A heavy, strange cousin of the proton has been seen a second time, but it seems to have lost a little weight. The omega-b-minus, also called the omega-sub-b baryon, is a three-quark particle related to protons and neutrons. It has been observed at the Collider Detector at the Fermi National Accelerator Laboratory in Illinois, scientists announced in a paper submitted to Physical Review D and available online at arxiv.org. But CDF’s measurement of the particle’s mass is significantly lower than a previous measurement, leaving researchers wondering what caused the discrepancy.
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“One or both of the measurements are missing the mark,” says CDF physicist Pat Lukens, a coauthor of the paper.
DZero, CDF’s sister detector, had observed the omega-b-minus in fall 2008 using the same proton accelerator, the Tevatron, at Fermilab (SN: 9/27/08, p. 9). Although CDF’s recent mass measurement of 6.054 billion electronvolts agrees better with the expected mass for an omega-b-minus particle than DZero’s measurement of 6.165 billion electronvolts, the mismatch in the results is disconcerting, the researchers say.