What is the test required by the Fourteenth Amendment for proof beyond a reasonable doubt?

[9 Cal.4th 439] "It is self-evident, we think, that the [Fourteenth] Amendment requirement of proof beyond a reasonable doubt and the Sixth Amendment requirement of a jury verdict are interrelated. It would not satisfy the Sixth Amendment to have a jury determine that the defendant is probably guilty, and then leave it up to the judge to determine ... whether he is guilty beyond a reasonable doubt. In other words, the jury verdict required by the Sixth Amendment is a jury verdict of guilty beyond a reasonable doubt.... [A]n instruction [misdefining proof beyond a reasonable doubt by effectively lowering its threshold] ... does not produce such a verdict." (Sullivan v. Louisiana, supra, 508 U.S. at pp. ---- - ----, 113 S.Ct. at pp. 2080-2081, italics in original, fn. omitted.)