Nucleus-Nucleus Potential Deduced from Experimental Fusion Cross Sections

Abstract

G. Goldhaber et al., to be published. 4 G. J. Feldman et al., Phys. Rev. Lett. 38, 1313 (1977. 5 Because charmed mesons are associatively produced by the strong or electromagnetic interaction, and are known to decay weakly [see J. E" Wiss et al., Phys. Rev. Lett. 37, 1531] with parity nonconservation the absolute parity of the D° cannot be determined and thus can be set to -1 by convention. 6 The presence of the decay D*-*Z>7r implies that the D and D* have odd relative parity if both are spinless, but then they could not couple to a photon in a P wave without violating parity conservation in electromagnetic production reaction e + e~-~D°D* 0 or D°D*°. This seems to be one of the dominant production modes for charmed mesons near threshold (see Ref. 3). 7 The helicity frame is oriented with its z axis (polar axis) along the direction of the D momentum in the overIt has been shown that nucleus-nucleus fusion cross sections can be predicted with remarkable accuracy from simple, classical, two-body models. 1,2 The basic ingredients of such models are (a) the assumption of a frozen shape of the colliding nuclei during their approach, (b) the assumption of a conservative two-body potential, and (c) the assumption of frictional forces which allow the system to be trapped in a region of attractive interaction.The validity of this general approach appears to be well established by its success; however, disturbing ambiguities remain with respect to points (b) and (c) above. These can be resolved all center of mass and its y axis along the productionplane normal. 8 J, D. Jackson, Lawrence Berkeley Laboratory Internal Note JDJ/76-1 (unpublished). 9 J.-E. Augustin et al., Phys. Rev. Lett. 34, 233 (1975) 0 10 Neutral two-body combinations with both tracks lacking time of flight are dropped from the analysis. This occurs for about 10% of the combinations. 11 Background effects were included by the addition of a 15% isotropic background in both production and decay angular distributions. The assumption of background isotropy was checked by background events from 50 MeV/c 2 sidebands in the Kir invariant-mass distribution. 12 The presence of secondary D 0v s only slightly distorts the cose distribution of Fig. 1(a) because of the small momentum of the D°'s in the D*° rest frame for D* pion decays. 13 Errors in the calculation of the expected curves are not included in these x 2 calculations. 14 We note that there is a 1.5-standard-deviation inconsistency in the widths of the peaks of Fig. 2. 15 S 0 L. Glashow, I. ELiopoulos, and L. Maiani, Phys. Rev. D 2, 1285 (1970); A. De Rujula, H. Georgi, and S. L. Glashow, Phys. Rev. D 12 9 147 (1975); M. K. Gaillard, B. W. Lee, and J. L. Rosner, Rev. Mod. Phys. jt7, 277 (1975). 16 G. Altarelli, N. Cabbibo, and L. Maiani, Phys. Rev. Lett. 35>, 635 (1975); S. R. Borchardt and V. S. Mathur, Phys. Rev. Lett. 36, 1287.only by further careful and systematic comparisons with experimental data. In order to make such a comparison meaningful, fusion excitation functions must be measured wit...

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