occasional meanderings in physics' brave new world

Name:
Location: New Zealand

Marni D. Sheppeard

## Monday, May 26, 2008

### Neutrino08 Day 1a

C. Galbiati represents the Borexino experiment, which observes solar neutrinos in real time using a spherical scintillation detector. Both 7Be and pep neutrinos are good sources for exploring the so called vacuum-matter transition. New results for 192 days of data were announced in this morning's talk: the 7Be result is $49 \pm 3$ counts per day per 100 ton. This is in good agreement with the MSW-LMA oscillation prediction of around 48, and rules out the no oscillation scenario at $4 \sigma$ (arxiv preprint 0805.3843).

Galbiati began with a summary of the (old) standard solar model and its agreement with helioseismology, which is no longer in such good agreement since the new estimate for metallicity appears to be a factor of 2 different. Can neutrino physics explain this discrepancy? One would like to use CNO* neutrinos to measure the metallicity of the core of the sun.

The next speaker was H. Robertson from the SNO collaboration. This is a 12 meter diameter, 1000 ton heavy water detector, with outer water shields. It has operated in three phases: (i) $D_{2}O$ (ii) $D_{2}O$ plus salt and (iii) $D_{2}O$ with 3He detectors. In the final phase, 36 strings of 3He detectors were deployed at a total length of 398m.

R. Hahn then confronted chemically challenged physicists with a talk about radiochemical experiments, including an historical interlude on Ray Davis, who was the first to observe solar neutrinos. He discussed the SAGE and GALLEX experiments. New results are a better fit to the constant flux line than previous results.

J. Klein outlined future solar neutrino experiments, noting the current focus on real time observations. One major goal is to look at the metallicity problem. Did Jupiter or Saturn somehow steal metals from the planetary protosphere? Or is something else going on? The correct value for solar surface metallicity may be obtained from 0805.2013.

* think Chemistry when you see capital letters, except in the last post