【By Observer News, Chen Sijia】On March 17, the Large Hadron Collider beauty (LHCb) experiment group of the European Organization for Nuclear Research (CERN) announced the discovery of a new particle, the singly charged doubly charmed baryon, which is a particle composed of one light quark and two heavy quarks. This important research result was mainly completed by Professor He Jibo from the School of Physical Sciences, University of Chinese Academy of Sciences, along with three undergraduate students.
In a statement, LHCb said that the singly charged doubly charmed baryon consists of two charm quarks and one down quark, similar in structure to the familiar proton, but instead of two up quarks, the two heavier charm quarks are used, increasing its mass four times compared to the original.
The statement said that this discovery has been announced at the 2026 Morion meeting currently being held in Italy, which helps physicists better understand how the strong interaction binds protons, neutrons and other composite particles together.
Quarks are the basic units that make up matter. There are six types of quarks in nature: up quarks, down quarks, strange quarks, charm quarks, bottom quarks, and top quarks. The first three are lighter, while the latter three are heavier. LHCb explained that mesons are composed of two quarks, and baryons are composed of three quarks, collectively known as hadrons. Protons and neutrons, which are well known, belong to baryons.
However, unlike stable protons, most hadrons are unstable and have very short lifetimes, making them difficult to observe directly. To produce these particles, high-energy particles need to be collided in devices like the Large Hadron Collider. These unstable hadrons decay rapidly, but the more stable particles produced by their decay can be detected, helping scientists infer the properties of the original particles.
According to the quark model proposed in the 1960s, there exists a "doubly charmed baryon" composed of two heavy quarks and one light quark. The newly discovered singly charged doubly charmed baryon is precisely this kind of special particle. The British magazine New Scientist called it "a cousin of the proton." Chris Parks, professor at the University of Manchester, said that the latest discovery is exciting, and scientists have been looking for such a particle.
An imaginative diagram of the singly charged doubly charmed baryon composed of two charm quarks and one down quark CERN
Vincenzo Vagnoni, spokesperson for LHCb, said that this is the first new particle discovered since the upgrade of the LHCb detector in 2023, and also the second time scientists have observed a baryon containing two heavy quarks in nearly 10 years.
Vagnoni said, "This achievement helps theoretical physicists test quantum chromodynamics models. This theory of strong interaction not only describes how quarks combine to form conventional baryons and mesons, but also includes more peculiar hadrons such as tetraquarks and pentaquarks."
In 2017, LHCb had discovered a doubly charged doubly charmed baryon composed of two charm quarks and one up quark. In its statement, LHCb pointed out that although the structures of these two particles are very similar, due to complex quantum effects, the predicted lifetime of the newly discovered singly charged doubly charmed baryon is shorter, and its observation is more difficult.
According to China News Network, the research on the singly charged doubly charmed baryon was mainly completed by Professor He Jibo from the School of Physical Sciences, University of Chinese Academy of Sciences, along with undergraduates Han Shuyu, Zhang Danyi from the University of Chinese Academy of Sciences, and Zhang Linnuo from the University of Science and Technology of China. The research also involved collaboration with institutions such as the University of Edinburgh in the UK, the European Organization for Nuclear Research, and the National Institute for Nuclear Physics in Italy.
During this research, Han Shuyu developed a charm baryon trigger algorithm based on machine learning, making important contributions to removing "cloned" particles in the new detector and accurately measuring the mass of the singly charged doubly charmed baryon.
Zhang Danyi completed the updated work on searching for the singly charged doubly charmed baryon in the data of the second phase of the LHCb operation, including re-optimizing event selection, adding new decay channels, and developing a data merging algorithm, laying the foundation for discovering the doubly charmed baryon using new physics data in 2024.
Zhang Linnuo made an important contribution to studying the doubly charmed baryon using data from 2024 during her summer student period at CERN in the summer of 2024, providing important input for improving the calibration of the detector.
According to the Science and Technology Daily, He Jibo said that this study shows that with solid training and guidance, our undergraduates are fully capable of engaging in pioneering, world-class frontier research. He pointed out that the discovery of this new particle will further deepen human understanding of the strong interaction and the quark model, and open new doors for future discoveries of new types of particles and exploration of the deep structure of matter.
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Original: toutiao.com/article/7618594779646984744/
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