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Jens 'n' Frens |
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On the pentaquark, it turns out this was sitting in my email for more than a week (emphasis and some mark-up added):... Efficient detectors downstream of the collision area looked for the evidence of the existence of various combinations of particles, including a short-lived state in which the K+ and the neutron had coalesced (drawing will be posted soon at www.aip.org/mgr/png ). In this case the amalgamated particle, or resonance, would have consisted of the three quarks from the neutron (two "down" quarks and one "up" quark) and the two quarks from the K+ (an up quark and a strange antiquark). The evidence for this collection of five quarks would be an excess of events (a peak) on a plot of "missing" masses deduced from K- particles seen in the experiment. ... Confirmation of this discovery comes quickly. A team of physicists in the US, led by Ken Hicks of Ohio University working in the CLAS collaboration at the Thomas Jefferson National Accelerator Facility, has also found evidence for the pentaquark. ...I suppose any unstable particle whose primary decay mode is into pieces that are already there (rather than one in which the fundamental constituents change their spots) can be called a resonance; the problem with resonances (by which I mean the reason I seem to be disparaging of them) is that there are so many of them. In the sixties, before the quark model had really taken hold, so many of these were discovered, each seemingly a new fundamental particle, that one prominent physicist facetiously suggested that the next year's Nobel Prize go to whoever did not discover a new particle that year. |
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