Transverse electron scattering form factors at low momentum transfer: Sensitivity to in-medium modifications of vector mesons? - art. no. 034307

Form factor measurements of M2 and M4 transitions to the lowest J(pi)=2(-) and 4(-) states, respectively, in Ca-48 with inelastic electron scattering at 180 degrees are reported for momentum transfers q similar or equal to 0. 4-0.8 fm(-1). These form factors complement previous measurements at higher q which have been treated by Lallena [Phys. Rev. C 48, 344 (1993)], as a t est case to derive information on in-medium modifications of the rho-meson mass. He deduced within the random-phase approximation (RPA) an effective m ass m(rho)(*)similar or equal to 0.9-0.95 m(rho) assuming simultaneous scal ing of the pi coupling constant (Brown-Rho scaling). The validity of the an alysis is critically assessed by comparing the measured form factors to sec ond random-phase approximation (SRPA) calculations with a pi+rho exchange i nteraction. The dependence of the form factors on the: choice of the intera ction and corrections such as mesonic exchange currents (MEC) are found to be of comparable magnitude to effects from a dropping of m(rho), and in-med ium effects hence cannot be clearly inferred from the data. To quantify the latter would require first the construction of an interaction which is cap able of describing simultaneously and optimally a large variety of low-ener gy nuclear properties in Ca-48. Remaining discrepancies in such a descripti on could then be studied with the aim to single out in-medium effects of th e type advocated by Lallena.