BaBar Data Hints At Physics Beyond The Standard Model

Experiments may just be showing some chinks in the massive armour of the Standard Model of particle physics. The Stanford Linear Accelerator (SLAC) experiment BaBar has just produced data that contradicts the Standard Model, but the confidence level is still not high enough to warrant the tag of a discovery. So the Standard Model stays where it is, at least for the moment. Physicists are waiting for a confirmation of the same anomalous effect from the Belle experiment.

The Decay Deal

So this is what’s happening. A particle called the B-bar meson (i.e. a bound state of a quark and an anti-quark in which the antiquark is a anti-bottom or b-bar) decays into a D-meson (i.e. a meson containing a down quark) and a tau anti-neutrino and a tau lepton. The problem is not in the decay products but in the rate of decay. The Standard Model predicts very definite rates for particle decays, but the observed decay rate is higher than what the Standard Model predicts. This excess is what has got physicists interested.

The confidence level of the observation is about 3.4 sigma, which is not enough to claim a discovery, which requires 5 sigma. Confidence level is a quantitative measure of how solid a set of data is. The higher the confidence level, the lesser the chances that the result is a mere fluctuation.

There is work to be done, though. Seasoned particle physicists are wary. BaBar spokesperson, Michael Roney, professor at University of Victoria, Canada is visibly enthusiastic:

The excess over the Standard Model prediction is exciting

but then puts up a cautious front with:

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.

And that’s exactly how these things work.

The LHC Angle to “New Physics”

Incidentally, this one is not coming from the LHC at CERN. LHC has been hard at work and the data it is churning out is killing off one ‘New Physics’ or Beyond Standard Model theory after the other, confirming the Standard Model even further. The greatest confirmation of the accuracy of the Standard Model will come from the Higgs discovery, which is where the irony lies. The irony is that, if the Higgs is discovered at 125-126 GeV range, and this is the likeliest scenario, physics beyond the Standard Model is a definite requirement.

As I mentioned, the wait now is for another experiment to repeat these results. Says Roney:

If they do, the combined significance could be compelling enough to suggest how we can finally move beyond the Standard Model.

 New physics beckons. 

The SLAC press release:

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Debjyoti Bardhan

Is a science geek, currently pursuing some sort of a degree (called a PhD) in Physics at TIFR, Mumbai. An enthusiastic but useless amateur photographer, his most favourite activity is simply lazing around. He is interested in all things interesting and scientific.