Phys. Rev. Lett. 98, 042501 (2007) [4 pages]Evidence for In-Medium Modification of the ϕ Meson at Normal Nuclear Density
See accompanying Physics Focus Invariant mass spectra of e+e- pairs have been measured in 12 GeV p+A reactions to detect possible in-medium modification of vector mesons. Copper and carbon targets are used to study the nuclear-size dependence of e+e- invariant mass distributions. A significant excess on the low-mass side of the ϕ meson peak is observed in the low βγ(=β/√1-β2) region of ϕ mesons (βγ<1.25) with copper targets. However, in the high βγ region (βγ>1.25), spectral shapes of ϕ mesons are well described by the Breit-Wigner shape when experimental effects are considered. Thus, in addition to our earlier publications on ρ/ω modification, this study has experimentally verified vector meson mass modification at normal nuclear density. © 2007 The American Physical Society URL:
http://link.aps.org/doi/10.1103/PhysRevLett.98.042501
DOI:
10.1103/PhysRevLett.98.042501
PACS:
25.40.Ve, 14.40.Cs, 21.65.+f, 24.85.+p
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