Shulou(Shulou.com)11/24 Report--

Imagine that we weigh a house on a very large scale, and then we break it down into individual bricks and we find that the sum of the bricks weighs more than the house. In the world of classical physics, we think this is impossible. But in the weird world of subatomic physics, it could happen. Assuming that protons are the houses mentioned above, those bricks are the quarks inside protons, and knowing more about them helps us understand the greatest mysteries of particle physics.

Every atom in the universe has at least one proton inside it. In fact, protons make up most of conventional matter. Thanks to decades of particle physics research, we know that protons are made up of smaller particles called quarks. Specifically, protons are made up of two basic "flavors" of quarks: up quarks and down quarks.

Some physicists have suggested that, in addition to these two quarks, protons have another fundamental component: charmed quarks. Charm quarks are another form of quark that behaves exactly the same as the up quark, except that they have much more mass, and a single charm quark has more mass than the entire proton. So, the idea of making protons out of it does sound a little strange. But thanks to another strange rule, it makes sense physically. On this tiny scale of reality, everything boils down to probability.

Physicists use equations to describe what quarks they see when they observe protons colliding at high speeds, and then they test them with experimental observations. About 99.5 percent of the time, when they looked at protons in these situations, they would see that it was made up of up and down quarks, as expected. But the other half percent of the time, they saw that it was also made of charm quarks, which is why bricks are heavier than houses.

Because charm quarks are rare and have short lifetimes, they account for only a small fraction of the total mass of protons in equations describing them. Physicists do often see short-lived charmed quarks in protons, but they call them extrinsic charmed quarks because they are not considered part of protons when they are not bombarded at high speeds.

However, some physicists believe that there are intrinsic charmed quark building blocks whether or not we smash protons in particle accelerators. It proved much more difficult to find evidence that protons were indeed composed of internally charmed quarks. Physicists have been chasing subtle clues to the intrinsic charm quark for decades, but a huge effect may have obscured it. Each proton also has a churning "ocean" of particles, and physicists must look for intrinsic charms in this noise.

If you analyze the data without considering specific models, you can't eliminate these noises. There are many plausible models of intrinsic charms, so physicists usually have to check each model to see if it matches experimental data. But research published in August 2022 uses a new technique: machine learning. The team fed 30 years of particle collision data into a computer and then let the computer match models to the data to look for evidence of intrinsic charm quarks.

Machine learning can look at a large number of different models at once, and it can determine which models best fit the data more efficiently than previous manual matching. Sure enough, the researchers did find evidence of intrinsic charm quarks. They even calculated the probability of finding one of the intrinsic charm quarks: about 0.6 percent. But is this evidence reliable? The research team said that the 5σ standard required by particle physics is not yet met.

Whether or not protons actually have such intrinsic charms, such ultra-precise tests are crucial to the future of particle physics. Researchers are delving deeper into the smallest parts of reality, which requires a high degree of accuracy, both in experimental design and in understanding the laws of nature.

This article comes from Weixin Official Accounts: Vientiane Experience (ID: UR4351), by Eugene Wang

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