But even first-rate physicists can get a measurement like this one wrong. Only first-rate physicists with complete dedication to the task could attempt it, carry it out, convince their many colleagues on the CDF experiment that they’d done it right, and get it through external peer review into Science. Why? This measurement, which took several many years of work, is probably among the most difficult ever performed in particle physics. I’d say the chance that wrong is substantial. However, as theoretical physicist Matt Strassler wrote on his blog on April 8: This is considered very low, and notably lower than the threshold at which a particle physics data point is considered to be evidence. And according to Kotwal, the odds of their measurement being a fluke are “1 in one billion”. According to ScienceNews, the measurement is “about twice as precise as the previous record”. The new measurement at Fermilab is similarly susceptible to being wrong. But subsequent tests confirmed that there was a glitch. If it had been true, it would have been the brightest bit of new physics. In a new infamous incident in 2011, a detector in Italy reported that it had spotted an elementary particle travelling at faster than the speed of light. We were so focused on the precision and robustness of our analysis that the value itself was like a wonderful shock.”ĭiscoveries like this often generate a lot of hype – only for subsequent attempts to reproduce the findings to come up short. Even a slight deviation could be a sign of new physics.Īshutosh Kotwal, a physicist at Duke University, a member of the CDF II team and lead author of the study, told Gizmodo, “We were very pleasantly surprised. Quantitatively, the new measurement is a small difference – but calculations based on the Standard Model are notorious as much for their complexity as for their precision. The Standard Model predicts the W boson’s mass to be 80.3 GeV. (By the mass -energy equivalence, GeV – units of energy – can be converted to mass by dividing by c2, where c is the speed of light in a vacuum.) Using this they calculated the particle’s mass to be 80.4 GeV (give or take a little). In the dataset the new team analysed, CDF II had recorded approximately four million W bosons.
All this happened before 2011, when the instruments in question shut down. Now we have the W boson mass anomaly ( published on April 7).Īt the Fermilab facility in Illinois, physicists smashed beams of protons and antiprotons into each other and recorded the fallout using a detector called CDF II. This was a potential sign of new physics that physicists are working on. Last year, physicists running experiments in New York reported that another elementary particle called a muon behaved differently in a magnetic field than the Model predicted. These deviations are broadly called ‘new physics’: they’re what physicists can use to fix the Standars Model. So when a Standard Model prediction is found to be wrong in an experiment, physicists can study the experiment more closely to understand where the value might have deviated. It also can’t explain why the Higgs boson is so heavy, why the universe has more matter than antimatter, why gravity is so weak or why the size of the proton is what it is. The Model can’t explain gravity and dark matter. The Standard Model is famously broken but physicists don’t know how. And far from being an embarrassment to physicists, who used the Standard Model to predict the W boson’s mass, they’re delighted. When two other particles exchange the W and/or Z bosons, they’re said to be acted on by the weak nuclear force.Īccording to a new measurement, the mass of W bosons appears to be higher than that predicted by the Standard Model. This force is mediated by two particles: the two W bosons and the Z boson. There are four fundamental forces in the universe one of them is the weak nuclear force: it’s involved in nuclear fusion reactions and for radioactive decay. And now there’s new evidence that it’s wrong about the mass of one particle.īosons are particles that carry force. There’s a framework of rules that describes how the elementary particles of our universe look 1 and behave that physicists have spent decades putting together, called the Standard Model.
Workers with the collider-detector at Fermilab, Illinois.
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