The Large Hadron Collider (LHC) is also a large hadron discoverer. The most famous atomic pulverizer near Geneva in Switzerland proved the existence of the Higgs boson in 2012. This discovery laid the final cornerstone of the current classification of elementary particles. But the Large Hadron Collider also collected dozens of non-elementary particles called hadrons-these particles, such as protons and neutrons, are made of quarks.
The newest hadron made its debut at the Virtual Conference of the European Physical Society on July 29, when Ivan Polyakov, a particle physicist at Syracuse University in New York Lifted the veil of a previously unknown strange hadron It consists of four quarks. This brings the hadron bounty of the Large Hadron Collider to 62. Record kept by Patrick Koppenburg, A particle physicist at the National Institute of Subatomic Physics in Amsterdam, Nikhef. “These are world firsts,” said Koppenburg of CERN at the European Particle Physics Laboratory, who is the host of the LHC.
The established pantheon of particles, called the Standard Model, describes the basic components of matter and the basic forces acting on them. It includes six quarks, six antimatter counterparts, and several other elementary particles, including electrons and photons. The Standard Model also includes rules for how quarks form composite particles called hadrons. Quarks are combined by a strong nuclear force, one of the four basic forces. The two most common quarks in nature are called “up” and “down”; their possible combinations include neutrons (one up and two down) and protons (two up and down).
Protons are the only known isolated and stable hadrons-neutrons are only stable when they are incorporated into the nucleus. All other hadrons are formed only briefly in the collision of other particles and decay within a fraction of a second. Therefore, the LHC creates new hadrons by causing high-energy frontal collisions between protons.
Most of the new hadron types of the LHC have been discovered by the LHCb, which is one of the four giant detectors in the 27-kilometer circular tunnel that houses the LHC, and the particles announced by Polyakov are no exception. Polyakov of the Moscow Institute of Theoretical and Experimental Physics and his collaborator Vanya Belyaev discovered the expected characteristics of a kind of “tetraquark” called Tcc+-a kind of tetraquark hadrons, by sifting through the data of proton collision fragments.
Four quarks are very unusual: most known hadrons consist of two or three quarks. In 2003, the High Energy Accelerator Research Organization (KEK) in Tsukuba, Japan, discovered the first four quarks, and LHCb discovered more. But the new one is strange. The previous tetraquarks are likely to be pairs of ordinary quark double states, which are connected to each other like atoms in a molecule, but theoretical physicist Marek Kalina believes that the latest quark may be true and tightly bound. The quartet. “This is a big deal. This is a new animal, not a hadron molecule. This is the first of its kind,” said Karliner, who helped predict particles with the same characteristics as Tcc+ in 2017 at Tel Aviv University in Israel. The presence.
Belyaev said that in nature, four quarks may only exist in the first moment of the universe, when all matter was compressed in an extremely narrow space. But recreating them helps physicists test their theories about how particles interact through strong nuclear forces.
The data revealed the properties of the new particles so precisely that Belyaev was stunned. “My first reaction was: it was my mistake,” he said. For example, the mass of a particle is approximately 4 times that of a proton, and its margin of error is nearly 3,000 times that of when the Higgs boson was discovered. Belyaev added that Tcc+ may have been found in early LHC data, but he and his LHCb colleagues have not discovered it until now because they have many other particles to look for.
The exploration of new hadrons will continue. The combination of dozens of quarks can produce hadrons. Kalina said that there are 50 possible 2-quark hadrons, of which only one has been observed, and there are 75 possible quark triplets (and as many antiquark triplets), of which nearly 50 have been observed. “We are sure that all other products exist, but they are difficult to manufacture,” Karliner said.
In addition, for each combination of quarks, there are almost an infinite number of possible heavier “excited states”—for example, distinguished by the speed at which they rotate—each of which is classified as a single particle. Many were discovered through experiments, and in fact most of the particles in the Koppenburg catalog are excited states. “Who knows how many other states are hidden in conspicuous places, sitting in the data on the laptop,” said Koppenburg, like Polyakov and Belyaev, who is also a member of the LHCb collaborative project.
But he also wants to know whether all these discoveries should be treated as discrete particles. “I am increasingly convinced that we need to better define what a particle is,” he said.
This article is reproduced with authorization and has been First published August 10, 2021.