Solar Fusion and The Coulomb Dissociation of 8B; What Have We Learned and Where Do We Go From Here?

Abstract

The much needed nuclear input to the Standard Solar Model, $S_{17}(0)$, has now been measured with high precision ($\pm$5% or better) by different groups and good agreement is found, even when very different methods are employed. We review the decade long research program to measure the cross section of the $^7Be(p,γ)^8B$ reaction using the Coulomb dissociation method, including the pioneering RIKEN1 experiment carried out during March 1992, followed by RIKEN2, GSI1, GSI2 and an MSU experiment. Our RIKEN and GSI data allow us to rule out the much tooted large E2 contribution to the Coulomb dissociation of $^8B$. Specifically recent results of the MSU experiment are not confirmed. The GSI1 and GSI2 high precision measurements are in good (to perfect) agreement with the newly published high precision measurements of direct capture with $^7Be$ targets. From these GSI-Seattle-Weizmann high precision data we conclude that the astrophysical cross section factor, $S_{17}(0)$, is most likely in the range of 20 - 22 eV-b. We point out to an additional large uncertainty (-10% +3%) that still exists due to uncertainty in the measured slope of the S-factor and the theoretical extrapolation procedure which may still lower $S_{17}(0)$ down to approximately 18.5 eV-b. For quoting $S_{17}(0)$ with an uncertainty of $\pm$5% or better, yet another measurement needs to be performed at very low energies, as recently discussed by the UConn-Weizmann-LLN collaboration for the CERN/ISOLDE facility.