Wednesday, October 5

We have just solved one of the great tongue twisters of modern physics: scientists have extracted the force from the strong force


An American team of physicists has announced that they have extracted force from the strong force. What seems like a strange tongue twister is an important advance in understanding one of the fundamental laws of particle physics, the force that holds together much of the fabric of matter throughout the Universe.


The strong force.
The strong nuclear force, or strong nuclear force, (the terminology may vary since it is a force with two components) is one of the four fundamental interactions (in addition to the weak nuclear force, the electromagnetic force, and the gravitational force) that they exist in the so-called “standard model” the most general theory we have in the field of particle physics.

The strong force is responsible not only for the atomic nuclei to stick together (not an easy task if we take into account that the positively charged particles, the protons, tend to repel each other).

It is also responsible for holding the quarks that make up protons and neutrons together to form these particles (collectively known as hadrons), but this “residual” interaction that occurs within atomic nuclei is slightly different from that within hadrons. .

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A spring that stretches.
This force is transmitted thanks to fundamental particles, the gluons. So important are they in holding the fabric of matter together that their name derives from the English word for glue. Unlike gravity, which gets weaker with distance, the strong nuclear force is more like a stretched spring: the further apart the particles are, the greater their strength or coupling.

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This is where the doubt arose, and it is relatively easy to calculate this coupling at short distances, but when the distance increases and with it the force, the calculation is impossible to solve in the same way. Until now, different models used to estimate the coupling at long distances (although we are still talking about very small fractions of a millimeter) implied different forecasts.

Some models predict that the force always gets stronger with distance, while others estimate that at some point it begins to decrease. A third, intermediate group theorized that, at a certain point, the force stabilizes, neither increases nor decreases.

Neither for you, neither for me.
“This is both a curse and a blessing,” explained Alexandre Deur, a researcher at the Jefferson Lab, a research center where they have managed to provide an empirical answer to this problem. And this answer that the researchers obtained corresponded to the middle way: the force seems to stabilize after surpassing a certain threshold.

Minimum power.
We are used to the enormous power of colliders like CERN’s LHC being the one that stands out in the headlines. But in this case it didn’t help. In fact, the particle accelerator used to carry out this experiment is not the one that can be found today in the Jefferson laboratory, but an old version of it with half the power, 6 GeV. The lower energy allows access to longer time scales and thus could longer distances between particles.

Cooperation is key, and laboratories with more powerful accelerators such as the LHC itself or the SLAC Accelerator, for example, have been key in determining this strong force on short space-time scales.

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From the empirical to the theoretical.
We are still far from a theory of everything that unifies what we know so far of the four forces that govern the interactions between subatomic particles, but this may be a new step in that direction. Not surprisingly, the strong force is responsible for 99% of the interactions of ordinary mass.

This experimental observation will allow physicists to discard some of the competing models that tried to give an answer to the question from the theory. In this way it should be possible to advance our knowledge not only of what surrounds us, but of the very bricks from which we are built.

In order to get an idea of ​​the importance of this force, it is enough to take into account that its residual form, not the one that keeps the quarks bound together but rather the protons and neutrons bound together in the atomic nucleus, is responsible for the nuclear energy, both in power plants and in atomic bombs.

Image | Helmholtz Center for Heavy Ion Research (GSI) particle accelerator, Achim Weidner

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