2021-06-30

This particle may have saved our universe

By yqqlm yqqlm

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This particle may have saved our universe

Researchers at the University of Oxford used data from the second run of the Large Hadron Collider to discover this kind of charm meson. This is a subatomic particle that contains both quark (the basic unit of matter) and antiquark, and can automatically switch between the two states of matter and antimatter.

Each particle has its own antimatter equivalent. They have the same mass, life span, and atomic spin, but they have opposite charges. Some particles, such as photons (light particles), their antiparticle is themselves; while other particles, benefiting from the so-called “quantum superposition” bizarre phenomenon, can exist in the form of matter and antimatter at the same time.

Charm meson belongs to the last category. Quantum superposition is derived from quantum mechanics (or the strange rules that govern the microcosm). Quantum superposition allows microscopic particles to exist in many different states at the same time, essentially a mixture of different particles, until someone observes these particles and chooses a state to start research. They are not only particles, but also have the properties of waves. The size of these waves at any given location in space represents the probability of finding a particle at that location.

When the charm meson (called “D0”) and its antiparticle equivalent (“anti-D0″) exist in a superposition state, the wave of D0 and the wave of anti-D0 overlap in many ways, Two other material particles are formed: D1 and D2. D1 and D2 are also in a superposition state. Although D1 and D2 are composed of the same particle (D0) and anti-particle (anti-D0) components, their mixture is slightly different, and thus have different masses and lifespans.

The reverse is also true; D1 and D2 can also be superimposed to produce D0 or anti-D0, depending on how they are superimposed on each other.

The co-author of the paper, experimental physicist at the University of Manchester and LHC spokesperson Chris Parks said: “You can think of D0 as a mixture of D1 and D2, or D1 by D0 and The composition of the anti-D0 mixture is just two ways of looking at the same phenomenon.”

The quality of these particle waves determines their wavelength, which in turn determines the way they interfere with each other, and the more important The difference in quality between D1 and the lighter D2. This difference in quality determines the speed at which the charm meson switches between its two states-matter (D0) and antimatter (anti-D0).

In order to measure at such a precise level, the researchers observed 30.6 million charm mesons. Charm mesons are produced after the collision of two protons in the Large Hadron Collider. After only a few millimeters of propagation, the charm meson quickly decays into other lighter particles. However, the ultra-precision detectors in the particle accelerator can help the team compare the nearest and farthest charm mesons. Then, researchers can use the difference in propagation distance to calculate the difference in quality between the two possible states.

This is also the second time scientists have discovered that a particle oscillates between matter and antimatter states in this way. The first discovery was in 2006, when the strange-b meson was observed. But the researchers say that observing this phenomenon in charm mesons is more difficult, because the particles usually decay before they transform.

Co-author Guy Wilkinson, an experimental physicist at the University of Oxford, said in a statement: “The uniqueness of the discovery of the oscillation phenomenon of charm meson particles is that it is not like b mesons. The oscillation of the charm meson is very slow, so it is extremely difficult to measure the oscillation of the particle before the charm meson decays rapidly.”

Particles that can switch between matter and antimatter are very important because they may be the answer to science The key to one of the biggest mysteries in the world. The mystery is: why the universe exists.

According to the Standard Model, which is the theory describing the elementary particles that make up the universe, at the beginning of the Big Bang, equal amounts of matter and antimatter were produced. However, the universe we live in today is almost entirely composed of matter. Since matter and antimatter will annihilate each other at the moment they come into contact, the universe will also annihilate itself at the moment or shortly after it was born in the Big Bang. So what caused the imbalance between matter and antimatter?

Some hypotheses believe that particles such as charm mesons protect our material universe from annihilation, especially when their conversion frequency from antimatter to matter is much higher than their conversion frequency from matter to antimatter. . The upgraded Large Hadron Collider will restart in September this year after being shut down for more than three years. In addition, Japan’s Bell2 experiment also plans to carry out similar meson research. At that time, researchers may be able to find some new clues. (Yunlin)