Electromagnetic Response of 12C: A First-Principles Calculation

The longitudinal and transverse electromagnetic response functions of C-12 are computed in a first-principles Green's function Monte Carlo calculation, based on realistic two- and three-nucleon interactions and associated one-and two-body currents. We find excellent agreement between theory and experiment and, in particular, no evidence for the quenching of the measured versus calculated longitudinal response. This is further corroborated by a reanalysis of the Coulomb sum rule, in which the contributions from the low-lying J(pi) = 2(+), 0(2)(+) (Hoyle), and 4(+) states in C-12 are accounted for explicitly in evaluating the total inelastic strength.