The Dissociation of 8B in the Coulomb Field and the Validity of the CD Method

Abstract

The GSI1, GSI2 (as well as the RIKEN2 and the corrected GSI2) measurements of the Coulomb Dissociation (CD) of 8B are in good agreement with the most recent Direct Capture (DC) 7Be(p,g)8B reaction measurement performed at Weizmann and in agreement with the Seattle result. Yet it was claimed that the CD and DC results are sufficiently different and need to be reconciled. We show that these statements arise from a misunderstanding (as well as misrepresentation) of CD experiments. We recall a similar strong statement questioning the validity of the CD method due to an invoked large E2 component that was also shown to arise from a misunderstanding of the CD method. In spite of the good agreement between DC and CD data the slope of the astrophysical cross section factor (S17) can not be extracted with high accuracy due to a discrepancy between the recent DC data as well as a discrepancy of the three reports of the GSI CD data. The slope is directly related to the d-wave component that dominates at higher energies and must be subtracted from measured data to extrapolate to zero energy. Hence the uncertainty of the measured slope leads to an additional uncertainty of the extrapolated zero energy cross section factor, S17(0). This uncertainty must be alleviated by future experiments to allow a precise determination of S17(0), a goal that so far has not be achieved in spite of strong statement(s) that appeared in the literature.Comment: Invited Talk, Spring Seminar on Nuclear Physics, May 20 - 24, 2007, Vico Equense, Italy. Work Supported by USDOE grant No. DE-FG02-94ER4087