Particle Physics: BaBar Data Hint at Cracks in the Standard

[weakmagneto]

Science Daily
June 18, 2012

Recently analyzed data from the BaBar experiment may suggest possible flaws in the Standard Model of particle physics, the reigning description of how the universe works on subatomic scales. The data from BaBar, a high-energy physics experiment based at the U.S. Department of Energy's (DOE) SLAC National Accelerator Laboratory, show that a particular type of particle decay called "B to D-star-tau-nu" happens more often than the Standard Model says it should.

In this type of decay, a particle called the B-bar meson decays into a D meson, an antineutrino and a tau lepton. While the level of certainty of the excess (3.4 sigma in statistical language) is not enough to claim a break from the Standard Model, the results are a potential sign of something amiss and are likely to impact existing theories, including those attempting to deduce the properties of Higgs bosons.

"The excess over the Standard Model prediction is exciting," said BaBar spokesperson Michael Roney, professor at the University of Victoria in Canada. The results are significantly more sensitive than previously published studies of these decays, said Roney. "But before we can claim an actual discovery, other experiments have to replicate it and rule out the possibility this isn't just an unlikely statistical fluctuation."

The BaBar experiment, which collected particle collision data from 1999 to 2008, was designed to explore various mysteries of particle physics, including why the universe contains matter, but no antimatter. The collaboration's data helped confirm a matter-antimatter theory for which two researchers won the 2008 Nobel Prize in Physics.

Researchers continue to apply BaBar data to a variety of questions in particle physics. The data, for instance, has raised more questions about Higgs bosons, which arise from the mechanism thought to give fundamental particles their mass. Higgs bosons are predicted to interact more strongly with heavier particles -- such as the B mesons, D mesons and tau leptons in the BaBar study -- than with lighter ones, but the Higgs posited by the Standard Model can't be involved in this decay.

http://www.sciencedaily.com/releases/20 ... 111823.htm

[Marshall]

This is an example of something that I think is very intriguing even if it does not ultimately get confirmed.
You can learn a lot, I think, from getting into this a bit.

I found the Stanford SLAC press release that is just slightly more technical.
http://www-public.slac.stanford.edu/bab ... taunu.aspx
And it gives the link to the journal article
http://arxiv.org/abs/1205.5442

One thing it shows is what an impregnable fortress the Standard Model is. It has been sitting there for 40 years and they've been trying really hard without being able to discover anything much wrong with it. The recent discovery of the Higgs at 125 GeV only CONFIRMS IT MORE. Instead of no Higgs or more than one, or Higges doing weird unexpected stuff they are finding a nice tame Higgs just like you'd expect---a "Standard Model Higgs".
So there is a kind of desperation.

The SLAC group painstakingly went over a lot of old data and came up with the news that there is a reaction that seems to happen a LITTLE MORE OFTEN than the Standard Model says to expect. They knew everybody was eager for a glimmer of hope that the Standard Fortress was wrong so they announced the finding.

The statistical significance is only 3-and-some sigma. Normally discoveries are only announced when they have 5 sigma. But here they reported at 3.4 sigma and presented the results at the Hefei conference on 24 May. The paper was submitted to one of the world's top journals *Physical Review Letters*.

You can see how interested and eager everyone is for anything which even slightly disagrees, even slightly undermines the Standard Fortress.

Also news like this gives a chance to learn some of the language. The SLAC machine collides an electron and a positron with a whole lot of energy, enough energy to create exotic massive particle antiparticle pairs. And at the right collision energy they get what is called a B meson and its counterpart, the B-bar meson.
Then in some rare cases the B-bar decays into a D meson, a neutrino, and something like an electron except a lot heavier, called a tau. Or maybe it's an anti-tau and/or an anti-neutrino. There are RULES governing what can decay into what and it would be good if I had the patience to learn them, and my moth-eaten mind could remember them. then I'd understand why particular reactions are allowed by nature.

We can always hope that this result is confirmed! And that it has the desired effect of causing the West Wing of the Standard Model to crumble, or one of its turrets to fall off. :-D It would be great. but, as they say, don't hold your breath.