occasional meanderings in physics' brave new world

Name:
Location: New Zealand

Marni D. Sheppeard

## Wednesday, May 28, 2008

### Neutrino08 MiniBooNE

Apologies to experimentalists for my complete inability to jot down all error figures when speakers flash up 40 slides in half an hour. Don't worry. Slides will all be made available on the conference site.

The 9am start, by S. Brice, was the MiniBooNE talk on oscillation searches! Brice briefly sketched the motivation of LSND observations and the detector setup, namely 3m of top dirt on a 12m sphere of 800 kiloton pure oil with 1280 inner PMTs*.

MiniBooNE has the largest sample of neutral current muon neutrino $\pi^{0}$, with 28600 $\pi^{0}$ events. The $\pi^{0}$ rate is measured to a few percent, which is important in considering backgrounds. A draft paper promises a 10% to 30% improvement (at 90% confidence) under about 1 $eV^{2}$ (he mentioned a $\chi^{2} = 12.45$). For comparisons with LSND, Karmen and Bugey see arxiv: 0805.1764. A maximum compatibility for these four experiments is estimated at only 4% at $\Delta m^{2} = 0.242$ and $\textrm{sin}^{2} 2 \theta = 0.023$.

Regarding the low E excess, they are near the end of comprehensive review, which is not quite ready, but Brice indicated that there really isn't any change. New effects considered in the analysis are
1. induced photonuclear effect from absorption removing 1 photon from a muon $\nu$ induced $\pi^{0}$ decay
2. some other hadronic processes. These turn out to have a small effect on the excess.
3. now have a better handling of beam $\pi^{+}$ production, which can decrease the excess
4. $\nu$ induced $\pi^{0}$ now better measured
5. better handling of radiative decay of $\Delta$ resonance
and new low E electron neutrino cuts, along with upgrades, indicate no appreciable excess above 475 MeV. He also showed some preliminary results regarding NuMI events (from 745km away) which indicate good agreement with Monte Carlo for muon neutrino CCQE. For electron neutrino CCQE there is a 1.26 $\sigma$ excess under 900 MeV.

For muon neutrino disappearance events they can reach a new region of phase space, and this result is also due out this summer. In summary, they have $6.6 \times 10^{20}$ protons on target (POT) in neutrino mode and $2.5 \times 10^{20}$ POT in antineutrino mode.

*that acronym was easy, but I spend a substantial fraction of talk time trying to figure out some of the more obscure ones

CarlBrannen said...

The delta m^2 numbers you're quoting are in units of 0.01eV^2 so they're really talking about 2.42x10^-3.

I'm rooting for 2.49x10^-3, and for 7.93x10^-5 for the other difference. Meanwhile, progress is being made on the new paper, which I hope is going to be more readable than most of my Clifford algebra ridden stuff.

And by the way, blogger's text identification problems are getting harder and harder.

May 29, 2008 4:19 AM
Kea said...

Yes, I must list a whole lot of your numbers at some point, and predictions such as hierarchy type, which is being discussed a lot here. Sorry about Blogger, Carl, but spam filtering is essential.

May 29, 2008 9:45 AM