Three-decade quest backs physics' 'Standard Model'

May 13, 2015
Credit: CERN

Scientists on Wednesday said that after a nearly three-decade bid they had detected a telltale change in a sub-atomic particle, further backing a key theory about the Universe.

Researchers at the world's biggest said they had observed an extremely rare event—the decay of the neutral B meson into a pair of muons, the heavy cousins of electrons.

The results provide further support for the so-called Standard Model, the conceptual framework for the particles and forces that constitute the cosmos, they said in the journal Nature.

Neutral B mesons are unstable composites of two kinds of particles called quarks, bound by the "strong" force.

Their decay into muons is predicted under the Standard Model. But getting evidence to confirm the prediction has been a puzzler since the mid-1980s.

For one thing, neutral B mesons themselves are produced in extreme conditions—in particle colliders or in cosmic-ray interactions, for instance—which makes them hard or very costly to study.

And the transition into muons only occurs about four times in every billion "decays."

Rival teams at CERN's Large Hadron Collider (LHC)—the massive underground lab near Geneva that straddles the Franco-Swiss border—worked separately on detecting the elusive event.

Event displays from the CMS (above) and LHCb (below) experiments on the Large Hadron Collider show examples of collisions that produced candidates for the rare decay of the Bs particle, predicted and observed to occur only about four times out of a billion. Images: CMS/LHCb collaborations

They released individual results in July 2013, but, separately, the data batches fell just short of the demanding threshold of accuracy for claiming a discovery.

Their combined analysis, now published in the benchmark peer-reviewed science journal, "easily exceeds this requirement," the European Organisation for Nuclear Research (CERN) said in a statement.

The paper said the experiments showed that Standard Model, which dates to the 1970s, had cleared another hurdle but others lay ahead.

"In the course of the past few decades, the Standard Model has passed critical tests derived from experiment, but it does not address some profound questions about the nature of the Universe," the authors said.

Event displays from the CMS (above) and LHCb (below) experiments on the Large Hadron Collider show examples of collisions that produced candidates for the rare decay of the Bs particle, predicted and observed to occur only about four times out of a billion. Images: CMS/LHCb collaborations

The framework does not, for instance, explain dark matter, the stuff that composes nearly 85 percent of the mass in the cosmos and is currently only detectable through its gravitational effect on visible matter.

The quest to understand dark matter is one of the priorities of the current work programme at the LHC, which began last month after a two-year upgrade.

The collider comprises a ring-shaped tunnel where proton beams are whizzed around in opposite directions at speeds approaching that of light.

At four locations in the tunnel, powerful magnets bend the beams, bringing them together so that some of the protons smash together—a brief, intense collision.

The sub-atomic rubble that results is then analysed to look for novel particles or clues about known ones.

In 2012, the LHC confirmed the Higgs Boson, the long-sought Standard Model particle that confers mass.

It earned the 2013 Nobel physics prize for two of the scientists who back in 1964 had theorised the boson's existence.

Explore further: Large Hadron Collider resumes collisions after upgrade

More information: Observation of the rare Bs0 →µ+µ− decay from the combined analysis of CMS and LHCb data, Nature (2015) DOI: 10.1038/nature14474

Read a press release

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13 comments

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Doug_Huffman
1.8 / 5 (12) May 13, 2015
The Standard Models are vastly verified. That may be mere ad-hockery (see E. T. Jaynes), but it is not falsifiability.

First, millennia ago, it was turtles all the way down. We have advanced to Quarks, quarks and gluons all the way down.
antialias_physorg
4.3 / 5 (17) May 13, 2015
First, millennia ago, it was turtles all the way down. We have advanced to Quarks, quarks and gluons all the way down.

Difference being: On "turtles all the way down" you can't base much in the way of prediction (or at any rate: predictions that're going to turn out as predicted...you know...the stuff technology is based on).
On QM and GR on the other hand...

Now that doesn't make them 'true' (no scientific theory can be proven as true)...but it makes these theories very, very good.
shavera
4.6 / 5 (16) May 13, 2015
Additionally, we acknowledge there are gaps. We don't pretend like the standard model is the definitive last answer to the question. But it answers a bloody great deal of questions that have been asked.

Look, when Einstein published relativity, it didn't mean Newtonian physics was somehow "invalid," we just found that it was only a valid approximation for certain physical regimes. Those regimes allow us, generally speaking, to do just about anything for which we've evolved functionality, but they weren't the last word.

When we find what lies beyond the standard model, we won't find that the standard model never worked (because, obviously it does, in some regimes) we'll just know more about what happens in the regimes where its approximate fit to the truth doesn't work as well.
malapropism
4.5 / 5 (8) May 13, 2015
The Standard Models are vastly verified. That may be mere ad-hockery (see E. T. Jaynes), but it is not falsifiability.

I do not see your point in this comment: the researchers posited an hypothesis, they tested it and failed to falsify it from the observed results (that is, they saw some of the rare events predicted by the Standard Model). What's the problem?
theon
2.3 / 5 (3) May 14, 2015
"The framework does not, for instance, explain dark matter,"
Well, it doesn't explain WIMP dark matter. The better so, all evidence points at its nonexistence, 3 decades of hunting in about 70 dedicated searches.
charlimopps
5 / 5 (3) May 14, 2015
"The framework does not, for instance, explain dark matter,"
Well, it doesn't explain WIMP dark matter. The better so, all evidence points at its nonexistence, 3 decades of hunting in about 70 dedicated searches.


Dark matter isn't a prediction. It's a very irritating, experimentally verified fact. It's up to science to explain what's causing it now. It absolutely does exist, much to the dismay of researchers. They are HOPING that it's WIMPs, because that would allow their current models to continue to work. If it's some other feature of the universe, they'll have a lot of work ahead.
haworth444
5 / 5 (1) May 14, 2015
sad when journalists cannot get simple facts right. The universe is 26.8% dark matter and 68.3% dark energy. Not sure which they are referring to. We only know what 5% of the Universe is. We should be humble.
charlimopps
not rated yet May 14, 2015
sad when journalists cannot get simple facts right. The universe is 26.8% dark matter and 68.3% dark energy. Not sure which they are referring to. We only know what 5% of the Universe is. We should be humble.

The article is correct, you are only "Sort of" correct. Mass and energy ARE equivalent but only if you consider an objects mass a measure of the energy it contains. But Energy is NOT mass. You can claim that they basically mean the same thing in a philosophical sense. If you found a way to harness dark energy you could even create matter that had mass. But of all the existing mass in the universe, Visible matter composes about 15% of it. DarkMatter is the other 85%. Check out: http://en.wikiped...ivalence
TimLong2001
not rated yet May 14, 2015
Have gluons ever been detected?
thaken
not rated yet May 14, 2015
These experiments are the, "same old / same old", partials are like bottles, smash the bottles, examine the fragments. It eventually breaks down to, Dark Energies, "sand".
vlaaing peerd
5 / 5 (1) May 15, 2015
"The framework does not, for instance, explain dark matter," that is a bit presumptuous, it could very well be something that fits in the Standard Model.
shavera
5 / 5 (4) May 15, 2015
TimLong2001: yes, gluons have been detected in approximately the same way as any other particle can be said to be detected.

When quarks leave a collision, they immediately "dress" themselves by pulling new quark/anti-quark pairs out of the vacuum. So, often times you can see two "back-to-back" jets of particles formed by these quarks and the particles they create.

But sometimes a third jet occurs. In this case, since it doesn't come with a "quark/anti-quark" pair, but creates particles through the strong force... then we can infer it is a gluon.
rufusgwarren
not rated yet May 18, 2015
Sooo, what were the controls used for verification?

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