Skip to main content

The Strange Story of Free Fractional Charge

The currently widely held wisdom is that quarks, the subatomic constituents that make up protons and neutrons, cannot be found in an unbound state, (i.e. roaming freely outside of a proton, neutron, or other particle made up of quarks).  The reasoning goes that the attractive force due to the strong force between two quarks is so powerful that if they are separated far enough apart, there will be enough energy stored in the  strong field to create two additional quarks that will immediately glom on to the two you were trying to separate in the first place, hence, no independent unbound quarks.

In 1977, however, Larue, Fairbank[1], and Hebard reported that they had found evidence indicating that free quarks did in fact exist[2].  Their experiment involved suspending a 1/4 mm superconducting niobium sphere in a magnetic field gradient[7] and causing it to oscillate in a vertical direction.  The researchers measured the effects reversing the polarity of an applied electric field had on the sphere's oscillation frequency. Using this data, they were able to calculate how much free charge was present on the sphere.  They wound up with the charge data shown below [3] (picture 2)


The scientific community at large, at least those who remember the work at all, tend to remember the penultimate incident in the history of the experiment.  Luis Alvarez suggested that to remove any possibility that humans had tainted the data by performing subjective data cuts, random numbers should be added to a newly taken data set.  That data was to be 'blind' analyzed and the results were to be reported.  What most people will tell you is that the published results after this analysis were less than conclusive.  What they'll leave out or don't know is that the published blind results contained a number of disclaimers that the graduate students in charge of the project had setup the apparatus incorrectly and that most of the inconclusiveness could just as easily be attributed to this poor setup.  

In 1989 after two years of retirement, William Fairbanks returned to Stanford to perform more work on the fractional charge experiment.  Sadly, he died soon thereafter on a morning jog after spending the night before working on the fractional charge experiment.  In an obituary befitting the X-Files the New York Times reported
"Although Dr. Fairbank retired two years ago as physics professor at Stanford University, he had been at work there the night before his death, trying to verify his report of 11 years ago concerning the existence of individual subatomic particles called quarks."[4]
While there are claims that the experiment was reproduced by other researchers, there are interesting inconsistencies in their methods.

1.  The follow-ons weren't done at liquid helium temperatures
2.  A ferromagnetic levitation system utilizing iron covered niobium spheres was used instead of the superconducting levitation system used in Fairbank's experiments.

A few years later in 1997, quasi-particles, combinations of electrons that behave in manners inconsistent with the behavior of a single electron were found to exhibit charge equal to 1/3 that of an electron's.  Is it possible that the experimental results of Fairbank et al. were a macroscopic demonstration or this behavior?  Instead, did they actually see free quarks, or was it all just experimental error?  What do you think?


References:
1.  Other notes on William Fairbank


2.  Fractional Charge Indicated
http://dx.doi.org/10.1103%2FPhysRevLett.38.1011
LaRue G., Fairbank W. & Hebard A. (1977). Evidence for the Existence of Fractional Charge on Matter, Physical Review Letters, 38 (18) 1011-1014. DOI: 

3.
http://dx.doi.org/10.1016%2F0168-9002%2888%2991113-8
Phillips J.D., Fairbank W.M. & Navarro J. (1988). Recent results in the search for fractional charge at Stanford, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 264 (1) 125-130. DOI:

4.  New York Times Obituary for William Fairbank

5.  arXiv open-access version of the quasi-particle discovery [pdf]

6.  National Academy of Sciences Bio of William Fairbank

Comments

Popular posts from this blog

Cool Math Tricks: Deriving the Divergence, (Del or Nabla) into New (Cylindrical) Coordinate Systems

The following is a pretty lengthy procedure, but converting the divergence, (nabla, del) operator between coordinate systems comes up pretty often. While there are tables for converting between common coordinate systems, there seem to be fewer explanations of the procedure for deriving the conversion, so here goes!

What do we actually want?

To convert the Cartesian nabla



to the nabla for another coordinate system, say… cylindrical coordinates.



What we’ll need:

1. The Cartesian Nabla:



2. A set of equations relating the Cartesian coordinates to cylindrical coordinates:



3. A set of equations relating the Cartesian basis vectors to the basis vectors of the new coordinate system:



How to do it:

Use the chain rule for differentiation to convert the derivatives with respect to the Cartesian variables to derivatives with respect to the cylindrical variables.

The chain rule can be used to convert a differential operator in terms of one variable into a series of differential operators in terms of othe…

Lost Phone

We were incredibly lucky to have both been in university settings when our kids were born.  When No. 1 arrived, we were both still grad students.  Not long after No. 2 arrived, (about 10 days to be exact), mom-person defended her dissertation and gained the appellation prependage Dr. 

While there are lots of perks attendant to grad school, not the least of them phenomenal health insurance, that’s not the one that’s come to mind for me just now.  The one I’m most grateful for at the moment with respect to our kids was the opportunities for sheer independence.  Most days, we’d meet for lunch on the quad of whatever university we were hanging out at at the time, (physics research requires a bit of travel), to eat lunch.  During those lunches, the kids could crawl, toddle, or jog off into the distance.  There were no roads, and therefore no cars.  And, I realize now with a certain wistful bliss I had no knowledge of at the time, there were also very few people at hand that new what a baby…

Lab Book 2014_07_10 More NaI Characterization

Summary: Much more plunking around with the NaI detector and sources today.  A Pb shield was built to eliminate cosmic ray muons as well as potassium 40 radiation from the concreted building.  The spectra are much cleaner, but still don't have the count rates or distinctive peaks that are expected.
New to the experiment?  Scroll to the bottom to see background and get caught up.
Lab Book Threshold for the QVT is currently set at -1.49 volts.  Remember to divide this by 100 to get the actual threshold voltage. A new spectrum recording the lines of all three sources, Cs 137, Co 60, and Sr 90, was started at approximately 10:55. Took data for about an hour.
Started the Cs 137 only spectrum at about 11:55 AM

Here’s the no-source background from yesterday
In comparison, here’s the 3 source spectrum from this morning.

The three source spectrum shows peak structure not exhibited by the background alone. I forgot to take scope pictures of the Cs137 run. I do however, have the printout, and…