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 Title Kaon Photoproduction and the Lambda Decay Parameter alpha_ Authors David Ireland,Michael Doring,Derek Glazier,J. Haidenbauer,Maxim Mai,R. Murray-Smith,D. Ronchen JLAB number JLAB-THY-19-3019 LANL number arXiv:1904.07616 Other number DOE/OR/23177-4767 Document Type(s) (Journal Article) Supported by U.S. Naval Research: No Supported by Jefferson Lab LDRD Funding: No Funding Source: Nuclear Physics (NP) Journal Compiled for Physical Review Letters Volume 123 Page(s) 182301 Refereed Publication Abstract: The weak decay parameter $\alpha_-$ of the $\Lambda$ is an important quantity for the extraction of polarization observables in various experiments. Moreover, in combination with $\alpha_+$ from $\bar\Lambda$ decay it provides a measure for the matter-antimatter asymmetry. The weak decay parameter also affects the decay parameters of the $\Xi$ and $\Omega$ baryons and, in general, any quantity in which the polarization of the $\Lambda$ is relevant. The recently reported value by the BESIII collaboration of $0.750(9)(4)$ is significantly larger than the current PDG value of $0.642(13)$. In this work we make an independent estimate of $\alpha_-$, using an extensive set of polarization data measured in kaon photoproduction in the baryon resonance region and constraints set by spin algebra. The obtained value is 0.721(6)(5). The result is corroborated by multiple statistical tests as well as a modern phenomenological model, showing that our new value yields the best description of the data in question. Our analysis supports the new BESIII finding that $\alpha_-$ is significantly larger than the previous PDG value. Any experimental quantity relying on the value of $\alpha_-$ should therefore be re-considered. Experiment Numbers: Group: THEORY CENTER Document: pdf DOI: https://doi.org/10.1103/PhysRevLett.123.182301 Accepted Manuscript: 1904.07616(1).pdf arxiv copy of AM Supporting Documents: Supporting Datasets: