CC interactions on oxygen-18 (and oxygen-17)

[JostMigenda]

At the proto-collaboration meeting, Neil McCauley pointed out that nu_e CC interactions on oxygen-17/18 have a much lower threshold energy than the analogous oxygen-16 interaction, which leads to much higher cross-sections at low energies.

After a brief search, I’ve found two relevant papers:

• Haxton: PRD 36 (1998) 2283 calculates the cross-sections theoretically. Fig. 1 shows the cross-section; the "bump" in the solid line at low energies comes from oxygen-17/18. This implies that those isotopes are negligible (compared to oxygen-16) at energies above ~20 MeV.
• Haxton & Robertson, arXiv:nucl-th/9806081 calculates the cross-sections averaged over the solar boron-8 flux and finds that the oxygen-18 event rate is about 6.7% of the total solar neutrino signal (i.e. ~14× smaller than elastic scattering on electrons), while the oxygen-17 interaction is negligible (cross-section and natural abundance are about 3.5 and 5 times smaller than for oxygen-18).

My very rough guess (based on this and the HK Design Report) is that we might see 100–200 events from this oxygen-17/18 channel in HK. This would be a little more than the oxygen-16 channel interaction in the worst case (Totani1998 model, no oscillations), but an order of magnitude fewer events then we’d see for the oxygen-16 channel in the NH/IH scenarios. Also, the oxygen-17/18 channel would depend only weakly on the mean neutrino energy.

[JostMigenda]

A new calculation by Suzuki et al. was posted on the arXiv a few weeks ago. For a Nakazato simulation, they find that the total number of events from oxygen-18 adds about 6–7% to the oxygen-16 number; below 20 MeV, it adds 20–30%.