Anti-matter falls down, just like matter

The uncertainty of science: In a difficult particle physics experiment that carries large margins for error, scientists have determined that gravity appears to affect anti-matter the same as matter.

Quantitatively, the experiment indicates that antimatter experiences a pull from gravity that’s 75% as strong as that on ordinary matter, give or take 20%—a statistical agreement between the two. Hangst says 99.9% of physicists would have predicted the result. Still, he notes, “You have to do the experiment with an open mind.”

One must understand that, at atomic levels, the influence of gravity is practically nil. Extracting a measurment of its influence outside the other more powerful forces that dominate atomic particles, magnetism, the weak force, and the strong force, is difficult, to put it mildly.

The key is that the experiment result showed some influence of gravity, in the expected direction.

New data contradicts accepted standard model of particle physics

The uncertainty of science: After years of analysis, physicists have refined their measurement of the mass of one important subatomic particle, and discovered that its weight violates the accepted standard model of particle physics, threatening to overthrow it entirely.

W bosons are elementary particles that carry the weak force, mediating nuclear processes like those at work in the Sun. According to the Standard Model, their mass is linked to the masses of the Higgs boson and a subatomic particle called the top quark. In a new study, almost 400 scientists on the Collider Detector at Fermilab (CDF) collaboration spent a decade examining 4.2 million W boson candidates collected from 26 years of data at the Tevatron collider. From this treasure trove, the team was able to calculate the mass of the W boson to within 0.01 percent, making it twice as precise as the previous best measurement.

By their calculations, the W boson has a mass of 80,433.5 Mega-electronvolts (MeV), with an uncertainty of just 9.4 MeV either side. That’s within the range of some previous measurements, but well outside that predicted by the Standard Model, which puts it at 80,357 MeV, give or take 6 MeV. That means the new value is off by a whopping seven standard deviations.

Further cementing the anomaly, the W boson mass was also recently measured using data from the Large Hadron Collider, in a paper published in January. That team came to a value of 80,354 MeV (+/- 32 MeV), which is comfortably close to that given by the Standard Model.

Personally, I always take this level of physics with a great deal of skepticism. The data involves a lot of assumptions and uncertainties. That other researchers came up with a different number illustrates this.

Nonetheless, these results could suggest that the standard model, the consensus theory for decades, is either incomplete, or wrong. The former would be more likely, but no possibility should be dismissed. And even if wrong, much of that model still works so well any new model must include large parts of it.

New data suggests muon is more magnetic that predicted

The uncertainty of science: New data now suggests that the subatomic particle called the muon is slightly more magnetic that predicted by the standard model of particle physics, a result that if confirmed will require a major rethinking of that standard model.

In 2001, researchers with the Muon g-2 experiment, then at Brookhaven, reported that the muon was a touch more magnetic than the standard model predicts. The discrepancy was only about 2.5 times the combined theoretical and experimental uncertainties. That’s nowhere near physicists’ standard for claiming a discovery: 5 times the total uncertainty. But it was a tantalizing hint of new particles just beyond their grasp.

So in 2013, researchers hauled the experiment to Fermi National Accelerator Laboratory (Fermilab) in Illinois, where they could get purer beams of muons. By the time the revamped experiment started to take data in 2018, the standard model predictions of the muon’s magnetism had improved and the difference between the experimental results and theory had risen to 3.7 times the total uncertainty.

Now, the g-2 team has released the first result from the revamped experiment, using 1 year’s worth of data. And the new result agrees almost exactly with the old one, the team announced today at a symposium at Fermilab. The concordance shows the old result was neither a statistical fluke nor the product of some undetected flaw in the experiment, says Chris Polly, a Fermilab physicist and co-spokesperson for the g-2 team. “Because I was a graduate student on the Brookhaven experiment, it was certainly an overwhelming sense of relief for me,” he says.

Together, the new and old results widen the disagreement with the standard model prediction to 4.2 times the experimental and theoretical errors.

That result is still not five times what theory predicts — the faux standard physicists apparently use to separate a simple margin of error and a true discovery — but it is almost that high, has been found consistently in repeated tests, and appears to be an unexplained discrepancy.

Not that I take any of this too seriously. If you read the entire article, you will understand. There are so many areas of uncertainty, both in the data and in the theories that this research is founded on, that the wise course is to treat it all with a great deal of skepticism. For example, the anomaly reported involves only 2.5 parts in 1 billion. While this data is definitely telling us something, but it is so close to the edge of infinitesimal that one shouldn’t trust it deeply.

A rehash of the available data has narrowed the search for the Higgs particle.

A rehash of the available data has narrowed the search for the Higgs particle.

Taken together with data from the other detector, ATLAS, Higgs overall signal now unofficially stands at about 4.3σ. In other words, if statistics are to be believed, then this signal has about a 99.996% chance of being right.

It all sounds very convincing, but don’t get too excited, because the fact is that statistical coincidences happen every day. Over at Cosmic Variance, Sean Carroll points out that there is a 3.8σ signal in the Super Bowl coin toss.

CERN announces an update on the search for the Higgs Boson

Not there yet: CERN announces an update on the search for the Higgs Boson.

The main conclusion is that the Standard Model Higgs boson, if it exists, is most likely to have a mass constrained to the range 116-130 GeV by the ATLAS experiment, and 115-127 GeV by CMS. Tantalising hints have been seen by both experiments in this mass region, but these are not yet strong enough to claim a discovery.

Higgs announcement from CERN on December 13

CERN will be making an announcement on the status of its search for the Higgs particle on December 13. From this interview of one of its scientists:

The thing I know for sure is that [CERN Director General] Rolf-Dieter Heuer, who must know the results of both experiments, says that on December 13 we will not have a discovery and we will not have an exclusion.

The inteview is fascinating, as he notes how the Higgs research might also have a bearing on the search for dark matter.