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Open Access Publications from the University of California

Study of 14O as a test of the unitarity of the CKM matrix and the CVC hypothesis


The study of superallowed beta decay in nuclei, in conjunction with other experiments, provide a test of the unitarity of the quark mixing matrix or CKM matrix. Nonunitarity of the CKM matrix could imply the existence of a fourth generation of quarks, right handed currents in the weak interaction, and/or new exotic fermions. Advances in radioactive beam techniques allow the creation of nearly pure samples of nuclei for beta decay studies. The subject of this thesis is the development of a radioactive beam of 14O and the study of the 14O halflife and branching ratio. The radioactive beam is produced by ionizing 12C14O radioactive gas and then accelerating with an ECR ion source. The 14O nucleus decays via superallowed beta decay with a branching ratio > 99 percent. The low Z of 14O is important for calculating reliable corrections to the beta decay that generally increase in with Z. The > 99 percent branching ratio can be established with modest precision on the complementary branching ratio.When this work began the experimentally determined CKM matrix was nonunitary by 2.5 standard deviations. Recent studies of Kaon, Hyperon, and B meson decays have been used to determine Vus and Vub matrix elements. In this work the halflife and branching ratio of 14O are measured and used to establish Vud. The unitarity of the CKM matrix is then assessed. The halflife of 14O was determined to be 70.683 +- 0.015 s and the GamowTeller branching ratio was found to be 0.643 +- 0.020 percent. Using these results the value of Vud is 0.9738 +- 0.0005. Incorporating the new values for Vus of 0.2272 +- 0.0030 and Vub of 0.0035 +- 0.0015 the squared sum of the first row of the CKM matrix is 0.9999 +- 0.0017 which is consistent with unitarity.

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