector mesons

Abstract

The photoproduction of vector mesons on various nuclei has been studied using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Laboratory. All three vector mesons ρ ω and φ are observed via their decay to e + e − . The possible in-medium effects on the properties of the ρ meson are of particular interest. The ρ spectral function is extracted from the data on carbon, iron and titanium, and compared to the spectrum from liquid deuterium, which is relatively free of nuclear effects. We observe no effects on the mass of the ρ meson, some widening in titanium and iron is observed consistent with the collisional broadening.

Theory and phenomenology of vector mesons in medium

“…When extrapolated to the expected phase boundary, the ρ spectral function 'melts' and resembles the form and magnitude of the perturbative q q correlator. In cold nuclear matter, it is compatible with QCD sum rule analysis [11] and qualitatively consistent with the new CLAS data for photoproduction off nuclei at JLab [7].…”

Experimental study of hadron properties in the nuclear medium

“…The CLAS experiment g7 at JLab measured the e + e − invariant mass spectra in the γ+ 2 H/C/Fe-Ti reactions [32]. Fig.…”

“…(a), (b), (c), (d) were adopted respectively from Refs. [27], [31], [32] and [33]. accounts for most of the tail region (m e + e − 0.7 GeV/c 2 ) in the g7 fit.…”

Pion Electromagnetic Form Factor and ??-meson Mass Shift at Finite Density

“…The NA60 collaboration has recently announced that the averaged ρ-meson spectral function shows a strong broadening but no shift in mass [7]. The CLAS collaboration has reported that the medium effects on the ρ-meson mass are not observed [8,9] and some widening of the ρ-meson decay width is seen for the Fe-Ti target. However, the E325 experiment at the KEK 12-GeV Proton Synchrotron has measured the invariant mass spectra of e + e − pairs in p + A reactions and has found that the ρ-meson mass is dropped by about 9 % [10].…”