We are standing on the shoulder of giants. Science builds on previous knowledge, but that knowledge must also be challenged and revised. /*thread*/

Lee and Yang were first to point out that left-right symmetry was not tested in weak interactions. They proposed and experiment implemented by Chien-Shiung Wu who confirmed this. Lee and Yang got the Nobel prize in 1957; Wu did not. One of the big mysteries of @NobelPrize .

In 1957 Lee and Yang also pointed out that weak decays of hyperons - unstable baryons with a strange quark - were left-right asymmetric (Phys. Rev. 108 1645).

This "parity" asymmetry was parametrised by a quantity α, which was then measured by several experiments. The first by Cronin, who would later discover CP violation.

In 2018 the knowledge of the α asymmetry for Λ baryons (composed of a strange quark, a down quark and an up quark) was 0.642±0.013, an average of 5 experiments run between 1963 and 1975.

Later in 2018, the BESIII experiment in Beijing revisited that, using pairs of a Λ baryon and a Λ̅ antibaryon produced in electron-positron collisions. https://arxiv.org/abs/1808.08917  .

The world average is updated to be only this measurement.

This value new was quickly confirmed by the CLAS experiment at Jefferson Lab @JLab_News (though their value is somewhat in between).

This poses a problem: The value of the α asymmetry has been used as input by several measurements.
The @cerncourier writes: https://cerncourier.com/a/lambda-hyperon-anomaly-confirmed/

In particular the measurement of the polarisation of the Λb⁰ baryon (beauty, up, down) relies on it. The polarisation describes how the spin of a particle aligns with the direction of the collision, an important test of how b quarks are produced in high-energy collisions.

Several measurements using the obsolete value as input were done by @ATLASExperiment, @CMSExperiment and @LHCbExperiment, for instance https://arxiv.org/abs/1302.5578 .

LHCb has now redone this measurement using the new value, and also determining it directly. https://twitter.com/LHCbPhysics/status/1253198397521231873?s=20

The Λb⁰ polarisation still comes out compatible with zero, and we also determine α to be 0.74. The 68% credibility interval spans [0.71, 0.78]. We thus confirm the BESIII result.

It is not the first time we need to update prior knowledge with measurements that are several standard deviations off. See for instance the lifetime of charmed baryons. https://twitter.com/LHCbPhysics/status/1141934572814372864?s=20

These old experiments often date from times when resolutions were not that great and the standards for assigning systematic uncertainties different.
I wonder how many other skeletons in the closet there are to be uncovered.