First observation of in-medium modifications of the omega meson

A. B. Gridnev; A. Ehmanns; A. Radkov; A. Roy; A. Süle; A. R. Gabler; B. Kopf; B. Krusche; B. Schoch; C. Morales; Ch. Funke; Ch. Schmidt; Ch. Weinheimer; Ch. Wendel; D. Bayadilov; D. Elsner; D. Menze; D. Trnka; D. Walther; E. Gutz; E. Klempt; F. Riek; F. Wilczek; Frank Klein; Fritz Klein; G. Anton; G. Suft; H. Dutz; H. Kalinowsky; H. Löhner; H. Schmieden; H. van Pee; I. Fabry; I. Horn; I. Jaegle; I. V. Lopatin; J. C. S. Bacelar; J. G. Messchendorp; J. Hössl; J. Junkersfeld; J. Langheinrich; J. Lotz; K. Essig; L. M. Pant; M. Fuchs; M. Konrad; M. Kotulla; M. Nanova; M. Ostrick; M. Pfeiffer; O. Bartholomy; P. Hoffmeister; P. Mühlich; R. Bogendörfer; R. Castelijns; R. Ewald; R. Gothe; R. Gregor; R. Novotny; R. Varma; S. Höffgen; S. Lugert; S. Schadmand; S. Shende; T. Mertens; T. Szczepanek; U. Thoma; V. Crede; V. Metag; V. V. Sumachev; W. Schön; Y. A. Beloglazov

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First observation of in-medium modifications of the omega meson

Abstract

The photoproduction of omega mesons on nuclei has been investigated using the Crystal Barrel/TAPS experiment at the ELSA tagged photon facility in Bonn. The aim is to study possible in-medium modifications of the omega meson via the reaction A(gamma, omega)X. Results obtained for Nb are compared to a reference measurement on a liquid hydrogen target. While for recoiling, long-lived mesons (pi, eta and etaprime), which decay outside of the nucleus, a difference in the lineshape for the two data samples is not observed, we find a significant enhancement towards lower masses for omega mesons with low momenta produced on the Nb target.Comment: Latex, 4 pages, 4 figures, accepted by Phys. Rev. Lett; references re-arranged, now references in chronological order in first paragrap