occasional meanderings in physics' brave new world

Name:
Location: New Zealand

Marni D. Sheppeard

## Wednesday, May 28, 2008

### Neutrino08 Day 3b

H. Ray discussed the Osc-SNS project for performing precision measurements using a spallation neutron source. They expect to reach 0.8 MW by the end of the (northern) summer and 1.4 MW at full power. Studying $\pi^{+}$ at rest decay for 29.8 MeV muon neutrinos allows, for instance, removal of the cosmic ray background. Of course one thing they plan to test is the LSND and MiniBooNE low E excess. This experiment can probe the 0.00001 to 0.01 $\textrm{sin}^{2} 2 \theta$ range (and 0.001 to 10 mass squared range), which heavily impacts supernovae and BBN physics. It should have 100 times the KARMEN statistics for sterile neutrino tests. The beam structure allows simultaneous neutrino and antineutrino modes. In question time, she estimated a 3.5 year wait until data taking, if all goes well.

Vanucci gave an interesting talk on searches for sterile neutrinos (of type [1]). He showed a plot of present limits from BBN and SM decays, which puts the allowed region above about 200 MeV. Can the MiniBooNE excess be interpreted this way? What about LHCb and ATLAS/CMS? In principle, these could extend the mass region to 4 GeV and 50 GeV respectively.

Afternoon sessions began with a run of talks on neutrinoless Double Beta decay, known as $0 \nu \beta \beta$. Kayser from Fermilab introduced the fundamental question of whether or not there is mass gap for the neutrino hierarchy. Cosmology puts $\sigma m_{i}$ at less than 0.17 to 1.0 eV. If there are 3 generations, this constrains the heaviest mass $m_{H}$ to be less than 0.07 to 0.4. Then the question motivating most of the afternoon's talks: are they Majorana? The $0 \nu \beta \beta$ amplitude is proportional to the effective Majorana mass $m_{\beta \beta} = | \sum m_{i} U_{ei}^{2} |$. How large is $m_{\beta \beta}$? A measurement of this value could tell us many things. For example, if the hierarchy is known to be inverted, and we find that $m_{\beta \beta} < 0.01$ eV, then the neutrinos are most probably not Majorana. More on this later.

I'm afraid I skipped the last session on Double Beta decay to, er, blog! Now off to the banquet and a trip to see the little blue penguins!

[1] Shaposhnokov, Nucl. Phys. B763 (2007) 49

Thanks for posting about the neutrino
conference, its good to get all the latest news about one the most mysterious known particles. I wonder if i can grab some professional eyeballs, to have a look at my paper, on if its possible to have the neutrino coupled to another long range interaction via the axial current, (bar phi gamma^5 gamma^v phi). I find it
is, provide there are KeV right handed states to make matter neutral and to shield the force from experimental detection, that it is indeed possible. And also show how this could lead to dark energy. The extra RHS states decay, annihilate down to a plasma of the lightest neutrinos, with sufficient (axi-magnetic) attraction to lead to a fluid with w just a little above -1, after redshift around 2.5. See my chirality site for details.

May 29, 2008 1:43 AM
Anonymous said...

Nice penguin pic. Looks better than the usual parrot, anyway.

May 29, 2008 9:21 AM