This morning brought about another suggestive (if I may be so bold so say that) experimental hint of new physics in the leptonic sector in the form of a paper from the MiniBooNE collaboration: “Unexplained Excess of Electron-Like Events From a 1-GeV Neutrino Beam (arXiv:0812.2243).”
Recall that the past two months have also brought us a speculative “multi-muon anomaly” at CDF (arXiv:0810.5357, see also Tommaso’s summary), the publication of the PAMELA cosmic-ray positron excess (arXiv:0810.4995, ), and related publications by ATIC4 (Nature) and HESS (arXiv:0811.3894) on the electron/positron spectrum. Apparently the leptonic sector has decided to be kind (if coy) to model-builders in light of LHC delays. Now, MiniBooNE joins in on the fun.
MiniBooNE neutrino low-energy excess. Image from arXiv:0812.2243.
For an excellent summary of the MiniBooNE experiment, see Heather Ray’s post on Cosmic Variance. (Unfortunately their TeX didn’t transfer over well since they moved to Discover… hopefully someone over there will fix up all the LaTeX tags that are now garbled?)
As I’m writing this Symmetry Breaking has published a post on the result that summarizes the recent news. Here’s my own quick-and-dirty summary as I understand it:
In April 2007, MiniBooNE published results that showed no signs of the LSND anomaly (hep-ex/0104049), leading many model-builders to immediately jump off the neutrino band-wagon (see Jester’s theory report). They noted, however, a curious excess in their data at lower energies, in an energy region that was not (at least on face value) related to the unrequited LSND hint for new physics. This was left for further investigation and data analysis.
Now after more than a year of said investigation and analysis, the excess is still there. (See image above.) What’s even more interesting, is that the bump does not appear as pronounced in the antineutrino sector, according to a recent report (see image below). LSND and the fresh-on-the-arXiv MiniBooNE paper were analyses based on neutrinos. It’s a bit surprising that the MiniBooNE antineutrino analysis doesn’t have a similar feature
MiniBooNE antineutrino data showing a much weaker signal at low energies compared to the neutrino data. Image from Fermilab.
I hope to spend some time reading up on this over the holidays, I should then be able to give a more coherent summary.
December 15, 2008 at 12:50 pm
Hi guys,
thanks for the link – which brought me here. Yes, the miniboone excess looks a lot like something interesting to understand. I wonder how well they know their pizero background…
I will check in the paper.
Cheers,
T.
January 8, 2009 at 9:48 pm
A silly question: what does LSND stands for?
January 27, 2009 at 10:12 pm
Hi,
As a MiniBooNE member, I thought I could help with a few points.
1 – LSND stands for “Liquid Scintillator Neutrino Detector.”
2 – The LSND excess was seen in antineutrinos, not neutrinos.
3 – MiniBooNE puts a very tight constraint on the pi0 background through a direct measurement of the NCpi0 process. Check out a thesis from one of our excellent students ( http://www-boone.fnal.gov/publications ) for a detailed description of the oscillation analyses.
Cheers,
Morgan
February 16, 2009 at 4:44 pm
[...] was marked by three interesting leptonic signals. The CDF multi-muon anomaly, PAMELA/ATIC, and the MiniBooNE excess. Of these three, PAMELA/ATIC have gotten the lion’s share of papers — but there have [...]