CN CYCLE SOLAR NEUTRINOS AND THE SUN'S PRIMORDIAL CORE METALLICITY

We argue that it may be possible to exploit neutrinos from the CN cycle and p-p chain to determine the primordial solar core abundances of C and N at an interesting level of precision. Such a measurement would allow a comparison of the Sun's deep interior composition with its surface, testing a key assumption of the standard solar model (SSM), a homogeneous zero-age Sun. It would also provide a cross-check on recent photospheric abundance determinations that have altered the once excellent agreement between the SSM and helioseismology. As further motivation, we discuss a speculative possibility in which the photospheric abundance-helioseismology puzzle is connected with the solar system metal differentiation that accompanied formation of the gaseous giant planets. The theoretical relationship between core C and N and the N-13 and O-15 solar neutrino fluxes can be made more precise (and more general) by making use of the Super-Kamiokande and Sudbury Neutrino Observatory (SNO) B-8 neutrino capture rates, which calibrate the temperature of the solar core. The primordial C and N abundances can then be obtained from these neutrino fluxes and from a product of nuclear rates, with little residual solar model dependence. We describe some of the recent experimental advances that could allow this comparison to be made (theoretically) at the similar to 9% level, and we note that this uncertainty may be reduced further as a result of ongoing work on the S-factor for N-14(p, gamma). The envisioned measurement might be possible in deep, large-volume detectors using organic scintillator, for example, Borexino or SNO+.