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The strong force holds atomic nuclei together.
But some nuclei are unstable and undergo radioactive decay, slowly releasing energy by emitting particles.
According to the Standard Model, forces are transmitted by particles.
It appeared to have the mass of roughly a medium-sized atom such as bromine.
The Standard Model was complete, and all the measurements we made hung together beautifully with the predictions.
These collisions briefly produce heavier particles that then decay back into lighter ones.
Antiprotons are the antimatter version of protons, with exactly the same mass but opposite charge.
Protons are made of smaller fundamental particles called quarks, and antiprotons are made of antiquarks.
It is the collision between quarks and antiquarks thatcreate W bosons.
W bosons decay so fast that they are impossible to measure directly.
So physicists track the energy produced from their decay to measure the mass of W bosons.
The prediction and the experiments always matched up until now.
The Fermilab team publishedinitial resultsusing a fraction of the data in 2012.
We found the mass to be slightly off, but close to the prediction.
The team then spent a decade painstakingly analyzing the full data set.
The process included numerous internal cross-checks and required years of computer simulations.
When the physics world finally saw the result on April 7, 2022, we were all surprised.
Physicists measure elementary particle masses in units of millions of electron volts shortened to MeV.
This may seem like a tiny excess, but the measurement is accurate to within 9 MeV.
This is a deviation of nearly eight times the margin of error.
When my colleagues and I saw the result, our reaction was a resounding wow!
Either the math is wrong, the measurement is wrong or there is something missing from the Standard Model.
First, the math.
for calculate the W bosons mass, physicists use the mass of the Higgs boson.
CERN experiments have allowed physicists tomeasure the Higgs boson massto within a quarter-percent.
Additionally, theoretical physicists have beenworking on the W boson mass calculations for decades.
While the math is sophisticated, the prediction is solid and not likely to change.
The next possibility is a flaw in the experiment or analysis.
Physicists all over the world are already reviewing the result to take a stab at poke holes in it.
But in my opinion, the experiment is as good a measurement as is currently possible.
Even before this measurement, some theorists hadproposed potential new particles or forcesthat would result in the observed deviation.
