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Particle physics

Strange days

Nature volume 424, pages 376–377 (2003)Cite this article

Three new subatomic particles have been found, and all survive for an unusually long time before they decay. Physicists now face the challenge of explaining this within the framework of the existing theory.

In the past two months, three different particles have been discovered, and explaining them has proved a challenge for theorists. Although not as extreme as the above example, each of these new particles has an unusually elongated lifetime. Two of them are 'mesons', each containing a strange anti-quark and a charm quark (the fourth quark type)2,3. The reason for their metastability is understood, but their detailed nature and dynamics remain to be resolved. The third particle4 is a member of the 'baryon' family of particles that also includes the proton and neutron. But, unlike the proton and neutron, this particle has some strange-quark content. In fact, unlike any other baryon known, it has overall one unit of 'positive strangeness'. It is an enigma. The quark model that now underpins the standard model was developed, in part, under the assumption that such things do not exist. And although it may be possible to interpret this particle as a combination of four quarks (two up, two down) and a strange anti-quark (providing that unit of positive strangeness), the challenge is to explain also why this 'pentaquark' does not fall apart more quickly.

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Figure 1: Quarks and particles.

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  1. Department of Theoretical Physics, University of Oxford, Keble Road, Oxford, OX1 3NP, UK

    Frank Close

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  1. Frank Close
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Close, F. Strange days. Nature 424, 376–377 (2003). https://doi.org/10.1038/424376a

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  • DOI: https://doi.org/10.1038/424376a

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