Thread by @newscientist

Protons are at the heart of every atom, but we still don’t fully understand what's in them

You might remember from school that they contain three tiny particles: two up quarks and one down quark

But new research has found they contain a charm quark too

newscientist.com/article/233407…

In the 1960s, physicists began smashing protons together to try and find out what was inside

They quickly learnt that, for most of the time, there were three small particles: two up quarks and one down

But there was also data that didn’t quite make sense
newscientist.com/article/mg2263…

In 1980, at an experiment at the European Muon Collaboration at CERN in Switzerland, data hinted that the proton might also contain a charm quark and its antimatter equivalent, an anticharm

But the result was imprecise and inconclusive, so the issue was never fully resolved...

Now, though, we have the advantage of more data and much more powerful computers

A group called the NNPDF collaboration, led by Juan Rojo at @VUamsterdam, used machine learning on a dataset of more than 500,000 collisions spanning decades

This machine learning model didn’t suffer any of the biases that humans do when coming up with proton structures

So it could try lots of different proton structures made of different quarks to see which fit the data best

So, what did their model find?

There was evidence that a small part of the proton’s momentum, around 0.5 per cent, comes from the charm quark

newscientist.com/article/221547…

“It’s remarkable that even after all these decades of study, we’re still finding new properties of the proton and, in particular, new constituents,” Juan Rojo told @AlexWilkins22

newscientist.com/article/216911…

It’s not a closed case though

The 5 sigma level of certainty, which is a 1 in 3.5 million chance of a fluke result, wasn't reached

But Juan Rojo and his team are confident, especially as it fits some data from a completely different experiment at the #LHC last year

Finding that the charm quark contributes to the proton is important for reasons beyond basic science, too

Physics experiments at the #LargeHadronCollider rely on accurate models of proton substructure for accurate results

newscientist.com/article/mg2533…

The @uw_icecube in Antarctica looks for rare neutrinos when cosmic rays hit particles in Earth’s atmosphere

But the probability of a cosmic ray hitting a nucleus and producing neutrinos depends on whether the proton contains charm, says Juan Rojo

newscientist.com/article/210040…

To learn more about the surprise discovery of a charm quark in the proton, read @AlexWilkins22's full story: newscientist.com/article/233407…