Then there was the collective effort of experimentalists who unraveled the tau-theta puzzle which motivated Lee and Yang… That was a huge and fascinating effort, involving cosmic-ray emulsion experiments at a level of organization that rivals large collaborations today, as well as the emerging accelerator groups in the 1950′s. History as recited just neglects that whole chapter.

I think there were 3 experiments that published nearly simultaneously on parity violation.. Wu and a bunch of other collaborators (why are her collaborators Ambler, Hayward, Hoppes, and Hudson forgotten about?)… also Lederman, Garwin, and Weinrich, and then Telegdi and Friedman. The latter two groups used pi-mu-e decay, and really did devilishly clever experiments.

Not to run down Madame Wu at all, she was great! But there are solid reasons why she did not end up with a Nobel Prize. It is not so easy to isolate discrimination in her case. Meitner is a much, much stronger case to blame on discrimination.

I think the Standard Model merely `describes’ parity violation. It remains a terrific question… where are the other handedness of neutrinos? Maybe they’re the dark matter. Or maybe they will pop up at the LHC. But excluding one whole handedness from the Standard Model feels more unnatural then any fine-tuning argument.

BTW, I’ve been really sickened by all the priority arguments over the dark energy. Yuk, a pox on them all.

All in all, M. Curie comes across as the exception. If I were more bitchy I’d say that the prize comittee didn’t realise Marie was a woman (it’s not unusual for French men to have Marie as a middle name). Her daughter, Irene, does rather screw up that idea, though.

Accounting for something is not the same thing as explaining it. The SM accounts for the fermion mass hierarchy but certainly doesn’t explain it. Ditto parity-violation…sorry.

In his early days Professor Samuels’ research involved
measuring the polarization of emitted gamma rays from
radioactive Co60 (cobalt-60), whose nuclear spins had been
aligned by external magnetic fields at very low temperatures
near -273 degrees Celsius. The radioactivity of Co60 consists

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Peter Martel

of gamma rays (high energy photons) and lower energy Beta
rays (electrons). Measurements of gamma ray polarization can
define the direction of transverse photon vibration; thus
permitting deduction of the nature of transitions between
different energy levels of the Co60 nucleus. There was a great
deal of physics associated with these measurements, which
involved low temperature, solid state, and nuclear physics. The
results were very interesting to nuclear physicists but probably
not extremely exciting for the Nobel Prize committee and the
physics community at large.

……..

What subsequently interested the Nobel Prize committee
were Beta (electron) measurements on Co60 initiated by a
Madame Wu of Columbia University. For much of the first
half of the 1900’s it was thought electrons coming from Co60
had a property called “parity”—a concept very dear to nuclear
physicists until the fifties when two theoreticians (T.D. Lee and

C.N. Yang) began uttering heretical questions about its validity
as applied to the “weak” force in nuclei. What appeals to
physicists is symmetry—they like to believe that nature is
symmetrical and makes no distinction between opposite sides
of a subatomic particle. In its simplest terms, the notion of
parity holds that events arising from subatomic decay have
mirror symmetry.
As an aside, it should be noted that there is also a strong
force binding neutrons and protons together in the nucleus.
Physicists are also happy with the existence of two other forces
known to high school students as electromagnetic and
gravitational forces. Besides these four forces, astrophysicists
sometimes speculate about the possibility of other forces in the
outer reaches of the cosmos.

Anyway, there were a lot of similarities between the
Samuels and Wu measurements. They both required very low
temperatures and magnetic fields, the latter serving to align the
nuclear spins in cobalt. To the amazement of Wu and her
collaborators when the magnetic field on the nuclear spins was

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Memoirs of a Hayseed Physicist

reversed the electrons ejected from the nucleus did not reverse
direction. Parity had not been conserved.

In spite of Professor Wu’s earth-shattering results she was
passed over for the Nobel, much to the surprise of the physics
community. The award went to Lee and Yang. The reason was
probably because she did little if any of the measurements
herself; instead she headed a large team at Columbia and the
US National Bureau of Standards in Maryland. And then, of
course, gender discrimination can never be ruled out in such
matters.

Here collaborator at Birkbeck, Aron Klug who won the Nobel Prize for their work there has often pointed out that if she had lived the prize should have been shared between them.

John– parity violation is pretty well understood within the Standard Model. The weak interactions couple to particles with left-handed helicity, but not to particles with right-handed helicity; they violate parity as much as possible. Parity violation is not directly tied to matter/antimatter asymmetry, but CP violation, combining parity with charge conjugation, almost certainly is. See Mark’s series of posts, beginning here.