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HK: Physik der Hadronen und Kerne
HK 24: Elektromagnetische und Hadronische Proben
HK 24.1: Gruppenbericht
Dienstag, 8. März 2005, 14:00–14:30, TU MA001
First observation of in-medium modifications of the omega meson in photonuclear reactions — •David Trnka — II. Physikalisches Institut, Heinrich-Buff-Ring 16, 35392 Giessen
One of the exciting topics in nuclear physics is the modification of experimentally observable properties of vector mesons such as mass and width, when embedded in a medium. A variety of theoretical models predict a mass shift of the ω-meson in the order of −140 MeV <m*−mV < −15MeV and a broadening of the width within a range of 20 to 50 MeV at normal nuclear densities (i.e. :[1]). A promising approach is to study the decay ω → π0+γ in photonuclear reactions. This mode accounts for 9 · 10−2 of the total width, while for the ρ it is only 6 · 10−4. Consequently it provides an exclusive probe to study the ω-meson properties in matter. Simulations prove that distortions due to FSI of the pions can be strongly suppressed ([2]) . The experiment was carried out at the ELSA accelerator facility in Bonn using the Crystal Barrel/TAPS detector array. C, Ca, Nb and Pb have been used as targets while the LH2 target was used as a reference measurement. An ω mass shift by about 10 % has been observed in the fully inclusive invariant mass spectra as well as after applying kinematical constraints to suppress rescattered pions. Furthermore, the dependence on the ω-momentum has been studied. Mass changes are only observed for ω-mesons with momenta less than 500 MeV/c.
[1] T. Renk et al. , Phys. Rev. C 66, (2002) 014902
[2] J. G. Messchendorp et al. , Eur. Phys. J. A. 11, 95-103 (2001)