Tuesday, July 12, 2011

The Death of Parity. DIE Parity, DIE !

Cary Grant and Madame Wu, circa 1966
On January 15, 1957, distinguished Columbia University physicist I.I. Rabi announced that parity was NOT conserved in certain particle interactions, and the physicists of the world were astounded. The actual experiment had been run by Madame Wu based on theory by Yang and Lee.

Wolfgang Pauli didn't believe parity was not conserved, saying before the results were announced:

"I do not believe that the lord is weak left-hander, and I am ready to bet a high sum that the experiments will give symmetrical results."

Afterwards, Pauli, who would die in 1958,  admitted:

"Now that the first shock is over, I begin to collect myself. Yes, it was very dramatic. On Monday, the twenty first, 8 p.m. I was supposed to give a lecture on the neutrino theory. At 5.pm. I received three experimental papers [reports on the first three tests of parity] ... I am shocked not so much by the fact that the Lord prefers the left hand as by the fact that he still appears to be left-handed symmetric when he expresses himself strongly. In short, the actual problem now seems to be the question: Why are strong interactions right-and-left symmetric?"

paraphrased from Martin Gardner's book: " The New Ambidextrous Universe: Symmetry and Asymmetry from Mirror Reflections to Superstrings", Third Ed., Chapter 22: The Fall of Parity

Chien-Shiung Wu (simplified Chinese吴健雄traditional Chinese吳健雄pinyinWú Jiànxíong, May 31, 1912 – February 16, 1997) was a Chinese-American physicist with expertise in the techniques of experimental physics and radioactivity. Wu worked on theManhattan Project (she helped to develop the process for separating uranium metal into the U-235 and U-238 isotopes by gaseous diffusion). She later performed experiments that contradicted the "Law of Conservation of Parity" and which confirmed the theories of colleagues. Her honorary nicknames include the "First Lady of Physics", the "Chinese Marie Curie", and "Madame Wu".

Parity violation

Although parity is conserved in electromagnetismstrong interactions and gravity, it turns out to be violated in weak interactions. The Standard Model incorporates parity violation by expressing the weak interaction as a chiral gauge interaction. Only the left-handed components of particles and right-handed components of antiparticles participate in weak interactions in the Standard Model. This implies that parity is not a symmetry of our universe, unless a hidden mirror sector exists in which parity is violated in the opposite way.
It was suggested several times and in different contexts that parity might not be conserved, but in the absence of compelling evidence these suggestions were not taken seriously. A careful review by theoretical physicists Tsung Dao Lee and Chen Ning Yang[2] went further, showing that while parity conservation had been verified in decays by the strong orelectromagnetic interactions, it was untested in the weak interaction. They proposed several possible direct experimental tests. They were almost ignored, but Lee was able to convince his Columbia colleague Chien-Shiung Wu to try it. She needed special cryogenic facilities and expertise, so the experiment was done at the National Bureau of Standards.
In 1956-1957 Wu, E. Ambler, R. W. Hayward, D. D. Hoppes, and R. P. Hudson found a clear violation of parity conservation in the beta decay of cobalt-60.[citation needed] As the experiment was winding down, with double-checking in progress, Wu informed her colleagues at Columbia of their positive results. Three of them, R. L. GarwinLeon Lederman, and R. Weinrich modified an existing cyclotron experiment, and they immediately verified the parity violation.[citation needed] They delayed publication of their results until after Wu's group was ready, and the two papers appeared back to back in the same physics journal.
After the fact, it was noted that an obscure 1928 experiment had in effect reported parity violation in weak decays, but since the appropriate concepts had not yet been developed, those results had no impact.[3] The discovery of parity violation immediately explained the outstanding τ-θ puzzle in the physics of kaons.
In 2010, it was reported that physicists working with the Relativistic Heavy Ion Collider (RHIC) had created a short-lived parity symmetry-breaking bubble in quark-gluon plasmas. An experiment conducted by several physicists including Yale's Donner Professor of Physics as part of the STAR experiment, which has been smashing atoms together since 2000, showed a variation in the law of parity itself.[4]

[edit]Intrinsic parity of hadrons

To every particle one can assign an intrinsic parity as long as nature preserves parity. Although weak interactions do not, one can still assign a parity to any hadron by examining thestrong interaction reaction that produces it, or through decays not involving the weak interaction, such as rho meson decay to pions.


Pat B said...

steven, when I read your stuff I feel like I need to go back to school...

Steven Colyer said...

Me too! The more we learn the stupider we feel, because we realize there is SO much more to learn! As our knowledge grows with time, our ignorance, the larger set, grows faster. Geometrically? Exponentially? Well, those are big-boy words, not sure what they mean. :-)

I'm too much of a generalist Pat. They don't PAY people to generalize.... only specialize. I'm zeroing in on what to specialize in, but it's taking the devil's own time. Well: Give time: time (I always say). Problem is, bill collectors don't see things that way. :-)

Phil Warnell said...

So we are interested if nature has a preference or is it an illusion. Ernst Mach long ago asked this question and yet never came to a resolution. Madame Wu inspired by Mach’s confusion believed that symmetry at a deeper level would be somehow preserved. I personally agree as finding nature as the best of illusionists with its greatest of demonstration being reality.

“Reality is merely an illusion, albeit a very persistent one.”
-Albert Einstein

Steven Colyer said...

I'm also willing to see a symmetry at a deeper level, and we will as soon as we build a particle accelerator with the same circumference as the galaxy ... (pauses)

We may have hit "the particle desert", meaning no "preons" or smaller-than-quarks/electrons, for a long way down.

In truth, if Sean Carroll and other's theories are to be believed, we have a parallel twin Universe, where right-hand symmetry applies. It's called "the shadow Universe', explains the presence of dark matter, yet no reputable physicist will stand by it. From Gardner's book, yet again.

Not to be out-quoted by Phil, I submit:

All that we see or seem is but a dream within a dream.

... Edgar Allan Poe

Unknown said...

I'm pretty sure the photograph with Cary Grant is of Madame Sylvia Wu, the restaurateur, not Madame Chien-Shiung Wu, the physicist.