3.3 sigma or 2 sigma for g-2 ? September 28, 2006
Posted by dorigo in news, physics, science.trackback
Just a brief note. I have assisted at the discussion of a laurea magistralis this morning, where the candidate discussed her theoretical calculation of the g-2 value for the tau lepton.
During her introduction to the discussion, she presented the discrepancy between experimental determination of muon g-2 and theoretical predictions as a 3.3 sigma effect. I was puzzled, since I had just read a review paper issued this very month on Hep-Ph which quoted a 2-sigma effect (see my former post in http://dorigo.wordpress.com/2006/09/20/muon-g-2-and-supersymmetry/).
Later her thesis advisor confirmed to me that the effect has been re-computed just last week, and explained that the largest contribution to the theoretical uncertainty arises from the hadronic corrections, which make critical use of the BaBar measurement of electron-positron cross section to hadrons as a constraint. It appears that as the uncertainty on the BaBar measurement has shrunk, so has the theory error, and the g-2 discrepancy.
I am intrigued…. I am now waiting for more information from my colleague.
than (5) pickaninny, child. (5) jammed, filled, crowded (2)
By the way, do we have some real standard about how to operate with the sigma (adition, division, etc)? I mean, even supposing that all the booklets on error analysis do -I hope- the same thing, the result -if we are looking at tenths of sigma- can be different if the sigma is estimated via a montecarlo.
Well, of course there can be differences if Joe estimates a discrepancy based on pseudoexperiments with some ansatz and a given random generator and Jane uses a different ansatz and generator. But the zeroth order result, to be sure the one we can all do by heart, should be the same.
Statistics is a bit like religion. There is a degree of belief involved, everywhere you turn.
Cheers,
T.